BOOKSHELF
Simplified Design of Linear Power Supplies
Simplified Design of Linear
Power Supplies, by John D. Lenk.
Published 1994 by ButterworthHeinemann. Hard covers, 246
pages, 241 x 160mm, ISBN 0-75069506-4. Price $62.95.
The Author says in his preface that
“this book has something for everyone”. The first six chapters cover
the basics for all phases of practical
design while the last chapter includes
over one hundred worked-out design
examples including: (1) an adjustable supply using an LM117 (LM317)
regulator; (2) a triple output power
supply using an LM117 regulator, two
LM107 opera
tional amplifiers and
two transistors; and (3) a computer
controlled supply using a 7475 latch
and an LM338 adjustable regulator.
Chapter 1, which covers linear
power supply basics, is not a good
beginning. It is obviously written
for beginners but has errors which
could cause confusion, especially if
an oscilloscope was used to compare
actual waveforms against those shown
for the half-wave and full-wave rectifier circuits on pages 2 and 3. The
Author shows the output waveforms
at the diodes for half-wave and fullwave rectification assuming there is
no capacitor but his circuits include
electrolytic filter capacitors, which
will dramatically change the viewed
waveforms.
Page 15 shows a diagram of an
adjustable shunt regulator. This has a
potentiometer between a 4.7 volt zener
to ground and a 15 volt source with the
caption “0 - 10V regulated” – again,
puzzling for the beginner, while the
more experienced will realise it should
read “4.7 to 15V regulated”.
Chapter 2 covers heatsinking in
linear power supplies. Among the
topics discussed in this chapter are
heatsink ratings, power dissipation,
mounting of components on heatsinks,
mounting surface preparation, thermal
compounds and the types of heatsinks
available for integrated circuits. The
majority, if not all of this information
would be familiar to the experienced
power supply designer.
Chapter 3 is titled an introduction
to discrete feedback regulators. The
author first discusses shunt voltage
regulators, including those with outputs both higher and lower than the
reference voltage. He then goes on to
detail series voltage and current regulators with a worked example for an
8V 4A unit. Details of adding parallel
pass transistors to increase the output
current are also discussed.
Chapter 4 moves on to modern integrated circuit (IC) based regulators and
covers the four basic sections: control,
bias, DC level shift and output. The
circuits for several commercial ICs are
shown, with methods of increasing the
output current and limiting the maximum current with excessive loads.
The Author also shows how to monitor the heatsink temperature and shut
down the regulator if the temperature
becomes excessive.
Chapter 5 is devoted to the basics of
IC operational amplifiers in discrete
linear voltage regulators. The chapter
starts with an explanation of the benefits the operational amplifier brings
to the designer. A discussion then
follows on suitable reference sources
and methods of obtaining output volt
ages higher than the reference voltage.
The chapter ends with details of the
methods for remote sensing.
Chapter 6 is concerned with linear
power supply testing. It deals with
measur
ing output and input-output
regulation, internal resistance, ripple,
transformer phasing and transformer
regulation.
It also covers the measurement
of transient recovery time, drift and
temperature coefficient. The chapter
finishes by showing methods for the
connection of multiple loads to one
power supply and two supplies to
multiple loads. Again, we noted errors
in the diagrams on pages 90, 91 & 95.
Chapter 7 is headed “Linear Supply
Design Examples” and occupies over
half the book. Disappointingly, it consists of virtually no original material,
only reprints of circuits from the major
manufacturers’ application notes.
Coincidentally, the three design
examples listed at the beginning of
this review and quite a few others in
this chapter were all taken from the
National Semiconductor Linear Applications Handbook, which would
surely be in every design engineer’s
library.
To sum up, a rather disappointing
book. While we did not read it from
cover to cover, several errors were
noted, which should not have appeared. And while circuits from 16
different suppliers are included, the
reader may be better off buying the
application notes of one of the major
manufacturers (eg, National, Motorola
or Harris). Our sample copy came from
the publish
ers, Butterworth Heine
mann Australia, PO Box 5557, West
Chats
wood, NSW 2057. Phone (02)
SC
372 5511. (R.J.W.)
July 1995 53
