Basic Electronics - Types of Transistors

 

There are many types of transistors in use. Each transistor is specialized in its application. The main classification is as follows.

Transistor Types

The primary transistor is the BJT and FET is the modern version of transistor. Let us have a look at the BJTs.

Bipolar Junction Transistor

A Bipolar junction transistor, shortly termed as BJT is called so as it has two PN junctions for its function. This BJT is nothing but a normal transistor. It has got two types of configurations NPN and PNP. Usually NPN transistor is preferred for the sake of convenience. The following image shows how a practical BJT looks like.

FET Terminals

Source

·        The Source terminal in a Field Effect Transistor is the one through which the carriers enter the channel.

·        This is analogous to the emitter terminal in a Bipolar Junction Transistor.

·        The Source terminal can be designated as S.

·        The current entering the channel at Source terminal is indicated as IS.

Gate

·        The Gate terminal in a Field Effect Transistor plays a key role in the function of FET by controlling the current through the channel.

·        By applying an external voltage at Gate terminal, the current through it can be controlled.

·        Gate is a combination of two terminals connected internally that are heavily doped.

·        The channel conductivity is said to be modulated by the Gate terminal.

·        This is analogous to the base terminal in a Bipolar Junction Transistor.

·        The Gate terminal can be designated as G.

·        The current entering the channel at Gate terminal is indicated as IG.

Drain

·        The Drain terminal in a Field Effect Transistor is the one through which the carriers leave the channel.

·        This is analogous to the collector terminal in a Bipolar Junction Transistor.

·        The Drain to Source voltage is designated as VDS.

·        The Drain terminal can be designated as D.

·        The current leaving the channel at Drain terminal is indicated as ID.

 

Types of FET

There are two main types of FETS. They are JFET and MOSFET. The following figure gives further classification of FETs.

FET Types

In the subsequent chapters, we will have a detailed discussion on JFET and MOSFET.