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Instructor’s Guide

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3091564100306

SECOND EDITION

Second Printing, June 2003

Copyright March, 2003 Lab-Volt Systems, Inc.

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i

Table of Contents

Section 1 – Workstation Inventory and Installation............................................................... 1-1

Inventory of Workstation ........................................................................................................ 1-1

Minimum Computer Requirements.................................................................................... 1-1

Equipment and Supplies..................................................................................................... 1-1

Equipment Installation ............................................................................................................ 1-1

Software Installation ............................................................................................................... 1-1

Section 2 – Introduction to F.A.C.E.T Curriculum................................................................ 2-1

Getting Started ........................................................................................................................ 2-2

Screen Buttons ........................................................................................................................ 2-3

F.A.C.E.T Help Screens and Resources.................................................................................. 2-4

Internet Access ........................................................................................................................ 2-5

Instructor Annotation Tool...................................................................................................... 2-5

Student Journal........................................................................................................................ 2-5

Assessing Progress .................................................................................................................. 2-6

Real-Number Questions and Answers .................................................................................... 2-8

Safety .................................................................................................................................... 2-11

Section 3 – Courseware ............................................................................................................. 3-1

Unit 1 – Introduction to Semiconductors................................................................................. 3-1

Exercise 1 – Semiconductor Component Identification.......................................................... 3-4

Exercise 2 – Circuit Location and Identification .................................................................... 3-8

Unit 2 – Diodes and Half-Wave Rectification........................................................................ 3-13

Exercise 1 – Diode DC Characteristics................................................................................. 3-15

Exercise 2 – Half-Wave Rectification................................................................................... 3-26

Unit 3 – Full-Wave Rectification and Filtering..................................................................... 3-37

Exercise 1 – Full-Wave Diode Bridge Rectification............................................................. 3-39

Exercise 2 – Power Supply Filtering..................................................................................... 3-46

Exercise 3 – Voltage Doubler ............................................................................................... 3-54

Unit 4 – Diode Wave Shaping and Zener Regulation........................................................... 3-67

Exercise 1 – Diode Wave Shaping........................................................................................ 3-69

Exercise 2 – The Zener Diode............................................................................................... 3-77

Exercise 3 – Zener Diode Voltage Regulation...................................................................... 3-84

ii

Unit 5 – Transistor Junctions and PNP DC Bias .................................................................. 3-97

Exercise 1 – Testing the Junctions of a Transistor................................................................ 3-99

Exercise 2 – PNP Transistor Current Control Circuit......................................................... 3-105

Unit 6 – Transistor Load Lines and Gain............................................................................ 3-119

Exercise 1 – Base-Emitter Bias Potentials .......................................................................... 3-121

Exercise 2 – Collector Current Versus Base Current.......................................................... 3-126

Exercise 3 – Transistor Circuit DC Voltages...................................................................... 3-131

Exercise 4 – Transistor Load Lines..................................................................................... 3-138

Appendix A – Pretest and Posttest Questions and Answers ................................................. A-1

Appendix B – Faults and Circuit Modifications (CMs) .........................................................B-1

Appendix C – Board and Courseware Troubleshooting....................................................... C-1

iii

Introduction

This Instructor Guide is divided into three sections and the appendices. It provides a unit-by-unit

outline of the Fault Assisted Circuits for Electronics Training (F.A.C.E.T) curriculum.

Section 1 – Workstation Inventory and Installation contains a list and description of

equipment and materials required for all units in this course of study as well as installation

instructions.

Section 2 – Introduction to F.A.C.E.T Curriculum provides a description of the courseware

structure, instructions on getting started with the multimedia presentation, and an explanation of

student-progress assessment methods.

Section 3 – Courseware includes information that enables the instructor to gain a general

understanding of the units within the course.

♦ The unit objective

♦ Unit Fundamentals questions and answers

♦ A list of new terms and words for the unit

♦ Equipment required for the unit

♦ The exercise objectives

♦ Exercise Discussion questions and answers

♦ Exercise Procedure questions and answers

♦ Review questions and answers

♦ CMs and Faults available

♦ Unit Test questions and answers

♦ Troubleshooting questions and answers (where applicable)

Appendices include the questions and answers to the Pretest and Posttest plus additional specific

information on faults and circuit modifications (CMs).

Please complete and return the OWNER REGISTRATION CARD included with the CD-

ROM. This will assist Lab-Volt in ensuring that our customers receive maximum support.

iv

THIS

SECTION 1 – WORKSTATION INVENTORY

AND INSTALLATION

Semiconductor Fundamentals Section 1 – Workstation Inventory and Installation

1-1

SECTION 1 – WORKSTATION INVENTORY AND INSTALLATION

Inventory of Workstation

Use this section to identify and inventory the items needed.

Minimum Computer Requirements 100% compatible Windows

®PC with Windows98 second edition or newer, NT, 2000, Me or XP;

Pentium class CPU, (Pentium II or newer); 126 MB RAM; 10 GB HDD; CD-ROM drive; SVGA

monitor and video card capable of 32-bit color display at 1024 x 768 resolution and sound

capabilities.

Equipment and Supplies The following equipment and supplies are needed for Semiconductor Fundamentals:

Quantity Description

1 F.A.C.E.T. base unit

1 SEMICONDUCTOR DEVICES circuit board

1 Multimeter

1 Oscilloscope, dual trace

1 Generator, sine wave

1 Student Workbook

1 Instructor Guide

Equipment Installation

To install the hardware, refer to the Tech-Lab (minimum version 6.x) Installation Guide.

Software Installation

Third Party Application Installation

All applications and files that the courseware launches, or that are required for the course should

be installed before the courseware. Load all third party software according to the manufacturers'

directions. Install this software to the default location and note that location. (Alternatively, you

can install this software to a different location that you designate.) Remember to register all

software as required.

No third-party software is required for this course.

Installation of Courseware and Resources

To install the courseware and resources, refer to the Tech-Lab (minimum version 6.x) and

Gradepoint 2020 (minimum version 6.x) Installation Guide.

Semiconductor Fundamentals Section 1 – Workstation Inventory and Installation

1-2

SECTION 2 – INTRODUCTION TO F.A.C.E.T

CURRICULUM

Semiconductor Fundamentals Section 2 – Introduction to F.A.C.E.T Curriculum

2-1

SECTION 2 – INTRODUCTION TO F.A.C.E.T CURRICULUM

Overview F.A.C.E.T curriculum is multimedia-based courseware. The curriculum gives students hands-on

experience using equipment and software closely associated with industry standards. It provides

students with opportunities for instruction in academic and technical skills.

All courses are activity-driven curricula. Each course consists of several units containing two or

more exercises. Each unit begins with a statement explaining the overall goal of the unit (Unit

Objective). This is followed by Unit Fundamentals. Next is a list of new terms and words then

the equipment required for the unit. The exercises follow the unit material. When students

complete all the exercises, they complete the Troubleshooting section and take the Unit Test.

The exercises consist of an exercise objective, exercise discussion, and exercise procedures. The

Exercise Conclusions section provides the students with a list of their achievements. Every

exercise concludes with Review Questions. Available circuit modifications (CMs) and faults are

listed after the review questions. Additional specific information on CMs and faults is available

in Appendix B.


2-2

Getting Started

Desktop

After the Tech-Lab System is installed, the TechLab icon appears on the desktop.

1. Click on the TechLab icon.

2. The student clicks on LOGON and selects his or her name.

3. The student enters his or her password and clicks on OK. (If he or she is creating a password,

four alphanumeric characters must be entered. The system will ask for the password to be

entered again for verification. Keep a record of the students' passwords.)

4. The previous two steps are repeated until all members of the student team have logged on.

Click on Complete and then Yes.

5. When the Available Courses menu appears, students click on the course name.

6. A window with the name of the course and a list of units for that course appears. Students

click on the unit name. The unit title page appears and the students are ready to begin.

Selecting Other Courses and Exiting the Courseware

1. Clicking on Exit when in a unit returns the student to the list of units for that course.

2. If students wish to select another unit, they click on it.

3. If students wish to exit F.A.C.E.T, they click on the X symbol in the upper right corner.

4. If students wish to select another course, they click on the Course Menu button. The

Available Courses menu screen appears. They may also exit F.A.C.E.T from this screen by

clicking on the LOGOFF button.


2-3

Screen Buttons

If you click on the F.A.C.E.T logo on the top right of the unit title page the About screen

appears. It acknowledges the copyright holder(s) of video and/or screen-capture material used in

the topic.

The Menu button calls these menus:

when on an exercise menu screen, it calls the Unit Menu.

when on an exercise screen, it calls the Exercise Menu.

when on a unit screen, it calls the Unit Menu.

The Bookmark button marks the current screen. A student can click on the button at any time in

the lesson. The second time the student clicks on the button, the page displayed when the button

was first clicked will return to the screen. Any bookmarks used during a lesson are not saved

when the student logs out of the lesson.

The Application Launch button opens third-party software.

Click on the Resources button to view a pop-up menu. The pop-up menu includes access to a

calculator, a student journal, new terms and words, a print current screen option, the Lab-Volt

authored Internet Website, and a variety of F.A.C.E.T help screens.

The Help button aids students with system information. On certain screens the Help button

appears to be depressed. On these screens, clicking on the Help button will access Screen Help

windows (context-sensitive help).

The Internet button opens an Internet browser. Students will have unrestricted access to all

search engines and web sites unless the school administration has restricted this usage.

Use the Exit button to exit the course.

The right arrow ⇒ button moves you forward to the next screen.

The left arrow ⇐ button moves you backward to the previous screen.


2-4

F.A.C.E.T Help Screens and Resources

There are three ways to access F.A.C.E.T help screens and other resources.

System Help Students access System Help by clicking on the Help button at the bottom of the screen when the

button does not appear to be depressed. The menu selections access a variety of system help,

navigation, and information windows.

Screen Help On certain screens, the Help button appears to be depressed. On these screens, clicking on the

Help button will access Screen Help windows. This is information specific to the content of that

particular screen.

Resources Students click on the Resources button to access the following windows.

Calculator

F.A.C.E.T 32-Bit Microprocessor Help

F.A.C.E.T Analog Communications Setup Procedure

F.A.C.E.T Digital Communications Help

F.A.C.E.T Electronics and Troubleshooting Help

F.A.C.E.T Fiber Optic Communications Help

F.A.C.E.T Math Help

Internet Link

New Terms and Words

Print Current Page

Student Journal


2-5

Internet Access

There are two ways for students to access the Internet:

The Internet button opens an Internet browser. Students have unrestricted access to all search

engines and websites unless the school administration has restricted this usage.

The Resources button pops up a menu that includes access to the Lab-Volt

authored Internet website. If students wish to access this site when they are not in

the lesson, then they must go to http://learning.labvolt.com.

NOTE: The Lab-Volt Internet site does not have content-filtering

software to block access to objectionable or inappropriate

websites.

Instructor Annotation Tool

The annotation tool gives the instructor the ability to add comments or additional information

onscreen. Refer to the Tech-Lab and GradePoint 2020 Installation Guide for detailed

information.

Student Journal

The student journal is an online notebook that each student can access while they are logged into

TechLab. The journal allows students to share notes with other students in their workgroups.

When used in conjunction with GradePoint 2020, the instructor may post messages, review, edit,

or delete any journal note.


2-6

Assessing Progress

Assessment Tools

Student assessment is achieved in several ways:

♦ Exercise questions

♦ Unit tests

♦ Pretest and Posttest

♦ Troubleshooting questions

Exercise and Troubleshooting Questions

Throughout the unit material, exercise discussion, exercise procedure, and troubleshooting

sections there are several types of questions with instant feedback. These questions occur in the

following formats:

♦ Multiple choice

♦ True-false

♦ Real-number entry

In most cases, when your students encounter a question set, they must answer these questions

before continuing. However, there are cases where students may progress to the next screen

without answering the questions. Lab-Volt recommends that you encourage your students to

complete all questions. In this way, students reinforce the material that's presented, verify that

they understand this material, and are empowered to decide if a review of this material is

required.

Review Questions

At the end of each exercise, there are review questions. The student receives feedback with each

entry. Feedback guides the student toward the correct answer.

Unit Tests

A unit test appears at the end of each unit. The test consists of 10 multiple-choice questions with

the option of having feedback. The Tech-Lab System defaults to no feedback, but the instructor

can configure the test so that students receive feedback after taking the test. You can randomize

questions in the unit test. Use the Tech-Lab Global Configurator to make feedback available,

randomize questions, and select other configuration options if desired. Refer to the Tech Lab

Quick-Start Guide for detailed information.


2-7

Pretest and Posttest

Every course includes a pretest and a posttest. These are multiple choice tests. Refer to the Tech

Lab Quick-Start Guide for detailed information on how to record student competency gains.

Grading

Student grades are based on exercise questions, troubleshooting questions, a unit test, and a

posttest. The default weighting value of the unit test and the threshold for passing the unit test

can be adjusted by using the Global Configurator of the Tech-Lab System. Refer to the Tech Lab

Quick-Start Guide for detailed information.

Student Progress and Instructor Feedback

Unit progress is available through the Unit menu. The Progress window allows the instructor and

student to view the percentage of the unit completed, number of sessions, and time spent on that

unit. The Progress window shows whether the Unit Test was completed. If the test was

completed, it indicates whether the student passed based on the scoring criteria.


2-8

Real-Number Questions and Answers

Throughout F.A.C.E.T courses students may encounter real-number questions such as the one

shown below. Answers to real-number questions are graded correct if they fall within an

acceptable tolerance range.

The answer to the question posed in the illustration above does not involve a recall value from a

previous question. It appears in the Instructor Guide (IG) as shown in the box below.

The information in the IG tells you where the question is located and the range of acceptable

answers. In this case, the acceptable answers fall within the range of the nominal answer plus or

minus 5 percent tolerance: (15 ± 5%).

Location: Exercise Procedure page:

se1p1, Question ID: e1p1a

VS = Vdc

Recall Label for this Question: V1

Nominal Answer: 15.0

Min/Max Value: (14.25) to (15.75)

Value Calculation: 15.000

Correct Tolerance Percent = true

Correct Minus Tolerance = 5

Correct Plus Tolerance = 5

This is the name the computer uses internally

to identify the input value. In this case, 14.5

will be stored under the name V1.

NOTE: The recall value V1 is not the same as

the voltage V1. The recall label does not

appear onscreen.

In this case, the answer to this question is not

based on a value recalled from a previous

question. Therefore, the Value Calculation is

equal to the Nominal Answer.

The word "true" tells you that the tolerance is

calculated as a percent.

e1p1 stands for

Exercise 1 Procedure screen 1

The computer

saves this input

value so that it can

be recalled for use

in later questions.


2-9

A second example (shown below) illustrates an answer that the computer grades using a value

recalled from a previous question.

When a real-number question is based on a recall value from a previous question, the Min/Max

Value shown in the Instructor Guide is based upon a calculation using the lowest and highest

possible recall value. It represents the theoretical range of answers that could be accepted by the

computer. (It is not the nominal answer plus or minus the tolerance.)

To find the actual range of answers that the computer will accept onscreen, you must use the

actual recall value (14.5 in this example) in your calculations; see below.

NOTE: After four incorrect answers, students will be prompted to press <Ins> to insert the

correct answer if this feature has been enabled in the configuration settings. When the question is

based on a value recalled from a previous question, answers obtained using the Insert key may

not match the nominal answers in this guide.

Location: Exercise Procedure page:

se1p5, Question ID: e1p5c

IT = mA

Recall Label for this Question: I1

Nominal Answer: 9.091 *Min/Max Value: (6.477) to (11.93)

Value Calculation: #V1#/1650*1000




Since the value for #V1# is 14.5, the

computer will accept answers in the

following range as correct:

14.5/1650*1000 ± 25% or

8.79 ± 25% or

6.59 to 10.99

This calculated range is different from the

Min/Max Value shown in the IG, which

was based upon a calculation using the

lowest and highest possible recall value.

Any letter enclosed in "#" signs refers to a

recall value from a previous question.


2-10

Recall Values in Text

Sometimes numbers displayed on screen are values recalled from input on previous screens.

Because these numbers are recall values, they will change for each student.

The Instructor Guide lists the recall label in place of a number in this question.

The value of 10

was recalled

from a previous

screen.

Location:Exercise Procedure page: se1p11, Question ID: e1p11c

IR2 = VR2/R2

= #V4#/3.3 kΩ

= mA



Min/Max Value: (2.489) to (3.164)

Value Calculation: #V4#/3.3




This is a

recall label

for a value

recorded in a

previous

question.

The correct

answer will

depend on the

value the student

recorded in the

previous question.


2-11

Safety

Safety is everyone’s responsibility. All must cooperate to create the safest possible working

environment. Students must be reminded of the potential for harm, given common sense safety

rules, and instructed to follow the electrical safety rules.

Any environment can be hazardous when it is unfamiliar. The F.A.C.E.T computer-based

laboratory may be a new environment to some students. Instruct students in the proper use of the

F.A.C.E.T equipment and explain what behavior is expected of them in this laboratory. It is up to

the instructor to provide the necessary introduction to the learning environment and the

equipment. This task will prevent injury to both student and equipment.

The voltage and current used in the F.A.C.E.T Computer-Based Laboratory are, in themselves,

harmless to the normal, healthy person. However, an electrical shock coming as a surprise will

be uncomfortable and may cause a reaction that could create injury. The students should be made

aware of the following electrical safety rules.

1. Turn off the power before working on a circuit.

2. Always confirm that the circuit is wired correctly before turning on the power. If required,

have your instructor check your circuit wiring.

