Explain how transistor works as a switch with i/p and o/p waveform

 Explain how transistor works as a switch with i/p and o/p waveform

                                               

                                                

Ans. First of all we have to start the transistor or we can say that activate the transistor . So for activating transistor , voltage ( Vbe ) should always in a forward bias and voltage ( Vce ) should always in reverse bias .

If we apply the voltage less than the cut off voltage or we can say that knee voltage , then transistor acts or behave as a open switch .

And if we apply the voltage more than the cut off or we can say that knee voltage , then transistor acts or behave as a close switch .

So , the derivation of these circuit is !

                         Input section of the circuit 

                   Vbb - Vb . Rb = 0

        i.e.     Vbe = Vbb - Ib . Rb    ....equation (1)

            Output section of the circuit 

                   Vcc - Ic . Rc - Vce = 0

                   Vce = Vcc - Ic . Rl

            i.e.   Vo = Vcc - Ic . Rl      ....equation (2)

     

             Therefore case (1)

        i.e.    Vin <  cut in voltage

                  Ib = 0

                  Ic = 0

               From equation (2)

                Vo = Vcc - Ic . Rl

                Vo = Vcc - 0 . Rl

       i.e.    Vo = Vcc       [ Off State ]

             

                      Case (2)

                 Vin  > cut in voltage 

                 Base current ( Ib ) is greater 

                 Collector current ( Ic ) is greater

                 Vo = Vcc - Ic . Rl

              But  ( Rl = Vcc )

        i.e.    Vo = Vcc - Vcc

                  Vo = 0              [ ON State ]