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The voltage level at the base-emitter junction is less than 0.7v.Both the base and input terminals are grounded which means to ‘0’v.The characteristics in cut–off region are: We can observe from the above characteristics, the pink shaded area at the bottom of the curves represents the Cut-off Region and the blue area to the left represent the Saturation region of the transistor. During this condition, there might be no requirement of using another signal transistor to drive this transistor. Few of the applications utilize a power transistor as a switching tool. The transistor as a switch circuit diagram is Transistor as a Switchīoth the types NPN and PNP transistors can be operated as switches. As a transistor switch, it operates in two regions and those are Saturation Region (fully-ON) and the Cut-off Region (fully-OFF). In the active region, the transistor works as an amplifier. A transistor can be operated in three modes, active region, saturation region, and cut-off region.

If the circuit uses the BJT transistor as a switch, then the biasing of the transistor, either NPN or PNP is arranged to operate the transistor at both sides of the I-V characteristics curves shown below.

The functioning of both NPN and PNP transistor is the same but differ in terms of their biasing and power supply polarity. Similarly, A PNP-type transistors are the composition of two P-type doped semiconductor materials between an N-type doped semiconductor layer as shown above. The collector terminal is intermediately doped and collects electrons from the Base.Īn NPN type transistor is the composition of two N-type doped semiconductor materials between a P-type doped semiconductor layer as shown above. The Base terminal is lightly doped and passes the emitter-injected electrons onto the collector. The emitter is a heavily doped terminal and it emits the electrons into the Base region. The transistor has three terminals, namely Base, Emitter, and Collector. Bipolar junction transistors are classified into to types

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