Introduction of BJT

Electron Devices

Chapter 4:

Bipolar Junction Transistors

Introduction

• Transistor is a three terminal device : Base, emitter in three be can operated configurations common base, common emitter and common collector.

• According to configuration it can be used for voltage as well as current amplification.

• The amplification in the transistor is achieved by passing input current signal from a region of low resistance to a region of high resistance. This concept of transfer of resistance has given the name TRANSfer‒resISTOR (TRANSISTOR).

Types of Transistors

• There are two types of transistors : Unipolar junction transistor and bipolar junction transistor.

• In unipolar transistor, the current conduction is only due to one type of charge carriers, majority carriers.

• The current conduction in bipolar transistor is because of both the types of charge carriers, holes and electrons. Hence this is called Bipolar Junction Transistor, hereafter referred to as BJT.

• In BJT output current is controlled by input current and hence it is a current controlled device.

Types of BJT

1. n‒p‒n type

2. p‒n‒p type

Advantages of BJT

1. Low operating voltage

2. Higher efficiency

3. Small size and ruggedness and

4. Does not require any filament power

Review Questions

1. What is transistor?

2. Explain the word transistor.

3. What are the types of transistors ?

4. What are the types of BJT?

5. State the advantages of a transistor.

6. What is the major difference between a bipolar and unipolar device?