3. Perform the experiments as you are instructed: do not deviate from the documentation.

4. Never touch “live” wires with your bare hands or with tools.

5. Always hold test leads by their insulated areas.

6. Be aware that some components can become very hot during operation. (However, this is not

a normal condition for your F.A.C.E.T. course equipment.) Always allow time for the

components to cool before proceeding to touch or remove them from the circuit.

7. Do not work without supervision. Be sure someone is nearby to shut off the power and

provide first aid in case of an accident.

8. Remove power cords by the plug, not by pulling on the cord. Check for cracked or broken

insulation on the cord.


2-12

SECTION 3 – COURSEWARE

SECTION 3 – COURSEWARE

Semiconductor Fundamentals Unit 1 – Introduction to Semiconductors

3-1

UNIT 1 – INTRODUCTION TO SEMICONDUCTORS

UNIT OBJECTIVE

Describe a semiconductor, identify semiconductor devices, and demonstrate their operation by

using circuits on the SEMICONDUCTOR DEVICES circuit board.

UNIT FUNDAMENTALS

Location: Unit Fundamentals page: sf2, Question ID: f2a

A semiconductor is a. neither a good conductor nor a good insulator.

b. a good conductor.

c. a good insulator.


The N and P types of semiconductor material have

a. no excess of free electrons and an excess of free electrons, respectively.

b. an excess of free electrons and no excess of free electrons, respectively.


The depletion region is a narrow band at the

a. end of the N region.

b. end of the P region.

c. junction of the N and P regions.

CMS AVAILABLE

None

FAULTS AVAILABLE

None


3-2

NEW TERMS AND WORDS

diodes – semiconductor devices consisting of P type material and N type material.

transistors – devices consisting of NPN or PNP semiconductor layers. Transistors allow a small

current to control the flow of a larger current.

semiconductor – a material, usually silicon or germanium, doped with impurities to create a

compound whose electrical resistance is greater than that of conductors but less than that offered

by insulators.

doping – the deliberate introduction of a specific type of impurity into very pure base material.

Doping is accomplished by many different processes, but it is always carefully controlled to

produce semiconductors with specific properties.

N type material – pure semiconductor material which has been doped with an impurity that

introduces free electrons into the semiconductor. The atoms of the doping material, sometimes

referred to as donor material, usually have a valence ring that contains one electron more than

those required to complete covalent bonds with base material atoms.

valence ring – the outermost electrons surrounding the nucleus of any atom. These electrons

interact with the valence electrons of neighboring electrons and are the main influences on the

electrical characteristics of the element.

P type material – pure semiconductor material which has been doped with an impurity that

introduces apparent positive charges (holes) into the semiconductor. The atoms of the doping

material, sometimes called acceptor material, usually have a valence ring that lacks one electron

from those necessary to complete covalent bonds with base material atoms.

free electrons – "extra" valence ring electrons that are not incorporated into covalent bonds.

These electrons result from doping pure base material with an N type impurity. They act as

current carriers in N type semiconductor material.

majority carriers – charges deliberately introduced into semiconductors to act as current

carriers. Electrons are the majority carriers in N type material; holes are considered to be the

majority carriers in P type material.

holes – positive charges in semiconductors resulting from incomplete covalent bonds. Holes

occur when pure base material is doped with a P type impurity.

anode – the diode region doped with P (positive) type material.

cathode – the diode region doped with N (negative) material.

zener – a diode designed to maintain a relatively constant voltage drop over a range of current

flows. Zeners are supplied in the same packages as "ordinary" diodes, but they operate in a

different way.

light-emitting diodes – (LED) a diode constructed to release energy in the form of light when

supplied with an electric current. The materials used in the construction of an LED determine the

color and brightness of the light.

bipolar transistor – a three-layer transistor constructed by NPN or PNP doping; more

commonly called junction transistors. Bipolar refers to the use of N and P doping materials.

emitter – an end region of a transistor. The emitter is doped with the same type of impurity as

the collector.


3-3

base – the center region of a transistor, between the emitter and collector. The base is always

doped with a material opposite in polarity to the emitter and collector doping. It is usually very

thin.

collector – an end region of a transistor. Physically, the collector area is usually the largest area

of a transistor because it is the region where most power is dissipated.

depletion region – an area very close to PN junction where a few charges from adjoining areas

tend to cross the border and neutralize each other.

EQUIPMENT REQUIRED

F.A.C.E.T. base unit

SEMICONDUCTOR DEVICES circuit board


3-4

Exercise 1 – Semiconductor Component Identification

EXERCISE OBJECTIVE

Identify various semiconductor devices. You will verify your knowledge by locating diodes and

transistors on the SEMICONDUCTOR DEVICES circuit board.

EXERCISE DISCUSSION

Location: Exercise Discussion page: se1d2, Question ID: e1d2a

Diodes have

a. one PN junction.

b. two PN junctions.


All diodes have

a. one electrical connection.

b. three electrical connections.

c. two electrical connections.


The schematic symbol for a zener diode is shown on the

a. left.

b. right.


Diode packages

a. are constructed from plastic, glass, or a combination of metal and glass or ceramic.

b. are tightly sealed to prevent contamination of the semiconductor by airborne gasses or

moisture.

c. have a dot or band of color to identify the cathode.

d. All of the above.


3-5


Junction transistors have

a. three regions of P and N semiconductor materials that can be arranged to form a PNP

or NPN transistor.

b. three junctions of P and N semiconductor materials that can be arranged to form PN, NP,

NNP, or PPN transistors.

c. two regions of P and N semiconductor materials that can be arranged to form a PN or NP

transistor.


The middle region of a transistor is the

a. collector, and the two end regions are the base and emitter.

b. emitter, and the two end regions are the base and the collector.

c. base, and the two end regions are the collector and emitter.


The symbol shows a(n)

a. NPN transistor.

b. PNP transistor.

EXERCISE PROCEDURE

Location: Exercise Procedure page: se1p2, Question ID: e1p2a

2. What type of packaging material is used for the diodes (CR1 and CR2) in the DIODES AND

1/2 WAVE RECTIFICATION circuit block?

a. metal and glass

b. glass

c. plastic

Location: Exercise Procedure page: se1p2, Question ID: e1p2c

3. Is the cathode or the anode of CR1 at the top in this circuit block?

a. anode

b. cathode


4. What type of diode is CR1 in the ZENER DIODE REGULATOR circuit block?

a. LED

b. zener

c. common diode


3-6


5. What type of diode is in the PNP DC BIAS circuit block?

a. LED

b. zener

c. common diode


6. What type of transistor is Q1 in the TRANSISTOR LOAD LINES AND GAIN circuit

block?

a. PNP

b. NPN


7. What type of transistor is Q1 in the PNP DC BIAS circuit block?

a. PNP

b. NPN


8. What packaging material is used for Q1 and Q2 in the TRANSISTOR JUNCTION circuit

block?

a. plastic

b. metal

REVIEW QUESTIONS

Location: Review Questions page: se1r1, Question ID: e1r1

1. The two regions of a diode are the

a. emitter and cathode.

b. anode and cathode.

c. base and cathode.

d. emitter and collector.


2. The symbol for the cathode of a zener diode is a(n)

a. straight line.

b. Z-shaped line.

c. arrow.

d. circle


3-7


3. How many electrical connections do transistors have?

a. three

b. two

c. four

d. one


4. A PNP transistor symbol has the emitter arrow pointing toward the

a. base.

b. emitter.

c. collector.

d. cathode.


5. The base region of a transistor is

a. always N type material.

b. always P type material.

c. one of the end regions.

d. between the emitter and collector.

CMS AVAILABLE

None

FAULTS AVAILABLE

None


3-8

Exercise 2 – Circuit Location and Identification

EXERCISE OBJECTIVE

When you have completed this exercise, you will be familiar with the functional circuit blocks

on the SEMICONDUCTOR DEVICES circuit board. You will verify your circuit knowledge by

identifying the circuit blocks and operating a transistor circuit.

EXERCISE DISCUSSION


The first five circuit blocks on the SEMICONDUCTOR DEVICES circuit board contain

a. a mixture of diode and transistor circuits.

b. only diode circuits.


The circuit blocks that contain NPN transistors are the

a. TRANSISTOR JUNCTION and the TRANSISTOR LOAD LINES AND GAIN circuit

blocks.

b. TRANSISTOR JUNCTION and the PNP DC BIAS circuit blocks.

EXERCISE PROCEDURE


1. Observe the circuit blocks on the SEMICONDUCTOR DEVICES circuit board. The circuit

block that contains four diodes connected in a diamond-shaped bridge circuit is the

a. ZENER DIODE REGULATOR circuit block.

b. VOLTAGE DOUBLER circuit block.

c. TRANSISTOR LOAD LINES AND GAIN circuit block.

d. FULL-WAVE RECTIFICATION WITH POWER SUPPLY FILTERS circuit block.


2. The circuit block that contains only one NPN transistor is the

a. PNP DC BIAS circuit block.

b. DIODE WAVESHAPING circuit block.


d. FULL-WAVE RECTIFICATION WITH POWER SUPPLY FILTERS circuit block.


3-9


3. The circuit block that contains positive and negative variable voltage supplies to bias the

diodes is the

a. DIODES AND 1/2 WAVE RECTIFICATION circuit block.

b. DIODE WAVESHAPING circuit block.

c. ZENER DIODE REGULATOR circuit block.

d. VOLTAGE DOUBLER circuit block.


5. Is the LED on or off?

a. on

b. off


6. Move the two-post connector as shown above. Is the LED on or off?

a. on

b. off


7. Observe the LED as you insert and remove the two-post connector a few times. Can you

compare the operation of transistor Q1 with an electrically controlled switch?

a. yes

b. no

REVIEW QUESTIONS


1. Excluding the connection space for the GENERATOR BUFFER, the SEMICONDUCTOR

DEVICES circuit board has

a. 6 circuit blocks.

b. 8 circuit blocks.

c. 5 circuit blocks.

d. 7 circuit blocks.


2. The DIODES AND 1/2 WAVE RECTIFICATION circuit block contains

a. two zener diodes.

b. two transistors.

c. one LED and one diode.

d. two common diodes.


3-10


3. The circuit block with the diode having a Z-shaped cathode is the

a. ZENER DIODE REGULATOR circuit block.

b. VOLTAGE DOUBLER circuit block.

c. DIODE WAVESHAPING circuit block.

d. PNP DC BIAS circuit block.


4. An LED is located in the

a. FULL-WAVE RECTIFICATION WITH POWER SUPPLY FILTERS circuit block.

b. TRANSISTOR LOAD LINES AND GAIN circuit block.

c. PNP DC BIAS circuit block.

d. VOLTAGE DOUBLER circuit block.


5. Four diodes and two transistors are located in the

a. FULL-WAVE RECTIFICATION WITH POWER SUPPLY FILTERS circuit block.

b. DIODES AND 1/2 WAVE RECTIFICATION circuit block.


d. TRANSISTOR JUNCTION circuit block.

CMS AVAILABLE

None

FAULTS AVAILABLE

None


3-11

UNIT TEST QUESTION

Depending on configurator settings, these questions may be randomized onscreen.

Location: Unit Test Question page: sut1, Question ID: ut1

Arrow (1) is pointing to the

a. anode.

b. cathode.

c. base.

d. collector.


The transistor (Q1) shown (PNP DC BIAS circuit block)

a. can be operated as a switch to turn the LED (DS1) on and off.

b. is an NPN transistor.

c. conducts when the positive terminal of the power supply is connected to R1.

d. is used only in an LED circuit.


You can distinguish an NPN transistor from a PNP transistor on a schematic drawing by the

a. size of the symbol outline.

b. direction of the emitter arrow.

c. shape of the cathode symbol.

d. width of the base symbol.



a. PNP transistor.

b. LED.

c. NPN transistor.

d. zener diode.


You can distinguish a zener diode from an ordinary diode on a schematic drawing by the

a. size of the symbol outline.

b. shape of the cathode symbol.

c. direction of the emitter arrow.

d. width of the base symbol.


3-12


The emitter region of a PNP transistor is constructed from

a. P type material.

b. N type material.

c. silicon.

d. germanium.


The anode of a diode is constructed from

a. P type material.

b. N type material.

c. either P or N type material.

d. a material that is a good conductor.



a. zener diode.

b. LED.

c. NPN transistor.

d. common diode.


The reference designation CR6 indicates that the component is a

a. transistor.

b. resistor.

c. diode.

d. capacitor.


Semiconductor material is

a. either germanium or silicon.

b. doped with an impurity to change the resistance.

c. neither a good conductor nor a good insulator.


Semiconductor Fundamentals Unit 2 – Diodes and Half-Wave Rectification

3-13

UNIT 2 – DIODES AND HALF-WAVE RECTIFICATION

UNIT OBJECTIVE

Demonstrate the principles of semiconductor diode operation and diode half-wave rectification

by using diode test circuits.

UNIT FUNDAMENTALS


Diodes normally permit

a. alternating current (ac) flow.

b. current flow in only one direction.


The barrier voltage for a silicon diode is about

a. 6.0V.

b. 0.6V.

c. 0.3V.


A diode is fully forward biased when

a. the applied voltage exceeds the barrier voltage.

b. there is no current flow.

CMS AVAILABLE

None

FAULTS AVAILABLE

None


3-14

NEW TERMS AND WORDS

barrier voltage – the voltage potential required for current flow through the depletion region of

a diode junction. The barrier voltage must be overcome by the forward bias voltage before

current can flow in a diode.

forward voltage drop (VF) – the condition that exists when the cathode of a diode is negative

with respect to its anode, and forward current flows.

forward biased – the condition that exists when the cathode of a diode is negative with respect

to its anode, and forward current flows.

reverse biased – the condition that exists when the anode of a diode is negative with respect to

the cathode.

pulsating dc – the rectifier output pulses of one polarity that corresponds to half-cycles of the

rectifier ac input voltage when the diode is forward biased.

ripple – the pulsations appearing in the output voltage of a rectifier circuit.

half-wave rectification – rectification in which output current flows only during half-cycles of

the ac input.

characteristic curve – a graphic representation of diode current flow versus diode voltage drop.

leakage current – the very small current that flows through a reverse biased diode.

minority carriers – free electrons in P type material, and holes (positive charges) in N type

material. Minority carriers are caused by the presence of tiny quantities of natural impurities in

the base semiconductor material. They are responsible for most reverse (leakage) current through

a semiconductor.

breakdown voltage – the reverse voltage that causes a diode to conduct heavily and

destructively in the "wrong" direction. Diodes should be selected to have a breakdown voltage

greater than any normally applied reverse voltage.

dynamic forward resistance (rF) – the apparent resistance of a conducting diode; calculated

from a measured change in diode voltage drop divided by a measured change in current.

rectification – the process of converting an alternating current into a pulsating direct current.

reverse recovery time (tRR) – the time required for a diode to stop conducting after forward bias

is removed. Reverse recovery time is due primarily to stored charges.

stored charges – positive and negative charges temporarily existing in a forward biased

semiconductor due to current flow. Stored charges reduce the efficiency of common

semiconductors at high frequencies because they increase the time required for a junction to

switch from the forward to reverse biased state.

EQUIPMENT REQUIRED



Multimeter

Oscilloscope, dual trace

Generator, sine wave


3-15

Exercise 1 – Diode DC Characteristics

EXERCISE OBJECTIVE

Test a diode in a typical diode circuit by using a diode dc characteristic curve. Verify results with

a multimeter.

EXERCISE DISCUSSION


The part of a diode dc characteristic curve that describes forward bias operation is the

a. right side.

b. left side.


The left part of the diode dc characteristic curve describes

a. forward bias operation of the diode.

b. reverse bias operation of the diode.


Does the above silicon diode dc characteristic curve show that the diode is conducting with an

applied voltage of +0.75V?

a. no

b. yes


Above the barrier voltage, the diode voltage drop

a. is nearly constant.

b. increases very rapidly.


When a diode is reverse biased, the very small current that flows is called

a. forward current.

b. leakage current.


3-16


The reverse current of a diode starts to increase rapidly when the reverse voltage reaches the

a. barrier voltage.

b. breakdown voltage.


As the forward current of a diode increases, the forward voltage

a. is absolutely constant.

b. increases slightly.


The forward resistance of a diode is very

a. low.

b. high.


Diodes can be damaged if the

a. maximum forward current is exceeded.

b. barrier voltage is exceeded.


A good diode is tested with an ohmmeter. When the diode is forward biased, the ohmmeter

reading should indicate

a. no current flow through the diode.

b. current flow through the diode.


The figure shows the ohmmeter connections to test the diode. The ohmmeter indicates an

overload. The diode is

a. bad.

b. good.


3-17

EXERCISE PROCEDURE


2. Connect the black (common) meter probe to the test point at the CR1 anode. Connect the red

meter probe to the test point at the CR1 cathode. Your meter reading indicates that the diode is

a. not conducting.

b. conducting.


3. Your meter reading indicates that the diode is

a. forward biased.

b. reverse biased.


4. Reverse the meter probes by connecting the red probe to the CR1 anode and the black probe to

the cathode. Your meter reading indicates that the diode is

a. not conducting.

b. conducting.


5. With the probes connected in this direction, your meter reading indicates that the diode is

a. forward biased.

b. reverse biased.


6. Is diode CR1 a good diode?

a. yes

b. no


VR1 = Vdc


Nominal Answer: –9.3

Min/Max Value: (–10.) to (–8.55)

Value Calculation: -9.3





3-18


VR2 = mVdc


Nominal Answer: 0.0

Min/Max Value: (–50) to (50)


Correct Tolerance Percent = false




10. Which diode is forward biased?

a. CR1

b. CR2


11. Which diode is reverse biased?

a. CR1

b. CR2

Location: Exercise Procedure page: se1p7, Question ID: e1p7e

12. Which diode circuit allows current to flow?

a. CR1

b. CR2

Location: Exercise Procedure page: se1p7, Question ID: e1p7g

13. Current flows through CR1 because it is

a. reverse biased.

b. forward biased.


