Power transistors have controlled turn-on and turn-off characteristics. The power transistors are mostly used in the switching mode. In fact, their applications in motor control circuits are becoming more and more popular. The transistors when used as switching elements, are operated in SATURATION REGION, resulting in a small on-state voltage drop. Power transistors are becoming a viable alternative to thyristors. When power transistors conduct an appreciable Current, the forward voltage drop is in the region of 0.3 to 0.8V. Therefore the power loss in a power transistors is lower than that of thyristors. The switching speed of modern transistors are much higher than that of thyristors and are extensively used in dc-ac and dc-dc converters, with inverse parallel connected diodes to provide bidirectional Current flow.
However, the voltage and current ratings of power transistors Available at present are not as high as those of thyristors and Therefore, transistors are normally used in Low-Medium Power Applications.
Power transistors have No surge current capacity and can withstand only a low rate of change of current.
CLASSIFICATION OF POWER TRANSISTORS
Power transistors are broadly classified into Three:-
1. Bipolar Junction Transistors
2. Metal oxide semiconductor field effect transistors (MOSFETs)
3. Insulated Gate Bipolar transistors (IGBTs)