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  • Analog Electronics

    Module 1: Semiconductor Diodes

    PREPARED BY

    Academic Services Unit

    August 2011

    Applied Technology High Schools, 2011

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 2

    Module 1: Semiconductor Diodes Module Objectives Upon successful completion of this module, students should be able to:

    1. Identify the purpose of the diode and give a brief description of its construction.

    2. Sketch the schematic symbol of a diode. 3. Identify the diode by its number code or package type. 4. Distinguish between the terminals of a diode. 5. Recognize whether a diode is forward biased or reverse biased by

    observing the voltage polarity. 6. Explain how the diode functions in the forward or reverse bias direction. 7. Test a diode and check its condition. 8. Explain the operation of a half-wave rectifier. 9. Explaing the operation of a full-wave bridge rectifier. 10. Build half-wave and full-wave rectifier circuits and test their functioning.

    Module Contents:

    Topic Page No.

    1.1 Introduction 3

    1.2 Diode identification 5

    1.3 Diode Operation 6

    1.4 Testing a Diode 7

    1.5 Diode Application 9

    1.6 Lab Activity 1 13

    1.7 Lab Activity 2 17

    1.8 Lab Activity 3 20

    1.9 Review Exercise 23

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 3

    1.1 INTRODUCTION

    The invention of semiconductor devices was a revolution, which lead to an

    impressive technological achievement that would endlessly alter modern

    society. Semiconductor devices, made electronics physically very small,

    including computers, certain types of medical diagnostic and treatment

    equipment, and popular telecommunication devices. A diode is a

    semiconductor device that allows current to flow in only one direction.

    A semiconductor in its pure form does not conduct current well because it

    has limited number of free electrons and holes. Doping is the process of

    increasing the conductivity of the semiconductor where in small amounts of

    impurities are added to a pure semiconductor. An N-type semiconductor has

    more number of electrons (negative charges) and a P-type semiconductor

    has more number of holes (positive charges). Sandwiching, or joining a P-

    type semiconductor with N-type semiconductor forms a diode. The diode is

    contained in a small capsule made of glass or plastic and has two terminals

    or electrodes and hence the name diode (di two and ode electrode). The

    electrode connected to the P-type is called the Anode A, and the electrode

    connected to the N-type is called the Cathode K. The cathode (K) is

    marked with a silver color band as shown in Figure 1(c). Figure 1(a) and

    1(b) shows the structure and symbol of the PN junction diode.

    K

    b) Diode Symbol

    A

    Anode

    (A) Cathode

    (K) N-TYPE

    Electrons +

    a) Diode Structure

    P-TYPE

    Holes

    c) Typical Diode

    Cathode (K)

    Figure 1: Diode structure and Symbol

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 4

    Diode Types

    According to the type of semiconductors they are classified into:

    Germanium diodes

    Silicon diodes

    According to their application, they are classified into the following:

    Rectifier diodes. Zener diodes.

    Light emitting diodes (LEDs). Photo diodes.

    Figure 2 shows commonly used diodes of different types.

    Photo DiodeZener Diode

    Low Power Diode

    Rectifier diode

    LED

    Figure 2 Typical Diodes of different types

    Diode Packing

    Diode is generally mounted in one of three basic packages shown in figure

    3. These are designed to protect the diode from mechanical stress and the

    environment. The size of the package indicates the current rating (larger

    size means higher current rating). Note that (DO) refers to Diode Outline.

    DO-5

    Figure 3 Diode packing types

    DO-8 DO-41

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 5

    1.2 Diode Identification There are hundreds of diodes, of different types and characteristics

    according to the way they are designed and made. In order to distinguish

    between them, each type is given a unique code so that it can be identified.

    In fact there are two main semiconductor numbering systems in use:

    1) Pro-Electron System: This numbering system originated in Europe

    and is widely used for semiconductors developed and manufactured by

    them.

    2) JEDEC System: This numbering system originated in the USA and is

    widely used for semiconductors manufactured in North America.

    1.1 Pro-Electron Numbering or Coding System First Letter Specifies Semiconductor

    Material Second Letter Specifies type of

    Diode

    A Germanium A Low power or signal

    B Silicon P Light detector

    Q Light Emitting Diode (LED)

    Y Rectifier

    EXAMPLE: BZY74-C6V3

    B = Si, Z = Zener diode, Y74 = Commercial or

    Industrial use, C = 5% of rating voltage.

