# Transistor: NPN Transistor And PNP Transistor

In all the fields of electronics, transistors are used for almost all practical purposes. A semiconductor is mainly used to manufacture two devices, those are diodes and transistors. For amplifying a signal, junction diode cannot be used. For that, another type of semiconductor device came into account and these transistors are also known as bipolar junction transistors. Generally, the transistor is an electronic device used for amplification of signals, or to switch electronic signals.

Junction transistors are set into operations in almost all the circuits due to their small sizes and also because no power is needed to cause the emission of electrons. It can be used as an amplifier, as an oscillator and also as a detector.

## Action of npn transistor

The figure below represents the circuit diagram of n-p-n transistor:

## circuit diagram of n-p-n transistor

The emitter-base ($V_{BE}$) battery connects the n-type emitter which is forward biased where as the collector-base ($V_{BC}$) battery connects the n-type collector which is reverse biased. Due to the forward bias, the majority charge carriers in the emitter are repelled towards the base. The electron-hole re-combination is very small in the base region because the base through holes are majority carriers, the base is lightly doped. Most of the electrons cross into the collector region.

## Action of p-n-p transistor

The figure below represents the circuit diagram of p-n-p transistor:

## circuit diagram of p-n-p transistor

The emitter-base ($V_{BE}$) battery connects the p-type emitter which is forward biased whereas the collector-base ($V_{BC}$) battery connects the p-type collector which is reverse biased. In this case, the majority charge carriers in emitter are holes which are repelled towards the base. As the base layer is thin, thus only little interaction occurs when electrons and holes combine. Most of the holes reach the collector. The current is carried by holes in p-n-p transistors.

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