Power transistor heat sinks

In a power transistor, to exchange heat to the surroundings, heat sinks are employed. It is a mechanical device with larger surface area. Here heat is exchanged by mechanisms like thermal convection and heat radiation. Usage of heat sink lowers then temperature of power transistor case. Heat sink also allows the power handling capacity of the transistors to reach rated maximum value. Heat sinks can be designed with different shapes and sizes. The main two varieties are natural convection coolers and shape on dissipators. Derating curve supplied by manufacturer is the variation of the power handling capacity of the power transistor as a function of the temperature. This curve gives an idea about capacity of heat sink and very much helpful while designing power transistor applications.