Mumbai University > Electronics and telecommunication engineering > Sem 3 > Analog electronics 1

Marks: 4M

Years: May 16

1.The maximum average power P_(D(max)) which a transistor can dissipate depends upon the transistor construction and may lie in the range from a few milliwatts to 200 W.

2.The power dissipated within a transistor is predominantly the power dissipated at its collector base junction. Thus maximum power is limited by the temperature that the collector-base junction can withstand.

3.For silicon transistor this temperature is in the range 150 to 225 °C, and for germanium it is between 60 to 100 °C. The collector-base junction temperature may rise because of two reasons:

-Due to rise in ambient temperature

-Due to self-heating

The self-heating can be explained as follows:

1.The increase in the collector current increases the power dissipated at the collector junction. This in turn further increases the temperature of the junction and hence increases in the collector current. The process is cumulative and it is referred to as self-heating.

2.The excess heat produced at the collector base junction may even burn and destroy the transistor. This situation is called 'Thermal runaway' of the transistor.