VR1 = mVdc


Nominal Answer: 0.0







3-19


VR2 = Vdc


Nominal Answer: 9.3

Min/Max Value: (8.556) to (10.04)






17. Which diode is forward biased?

a. CR1

b. CR2


18. Which diode is reverse biased?

a. CR1

b. CR2


19. In the circuit that you connected, which component determines the amount of current through

the forward biased diode (CR2) after the barrier voltage is exceeded?

a. CR2

b. R2

c. R1

d. CR1


3-20


IR2 = VR2/R2

IR2 = #V4#/3.3 kΩ

IR2 = mA


Nominal Answer: 2.818 ∗Min/Max Value: (2.489) to (3.164)






ICR2 = mA

Recall Label for this Question:

Nominal Answer: 2.818 *Min/Max Value: (2.439) to (3.227)

Value Calculation: #I1#





a. Measure VR2.



Min/Max Value: (0.141) to (0.423)

Value Calculation: .282




∗ NOTE: Min/Max Values shown are based upon a calculation using the absolute

lowest and highest recall value. By using the actual input in your calculations, you

will determine the correct value.


3-21


b. Calculate ICR2.


Nominal Answer: 0.085 ∗Min/Max Value: ( .041) to ( .133)






Calculate VD


Nominal Answer: 0.468 *Min/Max Value: ( .317) to ( .627)

Value Calculation: 0.75–#V9#





Measure VR2



Min/Max Value: (3.969) to (4.851)









3-22


Calculate ICR2.








Calculate VD


Nominal Answer: 0.59 *Min/Max Value: ( .145) to (1.062)

Value Calculation: 5–#V11#





Measure VR2


Nominal Answer: 9.4

Min/Max Value: (8.93) to (9.87)









3-23


Calculate ICR2.








Calculate VD.








26. Does your table data match the diode characteristic curve?

a. yes

b. no


VD = Vdc



Value Calculation: #V12#








3-24


28. Does VD remain nearly constant with an increase in ICR2 beyond #I5# mA?

a. no

b. yes

REVIEW QUESTIONS


1. Based on these measurements, CR1

a. tests good when CM 1 is off and bad when it is on.

b. tests good when CM 1 is on and bad when it is off.

c. is bad when CM 1 is on and off.

d. is good when CM 1 is on and off.


2. The forward voltage drop (VF) of a diode is

a. a desirable characteristic for circuit protection.

b. nearly constant when the diode is fully forward biased.

c. not related to the semiconductor material.

d. determined by the circuit resistance.


3. Leakage current

a. flows when the reverse breakdown voltage is exceeded.

b. flows when the barrier voltage is exceeded.

c. improves diode performance.

d. should be very small in a good diode.


4. A diode dc characteristic curve

a. describes the forward bias operation of the diode.

b. describes the reverse bias operation of the diode.

c. shows the forward voltage drop of the diode.



3-25


5. When a diode is forward biased, the cathode

a. is negative with respect to the anode.

b. is positive with respect to the anode.

c. has the opposite polarity with respect to the anode.

d. is reverse biased.

CMS AVAILABLE

CM 1 TOGGLE

FAULTS AVAILABLE

None


3-26

Exercise 2 – Half-Wave Rectification

EXERCISE OBJECTIVE

Demonstrate how a diode functions as a half-wave rectifier by using a typical half-wave rectifier

circuit. Verify results with an oscilloscope and a multimeter.

EXERCISE DISCUSSION


A half-wave rectifier circuit consists of a

a. load resistance.

b. diode and load resistance.

Location: Exercise Discussion page: se2d1, Question ID: e2d1c

A half-wave rectifier can produce

a. only a negative pulsating dc output.

b. only a positive pulsating dc output.

c. either a positive or negative pulsating dc output, depending on how the diode is

connected.


In the above circuit, current flows only during positive cycles of Vi because the

a. anode of CR1 connects to Vi at point A.

b. cathode of CR1 connects to Vi at point A.


In the circuit, current flows only during negative cycles of Vi because the

a. anode of CR2 connects to Vi at point A.

b. cathode of CR2 connects to Vi at point A.


A diode half-wave rectifier will conduct for

a. a complete ac cycle.

b. about 90º of an ac cycle.

c. a little less than 180º (half) of an ac cycle.


3-27


The output of a half-wave rectifier is

a. an ac voltage.

b. a pulsating dc voltage.


The diode half-wave rectifer output voltage (Vo(pk)) is less than the input voltage (Vi(pk))

because of the

a. diode forward voltage drop (VF) of about 0.6V.

b. load resistance voltage drop.


Suppose Vi(pk) increased to 4.0V. Use the following equation to calculate Vo(pk).

Vo(pk) = Vi(pk) – VF

Vo(pk) = V


Nominal Answer: 3.4

Min/Max Value: (3.298) to (3.502)






Why does Vo reach 0V before Vi?

a. Because Vi is not in phase with Vo.

b. Vo = 0V when Vi is below the forward voltage drop of about 0.6V.


If Vo(pk) = 5V, calculate Vo(avg).

Vo(avg) = 0.318 x Vo(pk)

Vo(avg) = V



Min/Max Value: (1.542) to (1.638)






3-28


The ripple frequency is

a. two times the input frequency.

b. the same as the input frequency.

EXERCISE PROCEDURE


5. On the DIODES AND 1/2 WAVE RECTIFICATION circuit block, which diode and resistor

circuit will produce a positive half-wave dc output?

a. CR1 and R1

b. CR2 and R2


6. Connect the channel 2 probe across load resistor R2, and observe the CR2 output waveform.

Do you observe a positive pulsating half-wave dc signal at the output of CR2 on channel 2?

a. yes

b. no


7. Connect the channel 2 probe across load resistor R1, and observe the CR1 output waveform.

Do you observe a negative half-wave dc signal at the output of CR1?

a. yes

b. no


8. Why is there no positive half-wave dc output from CR1 during the positive alternation of the

ac input signal?

a. Because CR1 is forward biased (cathode negative with respect to anode) during the positive

alternation of the ac input signal.

b. Because CR1 is reverse biased (cathode positive with respect to anode) during the

positive alternation of the ac input signal.


9. With the channel 2 probe connected across R1, set the horizontal sweep to 0.5 ms/cm. Move

the channel 2 coupling lever to GND and back to DC. The negative half-wave output signal is

a. an ac signal.

b. a pulsating dc signal.


3-29


Vo(pk) = Vpk


Nominal Answer: 0.5







12. What is the difference between the 1 Vpk ac input signal peak voltage and the output signal

peak voltage (Vo(pk)), measured in step 11?

= Vdc








13. What causes the peak output voltage (Vo(pk)) from a diode half-wave rectifier to be less than

the peak ac input voltage?

a. the diode forward voltage drop (VF)

b. the diode voltage drop across R2





3-30


14. Increase the ac input signal to 4.0 Vpk-pk. On the oscilloscope screen, measure the

difference between the 2 Vpk ac input voltage and the peak output voltage (Vo(pk)).

= Vdc



Min/Max Value: (0.385) to (0.715)






15. Did the difference between the peak ac input voltage and the peak output voltage remain

about the same after you increased the input from 2.0 to 4.0 Vpk-pk?

a. yes

b. no


16. Connect the channel 2 probe across R1. Is the difference between the negative peak ac input

voltage and the negative dc pulse about the same as the positive input and output?

a. yes

b. no


19. At point A, diode CR2 becomes

a. reverse biased.

b. forward biased and starts to conduct.


20. At point B, diode CR2

a. stops conducting because the ac input voltage is less than VF.

b. becomes forward biased.


21. Is the ac input voltage before point A and after point B sufficient to overcome the diode

barrier voltage?

a. yes

b. no


3-31


23. Calculate the average output voltage (Vo(avg)).

Vo(avg) = 0.318 x Vo(pk) = V



Min/Max Value: ( .935) to ( .973)






24. With a multimeter, measure the average dc voltage across R2.

Vo(avg) = V



Min/Max Value: (0.774) to (0.946)






25. Your measured Vo(avg) (#V19#) is less than your calculated Vo(avg) (#V18#) because

a. of multimeter measurement tolerances.

b. the actual dc output signal is less than 180º and the equation Vo(avg) = 0.318 x Vo(pk)

assumes a 180º signal.


26. Set the channel 2 vertical sensitivity to 0.2 V/cm, and set the horizontal sweep to 0.5 ms/cm.

The positive pulsating dc signal that is observed on the oscilloscope screen is called

a. ripple.

b. reverse recovery time.


27. Increase the frequency of the input signal to 10 kHz, and set the horizontal sweep to 20

µs/cm. The negative peaks on the output signal are caused by

a. frequency response.

b. reverse recovery time.


3-32


27. Increase the frequency of the input signal to 50 kHz. Would you conclude that reverse

recovery time of a diode adversely affects the diode's performance as a half-wave rectifier while

the input frequency increases?

a. yes

b. no


31. CM 7 is activated in the CR1 and R1 circuit to introduce a fault. Observe the half-wave

rectifier output on channel 2. Toggle CM 7 on and off by clicking on the CM button, and observe

the effect on the output. CM 7

a. puts a short circuit around R1.

b. connects the anode of CR1 to the ac input and the cathode to R1.

c. puts a short around CR1.

REVIEW QUESTIONS


1. The signal observed at the output of this circuit, with respect to circuit common, would be

a. positive pulsations.

b. negative pulsations.

c. alternating current.

d. None of the above.


2. In a half-wave rectifier circuit, the output voltage pulse width (diode conduction time)

a. is greater than half of the input cycle time.

b. equals half of the input cycle time.

c. depends on whether the anode or cathode connects to the ac input signal.

d. is slightly less than half of the input cycle time.


3. The peak voltage of the output of a silicon diode half-wave rectifier

a. equals the peak voltage of the ac input signal.

b. is less than the peak voltage of the ac input by about 0.6V, the value of the forward

voltage drop (VF).

c. depends on the frequency of the ac input signal if less than 1 kHz.

d. is greater than the peak voltage of the ac input by about 0.6V, the value of the forward

voltage drop (VF).


3-33


4. The signal observed at the output of this circuit, with respect to circuit common, would be

a. alternating current.

b. negative pulsations.

c. positive pulsations.



5. The average output (Vo(avg)) of a half-wave rectifier is calculated from which of the

following equations?

a. Vo(avg) = 0.5 x Vo(pk)

b. Vo(avg) = 0.318 x Vo(pk)

c. Vo(avg) = 0.318 x Vo(pk-pk)

d. Vo(avg) = 2.0 x Vo(pk)

CMS AVAILABLE

CM 7 TOGGLE

FAULTS AVAILABLE

None


3-34

UNIT TEST QUESTION



The diode dc characteristic curve bends sharply upward at a. the breakdown voltage.

b. the barrier voltage or forward voltage drop.

c. about 0.2 Vdc.

d. the leakage current.


If the anode of a diode is positive with respect to the cathode, the diode is

a. reverse biased and does not conduct current.

b. reverse biased and conducts current.

c. forward biased and does not conduct current.

d. forward biased and conducts current.


Leakage current flows in a diode

a. when it is forward biased.

b. when it is reverse biased.

c. after breakdown voltage is reached.

d. only if it is defective.


A good diode has

a. current flow when forward biased.

b. a very low leakage current in the microamp or picoamp range.

c. a constant forward voltage drop.



At the breakdown voltage of a diode, the

a. breakdown current increases rapidly and the diode may be destroyed.

b. forward current increases rapidly.

c. leakage current is very small.

d. reverse voltage increases rapidly.


3-35


Diode half-wave rectifiers get their name because the

a. load current flows only during half-cycles of the ac input.

b. output frequency is half of the ac input frequency.

c. output can be only positive dc pulses.

d. output voltage is half of the ac input voltage.


The dc pulsations at the output of a half-wave rectifier occur

a. at the same frequency as the ac input.

b. at half the frequency as the ac input.

c. at twice the frequency of the ac input.

d. independently of the ac input frequency.


This circuit is a

a. half-wave rectifier that produces negative dc pulses.

b. half-wave rectifier that produces positive dc pulses.

c. diode test circuit.

d. diode rectifier that produces a dc pulse with a polarity the same as the ac input.


Normal diode half-wave rectifier circuits cannot output pure dc pulses at input frequencies above

10 kHz because

a. of a low breakdown voltage at higher frequencies.

b. the barrier voltage increases significantly.

c. of the reverse recovery time of the diode.

d. of high leakage currents.


Because of the forward voltage drop of the diode in a half-wave rectifier circuit,

a. the peak output voltage is greater than the peak input voltage.

b. the load resistance must be less than 5 k•.

c. diode half-wave rectifiers have limitied applications.

d. the peak output voltage is less than the peak input voltage, and the dc pulse period is

less than 180º.


3-36

TROUBLESHOOTING

Location: Troubleshooting page: ttrba2, Question ID: trba2a

Is the circuit operating properly?

a. yes

b. no

Location: Troubleshooting page: ttrba3, Question ID: trba3

6. The faulty component is

a. CR1 (shorted).

b. CR2 (shorted).

c. R2 (shorted).

d. R1 (shorted).

CMS AVAILABLE

None

FAULTS AVAILABLE

Fault 4

Semiconductor Fundamentals Unit 3 – Full-Wave Rectification and Filtering

3-37

UNIT 3 – FULL-WAVE RECTIFICATION AND FILTERING

UNIT OBJECTIVE

Demonstrate full-wave rectification, filtering and voltage doubling by using calculated

and measured circuit conditions.

UNIT FUNDAMENTALS


A full-wave bridge rectifier converts a. only positive ac input alternations into dc output pulses.

b. only negative ac input alternations into dc output pulses.

c. positive and negative ac input alternations into dc output pulses.


The capacitor filter significantly reduces the large ripple of a bridge rectifier output because it

a. charges slowly and discharges quickly.

b. charges quickly and discharges slowly.


The dc output from a voltage doubler equals two times the ac input

a. peak-to-peak voltage.

b. peak voltage.

CMS AVAILABLE

None

FAULTS AVAILABLE

None


3-38

NEW TERMS AND WORDS

full-wave rectifier – a diode configuration in which positive and negative alternations of an ac

input signal are converted into a pulsating dc output signal.

bridge rectifier – a type of full-wave rectifier circuit.

electrolytic capacitor – a high-capacity capacitor that is polarized and used in power supply

filter applications.

capacitor filter – a capacitor used to average the output pulses of a rectifier circuit.

voltage doubler – a circuit designed to rectify, filter, and double the value of a peak ac input

voltage.

EQUIPMENT REQUIRED



Multimeter




3-39

Exercise 1 – Full-Wave Diode Bridge Rectification

EXERCISE OBJECTIVE

Demonstrate full-wave rectification by using a full-wave bridge rectifier circuit. Verify results

with an oscilloscope and a multimeter.

EXERCISE DISCUSSION


The full-wave bridge rectifier is

a. (A).

b. (B).


The output terminals of a full-wave bridge rectifier are the terminals marked with the

a. sine wave symbols.

b. plus (+) and minus (-) symbols.


During positive alternations of the ac input, diodes D1 and D3 are

a. forward biased and permit current through D3, R1, and D1.

b. reverse biased and block current flow through D3, R1, and D1.


When diodes D2 and D4 are forward biased during negative ac input alternations, the dc output

is a

a. negative pulse.

b. positive pulse.


During positive and negative alternations of the ac input, the current flows through the

load resistance in

a. different directions.

b. the same direction.


3-40


The pulsating dc output frequency of the full-wave rectifier is

a. equal to the ac input frequency.

b. two times the ac input frequency.


If the peak output voltage is 10.0 Vo(pk), calculate the average output voltage (Vo(avg)).

Vo(avg) = V



Min/Max Value: (6.233) to (6.487)





EXERCISE PROCEDURE


2. Resistor R1 is the

a. bridge rectifier.

b. load resistor.


8. Does the transformer primary-to-secondary have a step-down or step-up voltage relationship?

a. step-down

b. step-up


10. Are both alternations of the ac input waveform being rectified to dc pulses at the output?

a. yes

b. no


3-41


11. Measure the frequency (f) of the dc output pulsations across the R1 load resistance on

channel 2 of the oscilloscope.

f = Hz

Recall Label for this Question: F1


Min/Max Value: (184) to (216)






12. Set the channel 2 vertical sensitivity to 0.2 V/cm and the vertical mode to channel 2. Measure

the peak dc output voltage (Vo(pk)).

Vo(pk) = V


Nominal Answer: 9.0







13. Calculate the dc average output voltage (Vo(avg)). Use the following equation with your

measured value of Vo(pk) (#V1#V).

Vo(avg) = 0.636 x Vo(pk)

= V



Value Calculation: #V1# *0.636








3-42


14. Set your multimeter to dc volts. Measure the circuit average dc output voltage across R1. The

meter common connects to the negative (–) output terminal.

Vo(avg) = V


Nominal Answer: 5.4

Min/Max Value: (4.968) to (5.832)






15. The transformer secondary coil output was set to 20 Vpk-pk, or a peak voltage of 10 Vpk.

Your measured full-wave rectifier output peak voltage was #V1# Vpk.

The #(10 – V1 )# difference is due to the

a. transformer coil voltage drop.

b. forward voltage drop of the two diodes.


19. When diode D2 is conducting, its voltage drop (shown by the channel 2 waveform) is the

same as the

a. negative (highlighted) portions of the waveform shown above.

b. positive portion of the waveform shown above.


20. On the oscilloscope screen, measure the voltage drop across D2 (VD2) when it is conducting.

Measure VD2 from the ground reference line.

VD2 = V



Min/Max Value: (–0.75) to (–0.25)

Value Calculation: –0.500





3-43


21. During the negative (highlighted) portion of the channel 2 waveform, D2 is

a. reverse biased.

b. forward biased.


