Q.What are the operating regions of PBJT?

The power bipolar junction transistor (PBJT) was the first semiconductor device to give full control over both turn-on and turn-off in power circuits. It is a bipolar, current-controlled device: a small base current controls a much larger collector current.

Structurally, two heavily doped n+ regions with a lightly doped p base form an npn transistor, while two p+ regions with a lightly doped n base form a pnp transistor. Its three terminals are the collector, base and emitter, and the direction of the emitter arrow in the circuit symbol distinguishes npn (arrow outward) from pnp (arrow inward).

The output behaviour is read from the $I_C$ versus $V_{CE}$ characteristics, which show three operating regions:

• Cut-off region: with base current $I_B \le 0$ the collector current is almost zero — the device is OFF. …