power supply V EB and the collector-base junction is reverse biased by the bias power supply V CB . The forward bias decreases the depletion region across the emitter-base junction and the reverse bias increases the depletion region across the collector-base junction. Hence, the barrier potential across the emitter-base junction is decreased and that across the collector-base junction is increased. The voltage across the emitter- base junction is represented as V EB and that across the collector-base junction as V CB.
In an NPN transistor, the majority charge carriers in the emitter are electrons. As it is heavily doped, it has a large number of electrons. The forward bias across the emitter-base junction causes the electrons in the emitter region to flow towards the base region and constitutes the emitter current ( I E ). The electrons after reaching the base region recombine with the holes in the base region.
Since the base region is very narrow and lightly doped, the number of holes in it is not sufficient to recombine with electrons from emitter. Hence most of the electrons reach the collector region. Eventually, the electrons that reach the collector region will be attracted by the collector terminal as it has positive potential and flow through the external circuit. This constitutes the collector current ( I C ).
The holes that are lost due to recombination in the base region are replaced by the positive potential of the bias voltage V BE and constitute the base current ( I B ). The magnitude of the base current will be in microamperes as against - - - - - - - - Unit electronics and Communication of an NPN transistor in the common emitter mode is given in Figure . . The bias supply voltages V BB and V CC bias the base-emitter junction and collector-emitter junction respectively.
The junction potential at the base-emitter is represented as V BE and that at the collector-emitter as V CE . The rheostats R and R are used to vary the base current and collector current respectively. The