05-12-2017, 09:35 AM
As one of the important semiconductor devices, the transistor has found use in huge electronic applications, such as integrated systems, digital circuits and control systems. In both digital and analog domains, transistors are widely used for different applications such as amplification, logic operations, switching, etc. This article concentrates mainly and offers a brief explanation of the application of transistors as a switch.
The bipolar junction transistor or simply BJT is a semiconductor device with three layers, three terminals and two junctions. Almost in many applications, these transistors are used for two basic functions, such as switching and amplification.
The bipolar name indicates that two types of load operators are involved in the operation of a BJT. These two charge carriers are holes and electrons where the holes carry positive charge and the electrons are carriers of negative charge.
![[Image: NPN-and-PNP-Transistors.jpg]](https://www.electronicshub.org/wp-content/uploads/2015/02/NPN-and-PNP-Transistors.jpg)
The transistor has three regions, namely, base, emitter and collector. The emitter is a strongly doped terminal and emits electrons in the base. The base terminal is slightly doped and passes the electrons injected by the emitter to the collector. The collector terminal is half doped and collects electrons from the base. This collector is large compared to two other regions so it dissipates more heat.
The BJT are of two types NPN and PNP, both work the same but differ in terms of polarization and polarity of the power supply. In the PNP transistor, between two P-type materials, the N-type material is interspersed, while in the case of the NPN-type P material interspersed between two N-type materials. These two transistors can be configured in different types as common emitter, common collector and common base configurations.