22. D2 is forward biased during which alternation of the ac input waveform on channel 1?

a. negative

b. positive


23. What other diode in this circuit is forward biased during the negative alternation of the input

waveform?

a. D1

b. D3

c. D4


24. The positive voltage portion of the oscilloscope channel 2 waveform is across

a. diode D1 and load resistor R1.

b. load resistor R1.

c. diode D4.


25. During the positive portion of the input waveform, D1 is

a. reverse biased.

b. forward biased.


26. What other diode in this circuit is forward biased during the positive alternation of the input

waveform?

a. D2

b. D3

c. D4


27. Connect the channel 2 probe to the positive (+) terminal of the bridge. During the positive ac

input alternations, current flows through

a. D3, R1, and D1.

b. D2, R1, and D4.


3-44


28. During the negative ac input alternations, current flows through

a. D3, R1, and D1.

b. D2, R1, and D4.

REVIEW QUESTIONS


1. In this full-wave bridge rectifier, what diode groups are forward biased together?

a. D1 with D2, and D3 with D4

b. D1 with D4, and D3 with D2

c. D1 with D3, and D2 with D4

d. All diodes: D1, D2, D3, and D4


2. A full-wave bridge rectifier converts

a. positive ac input alternations into a pulsating dc output.

b. negative ac input alternations into a pulsating dc output.

c. negative and positive ac input alternations into a pulsating dc output.

d. a pulsating dc input into an ac output.


3. A full-wave bridge rectifier circuit conducts

a. only during negative input alternations.

b. only during positive input alternations.

c. only when the peak ac voltage is above 2V.

d. during positive and negative input alternations.


4. The output ripple frequency of a full-wave bridge rectifier is

a. double the input frequency.

b. the same as the input frequency.

c. half of the input frequency.

d. a function of the load resistance.


3-45


5. Which statement about a full-wave bridge rectifier is true?

a. The load current of a full-wave bridge rectifier is always in the same direction.

b. The peak dc output voltage is less than the peak ac input voltage by the forward voltage drop

of the two conducting diodes.

c. The average dc output voltage is 0.636 times the peak output voltage.


CMS AVAILABLE

None

FAULTS AVAILABLE

None


3-46

Exercise 2 – Power Supply Filtering

EXERCISE OBJECTIVE

Demonstrate how a filter significantly reduces the ripple of a pulsating dc output to a relatively

smooth dc voltage by using a capacitive input filter circuit. Verify results with a multimeter and

an oscilloscope.

EXERCISE DISCUSSION


A capacitive input filter is an electrolytic capacitor connected

a. across a rectifier output in parallel with the load.

b. in series with the load across a rectifier output.


When there is no load connected across the capacitive input filter, the rectifier output voltage is

a. maintained at the peak voltage.

b. kept at 0 Vdc.


At point B on the filter output waveform,

a. the rectifier is charging C1 and supplying current to RL.

b. C1 has been charged to the peak rectifier output voltage.

c. the rectifier output voltage has increased to the C1 voltage.

d. C1 is discharging through RL.


Between points C and D on the filter output waveform,

a. the rectifier is charging C1 and supplying current to RL.

b. C1 has reached the peak output voltage.

c. the rectifier output voltage has increased to the C1 voltage.

d. C1 is discharging through RL.


3-47


The discharge time of the capacitor filter is

a. shorter than the charge time and depends on the peak voltage of the rectifier.

b. is longer than the charge time and depends mainly on the product of the capacitance

and load resistance (RC time constant).


Is the ripple from a 20-µF capacitor filter larger or smaller than the ripple from a 10-µF

capacitor filter?

a. larger

b. smaller

EXERCISE PROCEDURE


2. The circuit that you connected is a

a. half-wave diode rectifier.

b. capacitor-input filter.

c. full-wave bridge rectifier without a load resistance.


7. The signal that you observe on channel 2 of the oscilloscope is

a. half-wave dc pulses.

b. filtered full-wave dc pulses.

c. unfiltered full-wave dc pulses.


8. On channel 2 of the oscilloscope, measure the peak output voltage (Vo(pk)) of the dc pulses in

reference to ground.

Vo(pk) = V



Min/Max Value: (11.05) to (14.95)






3-48


10. When you added C1 across the full-wave bridge rectifier, the capacitor formed a

a. half-wave diode rectifier circuit.

b. capacitor input filter at the bridge rectifier output.

c. full-wave bridge circuit with a load resistance.


11. The signal on channel 2 is a constant dc voltage because the

a. circuit is no longer a full-wave rectifier when C1 is connected at the output.

b. capacitor charges up to the peak output voltage and stays at that value because there is

no load resistance to discharge the capacitor.


12. With a multimeter, measure the dc output voltage across the bridge rectifier.

dc output voltage = Vdc



Min/Max Value: (11.25) to (13.75)






13. With C1 connected, is your measured dc output voltage of #V6# Vdc essentially equal to the

peak output voltage (#V5# Vdc) without C1 connected?

a. yes

b. no


14. Set channel 2 of the oscilloscope to ac with the lowest vertical sensitivity setting, and observe

if there is any ripple to the dc voltage across C1. Is the ripple content of the C1 voltage

insignificant?

a. yes

b. no


16. The output on channel 2 is the

a. unfiltered output of a diode full-wave rectifier across a 47 kΩ load.

b. filtered output of a diode full-wave rectifier across a 47 kΩ load.


3-49


17. Connect C1 and load resistor R2 (47 kΩ), as shown. The output on channel 2 is the

a. unfiltered output of a diode full-wave rectifier across a 47 kΩ load.

b. filtered output of a diode full-wave retifier across a 47 kΩ load.


Is there any ripple across the rectifier output with C1 and R2 connected?

a. yes

b. no


19. On oscilloscope channel 2, measure the ripple peak-to-peak voltage with C1 and R2

connected across the output.

Ripple = mVpk-pk









20. If necessary, adjust the ac signal at the transformer primary, shown on channel 1, to 20 Vpk-

pk. With a multimeter, measure the dc output voltage across C1 and R2.




Min/Max Value: (8.887) to (10.43)






21. With R2 connected in parallel with C1, the dc output voltage across the bridge rectifier

decreased from #V6# Vdc to #V8# Vdc because

a. of the voltage drop in the transformer secondary coil.

b. the ripple was reduced.


3-50


23. On oscilloscope channel 2, measure the ripple peak-to-peak voltage with C1, C2, and R2

connected across the rectifier.

Ripple = mVpk-pk









24. With a multimeter, measure the rectifier dc output voltage across C1, C2, and R2.




Min/Max Value: (8.878) to (10.42)






25. When the capacitance of the capacitor input filter was increased from 10 µF to 20 µF, your

measured ripple decreased from #V7# mVpk-pk to #V9# mVpk-pk, but the dc output voltage

remained essentially the same (#V8# Vdc to #V10Vdc). From your measurements, you can

conclude that increasing the capacitance of the capacitor input filter significantly decreases the

ripple of the rectified voltage,

a. but does not decrease the dc voltage level.

b. and decreases the dc voltage level.


26. Decrease the load resistance from 47 kΩ to 33 kΩ by removing R2 from and inserting R3 in

the circuit. When the load resistance is decreased, the circuit load or current is

a. decreased.

b. increased.


3-51


27. On oscilloscope channel 2, measure the ripple peak-to-peak voltage with C1, C2, and R3

connected.

Ripple = mVpk-pk









28. With a multimeter, measure the dc output voltage across C1, C2, and R3.




Min/Max Value: (8.4 ) to (9.86 )






For an unregulated power supply with a capacitor input filter, the load resistance

a. affects the ripple and the average dc voltage.

b. does not affect the ripple and the average dc voltage.


30. On channel 1 of the oscilloscope, check that the voltage at the T1 primary is 20 Vpk-pk.

While observing the ripple on channel 2, increase the external sine wave generator frequency to

500 Hz. Does the ripple content of the output voltage on channel 2 increase or decrease when

line frequency increases?

a. increases

b. decreases


3-52


32. CM 15 is activated to put a fault in the circuit. To observe the effect of the CM, toggle CM

15 on and off by clicking on <CM>. CM 15

a. disconnects R2 from the circuit.

b. disconnects C1 from the circuit.

c. shorts T1.

REVIEW QUESTIONS


1. A capacitor input filter is connected in

a. series with the load resistance.

b. parallel with the ac input to a bridge rectifier.

c. parallel with the load resistance.

d. series with the ac input to a bridge rectifier.


2. The average dc output voltage of a full-wave bridge rectifier with a capacitor input filter but

no load is

a. 0.636 times the peak voltage of the dc output pulses.

b. equal to the peak-to-peak voltage of the ac input.

c. 0 Vdc.

d. equal to the rectifier output peak voltage without a filter.


3. The peak-to-peak ripple voltage of a bridge rectifier with a capacitor input filter decreases

with an increase in the

a. capacitance.

b. load resistance.

c. frequency of the input.



4. A capacitor input filter decreases the ripple of a bridge rectifier from the volt range to the

millivolt range and maintains a high average dc output voltage because the capacitor charge and

discharge time constants are

a. small and large, respectively.

b. large and small, respectively.

c. both large.

d. both small.


3-53


5. If a 10 µF capacitor is placed in parallel with a 20 µF capacitor input filter at the output of a

bridge rectifier, the output ripple will

a. increase.

b. not change.

c. decrease.

d. have a lower frequency.

CMS AVAILABLE

CM 15 TOGGLE

FAULTS AVAILABLE

None


3-54

Exercise 3 – Voltage Doubler

EXERCISE OBJECTIVE

Demonstrate how to obtain a filtered dc voltage equal to double the peak

ac input voltage by using a voltage doubler circuit. Verify results with a multimeter and an

oscilloscope.

EXERCISE DISCUSSION


If two capacitors are connected in series and each capacitor is charged to 10 Vdc, the voltage

across the two capacitors is

a. 10 Vdc.

b. 20 Vdc.


Refer to the voltage doubler shown. When diode

a. CR1 conducts, capacitor C1 is charged.

b. CR2 conducts, capacitor C2 is charged.

c. Both of the above.


Suppose the input peak voltage (Vpk) is 15 Vpk. During the negative alternation of the ac input,

C2 is charged (VC2) to about

a. 30.0 Vdc.

b. 14.4 Vdc.


3-55


C1 is charged to 14.4 Vdc during the positive ac input alternation, and C2 is charged to 14.4 Vdc

during the negative ac input alternation. Calculate the maximum dc output voltage (VO) across

C1 and C2.

VO = Vdc



Min/Max Value: (28.22) to (29.38)






If the ac input frequency is 50 Hz, the output ripple frequency of a full-wave voltage doubler is

a. 100 Hz.

b. 50 Hz.

EXERCISE PROCEDURE


5. On oscilloscope channel 2, the peaks of the input signal to the voltage doubler are flattened

because

a. of the voltage drop in the T1 secondary coil during the period when each diode

conducts a relatively high current.

b. the C1 charged voltage is added to the C2 charged voltage.


6. On channel 2 of the oscilloscope, measure the peak input voltage to the voltage doubler.

Input Vpk = V



Min/Max Value: (8.925) to (12.08)






3-56


7. What value would you calculate for the doubler dc output voltage (across R1 and R2) based on

your measured peak input voltage of #V15#V (neglect the diode voltage drops)?

Calculated VO = Vdc



Min/Max Value: (17.85) to (24.15)






8. With the multimeter, measure the dc output voltage from the doubler (across R1 and R2).

Measured VO = Vdc



Min/Max Value: (17.17) to (23.23)






9. Do your calculated (#V16# Vdc) and measured (#V17# Vdc) output voltage values agree,

considering that the diode voltage drops are accounted for in the measured value?

a. yes

b. no


10. With the multimeter, measure the dc voltage charge across C2 (VC2).

VC2 = Vdc



Min/Max Value: (8.585) to (11.62)






3-57


11. With the multimeter, measure the dc voltage charge across C1 (VC1).

VC1 = Vdc



Min/Max Value: (8.585) to (11.62)






12. Does the sum of VC1 (#V19# Vdc) and VC2 (#V18# Vdc) equal the measured output

voltage (#V17# Vdc) within measurement tolerances?

a. no

b. yes


13. Connect the channel 2 probe to the output terminal at the top of C1. Connect the ground clip

to the bottom of C2. Adjust the oscilloscope to ac, and measure the ripple peak-to-peak voltage

of the dc output.

Ripple = mVpk-pk









14. On channel 2 of the oscilloscope, measure the frequency of the ripple. The ripple frequency

equals

a. the frequency of the ac input signal on channel 1.

b. two times the frequency of the ac input signal on channel 1.


3-58


15. CM 18 is activated to add a 39 kΩ load resistor across the output in parallel with R1 and R2.

You may turn CM 18 on and off by clicking on <CM>. Observe the output signal on

oscilloscope channel 2. With a 39 kΩ load, the dc output ripple peak-to-peak voltage

a. increased.

b. decreased.


16. On channel 2 of the oscilloscope, measure the dc output ripple peak-to-peak voltage with a

39 kΩ load (CM 18 on).

Ripple = mVpk-pk









17. With a multimeter, measure the dc output voltage from the voltage doubler with a 39 kΩ load

(CM 18 on).

VO = Vdc



Min/Max Value: (11.22) to (15.18)






3-59

REVIEW QUESTIONS


1. The most likely cause of the output voltage decreasing with CM 17 on is that CM 17 caused

a. open circuits in both diode circuits.

b. an increase in the capacitance of the two capacitors.

c. an open circuit between the input and one diode circuit.

d. an increase in the load resistance.


2. The output of a voltage doubler is about two times the

a. peak-to-peak voltage of the ac input.

b. peak ac input voltage.

c. voltage drop across both diodes.

d. voltage drop across the load resistor.


3. A resistor with a high value (100 kΩ) may be placed across each filter capacitor of a voltage

doubler to

a. equalize the capacitor voltage drops.

b. increase the capacitor voltage change.

c. increase the load resistance.

d. decrease the diode current.


4. In a voltage doubler circuit, each diode/capacitor pair of components conducts

a. for 90º of each ac input cycle.

b. during alternate cycles of the input voltage.

c. during the same half-cycle of the input voltage.

d. during alternate half-cycles of the input voltage.


5. The output ripple frequency of a full-wave voltage doubler

a. is two times the input frequency.

b. is half of the input frequency.

c. equals the input frequency.

d. depends on the capacitor values and load resistance.


3-60

CMs AVAILABLE

CM 18 TOGGLE, located on page 'se3p6'

CM 17 TOGGLE, located on page 'se3r1'

FAULTS AVAILABLE

None


3-61

UNIT TEST QUESTION



If the capacitance of a rectifier filter is increased, the

a. output ripple increases.

b. dc output voltage decreases significantly.

c. load current decreases.

d. output ripple decreases.


A full-wave bridge rectifier circuit has

a. 6 diodes.

b. 4 diodes.

c. 2 diodes.

d. 6, 4, or 2 diodes, depending on the configuration.


A voltage doubler circuit has

a. two capacitors connected in parallel.

b. each capacitor and diode pair connected in parallel.

c. two capacitors connected in series.

d. one capacitor connected in series with the load and another capacitor connected across the

load.


The output of an unfiltered full-wave rectifier is

a. pulsating dc.

b. pulsating ac.

c. a sine wave at twice the line frequency.

d. a relatively smooth dc voltage.


The purpose of a capacitor input filter is to

a. convert ac sine waves into pulsating dc.

b. convert dc ripple waves into dc pulses.

c. convert pulsating dc into pulsating ac.

d. smooth out pulsating dc.


3-62


The average dc output voltage of a nonregulated, filtered rectifier circuit will

a. decrease if the load resistance increases.

b. decrease if the load resistance decreases.

c. not change with changes in the load resistance.

d. not be affected by a change in the ac input voltage.


In a full-wave bridge rectifier, how many diodes conduct at the same time?

a. 6

b. 4

c. 2

d. 1


In a full-wave voltage doubler, how many diodes conduct at a time?

a. 6

b. 4

c. 2

d. 1


One advantage of full-wave rectification is that

a. it uses single alternations of the input voltage.

b. it uses both alternations of the input voltage.

c. it uses more components.

d. output filtering is not required.


The frequency of the dc pulses from a bridge rectifier

a. equals two times the ac input frequency.

b. equals half of the ac input frequency.

c. depends on the capacitance of the filter.

d. equals the ac input frequency.


3-63

TROUBLESHOOTING


Connect the channel 2 oscilloscope probe across R1, which is the output (VR1) of the full-wave

bridge rectifier. Are both alternations of the ac input waveform being rectified to dc pulses atthe

output?

a. yes

b. no

Location: Troubleshooting page: ttrba2, Question ID: trba2c

VR1 = Vdc

Recall Label for this Question: None


Min/Max Value: (6.237) to (7.623)







a. T1 (an open secondary coil).

b. R1 (shorted).

c. D2 (shorted).

d. T1 (an open primary coil).

Location: Troubleshooting page: ttrbb2, Question ID: trbb2a

Connect the channel 2 oscilloscope probe across R1, which is the output (VR1) of the full-wave

bridge rectifier. Are both alternations of the ac input waveform being rectified to dc pulses at the

output?

a. yes

b. no


3-64

Location: Troubleshooting page: ttrbb2, Question ID: trbb2c

VR1 = Vdc



Min/Max Value: (6.237) to (7.623)





Location: Troubleshooting page: ttrbb3, Question ID: trbb3


a. T1 (an open secondary coil).

b. R1 (shorted).

c. D2 (shorted).

d. T1 (an open primary coil).

