As one of the important semiconductor devices, the transistor has found use in huge electronic applications such as embedded 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, and so on. This article mainly focuses and gives a brief explanation of the application of transistors as a switch.
The bipolar junction transistor or simply BJT is a semiconductor device of three layers, three terminals and two together. 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 carriers are involved in the work of a BJT. These two charge carriers are holes and electrons where the holes are positive charge carriers and the electrons are negative charge carriers.
The transistor has three regions, namely base, emitter and manifold. 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 into the manifold. The collector terminal is doped and collects electrons from the base. This collector is large compared to two other regions so it dissipates more heat.
The BJTs are of two types NPN and PNP, both running are the same but differ in terms of bias and polarity of the power supply. In the PNP transistor, between two P-type materials, the N-type material is interleaved, whereas in the case of the P-type material of the NPN transistor interposed between two N-type materials. These two transistors can be configured in different types as Common emitter, common collector and common base configurations.
![[Image: NPN-and-PNP-Transistors.jpg]](http://www.electronicshub.org/wp-content/uploads/2015/02/NPN-and-PNP-Transistors.jpg)
