The Collector and emitter have holes as majority charge carriers while the Base has electrons as the majority charge carrier. The middle N-layer is called base while the other two layers are called collector and emitter. The thin N-layer is sandwiched between two thick P-layers. The PNP Transistor is formed by the combination of 2 P-Type layers and 1 N-Type layer. Thyristor and Silicon Controlled Rectifier (SCR) – Thyristors Applications.It leads to the NPN having a very small switch ON and Switch OFF time, therefore offering a very high switching speed. Since the majority charge carriers are electrons and they are fast, the recovery time of the NPN transistor is fast. NPN transistor switches ON by applying a positive voltage at the base terminal while switches off by applying low voltage 0v at the base terminal. Therefore, the majority charge carrier in the NPN transistor is electrons while the minority carrier holes. The little arrowhead pointing outwards of the emitter shows the current direction going outward of the emitter.Īs the majority of charge carriers in the collector and emitter are the electrons and they are responsible for the flow of current. The symbol of the NPN transistor also is used to identify the direction of the current. While the current is directly proportional to the base current. Therefore, in the NPN transistor, applying a positive pulse at the base causes a current which is in the direction from the collector to the emitter. As it is thin and lightly doped, the electrons combine with holes resulting in penetration in the depletion region that causes the electrons to flow from the collector terminal to the emitter terminal. Applying a positive voltage with respect to the emitter will push electrons in the base (p-region). The base is a thin P-Type layer having the majority of holes.

Pnp diode symbol