Describe the operation of transistor as a switch with suitable diagram.

Describe the operation of transistor as a switch with suitable diagram.
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1 Answer

Answer :

In Bipolar Transistor as a Switch the biasing of the transistor, either NPN or PNP is arranged to operate the transistor at both sides of the “ I-V ” characteristics curves. The areas of operation for a transistor switch are known as the Saturation Region and the Cut-off Region


 Working: Control input Vin is given to base through a current limiting resistor RB and Rc is the collector resistor which limits the current through the transistor .When a sufficient voltage V is given to input, transistor becomes ON & it goes into saturation. During this condition the Collector Emitter voltage VCE will be approximately equal to zero, ie the transistor acts as a short circuit & Vo = 0.


When input voltage V=0, transistor becomes OFF & it goes into cutoff. The transistor acts as an open circuit. During this condition the Collector Emitter voltage VCE=Vcc. Therefore Vo = Vcc.

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Open switch

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Table indicating transistor as switch

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