To cause the Base current to flow in a PNP transistor the Base needs to be more negative than the Emitter (current must leave the base) by approx 0.7 volts for a silicon device or 0.3 volts for a germanium device with the formulas used to calculate the Base resistor, Base current or Collector current are the same as those used for an equivalent NPN transistor and is given as. The Base voltage V B which is biased negative with respect to the Emitter and is connected to the Base resistor R B, which again is used to limit the maximum Base current. This time the Emitter is connected to the supply voltage V CC with the load resistor, RL which limits the maximum current flowing through the device connected to the Collector terminal. The voltage sources are connected to a PNP transistor are as shown. So for a PNP transistor to conduct the Emitter is always more positive with respect to both the Base and the Collector. The voltage between the Base and Emitter ( V BE ), is now negative at the Base and positive at the Emitter because for a PNP transistor, the Base terminal is always biased negative with respect to the Emitter.Īlso the Emitter supply voltage is positive with respect to the Collector ( V CE ). The construction of a “PNP transistor” consists of two P-type semiconductor materials either side of an N-type material as shown below. In other words for a PNP transistor, the Emitter is more positive with respect to the Base and also with respect to the Collector. Then, PNP transistors use a small base current and a negative base voltage to control a much larger emitter-collector current. The main difference between the two types of transistors is that holes are the more important carriers for PNP transistors, whereas electrons are the important carriers for NPN transistors. This produces a Positive- Negative- Positive type of configuration, with the arrow which also defines the Emitter terminal pointing inwards in the PNP transistor symbol.Īlso, all the polarities for a PNP transistor are reversed which means that it “sinks” current into its Base as opposed to the NPN transistor which “sources” current through its Base. Basically, in this type of PNP transistor construction, the two interconnected diodes are reversed with respect to the previous NPN transistor.

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