    6V3 = 6.3 Volt (Voltage rating) Z Zener (voltage reference)

    1.2 JEDEC Numbering or Coding System First Number Second Letter Subsequent numbers

    1 Diode N Semiconductor Serial number of device

    2 Bipolar Transistor

    3 FET

    4&5 Photo Coupler

    Example: This code 1N4001 means:

    1 Diode, N Semiconductor.

    4001 Serial number.

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 6

    1.3 Diode Operation

    Forward biased:

    A diode conducts only in one direction, and the conduction is from anode to

    cathode. When a diode is connected to the power supply such its anode (A)

    is connected to the positive terminal, and its cathode (K) is connected to the

    negative terminal as shown in figure 4, we say that it is forward biased

    (FB). The diode in FB-direction allows the current to flow from A to K as

    shown in Figure 4.

    Figure 4 Diode Operated in FB Direction

    DC+

    RThe Diode will conduct IF IF

    K

    A

    Reverse biased:

    A diode is reverse biased (RB) when its anode (A) is negative with respect

    to the cathode (K). The diode in RB-direction does not allow the current to

    flow as shown in Figure 5.

    Figure 5 Diode Operated in RB Direction

    DC+

    RThe Diode will not conduct

    K

    A

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 7

    1.4 Testing a Diode

    Testing the diode in forward direction with an Ohmmeter:

    Connect the positive meter-lead (Red) to the anode (A) and connect the

    negative meter-lead (Black) to the cathode (K) as shown in Figure 6a. A

    good diode must display low resistance (typically < 10) in FB. Note that

    the ohmmeter consists of an internal battery (1.5 V), which can FB or RB a

    diode.

    Figure 6a Testing the Diode in FB Direction

    IN 4001

    (A) Anode

    (K) Cathode

    Ohm

    met

    er

    Testing the diode in reverse direction with an Ohmmeter:

    Connect the positive meter-lead (Red) to the cathode (K), and the negative

    meter-lead (Black) to the anode (A) as shown in Figure 6b. A good diode

    must display a very high resistance (>1000 M) in RB. If both bias

    conditions display low resistance, then the diode is shorted, and if both bias

    conditions display very high resistance, then the diode is considered to be

    open.

    Figure 6b Testing the Diode in RB Direction

    IN 4001

    (A) Anode

    (K) Cathode

    Ohm

    met

    er

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 8

    Testing the diode in forward direction with a Digital Multimeter:

    Set the digital Multimeter knob to diode testing function. Now, connect the

    positive lead (Red) to the anode (A) and the negative lead (Black) to the

    cathode (K) as shown in Figure 7a. For a diode in a good condition the

    reading will be in the range of 0.3V for Ge and 0.7V for Si.

    Dig

    ital M

    ultim

    eter

    Figure 7a Testing the Diode in FB Direction

    IN 4001

    (A) Anode

    (K) Cathode

    Testing the diode in reverse direction with a Digital Multimeter:

    Connect the positive lead to the cathode and negative lead to the anode as

    shown in Figure 7b. For a diode in good condition, the reading will be 1.5V

    for both types. If in both cases the reading is 0V, then the PN junction is

    shorted, and if it is 1.5V the PN junction is open.

    IN 4001

    (A) Anode

    (K) Cathode

    Dig

    ital M

    ultim

    eter

    Figure 7b Testing the Diode in RB Direction

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 9

    1.5 Diode Application The diode has a unique ability to offer very little resistance to current flow in

    the forward-bias direction, but maximum resistance to current flow when

    reverse biased. For this reason, the diodes are used in rectification.

    Rectification is the process of converting ac to pulsating dc, and the diodes

    used for this purpose are called rectifier diodes.

    AC current behavior:

    During the positive alteration, AC current flows first in one direction,

    reaches the maximum (positive) and decreases to zero.

    During the negative alteration, the current follows the same manner in

    the opposite direction.

    In each alteration, AC current reverses its direction as shown in Figure 8.

    -ve

    I

    +ve

    -ve

    +ve

    I

    Positive half-cycle

    Negative half-cycle

    Figure 8 Alteration of AC current between (+ve) and (-ve)

    Half Wave Rectifier

    The half-wave rectifier circuit is constructed simply by connecting a diode

    between the secondary of a transformer and the load as shown in Figure 9.

    Figure 9 Half Wave Rectifier Circuit

    IF A

    Load AC

    K

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 10

    During the positive half-cycle, the diode conducts when the input voltage

    exceeds the barrier potential (0.7V for Silicon and 0.3V for Germanium

    diodes) and current flows through the load and returns along the 0V line.

    Only the positive half-cycle appears across the load as shown in Figure 10a.

    IF A K + +

    + AC Input Load

    Output

    Figure 10a Operation during Positive Half-Cycle During the negative half-cycle, the diode turns OFF (RB). This will prevent

    any current from flowing, and no voltage appears across the load as shown

    in Figure 10b.

