Junction Transistor Amplifier– Lesson-6:– Detailed … Devices...2008 Junction Transistor Lesson 6- " , Raj Kamal, 1 Junction Transistor Amplifier– Lesson-6:– Detailed Study

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


1.1. RevisionRevision


BJT Common BJT Common Base Base

configurationconfiguration

BJT Common BJT Common EmitterEmitter


BJT Common BJT Common Collector configurationCollector configuration

PNPPNP PNP

IBIE IC

Three configurations


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


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


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)


Formula for Collector Current ComponentsFormula for Collector Current Components

IC = ICmajority + ICOminority

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

Leakage component


3. Transistor 3. Transistor Alpha


Alpha dc Alpha dc

dc= IC ÷ IE = IC ………………… .. (1) IE

dc 0.90 to 0.998

IC = dc IE + ICB0 ……………………..(2)

Leakage component


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


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


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


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


First Approximation Relationship between First Approximation Relationship between IICCand and IIEE

IC IE

BJT Common BJT Common Base Base



Biasing Common BaseBiasing Common Base

VCCVEE VCCVEE

IB = 0 mA IB = 0 mA


Amplifying action Common BaseCommon Base


Input Input ii

iinput = vinput / Ri = 20 mV = 1 mA20


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


7. Transistor 7. Transistor Beta


Beta dc Beta dc

dc= IC ÷ IB = IC ………………… .. (1) IE

dc 50 to 400 range

IC = dc IB + ICE0 ……………………..(2)

Leakage component


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


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


IE = IC + IB

BJT Alpha and BetaBJT Alpha and Beta

IC/ = IC + IC /

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

= / (1 )

IC = IB

IE = IB ( + 1)


ICE0 = ICB0 / (1 )

BJT Alpha and BetaBJT Alpha and Beta

1/ = 1 + 1 / ;

ICE0 ICB0

+ 1= 1/ (1 )


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


End of Lesson 6End of Lesson 6

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Junction Transistor Amplifier– Lesson-6:– Detailed … Devices...2008 Junction Transistor Lesson 6- " , Raj Kamal, 1 Junction Transistor Amplifier– Lesson-6:– Detailed Study