Question

Choose the incorrect option according to self bias circuit?

(a) Voltage gain increases

(b) Stability factor is independent of collector resistance

(c) BJT can be used in either of the three configurations

(d) Excellent stability in collector current is achieved

This question was addressed to me during a job interview.

I want to ask this question from Transistor Bias Configuration in division Transistor Biasing and Low Frequencies of Analog Circuits

Answer 1

Right answer is (d) Excellent stability in collector current is achieved

Explanation: In a self bias circuit, due to emitter resistance a negative feedback exists. This decreases voltage gain. Also, stability factor S does not depend on collector resistance, only on base and emitter resistance and β, if required. \(S = \frac{(1+β)(R_B +R_E)}{R_B + (1+β)R_E}\).

S is least in self bias circuit, hence excellent stability is achieved.