Modes of operation in Transistor

Active Mode:

                   -Emitter-base junction->Forward Bias

                   -Collecter-base junction->Reverse Bias

Operation:
                This mode strengthen the weak signals.

                

The -ve potential of Vbe causes the free electron to move towards the base.This constitute EMITTER CURRENT.
Only few electrons recombines with holes and rest cross the base and enter the collector region.This cause base region very thin .


Thus the recombination of few electrons causes the BASE CURRENT to flow.
The electrons does not combine with the holes in the base enters in to the collector region .Since collector base is reverse bias,the negative attracts the electron.This constitute the COLLECTOR CURRENT.






Saturation Mode:
                        - Emitter-base junction->Forward Bias
                        -Collecter-base junction->Forward Bias 

                                   










In this mode,Transistor acts as a Closed switch   .




Cut-off Mode:      
         
                        - Emitter-base junction->Reverse Bias
                        -Collecter-base junction-> Reverse Bias  
                                                                 
In this mode,Transistor acts as a Open switch