Question

Which of the following is true?

(a) HC-A = HJ-C – HJ-A

(b) HC-A = HJ-C + HJ-A

(c) HJ-A = HJ-C – HC-A

(d) HJ-A = HJ-C + HC-A

I got this question by my college professor while I was bunking the class.

This question is from Thermal Stability topic in portion Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits

Answer 1

The correct answer is (d) HJ-A = HJ-C + HC-A

For explanation I would say: HJ-C is thermal resistance between junction and case and HC-A is thermal resistance between case and ambient. The circuit designer has no control over HJ-C. So, a proper approach to dissipate heat from case to ambient is through heat sink.