Location: Troubleshooting page: ttrbc2, Question ID: trbc2a

Connect the channel 2 oscilloscope probe across the output (R1 and R2). Is the output essentially

a constant dc voltage signal with no observable ripple?

a. yes

b. no

Location: Troubleshooting page: ttrbc2, Question ID: trbc2c

4. With a multimeter, mesure the dc voltage of the output (Vo).

Vo = Vdc



Min/Max Value: (17.17) to (23.23)





Location: Troubleshooting page: ttrbc3, Question ID: trbc3


a. CR2 (shorted).

b. CR1 (open).

c. C2 (open or not connected).

d. C1 (open or not connected).


3-65

Location: Troubleshooting page: ttrbd2, Question ID: trbd2a

Connect the channel 2 oscilloscope probe across the output (R1 and R2). Is the output essentially

a constant dc voltage signal with no observable ripple?

a. yes

b. no

Location: Troubleshooting page: ttrbd2, Question ID: trbd2c

4. With a multimeter, mesure the dc voltage of the output (Vo).

Vo = Vdc



Min/Max Value: (17.17) to (23.23)





Location: Troubleshooting page: ttrbd3, Question ID: trbd3


a. CR2 (shorted).

b. CR1 (open).

c. C2 (open or not connected).

d. C1 (open or not connected).

CMS AVAILABLE

None

FAULTS AVAILABLE

Fault 7

Fault 9

Fault 10

Fault 11


3-66

Semiconductor Fundamentals Unit 4 – Diode Wave Shaping and Zener Regulation

3-67

UNIT 4 – DIODE WAVE SHAPING AND ZENER REGULATION

UNIT OBJECTIVE

Demonstrate wave shaping, zener diode operation, and zener diode voltage regulation by using

diode circuits.

UNIT FUNDAMENTALS


The output of a diode wave shaping circuit a. converts dc to ac.

b. has a different output waveform than the input.

c. filters a pulsating dc signal.


The zener voltage of a zener diode is

a. equal to its forward voltage drop.

b. at its reverse breakdown voltage.


A zener diode voltage regulator maintains a nearly constant output voltage for

a. changes in the line voltage.

b. changes in the load current.

c. All of the above.

CMS AVAILABLE

None

FAULTS AVAILABLE

None


3-68

NEW TERMS AND WORDS

limiter – circuits that prevent voltage above or below a specified point from appearing at circuit

output terminals.

clamper – circuits that shift the reference level of a waveform from input to circuit output.

zener diode – a diode designed to operate in the avalanche region, maintaining a relatively

constant voltage drop over a range of current flows. The avalanche operating area of a diode

occurs when the cathode is positive with respect to the anode.

zener voltage – the nearly constant voltage produced by a zener diode.

voltage regulator – an IC that maintains a constant output voltage when both input voltage and

output loads change.

dc restorers – circuits that duplicate their input voltage at their output terminals but move or

shift the signal reference level; also called level shifters.

positive clamper – a circuit that sets or clamps the negative peaks of an input waveform.

negative clamper – a circuit that sets or clamps the positive peaks of an input waveform.

avalanche – the reverse voltage point where a PN junction breaks down to pass high values of

current.

EQUIPMENT REQUIRED



Multimeter




3-69

Exercise 1 – Diode Wave Shaping

EXERCISE OBJECTIVE

Demonstrate limiting and clamping by using diode circuits. Verify results with an oscilloscope.

EXERCISE DISCUSSION


A limiter (or clipper) circuit

a. smooths out dc pulses.

b. functions like a full-wave rectifier.

c. removes an extremity of an input wave.


In the first circuit, the output voltage is limited to about 0.6 Vdc when the diode is

a. forward biased during the positive input alternation.

b. reverse biased during the negative input alternation.


When VB is –6.4 Vdc, the negative output alternation is limited to about

a. –6.4 Vdc.

b. –7.0 Vdc.

c. –0.6 Vdc.


If a clamper circuit holds the positive peak of a square waveform to 0 Vdc, the output would

appear as shown in

a. (a).

b. (b).

c. (c).


If a clamper circuit holds the negative peak of a square waveform to 0 Vdc, the output would

appear as shown in

a. (a).

b. (b).

c. (c).


3-70


If the input square wave has a peak voltage of 15 Vpk, the magnitude of the positive

output peak above 0 Vdc is about

a. 30V.

b. 15V.

c. 20V.


If the input square wave has a peak voltage of 15 Vpk, the magnitude of the C1 capacitor charge

is about

a. +15 Vdc.

b. –15 Vdc.

c. –30 Vdc.

EXERCISE PROCEDURE


3. Connect the channel 2 probe across R2 and observe the output waveform. Is the output

waveform the same shape as the circuit input waveform?

a. yes

b. no


5. With the variable supply at the cathode of CR1 set to 0 Vdc, will the limiter circuit that you

connected limit the positive or negative alternation of the output signal?

a. negative

b. positive


6. Connect the channel 2 probe across circuit load resistor R2. What output alternation is being

limited?

a. negative

b. positive


3-71


Positive output peak = Vpk


Nominal Answer: 0.6







8. The # V1# Vpk that you measured is the

a. forward voltage drop of CR1.

b. voltage drop of R1.


9. Connect the circuit shown. Adjust the negative variable supply at CR2 to 0 Vdc. Use a

multimeter to measure the voltage. What input alternation is being limited?

a. negative

b. positive


10. Adjust the oscilloscope so that you can accurately measure the peak voltage (with reference

to ground) at which the negative output alternation is limited.

Negative output peak = Vpk



Min/Max Value: (–0.84) to (–0.36)






11. Connect the circuit shown. Set the channel 2 vertical sensitivity to 0.2 V/cm with a X10

probe (2 V/cm). With CR1 and CR2 in the circuit, what type of a waveform do you observe?

a. sine wave

b. square wave


3-72


12. Adjust the positive variable supply at CR1 for 2.0 Vdc. Use a multimeter to measure the

voltage. Did the positive or negative output alternation increase?

a. negative

b. positive


13. On channel 2 of the oscilloscope screen, measure the peak of the positive output alternation

from the 0 Vdc (ground) reference level.



Nominal Answer: 2.5







14. Adjust the negative variable supply at CR2 for –2.0 Vdc. Use a multimeter to measure the

voltage. Did the positive or negative output alternation increase?

a. negative

b. positive


15. On channel 2 of the oscilloscope screen, measure the peak of the negative output alternation

from the 0 Vdc (ground) reference level.




Min/Max Value: (–3) to (–2)






3-73


16. Would you conclude that the two-diode limiter (clipper) circuit can convert a sine wave into

a waveform that approximates a square wave?

a. yes

b. no


17. Based on the observed waveforms, is the output signal reference voltage shifted with respect

to the input signal reference voltage?

a. yes

b. no


Reference Voltage Level = mVdc


Nominal Answer: 0.0







21. Observe the clamper circuit output on channel 2. Is the output waveform's positive peak

clamped to about 0 Vdc (neglect the diode forward voltage drop)?

a. no

b. yes





Min/Max Value: (–12) to (–8)






3-74


23. Adjust the positive variable supply at CR1 for 3.0 Vdc. Use a multimeter to measure the

voltage. On channel 2, measure the voltage level to which the positive output peak is clamped,

with reference to ground.

Positive peak clamp voltage = Vdc


Nominal Answer: 3.0







25. Observe the clamper circuit output on channel 2. Is the output waveform's negative peak

clamped to about 0 Vdc (neglect the diode forward voltage drop)?

a. yes

b. no











27. Examine the ac sine wave input on channel 1 and the square wave output on channel 2. Is the

clamping circuit functioning as a dc restorer circuit?

a. no

b. yes


3-75


28. Adjust the negative variable supply at CR2 for –2.0 Vdc. Use a multimeter to measure the

voltage. On channel 2, measure the voltage level to which the negative output peak is clamped,

with reference to ground.

Negative peak clamp voltage = Vdc



Min/Max Value: (–2.5) to (–1.5)






30. CM 14 is activated. Observe the clamper output waveform displayed on channel 2 of the

oscilloscope. Based on the shape of the waveform, CM 14 made the circuit discharge time

constant too

a. short.

b. long.


31. To make the discharge time constant too short, CM 14

a. reduced the R2 load resistance.

b. increased the R2 load resistance.

REVIEW QUESTIONS


1. A diode limiter circuit is used

a. to convert dc to ac.

b. to clip or flatten an output alternation.

c. for full-wave rectification.

d. to reduce but not distort the amplitude of an ac signal.


2. A clamper circuit

a. rectifies and filters a sine wave.

b. converts a square wave into a sine wave.

c. converts a sine wave into a square wave.

d. shifts the input positive or negative amplitude extreme to a different output reference

voltage level.


3-76


3. You can adjust the clipping level of a limiter's output waveform by

a. adding a second capacitor to the circuit.

b. using two diodes in parallel.

c. adding a dc bias voltage to the diode.

d. changing the value of circuit resistance.


4. In order to have a nondistorted output waveform from a clamping circuit, the discharge time

constant

a. should be long compared to the input waveform period.

b. should be short compared to the input waveform period.

c. does not matter in relation to the input waveform period.

d. should be equal to the input waveform period.


5. In the circuit shown,

a. R1 is effectively out of the circuit because CR1 is forward biased.

b. CR1 cannot be forward biased because C1 blocks all dc voltages.

c. C1 charges through R1 and discharges through CR1.

d. C1 charges through CR1 and discharges through R1.

CMS AVAILABLE

CM 14

FAULTS AVAILABLE

None


3-77

Exercise 2 – The Zener Diode

EXERCISE OBJECTIVE

Demonstrate the operation of a zener diode by using a dc characteristic curve. Verify results with

a multimeter.

EXERCISE DISCUSSION


The avalanche or zener voltage of a zener diode is at the

a. forward bias voltage.

b. breakdown voltage.


The zener diode is

a. CR1.

b. CR2.


At the zener region of a dc characteristic curve for a zener diode, the

a. forward current increases very rapidly with a slight increase in voltage.

b. reverse current decreases very rapidly with a large increase in reverse voltage.

c. reverse current increases very rapidly with a slight increase in reverse voltage.


The zener test current (IZT) is at a point on the characteristic curve where the zener current

a. increases slowly with an increase in reverse voltage.

b. starts to increase very rapidly with a small increase in the zener voltage.


In the circuit shown, the zener current (IZ) would be

a. (VA – VZ)/R2.

b. VZ/R2.


3-78

EXERCISE PROCEDURE


2. Forward bias the zener diode (CR1) with an ohmmeter by connecting the red (positive) meter

lead to the anode and the black (negative) meter lead to the cathode. The meter indicates that the

zener diode is

a. conducting.

b. not conducting.


3. Reverse bias the zener diode (CR1) with an ohmmeter by connecting the red (positive) meter

lead to the cathode. The meter indicates that the zener diode is

a. conducting.

b. not conducting.


5. Measure the voltage across zener CR1 (VCR1).

VCR1 = Vdc



Min/Max Value: (–0.91) to (–0.49)






6. Does your measurement of VCR1 (#V9# Vdc) indicate that CR1 is forward or reverse biased?

a. reverse biased

b. forward biased


3-79


VCR1 = Vdc



Min/Max Value: (–0.91) to (–0.49)






8. Based on your VCR1 measurements of #V9# Vdc and #V10# Vdc when the supply voltage

was increased, would you conclude that the zener diode (CR1) is functioning like a rectifier

diode when it is forward biased?

a. yes

b. no


a. Measure VCR1.


Nominal Answer: 6.0







Measure VR3


Nominal Answer: 0.0







3-80


13. VA is set at 7.0 Vdc.

a. Measure VCR1.



Min/Max Value: (5.966) to (7.594)






b. Measure VR3.










a. Measure VCR1.



Min/Max Value: (6.028) to (7.672)






3-81


b. Measure VR3.



Min/Max Value: (87.75) to (302.3)







a. Measure VCR1.



Min/Max Value: (5.925) to (8.015)






b. Measure VR3.









20. Does your zener current (IZ) versus voltage drop (VCR1) data match a typical zener dc

characteristic curve?

a. yes

b. no


3-82


21. IZ is about 0 mA when VCR1 is less than #V15# Vdc because the zener

a. voltage has not been reached.

b. is forward biased.


22. Is the zener voltage (VZ) about #V17# Vdc?

a. no

b. yes


23. Is the zener test current (IZT) between #V18# mA and #V20# mA?

a. yes

b. no

REVIEW


1. A zener diode differs from a rectifier diode because

a. it is designed to operate at the forward voltage drop.

b. it is made from glass instead of ceramic material.

c. it is designed to operate at the breakdown voltage.

d. of the high breakdown voltage specification.


2. At the zener voltage, the reverse current

a. decreases very rapidly with small increases in reverse voltage.

b. equals the leakage current.

c. is a fixed value.

d. increases very rapidly with small increases in reverse voltage.


3. The zener voltage is the

a. reverse breakdown voltage of a zener diode.

b. forward voltage drop of a zener diode.

c. region where only leakage current flows in a diode.

d. voltage region before the breakthrough voltage.


3-83


4. The zener test current (IZT)

a. occurs at the knee of the reverse voltage and current curve.

b. occurs when the zener overheats due to excess power generation.

c. sets the zener voltage within its tolerance limits.

d. occurs when a forward bias is applied to the zener diode.


5. If the voltage drop is 1.0 Vdc across a 50Ω resistor in series with a zener diode having a zener

voltage of 6.8V, the zener current is (use Ohm's law: I = V/R)

a. 20 mA.

b. equal to IZT.

c. 50 mA.

d. 136 mA.

CMS AVAILABLE

None

FAULTS AVAILABLE

None


3-84

Exercise 3 – Zener Diode Voltage Regulation

EXERCISE OBJECTIVE

Demonstrate voltage regulation by using a zener diode voltage regulator. Verify results with a

multimeter.

EXERCISE DISCUSSION


The property of a zener diode that makes it possible to use the zener as a voltage regulator is the

nearly constant

a. forward voltage drop.

b. zener voltage (VZ) when reverse biased.


The purpose of RS in the zener diode regulation circuit is to

a. prevent IZ from reaching a damaging high value.

b. set the CR1 voltage.


When a zener voltage regulator controls the voltage at a value equal to the zener voltage, IT

equals

a. IL – IZ.

b. IL + IZ.


During normal operation of a zener voltage regulator, an increase in IL will

a. be offset by a decrease in IZ.

b. cause an increase in IT.


When the zener current decreases past the knee on the characteristic curve, the zener

voltage starts to

a. increase significantly with small decreases in the zener current.

b. decrease significantly with small decreases in the zener current.


3-85


% Load Regulation = %


Nominal Answer: 1.4

Min/Max Value: (1.344) to (1.456)






If VA increases and causes IT to increase by 15 mA, VO will remain about the same because the

a. IZ will increase by about 15 mA.

b. IL will decrease by about 15 mA.

EXERCISE PROCEDURE


a. Measure VO across R4 and R5.



Min/Max Value: (5.848) to (7.912)






b. Remove the two-post connector across R3, and measure VR3.









3-86





Min/Max Value: (5.831) to (7.889)


















Min/Max Value: (5.814) to (7.866)















3-87





Min/Max Value: (4.616) to (6.245)








Nominal Answer: 0.0







13. Does your VO and IL data match the typical curve for the circuit, within the measurement

tolerance?

a. yes

b. no


14. Based on your data, does the regulator have control of VO up to 20 mA of IL?

a. no

b. yes


15. Based on your data, does the regulator lose control of VO after 20 mA?

a. no

b. yes


3-88


16. The reason the regulator loses control after 20 mA of IL is that

a. IZ approaches 0 mA.

b. VA cannot provide a total current greater than 20 mA.


= %


Nominal Answer: 0.585 ∗Min/Max Value: (–26.2) to (36.81)

Value Calculation: ((#V25#–#V29#)/#V29#)100





20. Adjust the positive variable supply so that the line voltage (VA) equals 10.0 Vdc. The

voltmeter connections are shown for first adjusting VA, and then, measuring VO.



Min/Max Value: (5.925) to (8.015)






21. Reduce VA to 8.0 Vdc. Measure VO.

VO = Vdc



Min/Max Value: (5.814) to (7.866)









3-89


22. Reduce VA to 6.0 Vdc. Measure VO.

VO = Vdc



Min/Max Value: (4.828) to (6.532)






25. Does the zener voltage regulator control VO when VA varies between 8.0 Vdc and 10.0

Vdc?

a. yes

b. no


26. The zener voltage regulator lost control of VO when VA was reduced to 6.0 Vdc because the

a. load current was too low.

b. zener current was reduced to 0 mA.


27. Connect R3 in series with the zener (CR3) by removing the two-post connector, and measure

VR3.

VR3 = mVdc


Nominal Answer: 0.0







28. Does this measurement of VR3 (#V37# mVdc) confirm your answer to why the zener

regulator cannot control VO when VA equals 6.0 Vdc?

a. yes

b. no


3-90

REVIEW QUESTIONS


With R2 affected by CM 6, the zener diode voltage regulator

a. is operating properly.

b. is not regulating VO.

c. regulates VO only when R4 is set CCW to 1 kΩ.

d. regulates VO only when R4 is set CW to 0Ω.


2. CM 6 is still on so that you can see the effect of varying R4 on VO. Based on your observation

of VO as the value of R4 is changed,

a. the value of R2 is decreased from its original value (62Ω).

b. the circuit is opened at R2.

c. the value of R2 is increased to the point where the R2 voltage drop is greater than 4.0

Vdc.

d. the value of R2 is increased by about 50Ω.


3. During normal operation of the zener diode regulator shown, excess circuit voltage is dropped

across the

a. zener diode (CR2).

b. load resistors (R4 and R5).

c. series dropping resistor (R2).

d. power supply (VA).


