# Voltage Divider Bias-Basic Concepts in Electronic Engineering-Lecture Slides, Slides for Basic Electronics. Institute of Company Secretaries of India - ICSI

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This lecture was delivered by Dr. Burman Sanyal at Institute of Company Secretaries of India - ICSI for Basic Electronic Engineering course. Its main points are: Voltage, Divider, Bias, Beta, Temperature, Sensitive, Oper...
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Slide 1

Basic Electronic Engineering

Lecture 15

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Voltage Divider Bias

• Bias current ICQ and Bias Voltage VCEQ are a function of β

• β is temperature sensitive and varies with temperature

• It is desirable to construct a bias circuit that is less dependent or completely independent of β

• Voltage divider bias circuit provide an almost constant operating point

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Voltage Divider Bias

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Voltage Divider Bias

Base-Emitter Loop

• The voltage across R2 is the voltage at the base terminal

• To find the input voltage we can use the – Exact Method

– Approximate Method

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Voltage Divider Bias

Base-Emitter Loop (Exact Analysis)

• For exact analysis of the base-emitter loop we will use thevenin’s theorem

Thevenin Voltage (VTH)

1 2

2 TH CC

RV VR R     

 

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Voltage Divider Bias

Base-Emitter Loop (Exact Analysis)

Thevenin Resistance (RTH)

1 2

1 2 TH

R RR R R 

 

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Voltage Divider Bias

Base-Emitter Loop (Exact Analysis)

Thevenin Equivalent Circuit

( 1) TH BE

B B E

V VI R R 

  

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Voltage Divider Bias

Collector-Emitter Loop

• The collector-emitter loop is same

as that of emitter bias circuit

C CQ BI I I 

 CEQ CE CC C C EV V V I R R   

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Voltage Divider Bias

Base-Emitter Loop (Approximate Analysis)

• Ri is the base to emitter resistance from the input side

• If Ri is much larger than R2 then IB will be much smaller that I2

• For 210ER R 

2

1 2

CC B

V RV R R 

 

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Voltage Divider Bias

Base-Emitter Loop (Approximate Analysis)

E B BEV V V 

E E

E

VI R

CQ C EI I I 

 CEQ CE CC C C EV V V I R R   

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Voltage Divider Bias

For β=50

Find

• IB • IC • VC • VE • VCE • VB

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Voltage Divider Bias

For VCC = 22V and β = 50

Find

• VB • VE • IE • IC • VCE

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Voltage Divider Bias

Stability

For VCC = 22V

• Determine the variation in Q-point

• for the voltage divider bias circuit

• For β = 100

• For β = 50

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0 2 4 6 8 10 12 14 16 18 20 0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

C o ll e c to

r c u rr

e n t

Ic -

->

Collector-Emitter voltage VCE -->

Beta =50

Beta =100

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Voltage Divider Bias

Saturation current

Cut-off Voltage

 CE CC C C EV V I R R  

 CE CC C C EV V I R R  

CE (for V =0)CCCsat C E

VI R R 

C (for I =0)CE CCV V

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