Q.What is heat sink?

A heat sink is a device — usually a copper (or other metal) conductor of a suitable shape — attached to a transistor to absorb the unnecessary heat generated inside the device and radiate it to the surroundings, thereby safeguarding it. It is a simple but essential piece of thermal management for power transistors.

The need arises because the power dissipated inside a transistor raises its internal junction temperature, and a higher junction temperature lowers the device's power-handling capability and can lead to thermal runaway. A transistor's maximum power rating and its junction temperature are directly linked: the hotter the junction, the less power the device can safely handle. …