Cut off, Active and saturation regions of a Transistor

Cut off, Active and saturation  regions of a   transistor:

Transistor Biasing:-

                 The application of suitable dc voltages across the transistor terminals is called biasing. Each  junction of a transistor may be forward biased or reverse biased independently.These are following three different ways of biasing a transistor ,which is also known as modes of transistor operation.

Forward active:-

                        Emitter-Base junction is forward biased

                        Collector- base junction is reverse biased.

Saturation Region:-

                        

                    Emitter-Base junction  is forward biased

                    Collector- base junction is forward biased

In this mode transistor has a very large value of current. The transistor is operated in this mode, when it is used as a closed switch. 

Cut- off Region:-

                    Emitter-Base junction  is reverse biased

                    Collector- base junction is reverse biased

In this region both the junctions are Reverse Biased. In this mode transistor has zero current. The transistor is operated in this mode, when it is used as an open switch.

   Output characteristics of Common Emitter Transistor

    Modes of transistor action:

                   

S.no	Junction bias condition
1. 2. 3.	Mode	Emitter-base	Collector-base
	Forward-Active Saturation Cut-off	Forward Forward Reverse	Reverse Forward Reverse