Transistors

Transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals. Transistors are the building blocks of the digital revolution.

They consist of three terminals namely Emitter(E), Base(B) and Collector(C). An arrow in the transistor is commonly used to represent the direction of the current towards the ground and is always on the emitter leg.

The two basic types of transistors are

• NPN
• PNP

 

Figure 1: NPN and PNP Transistor Symbols

Arrow on the emitter leg facing outwards represents NPN transistor and facing inwards represents PNP transistor.

NPN Transistor:

NPN Transistor acts like a normally open push button but has no moving parts.Only when the base of the transistor is provided with the necessary voltage and current it turns ON the transistor else it remains in OFF state. The base acts like a control valve to control the flow. It behaves as a electronic switch.

PNP Transistor:

PNP Transistor acts like a normally closed push button. Only when the base of the transistor is provided with the necessary voltage and current it turns OFF the transistor else it remains in ON state. Its just the opposite of the NPN transistor