4. When the zener voltage regulator is operating normally, the output voltage is maintained fairly

constant at the zener voltage because

a. an increase in zener current compensates for an increase in load current.

b. a decrease in zener current compensates for a decrease in load current.

c. a decrease in zener current compensates for an increase in load current.



3-91


5. Within operating limits, a zener voltage regulator can maintain a fairly constant output voltage

for changes in

a. line voltage.

b. load current.

c. load resistance.


CMS AVAILABLE

CM 6

CM 6

FAULTS AVAILABLE

None


3-92

UNIT TEST



In clipping or clamping circuits, a bias voltage applied to the diode

a. must be negative.

b. must be positive.

c. is used to set the voltage at which the diode conducts.

d. can be applied only to the cathode of the diode.


In the reverse biased direction, a rectifier diode and a zener diode

a. have identical breakdown points.

b. have avalanche currents occurring at the breakdown voltage.

c. are turned on until the breakdown point is reached.

d. have different forward voltage drops.


A clipper circuit

a. limits output signals to certain frequencies.

b. limits amplitude extremes of a waveform.

c. clamps a waveform to a given reference level.

d. smooths out a pulsating dc voltage.


A clamper circuit

a. holds either amplitude extreme to a given reference level.

b. clips both amplitude extremes to obtain a reference level.

c. clamps the frequency to a fixed value.



Limiting can be produced by

a. a zener diode.

b. a diode in series with the input signal.

c. diodes in parallel with the input signal.



3-93


With respect to the period of the input signal to a clamper circuit, the

a. charge and discharge time constants should be short.

b. charge time constant should be short and discharge time constant should be long.

c. charge time constant should be long and discharge time constant should be short.

d. charge and discharge time constants should be long.


During normal operation of a zener diode regulation circuit, the zener current is selected to have

a value

a. in the soft region.

b. exactly at the knee region.

c. in the stiff region.

d. of less than 5 mA.


The zener voltage is

a. the forward barrier voltage.

b. never greater than 6.8 Vdc.

c. very unpredictable.

d. the reverse breakdown voltage.


During normal operation, if the supply voltage (VA) of a zener regulator circuit increases while

the load (RL) remains constant, then

a. total circuit current (IT) will not change.

b. IT will increase.

c. IT will decrease.

d. the circuit will fall out of regulation.


During normal operation, if the supply voltage (VA) of a zener regulator circuit increases while

the load (RL) remains constant, then

a. the zener current (IZ) will increase.

b. the load current (IL) will increase.

c. both the load and zener currents will increase.

d. both the load and zener currents will decrease.


3-94

TROUBLESHOOTING


VO = Vdc



Min/Max Value: (6.282) to (7.678)






VO = Vdc



Min/Max Value: (5.409) to (6.611)







a. CR1 (shorted).

b. R2 (open).

c. R4 (open).

d. R4 (wiper open).


5. Before a fault is inserted, verify that the positive clamper circuit is working properly. Connect

the channel 2 oscilloscope probe across R2 to observe and measure the output (VO) of the

positive clamper circuit output. In the output signal waveform a square wave with the bottom of

the square wave clamped to 0 Vdc?

a. yes

b. no


3-95


6. On channel 2 of the oscilloscope, measure the voltage level of the positive output peak above

0 Vdc. Positive peak voltage level = V










a. CR2 (shorted).

b. R2 (open).

c. R2 (resistance decreased to about 1 kΩ). d. C1 (shorted).

CMS AVAILABLE

None

FAULTS AVAILABLE

Fault 3

Fault 8


3-96

Semiconductor Fundamentals Unit 5 – Transistor Junctions and PNP DC Bias

3-97

UNIT 5 – TRANSISTOR JUNCTIONS AND PNP DC BIAS

UNIT OBJECTIVE

Test transistors and demonstrate a transistor switch by using PNP and NPN transistor circuits.

UNIT FUNDAMENTALS


The middle section of a transistor is the a. collector, which is wide and heavily doped.

b. emitter, which is wide and heavily doped.

c. base, which is thin and lightly doped.


The PNP transistor is

a. Q1.

b. Q2.


For the base-emitter junction of a PNP transistor to be forward biased, the base has to be more

a. positive than the emitter.

b. negative than the emitter.

CMS AVAILABLE

None

FAULTS AVAILABLE

None


3-98

NEW TERMS AND WORDS

junctions – the points of contact between the emitter and base or the base and collector sections

of a transistor.

PNP – a transistor type that has an N type material sandwiched between two P type materials.

NPN – a transistor type that has P type material sandwiched between two N type materials.

EQUIPMENT REQUIRED



Multimeter


3-99

Exercise 1 – Testing the Junctions of a Transistor

EXERCISE OBJECTIVE

Test a transistor by forward biasing and reverse biasing the junctions. Verify results with an

ohmmeter.

EXERCISE DISCUSSION


Testing a transistor with an ohmmeter can show if it

a. is open or shorted.

b. is a PNP or NPN type.

c. has a significant leakage.



Each of the two junctions of a transistor can be tested as if it were a

a. resistor.

b. diode.


The base-emitter junction of an NPN transistor conducts when forward biased. The transistor is

a. good.

b. bad.


The base-collector junction of an NPN transistor conducts when reverse biased. The transistor is

a. good.

b. bad.


The base-collector junction of a PNP transistor conducts when forward biased. The transistor is

a. good.

b. bad.


3-100


A transistor is in its off state. An ohmmeter reading connected across the collector and emitter

indicates that there is current flow. The transistor is

a. good.

b. bad.


The ohmmeter above is connected to

a. forward bias the base-emitter junction.

b. reverse bias the base-emitter junction.


The ohmmeter above is connected to

a. forward bias the base-collector junction.

b. reverse bias the base-collector junction.


The ohmmeter above indicates a zero reading.

a. The base-collector junction is shorted.

b. There is a short between the collector and emitter.

c. The transistor is not defective.

EXERCISE PROCEDURE


3. Your ohmmeter reading indicates that the base-emitter junction is

a. not conducting.

b. conducting.


4. Your measurement indicates that the Q1 base-emitter junction is

a. forward biased.

b. reverse biased.


6. Your meter reading indicates that the base-collector junction is

a. not conducting.

b. conducting.


3-101


7. Your measurement indicates that the Q1 base-collector junction is

a. forward biased.

b. reverse biased.


8. Because your measurements showed that the Q1 base-emitter and base-collector junctions are

forward biased when the base is more positive than the emitter or collector, Q1 is a(n)

a. PNP transistor.

b. NPN transistor.


9. Observe diodes CR1 and CR2 connected at the base of transistor Q1 on the TRANSISTOR

JUNCTION circuit block. If the black (negative-common) meter probe was connected at the

cathode of diode CR1 or diode CR2 while the red (positive) lead was connected to the Q1 base,

the diodes would be

a. forward biased.

b. reverse biased.


10. Can you conclude that the Q1 base-emitter junction behaves like diode CR2 and that the Q1

base-collector junction behaves like diode CR1?

a. no

b. yes


11. With a good transistor, the ohmmeter as connected would indicate

a. no conduction between the collector and emitter.

b. conduction between the collector and emitter.


12. CM 2 is activated to introduce a fault in Q1. Use the ohmmeter to test the junctions. The fault

is

a. in the Q1 base-collector junction.

b. between the Q1 collector and emitter.

c. in the Q1 base-emitter junction.


3-102


13. When CM 2 is on, the Q1 base-emitter junction is

a. open.

b. shorted.


15. Your meter reading indicates that the base-emitter junction is

a. not conducting.

b. conducting.


16. Your measurement indicates that the Q2 base-emitter junction is

a. forward biased.

b. reverse biased.


18. Your meter reading indicates that the Q2 base-collector junction is

a. not conducting.

b. conducting.


19. Your measurement indicates that the Q2 base-collector junction is

a. forward biased.

b. reverse biased.


20. Because your measurements showed that the Q2 base-emitter and base-collector junctions

are reverse biased when the base is more positive than the emitter or collector, Q2 is a(n)

a. PNP transistor.

b. NPN transistor.


21. Observe the TRANSISTOR JUNCTION circuit block. If the black (negative-common) meter

probe were placed at the anode of diode CR2 or diode CR3, the diodes would be

a. forward biased.

b. reverse biased.


3-103


22. Can you conclude that the Q2 base-emitter junction behaves like diode CR4 and that the Q2

base-collector junction behaves like diode CR3?

a. no

b. yes


23. With a good Q2 transistor, the ohmmeter as connected would indicate

a. no conduction between the collector and emitter.

b. conduction between the collector and emitter.

REVIEW QUESTIONS


1. Locate Q2 on the TRANSISTOR JUNCTION circuit block. CM 3 is activated. With an

ohmmeter, test the junctions of transistor Q2. Your tests show that

a. a base-emitter junction is shorted.

b. the base connection is open.

c. a short exists between the collector and emitter.

d. the collector connection is open.


2. When the base-emitter junction of a PNP transistor is forward biased, the

a. base is more negative than the emitter.

b. base is more positive than the emitter.

c. base is more positive than the emitter and collector.

d. collector is more positive than the base.


3. The base-collector junction of an NPN transistor is reverse biased when the

a. collector is more negative than the base.

b. base is more positive than the collector.

c. emitter is more negative than the base.

d. base is more negative than the collector.


3-104


4. An ohmmeter reads zero when the base-emitter junction of a PNP transistor is forward biased

or reverse biased. The junction is

a. functioning properly.

b. open.

c. shorted.

d. reverse biased.


5. The section that is sandwiched by the two outer sections of a transistor is the

a. base.

b. emitter.

c. collector.

d. CE junction.

CMS AVAILABLE

CM 2

CM 3

FAULTS AVAILABLE

None


3-105

Exercise 2 – PNP Transistor Current Control Circuit

EXERCISE OBJECTIVE

Demonstrate transistor current control by using a PNP transistor circuit. You will verify your

results with a multimeter.

EXERCISE DISCUSSION


For current to flow in a transistor, the base-emitter junction has to be

a. reverse biased.

b. forward biased.


The base-emitter junction forward bias voltage drop of a silicon transistor is about

a. 1.2 Vdc to 2.0 Vdc

b. 0.5 Vdc to 0.8 Vdc.


A transistor behaves like an open switch when the

a. base-emitter junction is reverse biased.

b. base-collector junction is reverse biased.


The transistor collector current (IC) is controlled by the

a. voltage of the power supply.

b. transistor base current (IB).

c. type (PNP or NPN) of transistor.


When maximum collector current (IC) flows, the transistor is operating at the

a. cutoff point.

b. saturation point.


3-106


The transistor collector and emitter currents

a. have a difference equal to the base current.

b. can be considered almost equal because the base current is very small.

c. vary directly with the base current.


EXERCISE PROCEDURE


2. In the circuit you connected, the PNP transistor (Q1) is

a. forward biased.

b. reverse biased.


3. The LED (DS1) is off because current is

a. flowing.

b. not flowing.


VA = Vdc



Min/Max Value: (–15.6) to (–14.4)






VBE = mVdc


Nominal Answer: 0.0


Value Calculation: 0





3-107


6. Is transistor Q1 conducting?

a. yes

b. no


7. Measure the voltage drop between the collector and emitter of Q1.

VCE = Vdc



Min/Max Value: (–15. ) to (–12.2 )






Is transistor Q1 conducting?

a. yes

b. no


9. Measure the voltage drop across the Q1 base-emitter junction with the meter common lead

connected to the emitter.

VBE = Vdc



Min/Max Value: ( –.91) to ( –.55)






10. The base-emitter junction is

a. forward biased.

b. reverse biased.


3-108


11. With Q1 conducting, measure the voltage drop between the emitter and collector.

VCE = Vdc



Min/Max Value: (–0.12) to (–0.04)






12. Transistor Q1 is operating at the

a. cutoff point.



13. Connect the voltmeter lead to the Q1 collector, and connect the common lead between R2

and DS1. Measure the voltage drop across collector resistor R2.

VR2 = Vdc



Min/Max Value: (11.05) to (14.95)






IC = mA


Nominal Answer: 13.0 ∗Min/Max Value: (10.72) to (15.4 )









3-109


16. Connect the voltmeter lead to the Q1 collector, and connect the common lead between R2

and DS1. Measure the voltage drop across collector resistor R2.

VR2 = Vdc


Nominal Answer: 2.5







IC = mA








18. The decrease in IC from #I1# mA to #V2# mA caused the LED to become

a. dimmer.

b. brighter.





3-110


19. Measure the voltage drop across the Q1 base-emitter junction with the meter common lead

connected to the emitter.

VBE = Vdc



Min/Max Value: (–0.8) to (–0.48)






20. Was the decrease in VBE from #V3# Vdc to #V4# Vdc caused by the lower base current?

a. yes

b. no


21. Is the PNP transistor (Q1) base-emitter junction still forward biased?

a. yes

b. no


22. With Q1 conducting less, measure the voltage drop between the collector and emitter, with

reference to the emitter.

VCE = Vdc



Min/Max Value: (–14) to (–8.4)






3-111

REVIEW QUESTIONS


1. Connect the circuit shown. The LED is not glowing, which indicates that no collector current

is flowing. With a voltmeter, check the voltage drops across the Q1 junctions. Your tests show

that the

a. base-emitter junction is shorted.

b. base-emitter junction is open.

c. base-collector junction is open.

d. base-collector junction is shorted.


2. When a transistor is operated as a switch, it operates

a. either at the saturation point or cutoff point.

b. in between the saturation and cutoff points.

c. always at the saturation point.

d. always at the cutoff point.


3. For a transistor to conduct, the

a. base-emitter junction has to be reverse biased.

b. base-collector junction has to be forward biased.

c. base-emitter junction has to be forward biased.

d. base resistor cannot be greater than 10 kΩ.


4. When a transistor is not conducting, the voltage drop across the collector and emitter (VCE)

terminals

a. approaches 0 Vdc.

b. is usually between 1 Vdc and 2 Vdc.

c. is not predictable.

d. is about equal to the supply voltage (VA).


5. The transistor collector current varies directly with the

a. base current.

b. type (NPN or PNP) of transistor.

c. value of the collector resistor.

d. reverse bias voltage drop of the base-emitter junction.


3-112

CMS AVAILABLE

CM 9 TOGGLE

CM 9

CM 9

CM 10

FAULTS AVAILABLE

None


3-113

UNIT TEST



A transistor is primarily

a. a voltage-controlling device.

b. a capacitance-controlling device.

c. a current-controlling device.

d. an inductance-controlling device.


A transistor has

a. four semiconductor regions.

b. three PN junctions.

c. two PN junctions.

d. two semiconductor regions.


When a transistor is operating in saturation as a closed switch, the

a. collector current is maximum.

b. collector current is minimum.

c. base-emitter junction is reverse biased.

d. collector-emitter voltage drop is maximum.


CIRCUIT VOLTAGES

VA = –10 Vdc

VB = –0.7 Vdc

VE = 0 Vdc

VC = –0.2 Vdc

a. base-emitter junction is forward biased and the LED is glowing.

b. base-emitter junction is reverse biased and the LED is not glowing.

c. base current is greater than the collector current.

d. collector current is greater than the emitter current.


In a PNP transistor, the

a. base has to be more negative than the emitter for the junction to be forward biased.

b. collector has to be more negative than the base for the junction to be reverse biased.

c. base is composed of negative semiconductor material.



3-114


For a PNP or NPN transistor to conduct, the

a. base-collector junction has to be forward biased.

b. voltage supply should be greater than 10 Vdc.

c. base-emitter junction has to be reverse biased.

d. base-emitter junction has to be forward biased.


When a transistor is at the cutoff point,

a. the collector current is 50% of maximum and the forward bias voltage is minimum.

b. only the base current flows between the emitter and base regions.

c. the transistor current is zero and the collector-emitter voltage equals the transistor

power supply voltage.

d. the base-collector junction is forward biased.


The relationship of the transistor currents is

a. IC = IB + IE.

b. IB = IC – IE.

c. IE = IB + IC.

d. IE = IC – IB.


A transistor is tested with an ohmmeter. When the base-emitter junction is forward biased or

reverse biased, the ohmmeter indicates no current flow through the junction. The transistor is

a. defective because there is no leakage current.

b. good because current never flows through a base-emitter junction.

c. defective because the base-emitter junction is open.

d. defective because the base-emitter junction is shorted.


A PNP transistor is tested with the ohmmeter leads connected as shown. What test is being

performed?

a. The base-collector junction is being tested when forward biased.

b. The base-emitter junction is being tested when forward biased.

c. The base-emitter junction is being tested when reverse biased.

d. The emitter-collector junction is being tested when reverse biased.


3-115

TROUBLESHOOTING


3. Before a fault is inserted, you will be given practice in checking a transistor junction. With an

ohmmeter, forward bias the Q1 base-emitter junction. Is there base-emitter junction forward

current (Q1 - IBE-FORWARD)?

a. yes

b. no


4. With an ohmmeter, reverse bias the Q1 base-emitter junction. Is there base-emitter reverse

current (Q1 - IBE-REVERSE)

a. yes

b. no

Location: Troubleshooting page: ttrba2, Question ID: trba2e

5. Is there current flow (Q1 - ICE) between the Q1 collector and emitter?

a. yes

b. no



a. Q1 (emitter-collector junction).

b. Q2 (base-emitter junction).

c. Q1 (base-collector junction).

d. Q2 (collector-emitter junction).


3. Before a fault is inserted, you will be given practice in checking a transistor junction. With an

ohmmeter, forward bias the Q1 base-emitter junction. Is there base-emitter junction forward

current (Q1 - IBE-FORWARD)?

a. yes

b. no


3-116


4. With an ohmmeter, reverse bias the Q1 base-emitter junction. Is there base-emitter reverse

current (Q1 - IBE-REVERSE)

a. yes

b. no

Location: Troubleshooting page: ttrbb2, Question ID: trbb2e

5. Is there current flow (Q1 - ICE) between the Q1 collector and emitter?

a. yes

b. no



a. Q1 (emitter-collector junction).

b. Q2 (base-emitter junction).

c. Q1 (base-collector junction).

d. Q2 (collector-emitter junction).

