Additional heat is dissipated from power transistor by using

Question

Question

This question was previously asked in

RRB ALP Electronics Mechanic 23 Jan 2019 Official Paper (Shift 2)

Answer 1

Heat Sink

A heat sink is a mechanical device. It is connected to a power transistor in order to dissipate heat generated.
The heat flows through the heat sink and is radiated to the surrounding air. If a heat sink is not used then all the heat has to be transferred from a transistor case to the surrounding air causing the case temperature to increase.
In a transistor, the collector-to-base junction temperature rises because of self-heating. The self-heating is due to the power dissipated at the collector junction.
This power dissipation at the junction causes the junction temperature to rise, and this in turn increases the collector current which causes a further increase in power dissipation.
If the phenomenon continues then it may result in permanent damage to the transistor. This is known as thermal runaway.