Working of NPN transistor

Reverse biased in the transistor is connected over the collector-base junction while forward biased is connected over the emitter-base junction. In this type of transistor VCB i.e. reverse biased voltage is more than forward biased voltage.

The emitter is highly doped in the NPN transistor. A bulk of the charge carrier draws near the base when the forward biased is connected over the emitter. Due to this, the emitter current referred as IE is generated. After that, the electron access into P-type and join with the holes.

On the other hand, the base of the NPN transistor is less doped. As a result of this, only a small number of electrons are able to combine and the rest of these forms base current IB. After that, the base current IB access into the collector region. A very high attractive force on the electrons moving toward collector junction is applied by the reversed bias potential of the collector region. This makes an accumulation of the electrons on the collector region.

The entire current of the emitter is access into the base. We will be able to say that the total of the collector or the base current forms emitter current.

Working of PNP transistor

Forward Biased is applied across the emitter-base junction. As a result, the emitter forces the holes in the base region. It forms the emitter current.

These holes draw into the N-type semiconductor and join with the electrons. Due to the thin base of the transistor and lightly doped only a number of holes are able to combine with the electrons and the rest of the holes draws into the collector space charge layer. And this forms the base current.

The reverse base region is applied across the collector base region. The holes which are accumulated throughout the depletion region are collected by the collector under the force of negative polarity. This forms the collector current.