chapter 3 transistors

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CHAPTER 3_TRANSISTORSCHAPTER 3_TRANSISTORSmuthmainnah

SLIDE 1SLIDE 1 SLIDE 2SLIDE 2


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CHAPTER 3: TRANSISTORS

MEC523

APPLIED ELECTRONICS &

MICROPROCESSOR

Objectives

Part 1Part 1

3.1 Characteristics of Transistors.3.1 Characteristics of Transistors.

Describe and understand the conceptDescribe and understand the concept

of semiconductor materials, types of of semiconductor materials, types of

semiconductors, and diode.semiconductors, and diode.

◦

Understand the diode applications -Understand the diode applications -

rectifiers and regulators.rectifiers and regulators.

◦

TRANSISTORS

Part 2Part 2

2.32.3 Bipolar Junction Transistor (BJT)Bipolar Junction Transistor (BJT)

Circuits: DC operation analysis.Circuits: DC operation analysis.

Lecturer: Nurul Muthmainnah Mohd Noor

Room: A14-6C, Bangunan 1, Kompleks Kejuruteraan,

Phone: 03-55442982

Prepared by Nurul Muthmainnah

Mohd Noor

Part 3Part 3

3.33.3 Bipolar Junction Transistor (BJT)Bipolar Junction Transistor (BJT)

Circuits: AC operation analysis.Circuits: AC operation analysis.

FACULTY OF MECHANICAL

ENGINEERING

COURSE OUTCOME

Upon completion of this course, students should beUpon completion of this course, students should be

able to:able to:

CO1CO1 Apply the fundamental concepts and

operational principles of circuit theory, digital logic

and m icroprocessor i n sol vi ng engineeri ng

problems {PO1, C4}.

CO2CO2 Apply knowledge of circuit theory, digital

electroni cs and m icroprocessor i nterfaci ngtechniques for mechatronic engineering design

{PO3, C5}.


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2

Transistors

Characteristics of

Transistors

Bipolar Junction

Transistor (BJT) Circuits

DC

AC

PART 1

Characteristics of Transistors.

Transistor Construction

There are two types of transistors:There are two types of transistors:

• pnp• pnp

• npn• npn

The terminals are labeled:The terminals are labeled:

• E - Emitter• E - Emitter

• B - Base• B - Base• C - Collector• C - Collector

Transistor OperationTransistor Operation

With the external sources, VWith the external sources, VEEEEand Vand VCCCC, connected as shown:, connected as shown:

•• The emitter-base junction is forward biasedThe emitter-base junction is forward biased

•• The base-collector junction is reverse biasedThe base-collector junction is reverse biased


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3

Currents in a TransistorCurrents in a Transistor Common-Base Configuration

Common-Base AmplifierCommon-Base Amplifier Output

Emitter current is the sum of the collectorEmitter current is the sum of the collector

and base currents:and base currents:

The collector current is comprised of twoThe collector current is comprised of two

currents:currents:The base is common to both inputThe base is common to both input

(emitter–base) and output (collector–(emitter–base) and output (collector–

base) of the transistor.base) of the transistor.

Input CharacteristicsInput CharacteristicsOutput CharacteristicsOutput Characteristics

The arrow in the graphic symbolThe arrow in the graphic symbol

defines the direction of emitterdefines the direction of emitter

c ur re nt ( co nv en ti on al f lo w)c ur re nt ( co nv en ti on al f lo w)

through the device.through the device.

◦

This curve shows theThis curve shows the

relationshiprelationship between of input currentbetween of input current

(I(IEE) t o i nput) to input voltage (Vvoltage (VBEBE) f or t hr ee) f or t hr ee

output voltageoutput voltage (V(VCBCB) levels.) levels.

This graph demonstratesThis graph demonstrates

the output current (Ithe output current (ICC) to an) to an

output voltage (Voutput voltage (VCBCB) for) for

v ar io us l ev el s o f i np utv ar io us l ev el s o f i np ut

current (Icurrent (IEE).).


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4

Operating Regions

• Active – Operating range of the amplifier.• Active – Operating range of the amplifier.

• Cutoff – The amplifier is basically off. There is voltage, but little• Cutoff – The amplifier is basically off. There is voltage, but little

current.current.

• Saturation – The amplifier is full on. There is current, but little• Saturation – The amplifier is full on. There is current, but little

voltage. voltage.

