Question

Which of the following biasing techniques are affected by thermal runaway?

(a) self bias

(b) collector to base bias

(c) fixed bias

(d) the biasing technique is identified by temperature effect

This question was posed to me in class test.

The doubt is from Thermal Stability topic in section Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits

Answer 1

The correct option is (c) fixed bias

Easy explanation: The collector current of a fixed bias transistor is IC= β(VCC-VBE)/RB. When the temperature is increased, the reverse saturation increases. The collector current also increases. This in turn increases the current again which leads to damage of transistor.