What is a PNP Transistor?
PNP transistor consists of two P type semiconductor material separated by thin N layer. Holes are the majority charge carriers and electron are the minority charge carriers.
Symbol of PNP Transistor:
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| Symbol of PNP transistaor |
The arrow is pointed inwards. This shows that the current flows from emitter to current.
Construction of PNP transistor:
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| Construction of PNP Transistor |
The PNP transistor consists of three terminals emitter, base and collector. It consists of one N type material placed in between two P type material. Emitter is moderately doped, base is lightly doped and collector is heavily doped.
Two diode Model of PNP transistor:
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| Two diode model of PNP Transistor |
A diode is a two terminal device which allows the current to flow in only one direction and resists the flow in the other direction. PNP Transistor is three terminal device which looks like two PN Junction diodes connected back to back.
These two diodes behaves like collector base junction and base emitter junction. When two diodes are merged and one terminal is taken as common it results in three terminal device.
PNP Transistor circuit:
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| PNP Transistor circuit |
The base emitter circuit is forward biased and collector base circuit is reverse biased. Here the polarity and the direction of the current is reverse when compared to the NPN transistor. The load resistance and a resistance at the base terminal are used to limit the current flow.
Working of PNP Transistor:
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| Working of PNP Transistor |
In PNP transistor the majority charge carriers are holes. So the current is formed due to the movement of holes.
Two batteries are used .The positive terminal of the first battery is connected to the emitter and negative terminal to the base. Thus it is forward biased. So the holes which is the majority charge carrier in P type move towards base.
This movement of holes constitutes emitter current IE. Some of the holes combine with the electrons in the base. Remaining holes move towards the collector, this forms the collector current IC.
These holes which reach the collector get neutralized by the electrons from the negative terminal in which the collector is connected. At the same time holes from emitter reach the collector.
This process continues and thus the current is due to the movement of holes. The collector current is due to the summation of emitter and base current.
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