Page 144 - Power Electronics Handbook

Chapter 6

Power semiconductor circuits - a rCsumC

6.1 Introduction

Chapters 1-5 have described components which are used in the design of
power semiconductor circuits. The remaining chapters introduce the
various circuits in which these power semiconductors may be used in order
to regulate the power to the load. Circuit principles are described since in
many cases several different types of power components may be used to
perform the same functions.
Because of the diversity of power semiconductor circuits, the present
chapter introduces the principles involved and these are then described
further in following chapters.

6.2 Power switches
This book is primarily concerned with the use of power semiconductors in a
switching mode, and therefore this is the basic type of power
semiconductor circuit which may be used. The switching characteristics of
the different components have already been described in Chapter 1, some
devices needing continuous drive on their gate terminal when conducting,
whilst others being triggered by pulses of current. Furthermore, some
devices can be turned off by their control terminal, whilst others require
the load current to be momentarily interrupted for twn-off. Chapter 7
describes some typical switching circuits and applications.

6.3 A.C. be control

In this application the power semiconductors are used to regulate the
power flowing from an a.c. source to an a.c. load. Figure 6.l(a) shows two
thyristors, connected in anti-parallel, which are used to control the power
from the a.c. supply across lines A and B to the load across C and D.
Instead of two thyristors a single triac could be used, although power
semiconductors which may be turned off by their gate terminals, such as
transistors and gate turn-off switches, are usually used in d.c. rather than
a.c. applications.

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