MANF360 Chapter 1 Semiconductor Diodes

Prof. Dr. Ismail Mohammed Hafez MANF360 Ch.1 Diodes ١ of 48

MANF360

Electronics and Instrumentation

CHAPTER 1 Semiconductor Diodes

Prof. Ismail Mohammed Hafez

Electronics and Communication Department College of Engineering

Ain Shams University (ASU)

Prof. Dr. Ismail Mohammed Hafez

MANF360 Ch.1 Diodes ٢ of 48

Chapter Contents

1.1 Introduction to Electronics 1.2 Semiconductor Materials 1.3 Semiconductor Diodes 1.4 Diode Characteristics 1.5 Diode Testing 1.6 Other Types of Diodes 1.7 Diode Circuit Analysis


MANF360 Ch.1 Diodes ٣ of 48

1.1 Introduction to Electronics

• The electronic equipments was designed using vacuum tubes. • The success in producing the first transistor in late 40’s led to

a revolution in electronic systems. • Complete systems now appear on wafers thousands of times

smaller than a single element of earlier networks. • The integrated circuits (ICs) now have 10 million transistors on

an area of few millimeters. • Application of electronics include:

– Communication – Consumer applications – Biomedical Engineering – Instrumentation / Control – Military


MANF360 Ch.1 Diodes ٤ of 48

first transistor

1947 Picture shows a point-contact transistor structure comprising the plate of n-type germanium and two line-contacts of gold supported on a plastic wedge.

Source: W. Shockley, “The path to the conception of the junction transistor”, IEEE Tr. on Electron Devices ED-23, 597 (1976).

1.1 Introduction to Electronics


MANF360 Ch.1 Diodes ٥ of 48

first monolithic integrated circuit

1961 Picture shows a flip-flop circuit containing 6 devices, produced in planar technology.

Source: R. N. Neyce, “Semiconductor device-and-lead structure”, U.S.Patent 2,981,877

1.1 Introduction to Electronics (cont.)


MANF360 Ch.1 Diodes ٦ of 48

first microprocessor

1971 Picture shows a four-bit microprocessor Intel 4004.

• 3 mm × 4 mm • 2300 MOS-FETs

Source:

Intel Corporation



MANF360 Ch.1 Diodes ٧ of 48

Pentium IV processor

2001 Picture shows an ULSI chip with 32-bit processor Intel Pentium 4.

• 17.5 mm × 19 mm • 42 000 000 components

Source:

Intel Corporation



MANF360 Ch.1 Diodes ٨ of 48

1.2 Semiconductors Materials Definitions 1. A Conductor is a material that supports a generous flow of charge

when a voltage source of limited magnitude is applied across its terminals.

2. An Insulator is a material that offers a very low level of conductivity when a voltage source is applied across its terminals.

3. A Semiconductor is a material that has a conductivity level somewhere between an insulator and a conductor.

• The Resistance R of a material is given by:

cmcml

RAor

A

lR cm .

.2

Ω=Ω

====

ρρ

where the constant ρ is called the resistivity of the material with dimension Ω.cm or Ω.m, l is its length and A is its cross section area.


MANF360 Ch.1 Diodes ٩ of 48

Range of conductivities

room temperature!

1.2 Semiconductors Materials (cont.)


MANF360 Ch.1 Diodes ١٠ of 48

1.2 Semiconductors Materials (continue) Definitions • Typical resistivity values are provided for three categories of

materials as shown in Table 1.1.

Table 1.1. Typical resistivity values Insulator Semiconductor Conductor

ρ Example ρ Example ρ Example

1012 Ω.cm Mica 103 Ω.cm Silicon (Si)

10-6 Ω.cm Copper 50 Ω.cm Germanium (Ge)

Notes: • Si and Ge are not the only semiconductor materials. • They can be manufactured to a very high purity level (0.9999..). • The addition of one part of proper impurity per million in a wafer of Si

or Ge can change that material from a relatively poor conductor to a good conductor of electricity.

4. doping process: The ability to change the characteristics of the material significantly through adding proper impurities.