Location: Troubleshooting page: ttrbc2, Question ID: trbc2a

2. Before a fault is inserted in the circuit, verify that the circuit is connected and operating

properly by observing the LED (DS1) and by measuring the Q1 collector-emitter voltage (VCE).

Is the LED (DS1) glowing brightly?

a. yes

b. no

Location: Troubleshooting page: ttrbc2, Question ID: trbc2c

3. Measure the Q1 collector-emitter voltage (VCE).

VCE = Vdc



Min/Max Value: ( –.5 ) to ( 0 )






3-117

Location: Troubleshooting page: ttrbc3, Question ID: trbc3

5. The component fault is

a. Q1 (open-emitter junction).

b. R2 (shorted).

c. Q1 (shorted base-emitter junction).

d. R1 (open circuit between R1 and VA).

CMS AVAILABLE

None

FAULTS AVAILABLE

Fault 1

Fault 2

Fault 5


3-118

Semiconductor Fundamentals Unit 6 – Transistor Load Lines and Gain

3-119

UNIT 6 – TRANSISTOR LOAD LINES AND GAIN

UNIT OBJECTIVE

Demonstrate how operating conditions and gain affect transistor circuit currents by using a

transistor dc or load line.

UNIT FUNDAMENTALS


For base current (IB) to flow, the base-emitter junction must be

a. forward biased.

b. reverse biased.


The current gain (βDC) equals

a. IC /IE.

b. IC /IB.


In the active region on the load line,

a. the base-emitter junction is forward biased and the base-collector junction is reverse

biased.

b. both junctions are forward biased.

c. the base-emitter junction is reverse biased.

CMS AVAILABLE

None

FAULTS AVAILABLE

None


3-120

NEW TERMS AND WORDS

load line – a plot of collector current versus collector voltage used to determine the best

transistor operating point.

saturation point – the operating point at which maximum collector current is flowing in a

forward biased transistor.

cutoff point – the operating point of a reverse biased transistor (not conducting).

quiescent point – the dc operating point of a transistor equal to about half of the supply voltage.

EQUIPMENT REQUIRED



Multimeter


3-121

Exercise 1 – Base-Emitter Bias Potentials

EXERCISE OBJECTIVE

Demonstrate the relationship between the transistor base-emitter voltage and the base current by

using a transistor circuit. Verify results with a multimeter.

EXERCISE DISCUSSION


Voltage applied across a PN transistor junction can bias the junction in either the forward or

reverse direction similar to a diode junction,

a. and two diodes connected back-to-back function like a transistor.

b. but two diodes connected back-to-back do not function like a transistor.


When the forward voltage drop of a transistor is reached, the forward current

a. increases at a constant rate with voltage.

b. increases very rapidly with very small increases in voltage.


For current to flow in a transistor circuit, the

a. base-collector junction has to be forward biased.

b. base-collector junction has to be reverse biased.

c. base-emitter junction has to be forward biased.

EXERCISE PROCEDURE


3. Is the base-emitter junction of Q1 (NPN) forward or reverse biased?

a. forward biased

b. reverse biased


3-122


4. Measure the Q1 base-emitter voltage with the collector open (VBEO).

VBEO = Vdc



Min/Max Value: (–2.625) to (–2.375)






5. Is forward base current flowing?

a. yes

b. no


VBEO = Vdc



Min/Max Value: (0.555) to (0.925)






8. With the change in the circuit, is the base-emitter junction of Q1 forward or reverse biased?

a. forward biased

b. reverse biased


b. Measure VBEO.



Min/Max Value: ( .454) to ( .756)






3-123


b. Measure VBEO.



Min/Max Value: ( .491) to ( .819)






b. Measure VBEO.









b. Measure VBEO.



Min/Max Value: ( .529) to ( .881)






21. Is there a similarity between your data of IBEO versus VBEO for a transistor and the forward

current versus forward voltage drop of a diode?

a. yes

b. no


3-124

REVIEW QUESTIONS


1. The base-emitter junction of a transistor

a. can only be reverse biased regardless of the applied voltage polarity.

b. can only be forward biased regardless of the applied voltage polarity.

c. can be forward or reverse biased depending on the polarity of the applied voltage.

d. has completely different forward dc characteristics than those of a diode.


2. Silicon diodes and transistors

a. have significantly different forward voltage drops.

b. both have forward voltage drops in the range of 0.5 to 0.75 Vdc.

c. differ because a transistor junction does not have a reverse breakdown voltage.

d. have forward current versus forward voltage relationships that are different.


3. The IBEO versus VBEO curve is shown. When the base-emitter forward voltage (VBEO) is at

0.50 Vdc, the base-emitter forward current (IBEO) of a silicon transistor

a. is above 2 mA.

b. starts increasing very rapidly.

c. starts decreasing very rapidly.

d. is less than 20 µA.


4. Refer to the curve. The base-emitter current (IBEO) with the collector open starts increasing

into the hundreds of microamps range after the base-emitter forward voltage (VBEO)

a. exceeds 0.70 Vdc.

b. exceeds 0.60 Vdc.

c. is greater than 0.40 Vdc but less than 0.55 Vdc.

d. exceeds 0.75 Vdc.


5. Refer to the curve. When the base-emitter current (IBEO) exceeds 2 mA, the base-emitter

forward voltage drop

a. starts decreasing.

b. is less than 0.5 Vdc.

c. can be considered essentially constant.

d. increases very rapidly.


3-125

CMs AVAILABLE

None

FAULTS AVAILABLE

None


3-126

Exercise 2 – Collector Current Versus Base Current

EXERCISE OBJECTIVE

Demonstrate the relationship of collector current to base current by using a transistor circuit.

Verify results with a multimeter.

EXERCISE DISCUSSION


Current flows in transistor Q1 because the

a. base-collector junction is reverse biased.

b. base-emitter junction is forward biased.


The emitter current of a transistor is 10 mA. The collector current would be about

a. 0.5 mA and the base current would be about 9.5 mA.

b. 9.5 mA and the base current would be about 0.5 mA.


IC = βDC x IB

= mA


Nominal Answer: 4.0







3-127

EXERCISE PROCEDURE


5. IC is 2.0 mA.

a. Measure the voltage drop across base resistor R6 (1 kΩ).

VR6 = Vdc



Min/Max Value: ( .006) to ( .04 )






7. IC is 6.00 mA.

a. Measure the voltage drop across R6 (1 kΩ).

VR6 = Vdc



Min/Max Value: ( .018) to ( .123)






9. IC is 10.00 mA.

a. Measure the voltage drop across R6 (1 kΩ).

VR6 = Vdc



Min/Max Value: ( .029) to ( .205)






3-128


12. Does your IC versus IB data fall between the plots for gains of 300 and 50?

a. yes

b. no


13. From your data, calculate the IB change required to increase IC from 2 mA to 10 mA.

Change in IB = µA


Nominal Answer: 94.0 *Min/Max Value: Value Calculation ± 1%

Value Calculation: (#V13#–#V11#)1000





14. Calculate the gain (βDC) of Q1 from the 0.094 mA change in IB for an 8.0 mA change in IC.

βDC = IC /IB

Recall Label for this Question: G1

Nominal Answer: 85.11 *Min/Max Value: Value Calculation ± 2%

Value Calculation: (8.0/#I10#)1000





15. Does your calculated gain (βDC) of #G1# from collector and base current measurements fall

within the gain specification limits of 50 to 300?

a. yes

b. no

* To compensate for tolerance accumulation overflow, Min/Max Values are not shown.


3-129

REVIEW QUESTIONS


1. The current gain property of a transistor permits

a. a small collector current (IC) to control a large base current (IB).

b. a small base current (IB) to control a large collector current (IC).

c. a small emitter current (IE) to control a large collector current (IC).

d. collector current (IC) to flow when the base-emitter junction is reverse biased.


2. The dc current gain (βDC) is expressed by which relationship?

a. βDC = IC /IB

b. βDC = IB /IC

c. βDC = IB /IE

d. βDC = IC /IE


3. The dc current gain (βDC) of the transistor used in this exercise was between

a. 5 and 30.

b. 50 and 300.

c. 300 and 500.

d. 30 and 50.


4. Suppose a collector current (IC) of 10 mA is required for a transistor with a gain (βDC) of

200. Calculate the base current (IB) by using the gain relationship (βDC = IC /IB).

a. 0.02 mA

b. 0.02 µA

c. 0.05 µA

d. 0.05 mA


5. The base current (IB) of a transistor is usually

a. 95 percent of the emitter current (IE).

b. 50 percent of the emitter current (IE).

c. 50 percent of the collector current (IC).

d. less than 5 percent of the emitter current (IE).


3-130

CMS AVAILABLE

None

FAULTS AVAILABLE

None


3-131

Exercise 3 – Transistor Circuit DC Voltages

EXERCISE OBJECTIVE

Demonstrate dc operating conditions of a transistor circuit by using an NPN transistor. Verify

results with a multimeter.

EXERCISE DISCUSSION


When a transistor is in saturation, the

a. two junctions are forward biased.

b. collector-emitter voltage approaches zero.

c. transistor currents are maximum.



When a transistor circuit is operating in the active (linear) region, the base-collector junction is

a. forward biased, the base-emitter junction is reverse biased, and the collector current is not

proportional to the base current.

b. reverse biased, the base-emitter junction is forward biased, and the collector current is

proportional to the base current.


When the collector voltage of a transistor equals the collector voltage supply, the transistor is

a. at the saturation point.

b. operating in the active region.

c. cut off.


3-132

EXERCISE PROCEDURE


VBE = Vdc



Min/Max Value: ( .487) to ( .811)






4. Based on your measured value of VBE (#V15# Vdc), the base-emitter junction is

a. forward biased.

b. reverse biased.


5. Measure the Q1 collector-emitter voltage.

VCE = Vdc









The base-collector junction is

a. forward biased.

b. reverse biased.


3-133


7. Measure the voltage drop across collector resistor R9 (100Ω).

VR9 = Vdc



Min/Max Value: (0.107) to (0.321)






9. Measure the voltage drop across base resistor R6 (1 kΩ).

VR6 = Vdc



Min/Max Value: (0.015) to (0.045)






VBE = mVdc


Nominal Answer: 0.0







12. Based on your measured value of VBE (#V19# mVdc), the base-emitter junction is

a. forward biased.

b. reverse biased.


3-134


13. Measure VCE.

VCE = Vdc









14. Your measured Q1 base voltage is #V19# mVdc, and your measured collector voltage is

#V20# Vdc. The base-collector junction is

a. forward biased.

b. reverse biased.


VR9 = mVdc


Nominal Answer: 0.0







VR6 = mVdc


Nominal Answer: 0.0







3-135


VBE = Vdc



Min/Max Value: ( .501) to ( .751)






20. Based on your measured value of VBE (#V23# Vdc), the base-emitter junction is

a. forward biased.

b. reverse biased.


The base-collector junction is

a. forward biased.

b. reverse biased.


22. Measure VR9.

VR9 = Vdc



Min/Max Value: ( .032) to ( .182)






3-136


24. Measure VR6.

VR6 = Vdc



Min/Max Value: ( .001) to ( .01 )





REVIEW QUESTIONS


1. This circuit shows the voltage conditions for the transistor circuit. The NPN transistor (Q1) is

operating

a. at the saturation point.

b. at the cutoff point.

c. in the active region.

d. with an open collector-base junction.


2. This circuit shows voltage conditions for the transistor circuit. Q1 is operating

a. at the cutoff point.

b. at the saturation point.

c. in the active region.

d. with a shorted base-emitter junction.


3. This circuit shows the voltage for the transistor circuit. Q1 is operating

a. with a short between the collector and emitter.

b. in the active region.

c. at the cutoff point.

d. at the saturation point.


3-137


4. This circuit shows the voltage conditions for the transistor circuit. Q1 is operating

a. at the cutoff point.


c. at the saturation point.

d. with a short between the collector and emitter.


5. CM 19 is activated to insert a fault in your transistor circuit. Make voltage measurements in

the Q1 transistor circuit when potentiometer R2 is set fully CCW for cutoff conditions, fully CW

for saturation conditions, and between CW and CCW positions for the active region. Your

voltage measurements indicate that the fault is

a. a low resistance short between the Q1 collector and emitter.

b. a short between the Q1 base and emitter.

c. an open base-emitter junction.

d. an open base-collector junction.

CMS AVAILABLE

CM 19

FAULTS AVAILABLE

None


3-138

Exercise 4 – Transistor Load Lines

EXERCISE OBJECTIVE

Determine the dc load line for a transistor circuit. Verify results with a multimeter.

EXERCISE DISCUSSION


The two end points of the dc load line are the

a. saturation point and Q-point.

b. cutoff point and saturation point.

c. Q-point and the cutoff point.


If VA = 10.0 Vdc and RC = 2 kΩ, the collector saturation current (IC(SAT) = VA/RC) equals

a. 20 mA.

b. 5 mA.

c. 0.2 mA.


If VA = 10.0 Vdc and RC = 2 kΩ, the cutoff point is where

a. IC = 0 mA and VCE = 10.0 Vdc.

b. IC = 2.0 mA and VCE = 0 Vdc.


The Q-point of a transistor circuit

a. is at the intersection of the dc operating conditions (IC, IB, and VCE) on the dc load line.

b. should be located at about the center of the dc load line.

c. will change if the base current changes.



3-139

EXERCISE PROCEDURE


3. At the saturation point, the collector-emitter voltage drop (VCE(SAT)) is considered to be

a. 0.0 Vdc.

b. 10.0 Vdc.


4. At the saturation point, the voltage drop across the collector resistors (R8 + R9) is considered

to be

a. 0.0 Vdc.

b. 10.0 Vdc.


IC(SAT) = VA/RC = 10.0 Vdc/1.1 kΩ = mA



Min/Max Value: (8.908) to (9.272)






6. At the cutoff point, the collector current is

a. greater than 5.0 mA.

b. 0.0 mA.


7. At the cutoff point, the collector-emitter voltage is considered to be

a. 0.0 Vdc.

b. 10.0 Vdc.


Measure the Q1 collector-emitter voltage. Can VCE(sat) be considered about 0 Vdc, as plotted

on the load line?

a. yes

b. no


3-140


10. Measure the voltage drop across R9 (100Ω) so that the collector saturation current can be

determined. VR9 = Vdc



Min/Max Value: ( .796) to (1.076)






11. Based on your measurement of VR9 (#V30# Vdc), IC(SAT) equals #V30# mA. Within

measurement tolerances, does the measured value of IC(SAT) agree with your load line

calculated value of IC(SAT) (#I30# mA)?

a. yes

b. no


Measure the collector-emitter voltage. Can VCE(CUTOFF) be considered 10.0 Vdc, as plotted

on the load line?

a. yes

b. no


VR9 = mVdc


Nominal Answer: 0.0







3-141


14. Based on your measurement of (#V31# mVdc), IC(CUTOFF) equals #V31#/100 mA. Does

the measured value of IC(CUTOFF) approximately agree with your load line value of

IC(CUTOFF) (0.0 mA)?

a. yes

b. no


15. From the dc load line shown, determine IC at a VCE of 5.0 Vdc.

IC = mA


Nominal Answer: 4.6







17. Measure the voltage drop across R9 (100Ω) so that the collector current with VCE at 5.0 Vdc

can be calculated. VR9 = Vdc



Min/Max Value: (0.376) to (0.564)






18. Based on your measurement of VR9 (#V32# Vdc), IC equals #V32# * 10 mA. Within

measurement tolerances, does the above measured value of IC agree with your load line value of

IC (#I31# mA) at a VCE value of 5.0 Vdc?

a. yes

b. no


3-142


19. Measure the voltage drop across R6 (1 kΩ) so that the base current (IB) with VCE at 5.0 Vdc

can be calculated. VR6 = Vdc



Min/Max Value: (0.003) to (0.057)






21. With VCE set to 5.0 Vdc, IC at 4.7 mA, and IB at 30 µA, the transistor circuit is operating

a. at cutoff.


c. at saturation.

These values may vary because they are based on the following recall value: #V32# and #V33#


22. The point on the load line at which VCE equals 5.0 Vdc is where the transistor circuit is

operating. This point is the

a. Q-point.

b. active-point.


24. An increase in RC from 1.1 kΩ to 4.8 kΩ

a. increases the collector saturation current.

b. decreases the collector saturation current.


3-143


25. For the connected circuit, RC = R7 + R9 = 4.8 kΩ. Calculate the collector saturation current.

IC(SAT) = VA/RC = 10.0 Vdc/4.8 kΩ

= mA



Min/Max Value: (2.038) to (2.122)






26. Did the cutoff point change with the increase in collector resistance to 4.8 kΩ?

a. yes

b. no


29. Measure the voltage drop across R9 (100Ω) so that the collector saturation current can be

determined. VR9 = Vdc



Min/Max Value: (0.172) to (0.258)






30. Based on your measurement of VR9 (#V34# Vdc), IC(SAT) equals #V34#*10 mA. Within

measurement tolerances, does the above measured value of IC(SAT) agree with your load line

calculated value of IC(SAT) (#I32# mA)?

a. yes

b. no


3-144


31. Compare the load lines for RC at 1.1 kΩ and at 4.8 kΩ. Which load resistor provides a better

range of collector current for the collector supply voltage of 10.0 Vdc?

a. the 4.8 kΩ load line

b. the 1.1 kΩ load line

REVIEW QUESTIONS


1. If necessary, measure only the R9 voltage drop between VA and the terminal next to the Q1

collector. The saturation point for the circuit is where

a. IC(SAT) = 0.0 mA and VCE = 10.0 Vdc.

b. IC(SAT) = 0.0 mA and VCE = 5.0 Vdc.

c. IC(SAT) = 4.3 mA and VCE = 0 Vdc.

d. IC(SAT) = 2.1 mA and VCE = 5.0 Vdc.