    IR A K

    + +

    + AC Input

    Load

    Output

    Figure 10b Operation during Negative Half-Cycle

    Output Voltage: The net result is that only the positive half-cycles of the AC

    input voltage appear across the load, providing a pulsating DC voltage at

    the output as shown in Figure 11. However, the amplitude of the output

    voltage is less than the input amplitude, and this is because of the forward

    voltage drop across the diode. Because this circuit produces output current

    only during one cycle, it is called a half-wave rectifier.

    Secondary Voltage (VS)

    Voltage across the Load

    Figure 11 Output of Half-Wave Rectifier Voltage

    VRL

    VS

    Conduct lab activity 1.

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 11

    Full Wave Rectifier

    The circuit in figure 12 rectifies AC by using a bridge of four diodes. It is

    therefore called a full-wave bridge rectifier.

    Figure 12: Bridge Rectifier

    During the positive half cycle, diodes D1 and D2 are forward biased, so they

    conduct. Diodes D3 and D4 are reverse biased and do not conduct. Current

    flows through the load as shown in figure 13.

    Figure 13: Conduction during positive half cycle

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 12

    During the negative half cycle as shown in figure 14, diodes D1 and D2 are

    reverse biased, so they do not conduct. Diodes D3 and D4 are forward

    biased and conduct.

    Figure 14: Conduction during negative half cycle

    The result is that the current continues to flow through the load in the same

    direction in both the half cycles. The output and input are shown in figure

    15. The rectifier produces output during both half cycles, and therefore it is

    100% efficient. In each half-cycle, current flows through two diodes, and

    therefore the output voltage is two voltage drops less than the input

    voltage.

    Figure 15: Input and Output Waveforms

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 13

    1.6 Lab Activity 1

    Objective

    To determine the diode polarity and understand the need for proper

    connection.

    Background Information

    A semiconductor diode (or diode) is made from a piece of P-type

    semiconductor and a piece of N-type semiconductor joined together as

    shown in figure 16.

    Figure 16: Diode construction

    The amount of current that flows through a diode when it conducts depends

    on the size and polarity of the applied voltage. Figure 17(a) shows the diode

    symbol, and figure 17(b) shows the types of diodes supplied in the feedback

    kit.

    Figure 17(a): Diode symbol

    Figure 17(b): Diode types

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 14

    Equipment Required

    Apparatus Quantity

    Electricity & Electronics Constructor, EEC470

    1

    Basic Electricity and Electronics Kit EEC471-2

    1

    Power supply unit 0 to 20 V (Feedback Power Supply 92-445)

    1

    Digital Multimeters 2

    Diode (1N4007), R = 4.7k 1-each

    Procedure

    1. As shown in the patching diagram of figure 18, construct the circuit of

    figure 19(a). (Note that the resistor limits the current to a safe value).

    Figure 18: Constructor-EEC470

    Figure 19(a): Diodes Circuit diagram

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 15

    2. Move knob of the power supply control to 0V position.

    3. Switch on the power supply.

    4. Set the power supply control to give 10 V on the meter.

    5. Record the current measurement in the first row of the result table figure

    20.

    6. Now, switch off the power supply.

    7. Reverse the 1N4007 diode to give the circuit of figure 19(b).

    Figure 19(b): Diodes Circuit diagram

    1. Switch on the power supply and readjust the voltage to 10 V.

    2. Read the new value of diode current and record it in the second row of

    the result table figure 20.

    3. Study your results and answer the questions on the next page.

    Observations:

    Write your observation in table below.

    Circuit Current (mA)

    Figure 19(a) IF = .

    Figure 19(b) IR = .

    Figure 20: Observation Table

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 16

    Questions 1) Which side of a diode should be connected to the positive voltage

    supply to make it conduct current?

    2) When the diode was connected the opposite way round was the

    current?

    a) slightly smaller

    b) much smaller

    c) too small to measure

    3) Which side of a diode should be connected to the positive voltage

    supply to make it stop current?

    Conclusion:

    The diode conduct current when the Anode is connected to the

    and the Cathode is connected to the

    The diode does not conduct current when the Anode is connected to

    the and the Cathode is connected to the

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 17

    1.7 Lab Activity 2

    Objectives:

    1. To learn to recognize a half-wave rectified sinusoidal voltage.

    2. To understand the term mean value as applied to a rectified

    waveform.

    3. To understand the effect of a reservoir capacitor upon the rectified

    waveform and its mean value.

    Equipment Required

    Apparatus Quantity

    Electricity & Electronics Constructor, EEC470.

    1

    Basic Electricity and Electronics Kit EEC471-2.

    1

    Power supply unit 0 to 20 V (Feedback Power Supply 92-445)

    1

    Power supply unit. ac supply; 12 V rms; 50 or 60 Hz.

