Active Region of a Transistor

The Active Region of a transistor is the region where the transistor is on and is receiving sufficient base current for collector current to conduct.

Basically, this is the region where the transistor is on and current conducts across the collector.

When a transistor operates in the active region, the collector current, Ic, is greater than the base current, IB, by a factor of beta (Ic=βdc x IB).

In the active region, the collector circuit acts like a current source.