2. The cutoff point for the circuit is where

a. IC = 0.0 mA and VCE = 5.0 Vdc.

b. IC = 0.0 mA and VCE = 10.0 Vdc.

c. IC = 4.3 mA and VCE = 0 Vdc.

d. IC = 2.1 mA and VCE = 5.0 Vdc.


3. A load line is shown for the circuit with a collector resistance of 2.3 kΩ when CM 20 is

activated. What is the collector current when VCE equals 3.0 Vdc?

a. 1.5 mA

b. 3 mA

c. 0 mA

d. 4.3 mA


4. In the circuit shown, the load line is determined by

a. VA and RC.

b. RB and IC.

c. IC and VCE.

d. VA and IB.


3-145


5. A transistor dc load line can be used to determine the

a. optimum quiescent point (Q-point).

b. base circuit resistance.

c. optimum base-collector voltage drop.

d. base-emitter voltage drop.

CMS AVAILABLE

CM 20

CM 20

CM 20

FAULTS AVAILABLE

None


3-146

UNIT TEST



The base-emitter junction forward voltage (VBE) of a silicon NPN transistor

a. is about 4.0 Vdc.

b. is about 0.7 Vdc.

c. is about 0.3 Vdc.

d. depends on the voltage polarity.


If the base of an NPN transistor is more negative than the emitter, the junction is

a. reverse biased.

b. forward biased.

c. conducting.

d. approaching the forward voltage drop.


The collector current (IC) of a transistor is controlled by the

a. emitter current (IE).

b. magnitude of the collector voltage supply (VA).

c. base-collector junction bias.

d. the base-current (IB).


The dc current gain (βDC) is expressed by

a. βDC = IC /IB.

b. βDC = IB /IC.

c. βDC = IB /IE.

d. βDC = IC /IE.


If a collector current (IC) of 15 mA is required in a transistor circuit with a current gain (βDC) of

300, the base current (IB) has to be

a. 0.0045 mA.

b. 20 mA.

c. 0.05 mA.

d. 0.02 mA.


3-147


When a transistor circuit is at the saturation point,

a. both junctions are forward biased.

b. the base-emitter junction is reverse biased.

c. the base-emitter junction is reverse biased and the base-collector junction is forward biased.

d. the base-emitter junction is forward biased and the base-collector junction is reverse biased.


When a transistor circuit is in the active region,

a. both junctions are forward biased.

b. the base-emitter junction is reverse biased.

c. the base-emitter junction is reverse biased and the base-collector junction is forward biased.

d. the base-emitter junction is forward biased and the base-collector junction is reverse

biased.


The dc load line is a plot of the

a. collector current (IC) versus the collector-emitter voltage (VCE).

b. base current (IB) versus the base-emitter voltage (VBE).

c. collector current (IC) versus the base current (IB).

d. collector current (IC) versus the base-emitter voltage (VBE).


The dc load line intersects the Y-axis and the X-axis at the

a. Q-point and the saturation point, respectively.

b. cutoff point and the saturation point, respectively.

c. saturation point and the breakdown point, respectively.

d. saturation point and the cutoff point, respectively.


The point at which the collector current (IC), the base current (IB), and the collector-emitter

voltage (VCE) intersect in the active region of the load line is the

a. breakdown point.


c. quiescent point (Q-point).

d. cutoff point.


3-148

TROUBLESHOOTING


4. Measure V2.

V2 = Vdc

Recall Label for this Question: V2B

Nominal Answer: 6.2







Are you confident that the NPN transistor circuit is functioning properly?

a. yes

b. no



a. Q1 (shorted base-collector junction).

b. Q1 (shorted base-emitter junction).

c. Q1 (excessive leakage between collector and emitter).

d. R7 (shorted).

CMS AVAILABLE

None

FAULTS AVAILABLE

Fault 12

Semiconductor Fundamentals Appendix A – Pretest and Posttest Questions and Answers

A-1

APPENDIX A – PRETEST AND POSTTEST QUESTIONS AND ANSWERS


Pretest and Posttest questions are the same.

1. Semiconductor devices are commonly constructed from

a. silicon.

b. aluminum.

c. diallyl phthalate.

d. sodium arsenate.

2. Semiconductor materials

a. have a resistance between that of a conductor and that of an insulator.

b. are superconductive at relatively high temperatures.

c. are very rare and expensive substance.

d. do not form crystalline structures.

3. The most important characteristic of semiconductor atoms is the

a. number of neutrons in the nucleus.

b. number of protons in the nucleus.

c. total number of electrons in all orbital shells.

d. number of electrons in the outer shell.

4. The term covalent bonding refers to the

a. adhesive used in mounting semiconductor wafers.

b. sharing of outer shell electrons between atoms in a crystal.

c. force that binds neutrons and protons in the atomic nucleus.

d. gravitational force between atoms.

5. Impurities are introduced into pure semiconductors by a carefully controlled process called

a. injection.

b. merging

c. osmosis.

d. doping.

6. Free electrons in semiconductors

a. are removed by constant purification.

b. are introduced by impurities.

c. reduce the efficiency of N type material.

d. are minority carriers in N type material.


A-2

7. The majority carriers in P type material are

a. protons.

b. neutrons.

c. holes.


8. A simple semiconductor device called a diode allows current to flow in only one direction

and

a. consists of three or more semiconductor PN or NP junctions.

b. consists of a single PN junction.

c. requires no introduced impurities.

d. requires a bias magnet for operation.

9. The three regions of a bipolar transistor are the

a. anode, the cathode, and the gate.

b. emitter, the base, and the collector.

c. cathode, the grid, and the plate.

d. source, the gate, and the drain.

10. The depletion region in a rectifier diode

a. becomes wider when the diode is reverse biased.

b. becomes more narrow when the diode is reverse biased.

c. can be eliminated by proper doping.

d. forms only in the P type material of the anode.

11. A well-designed silicon rectifier diode has

a. no forward voltage drop.

b. about a 0.3V forward voltage drop.

c. about a 0.7V forward voltage drop.

d. about a 0.7V reverse voltage drop.

12. When the anode of a rectifier diode is positive with respect to the diode's cathode, the diode

is

a. forward biased and conducting.

b. reverse biased and conducting

c. subject to destructive breakdown.

d. reverse biased and non-conducting.

13. Leakage current through a diode results from

a. the application of an excessive reverse voltage.

b. the application of an excessive forward voltage.

c. high junction capacitance or inductance.

d. minority carriers in the N and P type materials.


A-3

14. Rectification is the process of

a. converting pulsating dc to ac.

b. converting ac to pulsating dc.

c. removing ripple from pulsating dc.

d. purifying silicon or germanium.

15. The front-to-back ratio of a good diode can be checked

a. with an ohmmeter and should be less than 100 to 1.

b. with an ohmmeter and should be greater than 100 to 1.

c. with a milliammeter and should be 10 to 1 or less.

d. only with special instruments and should be 10 to 1 or less.

16. Reverse recovery time degrades the performance of common rectifier diodes in

a. high voltage, low frequency circuits.

b. high current, low frequency circuits.

c. any high current or high voltage application.

d. any high frequency application.

17. The output of a half-wave rectifier circuit is

a. twice the frequency of the input signal.

b. the same frequency of the input signal.

c. half the frequency of the input signal.

d. the same voltage as the input signal.

18. If the diode in a half-wave rectifier circuit is reversed, the

a. polarity of the dc output remains unchanged.

b. amplitude of the dc output is reduced.

c. polarity of the dc output is reversed.


19. A full-wave rectifier circuit

a. requires only a single diode.

b. requires two diodes in parallel.

c. is less efficient than a half-wave rectifier.

d. requires two or four diodes.

20. A diode bridge circuit

a. is a type of half-wave rectifier.

b. requires a center-tapped transformer secondary.

c. produces a ripple-free output waveform.

d. has four diodes that conduct in pairs.


A-4

21. Electrolytic capacitors are often used as power supply filters because they provide

a. high reactance at power line frequencies.

b. voltage doubling without additional components.

c. automatic phase reversal of negative peaks.

d. high capacitance in small packages.

22. In most power supply applications, full-wave rectifier circuits are preferred over half-wave

rectifier circuits because the full-wave rectifiers

a. are more efficient and easier to filter.

b. require fewer components.

c. provide a lower frequency output ripple.

d. use only positive peaks of the ac input.

23. You can reduce ripple in the output of any power supply by

a. increasing the capacitance of the filter circuit.

b. using diodes with higher breakdown ratings.

c. reducing the load resistance.

d. increasing the capacitive reactance of the filter circuit.

24. The capacitor in the filter circuit of a power supply

a. delivers energy to the load between peaks of the dc input.

b. delivers energy to the rectifier circuit..

c. absorbs energy from the load between peaks of the dc input.

d. absorbs energy from the load only during peaks of the dc input.

25. Transformers are used in power supplies to

a. convert line voltage to the proper level required by an application.

b. isolate dc secondary current from the power line.

c. step up or step down power line frequency.

d. convert dc at one voltage into dc voltage at another level.

26. The ripple in the output of a filtered power supply

a. is always twice the frequency of the line voltage.

b. is always half the frequency of the line voltage.

c. has a sawtooth waveform.

d. has a sinusoidal waveform.

27. In normal applications, a zener diode

a. is biased so that its cathode is negative with respect to its anode.

b. replaces a conventional rectifier diode.

c. replaces a high voltage rectifier diode.

d. is biased so that its cathode is positive with respect to its anode.


A-5

28. The voltage drop across a zener diode in normal use

a. varies directly with current flow.

b. varies inversely with current flow.

c. is either 0.3V or 0.7V.

d. remains nearly constant.

29. The current through a zener diode biased for normal applications

a. is maintained at a constant level by the zener.

b. must be limited by a series resistor.

c. is too small to measure with a multimeter.

d. does not result in any power dissipation.

30. A series diode limiter is similar in operation to a

a. half-wave rectifier.

b. full-wave rectifier.

c. dc to ac converter.

d. dc restorer.

31. A limiter circuit could be used to

a. convert a triangular waveform into a sine wave.

b. convert a sine wave into a square wave.

c. increase the amplitude of a signal.

d. limit a circuit's frequency response.

32. Clamping circuits use a diode and always include a(n)

a. capacitor.

b. inductor.

c. zener.

d. bias battery.

33. In a typical zener diode shunt regulation circuit where the source voltage varies, the voltage

across the

a. load resistance varies.

b. series dropping resistor varies.

c. zener varies.


34. Which of the following circuits allows a capacitor to charge quickly through a low

impedance and discharge slowly through a high impedance?

a. a clamper

b. a biased shunt limiter

c. a peak clipper

d. a slicer


A-6

35. The emitter of an NPN transistor is identified on a schematic diagram by

a. an arrow pointing toward the base.

b. an arrow pointing away from the base.

c. its position opposite the lead with an arrow.

d. its position between the base and the collector leads.

36. When a transistor is used in a class A amplifier circuit,

a. the base-emitter junction is reverse biased and the base collector junction is forward

biased.

b. both the base-emitter and base-collector junctions are forward biased.

c. the base-emitter junction is forward biased and the base-collector junction is

reverse biased.

d. both the base-emitter and base-collector junctions are reverse biased.

37. Transistor construction requires

a. germanium doped with N and P type materials.

b. silicon doped with N and P type materials.

c. three layers and two junctions.

d. a. or b., and c.

38. A PNP transistor is forward biased when its

a. base is negative with respect to its emitter.

b. base is positive with respect to its emitter.

c. collector is positive with respect to its emitter.

d. collector is negative with respect to its emitter.

39. The emitter of a PNP transistor is identified on a schematic diagram by

a. an arrow pointing toward the base.

b. an arrow pointing away from the base.

c. its position opposite the lead with an arrow.

d. it position between the base and collector leads.

40. When a transistor is forward biased,

a. most emitter current flows to the collector.

b. most emitter current flows to the base

c. base current divides between collector and emitter.

d. no current flows in the base circuit.

41. Transistors can be used as

a. amplifiers.

b. switches.

c. oscillators.



A-7

42. A power transistor can be identified by

a. its relatively large size.

b. its metal case or heat sink.

c. the voltage and current ratings in a specification sheet.


43. High gain transistors

a. require no base current to control a large collector current.

b. require a small base current to control a large collector current.

c. require a large base current to control a large collector current.

d. are always PNP.

44. The base voltage of a transistor in an amplifier circuit

a. varies with the signal, but base current remains nearly constant.

b. remains nearly constant, but base current varies with the signal.

c. should be high enough to keep the transistor saturated.

d. should be small enough to keep the transistor near cutoff.

45. A transistor load line is a graphical representation of the relationship between

a. collector voltage and collector current.

b. collector voltage and base current.

c. emitter current and base current.

d. collector voltage and base voltage.

46. The boundaries of a transistor load line can be determined if

a. transistor current gain and supply voltage are known.

b. transistor current gain and load resistance are known.

c. base current and transistor current gain are known.

d. supply voltage and load resistance are known.

47. The quiescent operating point of a transistor amplifier circuit is

a. determined by the dc bias level.

b. selected to be near the center of the load line.

c. about half of the supply voltage level.


48. If additional base current is applied to a saturated transistor,

a. collector current will increase significantly.

b. collector current will remain unchanged.

c. emitter current will decrease.

d. emitter-collector voltage will increase.


A-8

49. A transistor has a gain of 100. If the transistor's collector current is measured and found to be

exactly one ampere,

a. base current must be 100 mA.

b. emitter current must be 10 mA.

c. emitter current must be 1.01 mA.

d. base current must be 1 mA.

50. A transistor having a VCE of 8V and a collector current of 4A

a. is a small-signal amplifier.

b. must be able to dissipate 32 watts.

c. has an emitter current slightly less than 4A.

d. is saturated.

Semiconductor Fundamentals Appendix B – Faults and Circuit Modifications (CMs)

B-1

APPENDIX B – FAULTS AND CIRCUIT MODIFICATIONS (CMS)

CM SCHEMATIC

SWITCH NO.

FAULT ACTION

– 21 1 shorts Q1 base-collector

junction with 330Ω

– 22 2 shorts Q2 collector-

emitter junction

– 23 3 opens R4 wiper

– 24 4 shorts CR2

– 25 5 shorts Q1 base-emitter

junction

– 27 7 opens T1 secondary

– 28 8 places 1 kΩ in parallel

with 100-kΩ R2

– 29 9 shorts diode in lower left

quadrant of CR1 bridge

– 30 10 shorts CR2

– 31 11 opens C1

– 32 12 shorts Q1 base-emitter

junction

2 2 This CM is

used as a

fault.

shorts Q1 base-emitter

junction

3 3 – opens Q2 base

6 6 – R2 = 1062Ω

9 9 – R1 = 1.01 MΩ

10 10 – shorts Q2 base

14 14 – places 1000Ω in parallel

with 100-kΩ R2

15 15 This CM is

used as a

fault.

opens C1

17 17 – opens CR2

18 18 – places 39 kΩ in parallel

with series-connected R1,

R2

19 19 This CM is

used as a

fault.

shorts Q1 emitter-

collector junction with

100Ω

20 20 – R9 = 2300Ω

Semiconductor Fundamentals Appendix B – Faults and Circuit Modifications (CMs)

B-2

Semiconductor Fundamentals Appendix C – Board and Courseware Troubleshooting

C-1

APPENDIX C – BOARD AND COURSEWARE TROUBLESHOOTING

Circuit Board Problems

The F.A.C.E.T. equipment is carefully designed, manufactured, and tested to assure long,

reliable life. If you suspect a genuine failure in the equipment, the following steps should be

followed to trace a problem.

A. ALWAYS insert the board into a base unit before attempting to use an ohmmeter for

troubleshooting. The schematic diagrams imprinted on the boards are modified by the

absence of base unit switch connections; therefore, ohmmeter checks will produce erroneous

results with disconnected boards. Do not apply power to the base unit when you perform

resistance checks.

B. Information describing fault switch functions is provided in Appendix B in this instructor

guide.

Courseware Problems

The F.A.C.E.T. courseware has been written to meet carefully selected objectives. All exercises

have been tested for accuracy, and information presented in discussions has been reviewed for

technical content. Tolerances have been computed for all procedure and review question answers

to assure that responses are not invalidated by component or instrument errors.

Nevertheless, you or your students may discover mistakes or experience difficulty in using our

publications. We appreciate your comments and assure you that we will weigh them carefully in

our ongoing product improvement efforts.

As we address courseware problems, we will post corrections for download from our web site,

www.labvolt.com. Select the customer support tab, and then choose product line: F.A.C.E.T.

Select a course, select from a list of symptoms that have been addressed, and follow the

instructions.

Semiconductor Fundamentals Appendix C – Board and Courseware Troubleshooting

C-2

We will do our best to help you resolve problems if you call the number below. However, for

best results, and to avoid confusion, we prefer that you write with a description of the problem.

If you write, please include the following information:

• Your name, title, mailing address, and telephone number (please include the best time to

reach you).

• Publication title and number.

• Page number(s), and step and/or figure number(s) of affected material.

• Complete description of the problem encountered and any additional information that may

help us solve the problem.

Send your courseware comments to:

[email protected]

Lab-Volt Systems

P.O. Box 686

Farmingdale, NJ 07727

ATTN: Technical Support

If you prefer to telephone regarding hardware or courseware problems, call us between 9:00 AM

and 4:30 PM (Eastern time) at: (800) 522-4436 or (888)-LAB-VOLT.

Semiconductor Fundamentals



Instructor Guide

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