Electrical Engineering ⇒ Topic : Various Current Components in Transistor
VARIOUS CURRENT COMPONENTS IN TRANSISTOR
The various current components flowing through the forward biased junction and reverse biased junction are shown in Figure (a).
figure (a) Various current components in a P-N-P transistor.
The emitter current consists of hole current (IpE) and electron current (InE) where the ratio of IpE/InE is proportional to the ratio of the conductivity of the P-type material to that of N-type material. The conductivity is proportional to the doping level. Conductivity will be more if doping is more. The doping of emitter is made larger than that of the base in any commercial transistor. Therefore, the emitter current is mainly due to holes in the P-N-P transistor. All the holes crossing the emitter base junction will not cross the collector base junction because some of them will combine with the electrons and hence constituting the base current (IB = IpE - Ipc).
Figure (B) shows the common base configuration with emitter base junction open circuited. Hence, no current carriers will be injected into the base and hence emitter current is zero. The collector base junction is reverse biased and the collector current is equal to the reverse saturation current (ICB0) inspite of zero emitter current. Therefore, when the emitter base junction
Figure (B) Common base configuration with emitter-base junction open.
is forward biased and collector base junction is reverse biased, the total collector current is given by
IC = IpC + ICB0
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