Voltage Regulator Circuit Manual

152 Pages·1989·3.007 MB·English

by  Robert Traister (Auth.)

Voltage Regulator
Circuit Manual
Robert J. Traister
ACADEMIC PRESS, INC.
Harcourt Brace Jovanovich, Publishers
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Material reprinted from "Motorola Linear and Interface Integrated Circuits" and
"Motorola Linear/Switchmode Voltage Regulator Handbook," "Linear/Switchmode
Voltage Regulator Handbook 2," and "Power MOSFET Transistor Data" is copyright of
Motorola, Inc. and is used by permission.
Certain material has been reproduced with the express authorization of EXAR
Corporation. Copyright by EXAR Corporation.
Material from "Linear Databook I," "Voltage Regulator Handbook," "Linear Applications
Data Manual," and "Linear Applications Databook" is reprinted with permission of
National Semiconductor.
National's products are not authorized for use as critical components in life support devices or
systems without the express written approval of the president of National Semiconductor
Corporation. As used herein:
1. Life support devices or systems are devices or systems which, (a) are intended for surgical
implant into the body, or (b) support or sustain life, and whose failure to perform, when
properly used in accordance with instructions for use provided in the labeling, can be
reasonably expected to result in a significant injury to the user.
2. A critical component is any component of a life support device or system whose failure to
perform can be reasonably expected to cause the failure of the life support device or system,
or to affect its safety or effectiveness.
This book is printed on acid-free paper. @
Copyright © 1989 by Academic Press, Inc.
All Rights Reserved.
No part of this publication may be reproduced or transmitted in any form or
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from the publisher.
Academic Press, Inc.
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United Kingdom Edition published by
Academic Press Limited
24-28 Oval Road, London NW1 7DX
Library of Congress Cataloging-in-Publication Data
Traister, Robert J.
Voltage regulator circuit manual / Robert J. Traister.
p. cm.
ISBN 0-12-697410-1 (alk. paper)
1. Voltage regulators—Handbooks, manuals, etc. 2. Integrated
circuits—Handbooks, manuals, etc. I. Title.
TK2851.T66 1989
621.3 l'7-dc20 89-17544
CIP
Printed in the United States of America
89 90 91 92 9 8 7 6 5 4 3 2 1
For best of friends Dwight, Chris, and Keith Lisenbee
Preface
There has never been a lack of books about DC power supplies. It is
this large category of devices that has always been instrumental to
nearly every other category of electronic devices and circuitry. When
new technology electronic circuits are designed, there is almost al-
ways an equally state-of-the-art power supply in the background.
However, the demands placed upon DC power supplies by these new
technologies have brought the lowly regulated DC power supply to
the forefront on many occasions.
The reason for this is simple. DC power supplies have traditionally
been considered as afterthoughts. That is, the "high-tech" electronic
circuit was first designed, and then a conventional power supply
circuit was chosen to drive it. However, with technological advances,
the requirements of DC power supplies have become more stringent.
So stringent, in fact, that such supplies are now more often designed
as an integral part of the circuits they will later power. Fortunately,
as technology has advanced in other areas, such advancements have
been carried over into power supply design.
These advancements in DC power supply regulator circuits, how-
ever, have traditionally lagged (somewhat) behind the state-of-the-art
advances in other electronics fields. Perhaps this tradition is chang-
ing. This book was written to highlight, explain, and actually dem-
onstrate the latest techniques in DC regulator design. Many different
types of circuits are contained in these pages. Some are quite simple
from a construction standpoint, as the advanced technology men-
tioned earlier has been incorporated in silicon chips. The complexity
is handled by the IC manufacturer. A large section on switching
power supplies is included, as these types of circuits are the current
frontrunners in the DC regulator category; they offer excellent regu-
lation, power, and still, through IC chip technology, can be con-
structed inexpensively.
With the broad range of circuits found here, the technician or elec-
tronic engineer should be able to find circuits for driving almost any
X Preface
device imaginable. If the exact circuit is not found, then, certainly,
one which can be modified may be made to perform a specialized
function or functions. Each circuit is accompanied by a terse descrip-
tion that is written to aid the designer who needs to customize a
circuit.
A good overview of current power supply design is also included
in the opening pages of this text. This should serve to inform the
reader as to the changes in the art since the subject was last studied
formally. It is also a good review for those who have become a bit
rusty in this area of electronics design.
It is the hope of the author that this text will be useful, both from a
tutorial as well as from a direct design viewpoint. The current trend