    1

    Digital Multimeters. 2

    Oscilloscope. 1

    Diode (SY356/6), R = 10k, and Capacitor. 1-each

    Procedure

    1. Switch on the oscilloscope and the sinusoidal supply.

    2. With the oscilloscope dc coupled adjust the time-base and the Y

    amplifier sensitivity to obtain a steady trace of about 4 cm vertical and

    5 ms/cm horizontal. You should see a waveform as in figure 21.

    Figure 21: Half-wave Rectified Waveform

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 18

    3. As shown in the patching diagram of figure 22, construct the circuit of

    figure 23.

    Figure 22: Constructor-EEC470

    Figure 23: Half-wave Rectification

    4. Measure and record the time T and the ge Vpk

    5. Sketch the waveform and label it to show the periods when the diode

    is conducting and those when it is not.

    6. Time T depends upon the frequency of your power supply. For a 50Hz

    supply it should be 20 ms and for 60 Hz it should be 17ms.

    7. Confirm this: Vpk should be very nearly equal to the peak voltage of

    the alternating supply.

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 19

    Questions

    1) Why will Vpk not be exactly equal to this voltage?

    2) How much will it differ?

    Hint: The mean value of a half-sinusoid can be shown by geometry to

    be:

    3) Note the mean voltage indicated by the voltmeter, and compare it with the

    calculated value. ..

    4) The mean voltage you obtain is positive relative to zero. How could

    you obtain a negative voltage? (Confirm your answer by experiment).

    Conclusion:

    A simple diode circuit can convert a/an voltage to

    a/an voltage.

    The mean value of the rectified voltage can be increased by using a

    across the load.

    A half-wave rectified voltage gives appreciable ripple which however,

    can be reduced by .

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 20

    1.8 Lab Activity 3

    Objective: To understand the working of a diode bridge circuit as a full-wave rectifier

    and its advantage over half-wave rectifier.

    Equipment Required

    Apparatus Quantity

    Electricity & Electronics Constructor, EEC470.

    1

    Basic Electricity and Electronics Kit EEC471-2.

    1

    Power supply unit 0 to 20 V (Feedback Power Supply 92-445)

    1

    Power supply unit. ac supply; 12 V rms; 50 or 60 Hz.

    1

    Digital Multimeters. 2

    Oscilloscope. 1

    Bridge-Rectifier, R = 10k, and Capacitor. 1-each

    Procedure: Select the Bridge Rectifier from the component kit. It appears

    as in figure 24(a) and figure 24(b). Note how the rectifier terminals are

    labeled.

    (a) Bridge Module

    (b) Circuit

    Figure 24: Bridge Rectifier

    1. Note: Prior to connecting an ac power supply to the board, ensure the

    supply is isolated from ground.

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 21

    2. With the oscilloscope dc coupled adjust the time-base and the Y

    amplifier sensitivity to obtain a steady trace of about 4 cm vertical and

    5 ms/cm horizontal. You should see a waveform as in figure 25. Time

    'T' will be 10 ms for 50 Hz supply, and 8.5 ms for 60 Hz.

    Figure 25: Full-wave Rectified Waveform

    3. Construct the circuit of figure 26 as in the patching diagram of figure 25

    Figure 25: Constructor-EEC470

    Figure 26: Test Circuit (full-wave rectifier)

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 22

    4. Measure and record the time T and the peak voltage Vpk

    5. Sketch the waveform and label it to show the periods of each 2-diode.

    6. Note the value of Vpk.

    7. Note the mean value of output voltage indicated on the voltmeter.

    8. Compare these values with those obtained in Lab activity-2.

    9. Confirm this: Vpk should be very nearly equal to the peak voltage of

    the alternating supply.

    Conclusion:

    A bridge rectifier gives a greater mean value and fewer

    ripples for a given load and reservoir capacitor than a

    rectifier.

    The alternative full-wave circuit using a centre-tapped transformer and two

    diodes is less efficient than the bridge circuit because it requires a bigger

    transformer for a given output power.

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 23

    1.9 Review Exercise

    1. The cathode of a diode is made 4V positive of its anode.

    a) What is the name of this type of bias?

    ____________________________________________________________________

    b) Does current flow through the diode in this case?

    ____________________________________________________________________

    2. Draw a circuit of a half-rectifier, and draw a sketch of 3 cycles of it output waveform.

    Circuit Diagram:

    Waveforms:

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 24

    3. Draw the output voltage waveform of the rectifier for the indicated input voltage, as shown in the figure below. The 1N4003 is a specific rectifier diode with a barrier potential/forward voltage drop of 0.7V.

    4. Draw the bridge rectifier circuit, and sketch 3 cycles of its input and output waveforms.

    Circuit Diagram:

    Waveforms:

  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 25

    Notes

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  • ATE1210 Analog Electronics

    Module 1: Semiconductor Diode 26

    Notes

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