Design of Self Bias Circuit

Objective:

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

Components:

Equipment:

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 V_CC = 10V, R_E = 220 ohm I_C = 4mA V_CE = 6V, V_BE = 0.6V h_fe = 200

Note: V_E value should be 1/4^th or 1/10^th of V_CC.

I_B = I_C/

R_E = V_E/I_E = V_E/I_C

R_C = (V_CC - V_CE - V_E)/I_C

10R₂ <= R_E

V_BB=I_B*R_B+V_BE +(I_B+I_C)R_E

R₁=(V_CC/V_BB)*R_B

R₂=R_B/(1-V_BB/V_CC)

V_B = [R₂/(R₁ + R₂) ]V_CC

Procedure:

1. Calculate the values of R₁, R₂, R_C, R_E, 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 V_CC, measure the values of I_C, I_B, V_CE,V_BE.

Observations:

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 R_E in self biasing technique of CE configuration?