Question

Which of the following are true?

(a) TJ – TA = θPd

(b) TJ – TA = θ/Pd

(c) TJ – TA = θ+Pd

(d) TJ – TA = θ-Pd

I got this question during an interview.

This intriguing question comes from Thermal Runaway in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits

Answer 1

The correct answer is (a) TJ – TA = θPd

Easy explanation: The TJ is called as junction temperature which varies and TA is called as the ambient temperature which is fixed. The difference between these temperatures is directly proportional to the power dissipation. Here, θ is called as thermal resistance which is proportionality constant.