Diode, Transistor & Fet Circuits Manual

252 Pages·1991·4.043 MB·English

by  R. M. Marston (Auth.)

Newnes Circuits Manual Series
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Diode,
Transistor &
F ET Circuits
Manual
R.M. MARSTON
H N E W N ES
To Kirsty, Ashley and Brenda, with love.
Newnes
An imprint of Butterworth-Heinemann Ltd
Linacre House, Jordan Hill, Oxford OX2 8DP
^ PART OF REED INTERNATIONAL BOOKS
OXFORD LONDON BOSTON
MUNICH NEW DELHI SINGAPORE SYDNEY
TOKYO TORONTO WELLINGTON
First published 1991
© R.M. Marston 1991
All rights reserved. No part of this publication may be reproduced in any material
form (including photocopying or storing in any medium by electronic means and
whether or not transiently or incidentally to some other use of this publication)
without the written permission of the copyright holder except in accordance with
the provisions of the Copyright, Designs and Patents Act 1988 or under the terms
of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court
Road, London, England W1P 9HE. Applications for the copyright holder's
written permission to reproduce any part of this publication should be addressed
to the publishers.
British Library Cataloguing in Publication Data
Marston, R.M.
Diode transistor and FET circuits manual.
- (Newnes circuits manual series)
I. Title II. Series
621.3815
ISBN 0 7506 0228 7
Typeset by Vision Typesetting, Manchester
Printed and bound in Great Britain by
Redwood Press Ltd, Melksham, Wiltshire
To Kirsty, Ashley and Brenda, with love.
Newnes
An imprint of Butterworth-Heinemann Ltd
Linacre House, Jordan Hill, Oxford OX2 8DP
^ PART OF REED INTERNATIONAL BOOKS
OXFORD LONDON BOSTON
MUNICH NEW DELHI SINGAPORE SYDNEY
TOKYO TORONTO WELLINGTON
First published 1991
© R.M. Marston 1991
All rights reserved. No part of this publication may be reproduced in any material
form (including photocopying or storing in any medium by electronic means and
whether or not transiently or incidentally to some other use of this publication)
without the written permission of the copyright holder except in accordance with
the provisions of the Copyright, Designs and Patents Act 1988 or under the terms
of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court
Road, London, England W1P 9HE. Applications for the copyright holder's
written permission to reproduce any part of this publication should be addressed
to the publishers.
British Library Cataloguing in Publication Data
Marston, R.M.
Diode transistor and FET circuits manual.
- (Newnes circuits manual series)
I. Title II. Series
621.3815
ISBN 0 7506 0228 7
Typeset by Vision Typesetting, Manchester
Printed and bound in Great Britain by
Redwood Press Ltd, Melksham, Wiltshire
Preface
This book is, as its title implies, primarily a manual of circuits based
on 'discrete' semiconductor components such as diodes, transistors,
FETs, and associated devices, and as such it presents a total of over
340 carefully selected and outstandingly useful practical circuits,
diagrams, graphs and tables.
The manual is divided into four sections, and a total of twelve
chapter headings. The first chapter deals with ordinary diode and
rectifier circuits, and the second with special diodes such as zeners,
varicaps, and photosensitive and light-emitting types. The second
section comprises five chapters (Chapters 3-7) and deals with modern
bipolar transistors, and the third comprises four chapters (Chapters
8-11) and deals with major types of field-effect transistor (including
the JFET, MOSFET, and VMOS). The final chapter deals with the
unijunction transistor (UJT) and some of its thyristor counterparts
(such as the PUT, SUS, and SCS).
The book is specifically aimed at the practical design engineer,
technician, and experimenter, but will also be of interest to the
electronics student and the amateur. It deals with its subject in an
easy-to-read, down-to-earth, non-mathematical but very compre-
hensive manner. Each chapter starts off by explaining the basic
principles of its subject and then goes on to present the reader with a
wide range of practical circuit designs.
Throughout the volume, great emphasis is placed on practical
'user' information and circuitry, and this book, like all others in the
Circuit Manual series, abounds with useful circuits and data. All of the
semiconductor devices used in the practical circuits are modestly
priced and readily available types, with universally recognized type
numbers.
R.M. Marston 1991
1 Basic diode circuits
The solid-state diode is the most fundamental element used in modern
electronics, and is available in a variety of forms, including those of
signal detector, rectifier, zener 'voltage reference' diode, noise-
generator diode, varicap 'variable capacitance' diode, light-sensitive
diode (photodiode), and light-emitting diode (LED). This opening
chapter looks at the basic characteristics of these devices and shows a
variety of ways of using standard diodes and rectifiers.
Basic diode characteristics
The solid-state diode is a two-terminal device that readily passes
current in one direction, but blocks it in the other. Figure 1.1 shows a
the conventional symbol and b the basic structure of the modern
solid-state 'junction' diode; it is formed from a single p-n junction,
and the 'p' terminal is known as the anode and the 'n' terminal as the
cathode.
Figure 1.2 illustrates the basic characteristic of the diode. When it is
forward biased (with the anode positive relative to the cathode) it acts
Anode Anode
