What is a Transistor?

A transistor is a component used in many electronic circuits. It is used to amplify or switch electrical signals or power. They are composed of PN diodes (connected back to back) which in turn, are made of semiconductor materials. The semiconductor material used is mostly pure silicon, sometime germanium and certain other semiconductor materials are also used sometime. The working principle of the transistor is that the voltage or current applied to one pair of terminals controls the current through another pair of terminals.

The transistor has at least three terminals. The three terminals are Emitter, Collector, and Base. The Emitter is on the left side of the base and is moderately sized and is heavily doped. The Base is at the centre and this part is lightly doped and thin. The Collector is on the right side of the base and is larger than the emitter and is moderately doped. The junction between emitter-base is forward biased. The collector-base junction is reverse biased.

A transistor is covered in a cylindrical container. Three wires protrude out of the cylindrical container, one each from the emitter, base, and collector. The wires are unevenly spaced. The center wire is from the base. The wire from the collector is more separated from the base wire than the emitter wire.

Types of Transistors

Transistors are of many types and each type has its own application. The two important types are Bipolar Junction Transistor(BJT) and Field Effect Transistor(FET). The Bipolar Junction Transistors is a bipolar device. Bipolar meaning it has two PN junctions.BJT is configured in two ways either PNP or NPN. The Field Effect Transistor is a unipolar device made using either p-type or n-type material.

Application of Transistors

A transistor can be operated in three modes. The three modes are active region, saturation region, and cut-off region. It works as an amplifier in the active region. The saturation region (fully-ON) and the cut-off region (fully-OFF) is used when the transistor works as a switch.

Transistors can be used as Amplifiers and Switches. The process of increasing the amplitude of the voltage or current without altering the other factors is called Amplification. It is used in hearing aids and microphones as amplifiers. 

A transistor can also be used as a switch since a small electric current flowing through one part of it can cause a larger current flow through the other part of the transistor. They are used as a switch in a memory chip in computers. The transistors used as the chip can be switched on/off individually. They can be in two different states, it can store zero and one separately. The transistor as a switch can be put together to make logic gates. The logic gate compares many input current and gives a different value of output current. The logic gates work on the basis of a mathematical technique called Boolean Algebra. In the modern world application of transistors is limitless.