MANF360 Ch.1 Diodes ١١ of 48

1.2 Semiconductors Materials (continue) Definitions 5. The atomic structure of Si and Ge form a very definite shape, as shown in

Fig. 1.1, called crystal and the periodic arrangement is called lattice. in both atoms there are 4 electrons in the outmost (valence) shell

• The atom is composed of three basic particles: the neutron and the proton form the nucleus, while the electrons revolve around the nucleus in a fixed orbit.

Fig. 1.1, The Bohr model for atomic structure of (a) Si 14 [2,8, 4] and (b) Ge 32 [2,8,18, 4].


MANF360 Ch.1 Diodes ١٢ of 48

1.2 Semiconductors Materials (continue) 5. Atomic Structure (Continue) • Another atomic structure for Gallium 31 [2,8,18, 3] which has 3 valence

electrons and Arsenic 33 [2,8,18, 5] has 5 valence electrons as shown in Fig. 1.2.

Fig. 1.2, The Bohr model for atomic structure of (a) Ga 31 [2,8,18, 3] and (b) As 33 [2,8,18, 5] .


MANF360 Ch.1 Diodes ١٣ of 48

1.2 Semiconductors Materials (continue) Definitions 6. covalent bond: In pure Si or Ge crystals, 4 valence electrons are bonded to

4 adjacent atoms as shown in Fig. 1.3. This is called covalent bond.

Fig. 1.3 Covalent bonding of the silicon atom


MANF360 Ch.1 Diodes ١٤ of 48

1.2 Semiconductors Materials (continue) 6. covalent bond (Continue) • In pure GaAs crystal, 3 valence electrons of Ga are bonded to 5 valence

electrons of As adjacent atoms as shown in Fig. 1.4. This is called covalent bond.

Fig. 1.4 Covalent bonding of the GaAs crystal


MANF360 Ch.1 Diodes ١٥ of 48

1.2 Semiconductors Materials (continue)

Summary • A semi conductor material is a material that has a conductivity

(ρρρρ ) level somewhere between the extremes of an insulator and a conductor.

• Semiconductor materials are characterized by: a) One basic property of the semiconductor materials is that their

electric characteristics are highly dependent on the level of impurities in them.

b) Increasing the impurities level in a semiconductor material increases the material’s conductivity.

c) The most 2 popular materials used in semiconductor industry are SILICON and GERMANIUM

d) Si and Ge are characterized by having 4 valance electrons in the outmost orbit from the nucleus

e) The atoms within the structure of the material are connected by Bonds that is created through sharing of the valence electrons (Covalent Bond).


MANF360 Ch.1 Diodes ١٦ of 48

1.2 Semiconductors Materials (cont.) Definitions 7. Intrinsic Materials • Semiconductor materials with low level of

impurities are called, intrinsic semiconductors.

• The free electrons in the material due to only to natural causes are referred to as intrinsic carriers. At room temperature, there are approximately 1.5x1010 free carriers/cm3 for the intrinsic Si material and 2.5x1013 free carriers/cm3 for the intrinsic Ge material. Therefore, ρGe<< ρSi.

8. Negative temperature coefficient: An increase in temperature leads to an increase in the number of free electrons (carriers) in the material. In other words the resistance of semiconductor materials decreases as temperature increases which is referred to as negative temperature coefficient.

9. positive temperature coefficient: in conductors, the resistance increases as the temperature increases which is referred to as positive temperature coefficient.

+4 - -

+4

+4 +4

- -

- -

+4

- - +4

- - +4

- -

+4 - -

+4 - -

- -

- -

- -

- -

-

-

-

-

- - -

-

-

- -

-

intrinsic semiconductors

Temperature


MANF360 Ch.1 Diodes ١٧ of 48

1.2 Semiconductors Materials (continue) Definitions 10. Energy Levels • Electrons rotate around the nucleus in discrete energy levels as

shown in Fig. 1.5. • The closer the electron to the nucleus, the more energy it needs to

overcome the bond that relates it to the nucleus and become free. • Therefore, the valence level electrons are weakest electrons related

to the nucleus.

