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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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 2
1.1. RevisionRevision
2008 Junction Transistor Lesson 6- " , Raj Kamal, 3
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 4
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 5
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 6
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)
2008 Junction Transistor Lesson 6- " , Raj Kamal, 7
Formula for Collector Current ComponentsFormula for Collector Current Components
IC = ICmajority + ICOminority
ICO = Collector Current with emitter terminal open (not connected)
Leakage component
2008 Junction Transistor Lesson 6- " , Raj Kamal, 8
3. Transistor 3. Transistor Alpha
2008 Junction Transistor Lesson 6- " , Raj Kamal, 9
Alpha dc Alpha dc
dc= IC ÷ IE = IC ………………… .. (1) IE
dc 0.90 to 0.998
IC = dc IE + ICB0 ……………………..(2)
Leakage component
2008 Junction Transistor Lesson 6- " , Raj Kamal, 10
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 11
4. Input and Output Characteristics of 4. Input and Output Characteristics of transistor in common basetransistor in common base
2008 Junction Transistor Lesson 6- " , Raj Kamal, 12
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 13
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 14
First Approximation Relationship between First Approximation Relationship between IICCand and IIEE
IC IE
BJT Common BJT Common Base Base
configurationconfiguration
2008 Junction Transistor Lesson 6- " , Raj Kamal, 15
Biasing Common BaseBiasing Common Base
VCCVEE VCCVEE
IB = 0 mA IB = 0 mA
2008 Junction Transistor Lesson 6- " , Raj Kamal, 16
Amplifying action Common BaseCommon Base
2008 Junction Transistor Lesson 6- " , Raj Kamal, 17
Input Input ii
iinput = vinput / Ri = 20 mV = 1 mA20
2008 Junction Transistor Lesson 6- " , Raj Kamal, 18
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 19
5. Input and Output Characteristics of 5. Input and Output Characteristics of transistor in common emitter transistor in common emitter
2008 Junction Transistor Lesson 6- " , Raj Kamal, 20
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 21
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 22
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 23
npn transistor in a simple circuit, known as‘common-emitter’ amplifier
2008 Junction Transistor Lesson 6- " , Raj Kamal, 24
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 25
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 26
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 27
6. Input and Output Characteristics of 6. Input and Output Characteristics of transistor in common collector transistor in common collector
2008 Junction Transistor Lesson 6- " , Raj Kamal, 28
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 29
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 30
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 31
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 32
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 33
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 34
7. Transistor 7. Transistor Beta
2008 Junction Transistor Lesson 6- " , Raj Kamal, 35
Beta dc Beta dc
dc= IC ÷ IB = IC ………………… .. (1) IE
dc 50 to 400 range
IC = dc IB + ICE0 ……………………..(2)
Leakage component
2008 Junction Transistor Lesson 6- " , Raj Kamal, 36
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 37
8. Relation Between Transistor Alpha and 8. Relation Between Transistor Alpha and Beta
2008 Junction Transistor Lesson 6- " , Raj Kamal, 38
IE = IC + IB
BJT Alpha and BetaBJT Alpha and Beta
IC/ = IC + IC /
1/ = 1 + 1 / ; = / ( + 1)
= / (1 )
IC = IB
IE = IB ( + 1)
2008 Junction Transistor Lesson 6- " , Raj Kamal, 39
ICE0 = ICB0 / (1 )
BJT Alpha and BetaBJT Alpha and Beta
1/ = 1 + 1 / ;
ICE0 ICB0
+ 1= 1/ (1 )
2008 Junction Transistor Lesson 6- " , Raj Kamal, 40
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
2008 Junction Transistor Lesson 6- " , Raj Kamal, 41
End of Lesson 6End of Lesson 6
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