Junction Transistor Amplifier– Lesson-6:– Detailed … Devices...2008 Junction Transistor Lesson 6- " , Raj Kamal, 1 Junction Transistor Amplifier– Lesson-6:– Detailed Study - [PDF Document] (2024)

2008 Junction Transistor Lesson 6- " , Raj Kamal, 1

Junction Transistor Amplifier–Lesson-6:– Detailed Study of

Currents in a Transistor, Transistor Alfa and Characteristics of transistor

in common base, common emitter and common collector configuration

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1.1. RevisionRevision

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BJT Common BJT Common Base Base

configurationconfiguration

BJT Common BJT Common EmitterEmitter

configurationconfiguration

BJT Common BJT Common Collector configurationCollector configuration

PNPPNP PNP

IBIE IC

Three configurations

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2.2. Current Components due to holes and Current Components due to holes and electrons in E, B, and C regionselectrons in E, B, and C regions

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PNP forward biased junctionPNP forward biased junction

IE = IEP + IEN = 1 + 2 + 5IB = IBR + IBE = IBR + IEN = – (4 + 5)IC = IEP – IBR = 2

electrons holes

EI CI

BI

5 41

23

IEP

–IEN

IBR

Electronflux

Holefluxand current

–IBR–IBE

Majority Carrier Minority Carrier

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Current componentsCurrent components1 = hole current lost due to recombination in base, IBR

2 = hole current collected by collector, ~ IC

1 + 2 = hole part of emitter current, IEP

5 = electrons injected across forward biased E-B junction, (– IBE);

same as electron part of emitter current, – IEN

4 = electron supplied by base contact for recombination with

holes lost, – IBR (= 1)

3 = thermally generated e & h making up reverse saturation

current of reverse biased C-B junction. (generally neglected)

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Formula for Collector Current ComponentsFormula for Collector Current Components

IC = ICmajority + ICOminority

ICO = Collector Current with emitter terminal open (not connected)

Leakage component

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3. Transistor 3. Transistor Alpha

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Alpha dc Alpha dc

dc= IC ÷ IE = IC ………………… .. (1) IE

dc 0.90 to 0.998

IC = dc IE + ICB0 ……………………..(2)

Leakage component

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Alpha ac (Common Alpha ac (Common base short circuit base short circuit

amplification factor)amplification factor)ac= IC ÷ IE = IC …………….. (1)

IEac dc 0.90 to 0.998

IC = dc IE + ICB0 ……………………..(2)Leakage component

means small change in

VCB = constant

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4. Input and Output Characteristics of 4. Input and Output Characteristics of transistor in common basetransistor in common base

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Emitter characteristics (input Characteristics) Emitter characteristics (input Characteristics) of baseof base--emitter region amplifier in the dc emitter region amplifier in the dc

mode Common basemode Common base

0.7 VVBE (V) VBE (V)

IE (mA) Active Region

Active Region

VBE

IE

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Active region

Saturation

region

Active region

VBE 0.7 vVBE 0.7 vVBE 0.7 vVBE 0.7 v

VBE OR << 0.7 V

VBE 0.7 v

Output Characteristics Common BaseOutput Characteristics Common Base

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First Approximation Relationship between First Approximation Relationship between IICCand and IIEE

IC IE

BJT Common BJT Common Base Base

configurationconfiguration

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Biasing Common BaseBiasing Common Base

VCCVEE VCCVEE

IB = 0 mA IB = 0 mA

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Amplifying action Common BaseCommon Base

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Input Input ii

iinput = vinput / Ri = 20 mV = 1 mA20

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Current iinput transfers from a low Ricircuit to high Ro circuit

• ac = 1, iC = iEiL = iinput = 1 mAvL = IL. R = 1 mA. 5 k= 5 V

Voltage Amplification = vL/vinput = 5 V 20 mV

= 250Generally 50 to 300

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5. Input and Output Characteristics of 5. Input and Output Characteristics of transistor in common emitter transistor in common emitter

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BaseBase--emitter region amplifier in the dc mode emitter region amplifier in the dc mode Input Characteristics (also base Input Characteristics (also base

characteristics) in common emitter amplifiercharacteristics) in common emitter amplifier

0.7 VVBE (V) VBE (V)

IB (A)

Active Region

Active Region

VBE

IB

VCE = 1V VCE = 10V

VCE = 20V

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Saturation

region

Active region

Output Characteristics (also called collector Output Characteristics (also called collector characteristics) of Common Emitter characteristics) of Common Emitter