Approximations

Emitter and collector currents:Emitter and collector currents:

Base-emitter voltage:Base-emitter voltage:

Alpha (α)Alpha (Alpha (α) is the ratio of) is the ratio of IICCtoto IIEE::

Ideally:Ideally:α = 1= 1

In reality:In reality:α is between 0.9 and 0.998is between 0.9 and 0.998

Transistor Amplification

Omit DC biasing to demonstrate AC responseOmit DC biasing to demonstrate AC response◦

AssumeAss ume RRiiandan d RRoofrom input & output characteristic curvesfrom input & output characteristic curves◦

Alpha (Alpha (α) in the AC mode:) in the AC mode:


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5

Common–Emitter Configuration Common-Emitter Characteristics

Common-Emitter Amplifier Currents

Ideal CurrentsIdeal Currents

Beta (β)β represents the amplification factor of a transistor. (represents the amplification factor of a transistor. (β is sometimesis sometimesreferred to asrefe rred to a s hhfefe, a term used in transistor modelling calculations), a term used in transistor modelling calculations)

The emitter is common to bothThe emitter is common to both

input (base-emitter) and outputinput (base-emitter) and output

(collector-emitter ).(collector-emitter ).

The input is on the base and theThe input is on the base and the

output is on the collector.output is on the collector.

Actual CurrentsActual Currents

CollectorCollector

CharacteristicsCharacteristics

WhenWhen IIBB= 0= 0μA the transistor is in cutoff, butA the transistor is in cutoff, butthere is some minority current flowingthere is some minority current flowing

calledcalled IICEOCEO..

Base Characteristics

IICBOCBOis usually so small that it canis usually so small that it can

be ignored, except in high powerbe ignored, except in high powertransistors and in hightransistors and in hightemperature environments.temperature environments.


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Beta (β)β represents the amplification factor of a transistor. (represents the amplification factor of a transistor. (β is sometimesis sometimesreferred to asrefe rred to a s hhfefe, a term used in transistor modelling calculations), a term used in transistor modelling calculations)

Beta (β)

Beta (β)

Relationship between amplification factorsRelationship between amplification factorsβ andandα

Relationship Between CurrentsRelationship Between Currents

Common–Collector Configuration

The input is on the base andThe input is on the base and

the output is on the emitter.the output is on the emitter.

DeterminingDeterminingβ from a Graphfrom a Graph

BothBothβ values are usually reasonably close and are often used interchangeablyvalues are usually reasonably close and are often used interchangeably


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PP

CmaxCmax = V= VCBCBIICC

PPCmaxCmax = V= VCECE

II

CC

PPCmaxCmax = V= VCECE

II

EE

Common-base:Common-base:◦

Common-emitter:Common-emitter:◦

Common-collector:Common-collector:◦

Transistor Specification SheetTransistor Specification Sheet

Common–Collector Configuration

The characteristics are similarThe characteristics are similar

to those of the common-to those of the common-

emitter configuration, exceptemitter configuration, except

the vertical axis is Ithe vertical axis is IEE..

Operating Limits for Each ConfigurationOperating Limits for Each Configuration

VVCECE i s at m axim um and Ii s at m axim um and ICC i s ati s at

minimum (Iminimum (ICmaxCmax= I= ICEOCEO) in the cutoff ) in the cutoff

region.region.

◦

IICC i s at m axim um and Vi s at m axim um and VCECE i s ati s at

minimum (Vminimum (VCEmaxCEmax = V= VCEsatCEsat = V= VCEOCEO))

in the saturation region.in the saturation region.

◦

The transistor operates i n theThe transistor operates i n the

active region between saturationactive region between saturation

and cutoff.and cutoff.

◦

◦

Power DissipationPower Dissipation


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PART 2

Bipolar Junction Transistors

(BJT) Circuits:

DC BIASING ANALYSIS

Biasing

Biasing:Biasing:

The DC voltages applied to a transistor in order to turn it on soThe DC voltages applied to a transistor in order to turn it on so

that it can amplify the AC signal.that it can amplify the AC signal.

Operating PointOperating Point

The DC input establishesThe DC input establishes

an operating oran operating or

quiescent pointquiescent point calledcalled

the Q-point.the Q-point.

The Three States of OperationThe Three States of Operation

• Active or Linear Region OperationActive or Linear Region Operation

Base–Emitter junction is forward biased

Base–Collector junction is reverse biased

• Cutoff Region OperationCutoff Region Operation

Base–Emitter junction is reverse biased

• Saturation Region Operation• Saturation Region Operation

Base–Emitter junction is forward biased

Base–Collector junction is forward biased


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From Kirchhoff’s voltageFrom Kirchhoff’s voltage

law:law:

Solving for base current:Solving for base current:

Collector current:Collector current:

From Kirchhoff’s voltage law:From Kirchhoff’s voltage law:

DC Biasing Circuits

• Fixed-bias circuit

• Emitter-stabilized bias circuit

• Collector-emitter loop

• Voltage divider bias circuit

• DC bias with voltage feedback

Fixed BiasFixed Bias

The Base-Emitter LoopThe Base-Emitter Loop Collector-Emitter LoopCollector-Emitter Loop


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Saturation

When the transistor is operating in saturation, current through theWhen the transistor is operating in saturation, current through the

transistor is at its maximum possible value.transistor is at its maximum possible value.

