# Design of Self Bias Circuit

Objective:

To design and verify a Self Bias circuit for a given operating point.

Components:

S.No. Name Quantity
1 Transistor BC107 1(One) No.
2 Resistors According to values calculated

Equipment:

S.No. Name Quantity
1 Dual DC Regulated Power supply (0 – 30 V) 1(One) No.
2 Digital Ammeters  ( 0 – 200 mA) 1(One) No.
3 Digital Voltmeter (0-20V) 1(One) No.
4 Connecting wires (Single Strand)

Circuit Diagram:

Operation:

A self bias circuit stabilizes the bias point more appropriately than a fixed bias circuit. In this experiment CE configuration is used and a self bias circuit is designed and verified.

Calculations:

Given VCC = 10V, R= 220 ohm I= 4mA VCE = 6V, VBE = 0.6V hfe = 200

Note: VE value should be 1/4th or 1/10th of VCC.

I= IC/

R= VE/I= VE/IC

R= (VCC - VCE - VE)/IC

10R2 <= RE

VBB=IB*RB+VBE +(IB+IC)RE

R1=(VCC/VBB)*RB

R2=RB/(1-VBB/VCC)

V= [R2/(R+ R2) ]VCC

Procedure:

1. Calculate the values of R1, R2, RC, RE, according to the given specifications and design equations.
2. Connect the circuit as shown in the circuit diagram with the designed values.
3. Apply voltage VCC, measure the values of IC, IB, VCE,VBE.

Observations:

Parameter Theoritical Practical
VCE
VBE
IC
IB

Precautions:

1. The supply voltage should not exceed the rating of the transistor
2. Loose connections should be avoided.

Result:

The self bias circuit is designed and verified.

Outcomes:

Students are able to design self bias circuit and test its performance for a given operating point.

Viva Questions:

1. What are the advantages of self bias?
2. What are the various other techniques available for biasing?
3. What is the best biasing technique among all biasing technique?
4. Why biasing circuit is needed for amplifier?
5. What is the effect of input dc signal on Q-point?
6. What is Pc max?
7. What is thermal runaway?
8. What is the reason for thermal runaway?
9. Can DC signal be amplified by CE or CB amplifier?
10. What type of feedback is provided by RE in self biasing technique of CE configuration?
• Updated
Oct 04, 2015
• Views
23,689
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