Transistor action

                                  Working of a p-n-p transistor     

Before starting this please refer to the basic framework of a transistor( http://dutta60.blogspot.in/2014/08/bipolar-junction-transistorsbasic.html)for better understanding of this following article.So let's start.........

You can observe from the following figure that the emitter base junction is forward biased with the help of voltage VEE(For information on biasing refer to- http://dutta60.blogspot.in/2014/07/biasing-of-diode.html) and collector base junction is reverse biased with the help of voltage VCC.Always remember the above two things for a p-n-p transistor.The forward bias of the emitter base junction helps the movement of holes in the p-region and electrons in the base region towards the junction thereby reducing the depletion width.On the other hand ,the reverse bias of the collector base junction increases the depletion width .

The Holes in the emitter region are accelarated towards the base junction due to the electrostatic influence of the battery (VEE).As the base is slightly doped only 1%of the total holes injected into it combine with electrons which further validates the fact that base current IB is indeed very small.After this ordeal,again what happens is that holes rush towards the collector through the base and nearly (97. 99%) of  holes are collected in the collector region.Now for one hole reaching the collector an electron is released from VCC to neutralise the hole as depicted by the above image.Now again a counter effect is produced due to the neutralisation where in the emitter region a covalent bond is broken and an electron is liberated which enters the respective battery.

So,it can be summed up by saying current is carried by holes in the internal circuit and by electrons in the external circuit.

Mathematical relation to find the base current:-

IE =  IB + IC

Hope this post helps.Your comments are welcome .Happy Reading!!!