Load Line AnalysisLoad Line Analysis

Circuit Values Affect the Q-Point Circuit Values Affect the Q-Point

The end points of the load lineThe end points of the load line

are:are:

The Q-point is the operating point:The Q-point is the operating point:

•• where the value of Rwhere the value of RBBsets the value of Isets the value of IBB•• that sets the values of Vthat sets the values of VCECEand Iand ICC


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Circuit Values Affect the Q-Point Emitter-Stabilized Bias CircuitEmitter-Stabilized Bias Circuit

Adding a resistor (RE)

to the emitter circuit

stabilizes the bias

circuit.

Base-Emitter LoopBase-Emitter Loop Collector-Emitter LoopCollector-Emitter Loop


law:law:

Also:Also:


law:law:

Since ISince IEE= (= (β+ 1)I+ 1)IBB::

Solving for ISolving for IBB::


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Improved Biased StabilityImproved Biased Stability Example 2.2Example 2.2

Parallel Diode Configurations: Example 2.3Parallel Diode Configurations: Example 2.3

Determine VDetermine Voo,, II11,,IID1,D1,and Iand ID2D2forfor the parallel diode configurationthe parallel diode configuration

Parallel Diode Configurations: Example 2.4Parallel Diode Configurations: Example 2.4

For the reversed diode configuration,For the reversed diode configuration,

determinedeter mine VVDD, V, VRRandand IIDD..

Determine the current I for the network of figure.Determine the current I for the network of figure.


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Half-Wave RectificationHalf-Wave Rectification

Th e d io de o nl yT he di ode o nl y

conducts when itconducts when it

is forward biased,is forward biased,

the re fore onlythe refo re only

half of the AChalf of the AC

cycle passescycle passes

through the diodethrough the diode

to the output.to the output.

Because the diode is only forward biased forBecause the diode is only forward biased for

one-half of the AC cycle, it is also reverse biasedone-half of the AC cycle, it is also reverse biased

for one-half cycle.for one-half cycle.

◦

It is important that the reverse breakdownIt is important that the reverse breakdown

voltage rating of the diode be high enough tovoltage rating of the diode be high enough to

withstand the peak, reverse-biasing AC voltage.withstand the peak, reverse-biasing AC voltage.

◦

Full-Wave Rectification

The most familiar network for performingThe most familiar network for performing suchsuch

a function appears in Figure with its four diodes ina function appears in Figure with its four diodes in

a bridge configuration.a bridge configuration.

The rectification process can be improved by using a full-wave rectifierThe rectification process can be improved by using a full-wave rectifier

circuit.circuit.

◦

The dc level obtained from a sinusoidal input can be improved 100% using aThe dc level obtained from a sinusoidal input can be improved 100% using a

process called full-wave rectification.process called full-wave rectification.

◦

Full-wave rectification produces a greater DC output.Full-wave rectification produces a greater DC output.◦

Transistor Switching Networks

Transistors with only the DC source applied can be used as electronicTransistors with only the DC source applied can be used as electronic

switches.switches.

PIV (PRV)

Bridge Network


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Switching Circuit Calculations Switching Time

Troubleshooting Hints

•• Approximate voltagesApproximate voltages

–– VVBE ~=BE ~=.7 V for silicon transistors.7 V for silicon transistors

–– VVCECE~=~= 25% to 75% of V25% to 75% of VCCCC

•• Test for opens and shorts with an ohmmeter.Test for opens and shorts with an ohmmeter.

•• Test the solder joints.Test the solder joints.•• Test the transistor with a transistor tester or a curve tracer.Test the transistor with a transistor tester or a curve tracer.

•• Note that the load or the next stage affects the transistor operation.Note that the load or the next stage affects the transistor operation.

PNP Transistors

The analysis for pnp transistor biasing circuits is the same as that forThe analysis for pnp transistor biasing circuits is the same as that for

npn transistor circuits. The only difference is that the currents arenpn transistor circuits. The only difference is that the currents are

flowing in the opposite direction.flowing in the opposite direction.

