Transistor as a switch

The transistor is a three-terminal, bipolar, current-controlled device. It works in three different regions: Active, Cutoff, and Saturation according to applied biasing conditions. In this circuit, a square wave input is applied. When the input is high, the transistor is turned on and works in the saturation region. So maximum current IC flows through the transistor as well as LED. Hence LED emits light. When the input is low (low means not enough to turn on the transistor), the transistor remains in the cutoff. So current I zero thus LED does not emit the light. As the input is a square wave, the LED will turn on and off alternately. If the output is observed on CRO from the collector then it will be also a square wave but out of phase by 180° with C is input. Thus transistor is working as a switch that can be made on or off by an external input.
#electronics #transistor #resistor #Switch