A bipolar junction transistor (BJT) can function as a switch by operating either in the saturation region (ON state) or the cutoff region (OFF state) depending on the input signal. When turning the BJT ON (conducting state), an adequate base current is applied to forward bias the base-emitter junction, enabling a higher collector current from collector to emitter. This state represents the transistor behaving like a closed switch, permitting current flow. Conversely, when turning the BJT OFF (non-conducting state), the base current is decreased to a level that maintains the base-emitter junction in reverse bias, preventing significant collector current flow. This setup functions akin to an open switch, obstructing current flow between collector and emitter.
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