Saturation current:Saturation current:

To ensure saturation:To ensure saturation:

Emitter-collector resistance atEmitter-collector resistance at

saturation and cutoff:saturation and cutoff:

Transistor switching times:Transistor switching times:


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ZenerZener Diodes: Basic Zener regulatorDiodes: Basic Zener regulatorZenerZener Diodes:Diodes: VVii and Rand R

The applied dc voltage is fixed, as is the load resistor. The analysis can fundamentally beThe applied dc voltage is fixed, as is the load resistor. The analysis can fundamentally be

broken down into two steps.broken down into two steps.

ZenerZener Diodes:Diodes: VVii and Rand R

The applied dc voltage is f ixed, as is the load resistor. The analysis canThe applied dc voltage is f ixed, as is the load resistor. The analysis can

fundamentally be broken down into two steps.fundamentally be broken down into two steps.


The applied dc voltage is f ixed, as is the load resistor. The analysis canThe applied dc voltage is f ixed, as is the load resistor. The analysis can

fundamentally be broken down into two steps.fundamentally be broken down into two steps.

Basic Zener

regulator

Substituting the Zener equivalent for the “on”Substituting the Zener equivalent for the “on”situation.situation.

The voltage divider rule:The voltage divider rule:

Substituting the Zener equivalent for the “on”Substituting the Zener equivalent for the “on”situation.situation.

The power dissipated by the Zener diode is determined byThe power dissipated by the Zener diode is determined by

which must be less than thewhich must be less than thePP ZM ZM specified for the device.specified for the device.

Since voltages across parallel elements must be the same :-Since voltages across parallel elements must be the same :-

The Zener diode current must be determined by anThe Zener diode current must be determined by an

application of Kirchhoff’s current law.application of Kirchhoff’s current law.


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* NOTE* NOTE

a) If the Zener diode is in the “on” state, the voltage across the diode is not V volts. When thea) If the Zener diode is in the “on” state, the voltage across the diode is not V volts. When the

system is turned on, the Zener diode will turn “on” as soon as the voltage across the Zenersystem is turned on, the Zener diode will turn “on” as soon as the voltage across the Zener

diode isdio de is VVZZ volts. It will then “lock in” at this level and never reach the higher level of V volts.volts. It will then “lock in” at this level and never reach the higher level of V volts.

b) Zener diodes are most frequently used in regulator networks or as a reference voltage. Forb) Zener diodes are most frequently used in regulator networks or as a reference voltage. For

values of applied voltage greater than required to turn the Zener diode “on,” the voltage acrossvalues of applied voltage greater than required to turn the Zener diode “on,” the voltage across

the load will be maintained atthe load will be maintained at VVZZvolts. If the Zener diode is employed as a reference voltage, itvolts. If the Zener diode is employed as a reference voltage, it

will provide a level for comparison against other voltages.will provide a level for comparison against other voltages.

Example 2.5Example 2.5

ZenerZener Diodes:Diodes: Fixed Vi, variable RL

Firstly, the Zener is in the “on” state. Too small a load resistanceFirstly, the Zener is in the “on” state. Too small a load resistance RR LLwill result in awill result in a

voltagevoltageVV LLacross the load resistor less thanacross the load resistor less than VV ZZ ,,and the Zener device will be in theand the Zener device will be in the

“off” state.“off” state.

Same as before,Same as b efore, VVLL=V=VRR

Example 2.6Example 2.6

Zener diode regulatorZener diode regulator


Solve RSolve RLL

The voltage across R remains fixed atThe voltage across R remains fixed at

TheTheIIRRremains fixed atremains fixed at

The Zener currentThe Zener current

A minimumA minimumII ZZ whenwhen II LL is a maximumis a maximum

and a maximumand a maximumII ZZ whenwhenII LL isis

aa minimum value sinceminimum value sinceII RR is constantis constantThe maximumThe maximum II LL

The minimumThe minimumII LL

The maximum load resistanceThe maximum load resistance


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SLIDE 67SLIDE 67

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END of CHAPTER 2

ZenerZener Diodes:Diodes: Fixed RL, variable Vi Example 2.6Example 2.6


Determine the range of values ofDetermine the range of values of VV ii

that will maintain the Zenerthat will maintain the Zener

diode of figure in the “on” state.diode of figure in the “on” state.

Let's do exercisesLet's do exercises

Firstly, the Zener is in the “on” state.Firstly, the Zener is in the “on” state.Same as before,Same as b efore, VVLL= V= VRR

The maximum value ofThe maximum value ofVV ii is limited by the maximum Zener currentis limited by the maximum Zener current II ZM ZM . Since. Since II ZMZM == II RR -- II LL..

VVii= V= Vimin,imin,

SinceSince II LL is fixed atis fixed atVV ZZ /R /R LLandandII ZM ZM is the maximum value ofis the maximum value ofII ZZ , the maximum, the maximumVV ii is defined byis defined by

chapter 3 transistors

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