Draw the symbol of a p-n-p transistor. Show the biasing of a p-n-p transistor and explain the transistor action.

Explanation

Symbol for p-n-p transistor

Action of p-n-p Transistor. In a p-n-p transistor, when the emitter is forward biased, the holes in the emitter and the electrons in the base begin the move towards the junction, holes in the emitter and the electrons in the base begin to move towards the junction, holes being attracted by the negative terminal and the electrons by the positive terminal of the battery. On reaching the base emitter junction a small fraction of total number of holes with electrons to get neutralized . As the base layer is very thin the collector is kept at high negative potential , almost all the holes are attracted by the collector, producing a hole-current between the emitter and collector (See figure)

The emitter current `I_(e)` is the sum of base current and the collector current.
i.e. `I_(e)=I_(b)+I_(e)`
So `I_(c) lt I_(e)`
Working of p-n-p
In working of `p-n-p, as each hole reaches the collector an electron is emitted from the negative terminal of battery and the hole is neutralized. Simultaenously a covalent bond is broken near th emitter electron the electron so produced enter the positive terminal of the forward bias battery and the hole starts its journey towards the emitter base junction. Holes are the current carriers in p-n-p transistor however the current in the outer circuit is always due to flow of electrons.