Introduction to power BJT
Bipolar Junction Transistor (BJT or Bipolar Transistor):
- Power Bipolar Junction Transistor (BJT) is the first semiconductor device to allow full control over its Turn on and Turn off operations.
- It simplified the design of a large number of Power Electronic circuits that used forced commutated thyristors at that time and also helped realize a number of new circuits.
- Subsequently, many other devices that can broadly be classified as “Transistors” have been developed. Many of them have superior performance compared to the BJT in some respects. They have, by now, almost completely replaced BJTs.
- However, it should be emphasized that the BJT was the first semiconductor device to closely approximate an ideal fully controlled Power switch.
- Other “transistors” have characteristics that are qualitatively similar to those of the BJT (although the physics of operation may differ).
- Hence, it will be worthwhile studying the characteristics and operation a BJT in some depth. From the point of view of construction and operation BJT is a bipolar (i.e. minority carrier) current controlled device.
- It has been used at signal level power for a long time. However, the construction and operating characteristics of a Power BJT differs significantly from its signal level counterpart due to the requirement for a large blocking voltage in the “OFF” state and a high current carrying capacity in the “ON” state.