Fig. 1.5 Energy levels: discrete levels in isolated atomic structures


MANF360 Ch.1 Diodes ١٨ of 48

1.2 Semiconductors Materials (continue) 10. Energy Levels (continue) • The conduction and valence bands for different materials are shown in Fig.

1.6. the energy is defined by: W = QV [ev] and 1 ev = [1.6x10-19] x 1V = 1.6x10-19 J • At 0oK all valence electrons are locked in their outermost shell of the atom. • At room temperature, a large number of valence electrons have acquired

sufficient energy to leave the valence band, cross the energy gap defined by Eg and enter the conduction band.

Fig. 1.6 conduction and valence bands of an insulator, a semiconductor, and a conductor.


MANF360 Ch.1 Diodes ١٩ of 48

1.2 Semiconductors Materials (continue) 11. Extrinsic Materials • A semiconductor material that has been subjected to a doping process is

called an extrinsic material. • If the doping process is achieved using another materials that has 5 valence

electrons, like phosphorus, antimony or arsenic then the resulting material is called an n-type material as shown in Fig. 1.7.

• Four covalent bonds are formed, the 5th electron is relatively free. • Diffused impurities with 5 valence electrons are called donor atoms.

Fig. 1.7 (a) Antimony impurity in n-type material (b) Effect of donor impurities on the energy band structure

(a) (b)


MANF360 Ch.1 Diodes ٢٠ of 48

1.2 Semiconductors Materials (continue) 11. Extrinsic Materials (continue) • Similarly, if the doping is achieved using another material that has 3 valence

electrons such as boron, gallium or indium, then the resulting material is called p-type material as shown in Fig. 1.8.

• There is insufficient number of electrons to complete the covalent bonds of the formed lattice.

• The resulting vacancy is called a hole and is represented by (+) sign • The resulting vacancy will readily accept a free electron. • Diffused impurities with 3 valence electrons are called acceptor atoms.

Fig. 1.8 Boron impurity in p-type material


MANF360 Ch.1 Diodes ٢١ of 48

1.2 Semiconductors Materials (continue) 12. Majority and Minority Carriers • In an intrinsic material, some of the valence electrons may become free due

to some gained energy form temperature or light. Those free electrons leave equal number of positive holes in the intrinsic material.

• Doping the semiconductor with 5 valence electron materials creates an n-type semiconductor, where electrons are the majority carriers while the holes resulted form liberation act of the intrinsic material are the minority carriers

• Similarly for p-type semiconductor, the holes are the majority carries while the electrons are the minority carries The effect of hole on conduction is shown in Fig. 1.9 .

Fig. 1.9 Electron versus hole flow.


MANF360 Ch.1 Diodes ٢٢ of 48

1.2 Semiconductors Materials (continue) 12. Majority and Minority Carriers (continue) • In the n-type material, the electron is called the majority carrier and the hole

is the minority carrier. When the fifth electron of a donor leaves the parent atom, it becomes a positive ion or donor ion as shown in Fig. 1.10 (a).

• In the p-type material, the hole is called the majority carrier and the electron is the minority carrier. When the acceptor atom receives an electron it becomes a negative ion or acceptor ion as shown in Fig. 1.10 (b).

Fig. 1.10 (a) n-type material; (b) p-type material.


MANF360 Ch.1 Diodes ٢٣ of 48

1.3 Semiconductor Diodes 1. Diode Construction • One end of a silicon or germanium crystal can be doped as a p-type material

and the other end as an n-type material. The result is a p-n junction.as shown in 1.11.

• At the p-n junction, the negatively charged atoms of the n-type side are attracted to the positively charged atoms of the p-type side.

• The electrons in the n-type material migrate across the junction to the p-type material (electron flow).

• Or you could say the ‘holes’ in the p-type material migrate across the junction to the n-type material (conventional current flow).

• The result is the formation of a depletion region around the junction.

Fig. 1.11 (a) p-n junction; (b) Diode symbol; (c) depletion region.