IB= 10 A

30 A

50 A70 A

90 A

IB= 0 A ICE0 ICB0

Cut-off region region

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pnp transistor as common emitter amplifierpnp transistor as common emitter amplifier

p

pn

C

B

E+

RB

IB

IE

IC

RC

IC

IC

IE

IB

C

B

E

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npn transistor in a simple circuit, known as‘common-emitter’ amplifier

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Relationship between Relationship between IICC and and IIBB

IB = IC IE

BJT Common emitter configuration BJT Common emitter configuration

IC = IE + ICB0

Leakage current

IC = ( IC + IB ) + ICB0

(1 ) IC = IB + ICB0IC = /(1 ) IB + ICB0 /(1 )

= Current gain = [IC / IB] at constant VCE

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IICEOCEO

If = 0.996 then when at IB at 0 A IC = 0.996/(0.004) . 0 A + ICB0 /(0.004)

= ICB0 /(0.004) = 250 ICB0

IC / ICB0 = 250 at IB = 0 ICEO = ICBO / (1 - ) at IB = 0

For linear very small distortion amplifier cut-off for common emitter configuration is at IC = ICEO

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pnp transistor as common emitter amplifier at pnp transistor as common emitter amplifier at CutCut--Off IOff ICC = I= ICE0CE0

p

pn

C

B

E+

RB

IB

IE

IC

RC

IC

IC

ICE0

IB = 0C

B

E

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6. Input and Output Characteristics of 6. Input and Output Characteristics of transistor in common collector transistor in common collector

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BaseBase--collector region amplifier in the dc mode collector region amplifier in the dc mode Input Characteristics (also collector Input Characteristics (also collector

characteristics) in common collector amplifiercharacteristics) in common collector amplifier

0.7 VVBC (V) VBC (V)

IC (mA)

Active Region

Active Region

VBC

IC

VEC = 1V VEC = 10V

VEC = 20V

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Saturation

region

Active region

Output Characteristics (also called emitter Output Characteristics (also called emitter characteristics) of Common Collector characteristics) of Common Collector

IC= 1 mA

3 mA

5 mA7 mA

9 mA

IC= 0 mA IE IEC0

Cut-off region

IE

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pnp transistor as common collector amplifierpnp transistor as common collector amplifier

p

pn

E

B

C+

IB

IC

IE

RE

IE

IE

IC

IB

E

B

C

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Relationship between Relationship between IICC and and IIEE

IB = IE IC

BJT Common collector configuration BJT Common collector configuration

IE = IC/ + IEC0

Leakage current

IE = ( IC / ) + IEC0

IE = 1 IC + IEC0

Current gain = [IE / IC] at constant VCE

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IICEOCEO

If = 0.996 then when at IB at 0 A IE = (0.996) 1 . IC mA IE / IC 1 at IB = 0

For linear very small distortion amplifier cut-off for common collector configuration is at IE = IC + IECEO

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pnp transistor as common collector amplifier pnp transistor as common collector amplifier at Iat ICE0CE0

p

pn

C

B

E+

IB

IE

IC

RC

IC

IC

ICE0

IB 0C

B

E

Very High Impedance at input

low Impedance at input

Current iinput transfers from a high Ri circuit to low Ro circuit

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7. Transistor 7. Transistor Beta

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Beta dc Beta dc

dc= IC ÷ IB = IC ………………… .. (1) IE

dc 50 to 400 range

IC = dc IB + ICE0 ……………………..(2)

Leakage component

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Beta ac (Common Beta ac (Common emitter forward current open circuit emitter forward current open circuit

amplification factor)amplification factor)ac= IC ÷ IB = IC …………….. (1)

IB ac dc 50 to 400

IC = dc IB + ICE0 ……………………..(2)Leakage component

means small change in

VCE = constant

Related to hFE

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8. Relation Between Transistor Alpha and 8. Relation Between Transistor Alpha and Beta

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IE = IC + IB

BJT Alpha and BetaBJT Alpha and Beta

IC/ = IC + IC /

1/ = 1 + 1 / ; = / ( + 1)

= / (1 )

IC = IB

IE = IB ( + 1)

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ICE0 = ICB0 / (1 )

BJT Alpha and BetaBJT Alpha and Beta

1/ = 1 + 1 / ;

ICE0 ICB0

+ 1= 1/ (1 )

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SummarySummary

We learnt Current components in a transistor Input and output circuit characteristics

in Three configurations- Common base, common emitter and Common collector

Alfa dc and alpha ac Beta and beta ac

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End of Lesson 6End of Lesson 6