Question

High power transistors are used usually mounted on a physical large piece of metal known as ?

Answer 1

Answer:

There is not a clear cut difference between ‘ordinary’ transistors used in voltage amplifiers and power transistors, but generally Power transistors can be categorised as those than can handle more than 1 Ampere of collector (or Drain in the case of FETs) current.

Because power transistors, such as those shown in Fig. 5.1.1 handle larger currents and higher voltages, they have a different construction to small signal devices. They must have low output resistances so that they can deliver large currents to the load, and good junction insulation to withstand high voltages. They must also be able to dissipate heat very quickly so they do not overheat. As most heat is generated at the collector/base junction, the area of this junction is made as large as possible.

Power and Temperature

The maximum power rating of a transistor is largely governed by the temperature of the collector/base junction as can be seen from the power de-rating graph in Fig. 5.1.2. If too much power is dissipated, this junction gets too hot and the transistor will be destroyed, a typical maximum temperature is between 100°C and 150°C, although some devices can withstand higher maximum junction temperatures. The maximum power output available from a power transistor is closely linked to temperature, and above 25°C falls in a linear manner to zero power output as the maximum permissible temperature is reached.

Explanation:

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