We can use our knowledge of diodes to identify the type of transistor we are working with.

As we have already discussed, the PNP transistor is a device made of two diodes connected end to end. To properly identify a device, we need to have a proper understanding of the device with which we are working with.

Given that there are two types of transistors, there can be a difficulty in identifying a given transistor for proper usage.

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. From 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.

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