(a) (b) (c)


MANF360 Ch.1 Diodes ٢٤ of 48

1.3 Semiconductor Diodes (continue)

2. Diode Biasing • A diode has three operating conditions: a) No bias b) Forward bias c) Reverse bias a) No Bias as shown in Fig. 1.12 • No external voltage is applied: VD = 0V • No current is flowing: ID = 0A • Only a modest depletion layer exists

Fig. 1.12 A p–n junction with no external bias. (a) a diode symbol, with the defined polarity and the current direction (b) An internal distribution of charge;

(c) demonstration that the net carrier flow is zero at the external terminal of the device when VD = 0 V.

(a) (c) (b)


MANF360 Ch.1 Diodes ٢٥ of 48

1.3 Semiconductor Diodes (continue) 2. Diode Biasing (Continue) b) Reverse bias as shown in 1.13 • External voltage is applied across the p-n junction in the opposite polarity of

the p- and n-type materials. • The reverse voltage causes the depletion layer to widen. • The electrons in the n-type material are attracted toward the positive terminal. • The holes in the p-type material are attracted toward the negative terminal.

Fig. 1.13 Reverse-biased p–n junction. (a) Internal distribution of charge under reverse-bias conditions; (b) reverse-bias polarity and direction of reverse saturation current.


MANF360 Ch.1 Diodes ٢٦ of 48

1.3 Semiconductor Diodes (continue) 2. Diode Biasing (Continue) b) Forward bias as shown in Fig. 1.14 • External voltage is applied across the p-n junction in the same polarity as the

p- and n-type materials. • The forward voltage causes the depletion layer to narrow. • The electrons and holes are pushed toward the p-n junction. • The electrons and holes have sufficient energy to cross the p-n junction.

Fig. 1.14 Forward-biased p–n junction. (a) Internal distribution of charge under forward-bias conditions; (b) forward-bias polarity and direction of resulting current.

(b)


MANF360 Ch.1 Diodes ٢٧ of 48

1.3 Semiconductor Diodes (continue) 3. Ideal Diode (Fig. 1.15) • A diode is a 2-terminal device. • A diode ideally conducts current in only one direction.

• The voltage across the diode is 0V • The current is infinite • The forward resistance is defined as

RF = VF / IF • The diode acts like a short.

• All of the voltage is across the diode • The current is 0A • The reverse resistance is defined as

RR = VR / IR • The diode acts like open.

(a)

Fig. 1.15 The Ideal Diode (a) Symbol (b); Conduction Region; (c) Non-Conduction Region

(b) (c)


MANF360 Ch.1 Diodes ٢٨ of 48

1.3 Semiconductor Diodes (continue)

4. Diode Symbol and Packaging • The anode is abbreviated A • The cathode is abbreviated K

Fig. 1.15 Different types and shapes of diodes


MANF360 Ch.1 Diodes ٢٩ of 48

1.4 Diode Characteristics 1. Diode Equations a) In Forward Bias Region (Fig.1.16) • The forward bias region is entered when the terminal voltage v is positive. • In this region, the i-v characteristics can be approximated by the equation:

sVV

sVV

sD IeIeII TDTD −=−= // )1(

c) The Reverse Bias Region (Fig.1.16) • From the characteristics, the R.B region is entered when the terminal

voltage becomes less than zero and greater than the break down voltage. • In this region, the diode current is almost constant and equals to the

saturation current Is VD < 0 gives ID = Is e-ve - Is≈ 0 - Is = - Is

20,2.25 temproomatmVq

kTVT == TnVv

sD eIi /=

Where Is.. is the reverse saturation current VT…is the thermal voltage and is given by:

Diode equation

Where k = Constant = 11600/n; n = 1 for Ge and n = 2 for Si T is the degree in Kelvin = Tc+ 273o

• Plot of the diode equation is shown in Fig.1.16, for VD > 0 the first term of the diode equation will grow exponential.

b) For No Bias (Fig.1.16) VD = 0 gives ID = Is e0 - Is= Is - Is = 0


MANF360 Ch.1 Diodes ٣٠ of 48

1.4 Diode Characteristics (continue)

Fig. 1.16 Silicon semiconductor diode characteristics.

The Diode Characteristic Curve is shown in Fig. 1.16, note that:

• The change of vertical scale, for positive value of ID the scale is mA and negative value of ID the scale is µA or nA.

