Explain the working of an npn transistor.

Working of npn transistor: In an npn transistor is demonstrated in the figure. The emitter base junction is forward biased whereas the collector base junction is in reversed biased. The forward biased voltage VEB is fairly small, while the reverse biased voltage VCB is considerably large.

Since the emitter base junction is forward biased, several of electrons (majority carrier) in the emitter (in n-type region) are pushed in the direction of the base. It constitutes the emitter current I_E. Whereas these electrons enter the p-type material (base), they tend to merge with holes. Since the base is lightly doped and extremely thin, only some electrons (less than 5 percent) combine along with the holes to constitute base current I_B. The remaining electrons (more than 95 percent) diffuse across the thin base region and reach collector space charge layer. Such electrons then come under the affect of positively biased n- region and are collected or attracted by the collector. It constitutes the collector current I_C. Therefore, it is seen that almost the whole emitter current flows in the collector circuit. The emitter current is the sum of the collector, and base current. I_E =I_C + I_B.

npn Transistor Circuit