The two transistors PNP and NPN can be used interchangeably in most electronic circuits, taking into account the polarities of the voltages and the current flow’s direction. As collector voltage is always less than the base voltage and the base voltage is less than the emitter voltage, generally in a PNP transistor, the emitter voltage is always more positive than the other two terminals. The base is always negative biased with respect to the emitter. This makes the base negative and the emitter positive. Voltage across the base and emitter is according to the junction bias. The symbolic representation of the PNP transistor is the same as that of another type of transistor NPN except that now the direction of the arrow is from emitter to base whereas in NPN transistor, the arrow points from base to emitter. The above diagram shows the schematic diagram of the PNP transistor, though the thickness of each layer is not to scale. The PNP transistor configuration is shown below. The PNP transistor is a current-controlled device. Similarly, the junction between the collector and base can be called collector-base diode or collector diode.įrom the configurations of the PN junctions as given above, we can make out that the emitter diode is always forward biased and the collector diode is reverse biased. The junction between the emitter and base may be called emitter-base diode or emitter diode. The collector is always reverse biased.īecause the transistor has two PN-junctions, it is like two diodes.
The section on the other side of the emitter that collects the charges is called the collector. The base-collector junction is reverse biased which provides a high resistance in the collector circuit. The base-emitter junction is forward biased allowing a low resistance for the emitter circuit. The middle section of the transistor, which forms the two PN-junctions between emitter and collector, is called the base. To supply a large number of charge carriers, the emitter is always in forward biased when compared to the base. The work of the emitter is to supplies charge carriers.
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