• for positive value of VD the scale is in tenth of volt and negative value of VD the scale is in tens of volt .

2. Diode Characteristics Curve


MANF360 Ch.1 Diodes ٣١ of 48


Fig. 1.17 Zener region

• From the Diode Characteristic Curve shown in Fig. 1.17, note that: • The Zener region is in the diode’s reverse-bias region. • At some point the reverse bias voltage is so large the diode breaks down and

the reverse current increases dramatically. • The voltage is called the Zener potential VZ. This process is also called an

ionization, avalanche region, break down region or Zener region. • The diodes employing this region are called Zener Diode.

3. Diode breakdown

• This maximum reverse-bias voltage that can be applied before entering the Zener region is called the avalanche breakdown voltage, the Peak Inverse Voltage (PIV) or Peak Reverse Voltage (PRV) or Break Reverse Voltage (BRV).

• The current is called avalanche current.


MANF360 Ch.1 Diodes ٣٢ of 48


Fig. 1.18 Comparison of Ge, Si, and GaAs diodes.

4. Comparison of Ge and Si diodes (Fig. 1.18)

• In conclusion silicon devices enjoy a significantly higher level of development and utilization in design due to their better characteristics.

Ge Diode Si Diode Characteristic

Low up to 400 V

High up to 1000 V

PIV

Low High Current Rating

Low up to 100oC

Wide up to 200oC

Temperature Range

VT=0.3 V VT=0.7 V Threshold Voltage

IS=1 to 2 µA IS=10 nA R. Saturation Current

• From Fig. 1.18 we can come to the following comparison:


MANF360 Ch.1 Diodes ٣٣ of 48


Fig. 1.19 Variation in Si diode characteristics with temperature change.

5. Temperature Effects (Fig. 1.19) Si Diode Characteristic

Decreases as temperature Increases

Threshold Voltage

IS doubles for every 10oC IS change rapidly as temperature

Increases At 25oC IS =1 to 2 µA At 100oC IS =100 µ A

R. Saturation Current

• As temperature increases it adds energy to the diode.

• It reduces the required forward bias voltage for forward-bias conduction.

• It increases the amount of reverse current in the reverse-bias condition.

• It increases maximum reverse bias avalanche voltage.

• Germanium diodes are more sensitive to temperature variations than silicon diodes.


MANF360 Ch.1 Diodes ٣٤ of 48

a) DC or static resistance • Based on the DC voltage and

currents determined form the analysis of the circuit, the position of the operating point Q is specified.

• For a specific applied DC voltage VD, the diode has a specific current ID as shown in Fig. 1.20. The diode resistance RD given by:


Fig. 1.20 Determining the dc resistance of a diode at a particular operating point.

• Semiconductors act differently to DC and AC currents. • There are three types of resistances:

a) DC or static resistance b) AC or dynamic resistance c) Average AC resistance

6. Diode Resistance

QD

DD I

VR =

Operating Point (Q)


MANF360 Ch.1 Diodes ٣٥ of 48


QD

D

QD

DD dI

dV

I

Vr =

∆∆=

b) AC or dynamic resistance (In the forward bias region) • Used in diode applications where ac signals are present. This means

the operating signal position will vary instantaneously. • It is dependant on the shape of the i-v characteristics of the diode

since it represents the slope of the line that is tangential to the characteristics at the operating point and is given by:

6. Diode Resistance (continue)

Dd I

r026.0=

• rD ranges from a typical 0.1Ω for high power devices to 2Ω for low power, general purpose diodes. In some cases rD can be ignored.

• From the diode equation we can drive this simplified equation to calculate the ac resistance as:

In the reverse bias region: • rD = ∞ which means that the resistance is essentially infinite. The diode

acts like an open.


MANF360 Ch.1 Diodes ٣٦ of 48

c) Average AC resistance

• Used when the input signal is large enough to bring up a swing like that shown in Fig. 1.21.

• AC resistance can be determined by selecting two points on the characteristic curve developed for a particular circuit. The diode resistance rav given by:


Fig. 1.21 Determining the average ac resistance between indicated limits.

