Power Electronics

21

Power Electronics

577

Power

Electronics

21.1

21.2

21.3

21.4

21.5

21.6

21.7

21.8

21.9

21.10

21.11

21.12

21.13

21.14

21.15

Power Electronics

The Triac

Triac Construction

SCR Equivalent Circuit of Triac

Triac Operation

Triac Characteristics

Triac Phase Control Circuit

Applications of Triac

The Diac

Applications of Diac

Unijunction Transistor (UJT)

Equivalent Circuit of a UJT

Characteristics of UJT

Advantages of UJT

Applications of UJT

INTRODUCTION

INTRODUCTION

S

ince the 1950’s there has been a great upsurge in the development, production and applications

of semiconductor devices. Today there are well over 100 million semiconductor devices manufactured in a year. These figures alone indicate how important semiconductor devices have

become to the electrical industry. In fact, the present day advancement in technology is largely

attributed to the widespread use of semiconductor devices in the commercial and industrial fields.

One major field of application of semiconductor devices in the recent years has been to control

large blocks of power flow in a system. This has led to the development of a new branch of engineering called power electronics. The purpose of this chapter is to acquaint the readers with some important switching devices much used in power electronics.

21.1 Power Electronics

The branch of electronics which deals with the control of power at 50 Hz (i.e. supply frequency) is

known as power electronics.

Principles of Electronics

578

There are many applications where it is desired to control (or regulate) the power fed to a load

e.g. to change the speed of a fan or motor. So far we have been using electrical methods to exercise

such a control. However, electrical methods do not permit a *fine control over the flow of power in

a system. Moreover, there is a considerable wastage of power. In the recent years, such semiconductor devices have been developed which can exercise fine control over the flow of large blocks of

power in a system. Such...