9 1
Ρ
η
ό
Cathode Cathode
(a) (b)
Figure 1.1 Symbol (a) and structure (b) of solid-state diode
2 Diode, Transistor & FET Circuits Manual
(а) (b)
Figure 1.2 Diode conduction when (a) forward and (b) reverse-biased
like a low resistance and readily passes current, but when reverse
biased (with the anode negative relative to the cathode) it acts like a
high resistance and passes near-zero current: this action is implied by
the basic diode symbol, which resembles an arrow pointing in the
direction of easy current conduction.
Conventional junction diodes are made from either germanium or
silicon materials. Figure 1.3 compares the basic characteristics of the
two types of device when operated at a normal room temperature of
20°C; note the following important points.
(1) A forward-biased junction diode passes little forward current
{If) until the applied forward voltage (K ) exceeds a certain
f
'knee' value (typically 150-200 mV in germanium diodes, 550-
/f (mA)
20 m A-7
10 mA-l
20 V 10 V
J L
ι ι 1 1 Г*
0.2 0.4 0.6 0.8 1.0
h2
Ge
h4
'rev <μΑ)
Figure 1.3 Basic characteristics of germanium (Ge) and silicon (Si)
junction diodes (at 20°C)
Basic diode circuits 3
600 mV in silicon types). When a diode is operated beyond its
knee value, small increases in V cause large increases in J , e.g.
{ f
the devices forward dynamic impedance (Z ) is inversely propor-
f
tional to applied voltage.
(2) The Z of a silicon diode has a typical value (in ohms) of 25/7,
f
where / is measured in milliamperes; i.e. Z = 25 ohms at 1 mA,
f
2.5 ohms at 10 mA, and 0.25 ohms at 100 mA. The Z of a
f
germanium diode is greater than that of a silicon type;
consequently, its V usually exceeds that of a silicon type at I
{ {
values greater than a few tens of milliamperes.
(3) When a diode is reverse-biased by an amount greater than 1 V or
so it passes a reverse leakage current (/ ) that is almost directly
r
proportional to the reverse voltage (V ) value. At normal room
r
temperatures I values are measured in microamperes in ger-
T
manium devices and in nanoamperes in silicon types. J is highly
r
temperature dependent, and typically doubles for each 8°C
increase in junction temperature.
Because of their low knee voltage values, germanium diodes are
used almost exclusively in low-level 'signal detection' applications.
The great majority of junction diodes are silicon types, and can be
used in many general-purpose applications; diodes that have high
reverse voltage and forward current ratings are, by convention,
usually called 'rectifiers'.
Special diode characteristics
Ordinary silicon diodes have several special characteristics additional
to those already described; the most important of these are illustrated
in Figures 1.4-1.7.
If a silicon diode is increasingly reverse-biased a point is eventually
reached where the reverse current suddenly starts to increase, and any
further increase in V causes a sharp rise in 7 , as shown in Figure 1.4.
r r
The voltage at which this action occurs is known as the avalanche or
'zener' value of the device, and is very sharply defined. Some silicon
diodes are specially manufactured to exploit the zener effect, and can
be used as 'reference voltage' generators; such devices are depicted by
the circuit symbol shown in the diagram.
All zener diodes have impedances that inherently fluctuate in a
rapid and random manner, and can thus be used as excellent 'white-
noise' sources.
4 Diode, Transistor Sc F ET Circuits Manual
/f (mA)
Zener
diode
symbol
К
• ZNeneror
avalanche
voltage
m A
/rev < )
Figure 1.4 Zener diode symbol and characteristics
V (mV)
f
Temperature (°C)
Figure 1.5 Thermal characteristics of a silicon diode at l = l m A
f
If a silicon diode is forward-biased via a constant-current gen-
erator, its Vf value varies with junction temperature at a rate of
- 2 mV/°C, as shown in Figure 1.5. Thus, if V = 600 mV at + 20°C, it
f
falls to 440 mV at 100°C or rises to 740 mV at - 50°C. Silicon diodes
can thus be used as tempera ture-to-vol tage converters.
If a silicon diode is reverse-biased from a high-impedance source
(as shown in Figure 1.6) and its junction capacitance is measured, it
will be found to decrease (from perhaps 17pF at —1 V to maybe
10 pF at — 8 V) as the reverse bias is increased. Some silicon diodes
Basic diode circuits 5
δ 1 2 4 8
Reverse volts, V
rev
Figure 1.6 Varactor (varicap) diode symbol and typical characteristics
are specially manufactured to exploit this 'voltage-variable-
capacitor ' effect; they are known as 'varicap' or Varactor diodes, and
are depicted by the circuit symbol shown in the diagram.
When p-n junctions are reverse-biased their leakage currents and
impedances are inherently optosensitive; they act as very high
impedances under dark conditions and as low impedances under
bright ones. Normal diodes have their junctions shrouded in opaque
material to stop this unwanted effect, but some are specially
manufactured to exploit it; they are called photodiodes, and use the
symbol shown in Figure 1 Ja. Some of these photodiodes are designed
to respond to visible light, and some to infra-red (IR) light.
Ô ô
(a) (b)
Figure 1.7 Photodiode (a) and LED (b) symbols
Another useful type of 'junction diode' device is the LED, or light
emitting diode, which is made from an exotic material such as gallium
phosphide or gallium arsenide, etc., and which may be designed to
emit either red, green, yellow, or infra-red light when suitably
forward-biased. These devices use the symbol shown in Figure 1.7ft.