PNP or NPN Transistor?

A PNP transistor is a type of bipolar junction transistor (BJT) that consists of three layers of semiconductor material. The three layers are doped with two types of impurities: P-type (positively charged) and N-type (negatively charged).

In a PNP transistor, the middle layer, called the base, is P-type, while the outer layers, known as the emitter and collector, are N-type. The base terminal is responsible for controlling the flow of current between the emitter and collector terminals.

When a positive voltage is applied to the base terminal with respect to the emitter, it creates a forward bias condition. This allows current to flow from the emitter to the base region, and then from the base to the collector region. In other words, the PNP transistor is active when the base-emitter junction is forward-biased.

PNP transistors are commonly used in applications where the majority charge carriers are holes (P-type) rather than electrons (N-type). They are often used in amplification circuits, switching circuits, and as current sources or sinks.

It's worth noting that the operation and characteristics of PNP transistors are the opposite of NPN transistors, where the majority charge carriers are electrons.