Question

A silicon power transistor is operated with a heat sink HS-A=1.5°C/W. The transistor rated at 150W (25°C) has HJ-C=0.5°C/W and the mounting insulation has HC-S=0.6°C/W. What maximum power can be dissipated if the ambient temperature is 40°C and (TJ)MAX=200°C?

(a) 70.6W

(b) 61.5W

(c) 37.8W

(d) 56.9W

This question was posed to me during an online exam.

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

Answer 1

The correct option is (b) 61.5W

For explanation: PD=(TJ-TA)/ HJ-C +HC-S +HS-A

=200-40/0.5+0.6+1.5=61.5W.