^Transistor

^Transistor

1. Emitter is the section on one side of transistor that supplies charge carriers. It is of moderate size & heavily doped. Collector is the section on the other side of transistor that collects the charge carriers. It is moderately doped but larger in size. Base is the middle section of transistor that forms two pn junctions with emitter and collector. It is very thin and lightly doped so as to pass most of the emitter injected charge carriers to the collector.
2. A transistor is also called Bipolar Junction Transistor (BJT), as in it current is due to both majority & minority charge carriers.
3. Input of a transistor is always forward biased, output is reverse biased & the common terminal is grounded.
4. Current in both npn & pnp transistor is I_E = I_B + I_C. As the base current I_B is very small thus I_E » I_C._. A transistor transfer almost the same electric current from low resistance path to high resistance path and hence is named as transistor. This transistor action makes it useful in transistor amplifier.
5. A transistor can be used as a switch, amplifier, oscillator & NOT gate.