Download Use of a heat sink :

Use of a heat sink :
 When power is dissipated in a transistor, the heat generated must flow from
the collector-base junction to the transistor case, and then to the surrounding
atmosphere.
 When only a very small amount of power is involved, as in a small-signal
transistor, the surface area of the transistor case is normally large enough to
allow all of the heat to escape.
 For large power dissipations that can occur in high power transistors, the
transistor surface area is not large enough. Heat sinks must be used to increase
the area in contact with the atmosphere.
 For small transistors with Top-hat-type metal cans, the clip-on star-type
heat sinks are used as shown in figure a.
 For high-power transistors, large heat sinks are available as shown in figure b.