There can be two cases when transistor is used as a switch. If input is “1” output will be “0” similarly if input is “0” output will be “1”īut how can a transistor be used as an INVERTER ? Consider an NPN transistor connected as shown in the above figure. INVERTER is a logic gate which inverts the input. Although there are many logic families like TTL, ECL, CMOS etc (complicated stuff) But, lets talk about the simplest application where a BJT can be used as an INVERTER. Almost any electronic device works on these two logic standards. In digital circuits, we often refer to digital logic “1” and “0” which can be referred as logic “High” or logic “Low”. Transistor as you know is basically, a three terminal device consisting of Base, emitter and collector. But did you know how transistor is used a switch ? What properties of transistor allows it to be used as a switch ?

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