Breakdown Region of a Transistor

The Breakdown Region of a transistor is the region where the collector voltage, Vcc, is so large that the collector-base diode breaks down, causing a large, undesired collector current to flow.

When the collector-base voltage is too large, the collector-base diode breaks down, so that the collector conducts electricity. So even though the base of the transistor doesn't receive any current, the transistor still conducts across the collector. This is called the breakdown region.

The breakdown region should always be avoided in transistor circuits. This is achieved by not placing too much bias voltage on the collector.