Question

The stability factor for a self biased transistor is_________

(a) 1 – RTH/RE

(b) 1 + RTH/RE

(c) 1 + RE/RTH

(d) 1 – RE/RTH

This question was addressed to me in homework.

I need to ask this question from Self-Bias in division Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits

Answer 1

Correct option is (b) 1 + RTH/RE

To elaborate: The stability of the circuit is inversely proportional to the stability factor. The emitter resistor is very large when compared to the Thevenin’s resistance. When β is not that large, then S=(1+ β)( RTH+ RE)/ (1+ β)RE+ RTH.