6. Diode Resistance

D

Dav I

Vr

Λ∆=


MANF360 Ch.1 Diodes ٣٧ of 48

1.4 Diode Characteristics (continue) 7. Diode Specification Sheets

• Data about a diode is presented uniformly for many different diodes. This makes cross-matching of diodes for replacement or design easier.

• Data of semiconductor devices are usually provided by the manufactures in one of two forms:

a) Brief description of the device parameters b) Examination of parameters through tables and graphs

1. VF: Forward voltage at a specific current and temperature. 2. IF: Maximum forward current at a specific temperature. 3. IS: Maximum reverse saturation current at a specific temperature. 4. PIV or PRV or BRV: Maximum reverse voltage at a specific temperature. 5. Power dissipation: Maximum power dissipated at a specific temperature. 6. C: capacitance levels in reverse bias. 7. Trr: Reverse recovery time. 8. Temperatures: operating and storage temperature ranges. 9. Frequency range: operating frequency range.


MANF360 Ch.1 Diodes ٣٨ of 48

1.4 Diode Characteristics (continue) 8. Diode Equivalent Circuits

Fig. 1.22 Ideal versus actual semiconductor characteristics.

• An equivalent circuit is a combination of elements properly chosen to best represent the actual terminal characteristics of a device or a system in a particular operating region.

• The symbol of the device can be removed from a schematic and the equivalent inserted in its place, the result is a network that can be solved using traditional circuit analysis techniques.

• There are three models of diode equivalent circuits: a) Ideal Equivalent Circuit b) Piecewise Linear Equivalent Circuit

c) Simplified Equivalent Circuit

A) Ideal Equivalent Circuit • An ideal diode conducts current in

only one direction as shown in Fig. 1.22.

• It represents a switch as follows: On or short circuit when VD > 0 V Off or open circuit when VD < 0 V


MANF360 Ch.1 Diodes ٣٩ of 48

1.4 Diode Characteristics (continue) 8. Diode Equivalent Circuits (continue)

b) Piecewise Linear Equivalent Circuit • The diode Characteristic is approximated by a straight line segment as shown

in Fig. 1.23. The slope represents the average resistance rav and VK=VD=0.7 V. Since ID=0 at VD=0.7 V and ID=10 mA at VD=0.8 V rav is calculated as:

Fig. 1.23 Piecewise linear equivalent circuit (a) Defining a straight-line segment to approximate the characteristic curve; (b) Components of the piecewise-linear equivalent circuit.

(a)

(b)

Ω==−

−==∆∆ 10

10

1.0

010

7.08.0

mA

V

mAr

IV

D

Dav


MANF360 Ch.1 Diodes ٤٠ of 48


c) Simplified Equivalent Circuit • For most applications the average resistance rav is removed because it has a

small value compared to the other elements of the network. This model is shown in Fig. 1.24.

• In both models the ideal diode is included to establish that there is only one direction of conduction through the device.

Fig. 1.24 Piecewise linear equivalent circuit (a) The approximated diode characteristic;

(b) Components of the simplified equivalent circuit.

(a) (b)


MANF360 Ch.1 Diodes ٤١ of 48


Example 1.1 For the diode circuit shown in Fig. 1.25, if E = 10 V and R = 1 kΩ determine the

current ID and voltage VR using: a) The diode piecewise linear equivalent circuit with VD=0.7 V and rav=10 Ω. b) the diode simplified equivalent circuit. c) the ideal diode model. d) Compare the obtained results in the three cases.

