What are the operating states of the following three operating regions of transistors: saturation region, active region, and cut-off region?
|Saturation region:||As the base current increases, the voltage between both terminals of the load resistance (VRl = IC × Rl) becomes larger. In the figure below, a -> b on the load line. If the power supply voltage is constant, the collector current past c on the load line does not increase no matter how much the base current increases, and the voltage between the collector and the emitter is minimized. |
This minimum voltage is called the collector saturation voltage VCE (sat).
The state of this region means that switch operation is on.
|Active region:||The light blue region in the figure below is the region where the change of the input signal on which the center is set at point b of the load line, which is a suitable base current, can be amplified without distortion to a large collector current change. |
|Cut-off region:||Even if the base pin is left open, collector cut-off current ICEO (no general ratings exist) flows between the collector and emitter. This region is called the cut-off region (collector cut-off region). |
The state of this region means that switch operation is off.
Related item: Collector saturation voltage