Fig. 1.25 A diode circuit

Solution a) Replace the diode by its piecewise linear

equivalent circuit as shown in Fig. 1.26 (a), we have:

E = VD + ID (rav + R) 10 = 0.7 + ID (10 +1000) ID = 9.3/1010 = 9.21 mA IDQ = 9.3/1010 = 9.21 mA VR = 9.21 mA x 1 k Ω = 9.21 V


MANF360 Ch.1 Diodes ٤٢ of 48


Example 1.1 Solution (Continue)

Fig. 1.26 The diode circuit including the diode model

(a)

(b)

(c)

b) Replace the diode by its simplified equivalent circuit as shown in Fig. 1.26 (b), we have: E = VD + ID R

10 = 0.7 + ID (1000) ID = 9.3/1000 = 9.23 mA IDQ = 9.3/1000 = 9.23 mA VR = 9.23 mA x 1 k Ω = 9.23 V

c) Replace the diode by its ideal equivalent circuit as shown in Fig. 1.26 (c), we have: E = VD + ID R

10 = ID (1000) ID = 10/1000 = 10 mA IDQ = 10 mA VR = 10 mA x 1 k Ω = 10 V


MANF360 Ch.1 Diodes ٤٣ of 48

1.5 Diode Testing • There are several methods for the diode testing which include :

a) Diode checker b) Ohmmeter c) Curve tracer

a) Diode checker • Many digital multimeters have a diode checking function. The diode should be

tested out of circuit. A normal diode will exhibit its forward bias voltage: a) Silicon diode ≅ 0.7V b) Germanium diode ≅ 0.3V

Fig. 1.27 Diode Testing using Diode checker (a) Digital display meter; (b) Diode Characteristics.

(a) (b)


MANF360 Ch.1 Diodes ٤٤ of 48

1.5 Diode Testing

b) Ohmmeter • An ohmmeter set on a low Ohms scale can be used to test a diode. The diode

should be tested out of circuit as shown in Fig. 1.28.

Fig. 1.28 Diode Testing using an Ohmmeter (a) Forward bias; (b) Reverse bias

(a) (b)


MANF360 Ch.1 Diodes ٤٥ of 48

1.5 Diode Testing (continue) c) Curve tracer • A curve tracer is a specialized type of test equipment. It displays the

characteristic curve of the diode in the test circuit. This curve can be compared to the specifications of the diode from a data sheet.

• The diode should be tested out of circuit as shown in Fig. 1.29. • More details about diode testing will be given in the Lab.

Fig. 1.29 Diode Testing using a curve tracer (a) Curve tracers (b) The output

(a) (b)


MANF360 Ch.1 Diodes ٤٦ of 48

1.6 Other Types of Diodes • There are other types of diodes used in many applications which include :

a) Zener diode b) Light-emitting diode c) Diode arrays

Fig. 1.30 Zener diode (a) Symbol (b) Zener diode characteristics with the equivalent model for each region

a) Zener diode A Zener is a diode with the

symbol shown in Fig. 1.30 operated in reverse bias at the Zener voltage (VZ). Common Zener voltages are between 1.8V and 200V

(a)

IR is Max reverse current at VR

(b)

IZK is Max knee current

IZT is the test current

IZM is Max regulator current


MANF360 Ch.1 Diodes ٤٧ of 48

1.6 Other Types of Diodes (continue) b) Light Emitting Diode (LED) • LED is a diode that will give off visible light

when it is energized. • The process of giving off light by applying an

electric source is called electroluminescence as shown in Fig. 1.31.

• Many materials are used to produce LEDs such as Gallium Arsenide Phosphide (GaAs) or Gallium Phosphide (GaP). The number of photons of light energy emitted is sufficient to create a very visible light source.

• LED displays are available in many sizes [length from 0.1 to 1 inch], shapes and colors [Red, Green, Orange, and white].

• The operates at a voltage in the range of 1.7V to 3.3 V.

• LEDs are used in digital displays, calculators, watches, and all forms of instrumentation.

Fig. 1.31 (a) Process of electroluminescence in the LED; (b) graphic symbol; (c) Seven

segment display

(a)

(b)

(c)


MANF360 Ch.1 Diodes ٤٨ of 48

1.6 Other Types of Diodes (continue) c) Diode arrays • Multiple diodes can be packaged together in an integrated circuit (IC). • A variety of combinations exist as shown in Fig. 1.32.

Fig. 1.32 Diode arrays (a) Integrated Circuit (IC); (b) Common anode; (c) Common cathode

(a) (b) (c)

MANF360 Chapter 1 Semiconductor Diodes

Documents

Transcript of MANF360 Chapter 1 Semiconductor Diodes