is toward ever-advancing DC power supply designs. No longer can
the DC regulator circuit be taken for granted or treated as a bother-
some necessity. Now more than ever, a poor DC regulator design
results in a poor overall system or device. In other words, no elec-
tronic circuit can ever be better than the power supply that drives it.
Robert /. Traister
Chapter 1
Voltage Regulator Design Criteria
In designing and building regulated power supplies to meet demand-
ing applications, the designer's first obligation is to select the solid-
state regulator device(s) adequate to meet the voltage/current param-
eters of the intended circuit. The standard means of obtaining this
information is via a manufacturer's data sheet.
Once the device determination has been made, the somewhat more
difficult task of selecting a suitable circuit configuration must be han-
dled. Initial designs are devised and compared to determine the cir-
cuit configuration that best meets the design criteria. This chapter*
will discuss the various circuit configurations applicable to linear IC
voltage regulators and switching regulator designs.
* Portions reprinted from "Linear/Switchmode Voltage Regulator Handbook." Cour-
tesy of Motorola, Inc.
1
2 1. Voltage Regulator Design Criteria
Positive Fixed Configurations
The basic current configuration for positive, three-terminal regulators
is shown in Fig. 1. Depending on which type of regulator device is
used, such a configuration is capable of providing output currents in
the 3-A range. It can be seen that this is an extremely simple design
which is quickly constructed using a bare minimum of components.
While such circuits do not offer the extremely high regulation char-
acteristics of switching designs, the low complexity is preferable for
applications that can accommodate the lower regulation efficiency.
Figure 2 shows a method by which greater output current can be
obtained with a three-terminal positive regulator configuration. With
the Motorola regulators specified throughout this discussion, it is
usually most economical to use the 1-A units in such a configuration,
although any of them can be pulled into service. Here, an external
pass transistor is utilized. Therefore, the output current is limited
only by the feedthrough capabilities of the pass element. The degree
of regulation is the same as that of the former circuit and is deter-
mined by the three-terminal regulator.
In addition to providing voltage regulation, the three-terminal pos-
itive regulator can also be used quite effectively as a circuit regulator
in applications where a constant current source is needed. Figure 3
shows such a configuration, in which the output current can be ad-
justed to any value from approximately 8 mA up to the available
output current of the regulator. Five-volt regulators should be used to
obtain the greatest output voltage compliance range for a given input
voltage.
1 DEVICE 19.
V|N O -o—\ Ovc
MC78LXX 0.1A
MC78MXX 0.5A
MC78XX 1.0A
CIN 0.33MF MC78TXX 3.0A Co
T
ΊΝ- required if regulator is located more than a few («2" to 4") inches away from input supply
capacitor; for long input leads to regulator, up to 1μΡ may be needed for CjN. C)N should be a
high frequency type capacitor
C0: improves transient response
XX: these two digits of the type number indicate nominal output voltage.
Fig. 1. Basic circuit configuration for positive, fixed-output three-terminal
regulators.
1. Voltage Regulator Design Criteria 3
MJ2955
V|N 0.12Ω or Equiv
Input 5W
+ 10V
•SC(Q1)
•SCTOT.
hO + ·
Output + 5V
•scdci)
XX = 2 digits of type number indicating voltage.
R: used to divert IC regulator bias current and determines at what output current level Q1 begins
vBEON(Q1) _ ^0.6V .
conducting. 0<R< •SCTOTS 'sciQD+'scdcD
BIAS0C1)
Values shown are for a I 5V, 5AJ regulator using an MC7805CK on a 2.5° C/W heatsink and Q1 on a
1°C/W heatsink for TA up to 70 C.
Fig. 2. Current boost configuration for positive, three-terminal regulators.
Fig. 3. Adjustable output
voltage configuration.
V, Output
• + » o-\ MC7805C hO-
Input
0.1
0.33MF
MF
10 k
ho *~
1 k
MC1741G
T
V0=7V to 33V; V|N-V0 > 2V; VJN>35V
4 1. Voltage Regulator Design Criteria
IC1
2N6576
V0
O- MC7824CT -o
60V
48V
R1
5.6 K 0.33 MF JOMF, 50V
1/2 W
IN4001
D1
Ί
IN4749
24V, 1W
V0=Vz1+24; R1- [ j-g ]xhFE(Q2)
Values shown are for a|48V, 1 Ä|regulator; Q1 mounted on a 10 C/W heatsink and IC1 mounted on a
2° C/W heatsink for TA up to +70° C.
Fig. 4. High-output voltage configuration.
IC1
XX=2 digits of type number indicating voltage
V,N-30
R1=S( 1.5 )xhFEQi; vCEOQ1>vIN
Values shown for VJN=60V; Q1 should be mounted on a 2 C/W heatsink for operation at T^ up to
+70 C. IC1 should be appropriately heatsinked for the package type used.
Fig. 5. Preregulator for high-input voltages.
1. Voltage Regulator Design Criteria 5
In designs where voltage output is to exceed 24 V DC, the configu-
ration shown in Fig. 4 may be used. In this schematic, a zener diode
(Zl) sets the output voltage while Z2, Dl, and Ql assure that the
regulator IC does not have more than 30 V DC across it during short-
circuit conditions. In some applications, it may be necessary to power
a three-terminal regulator from a supply voltage that is greater than
V , a value that is limited to less than 40 V. Figure 5 shows how a
IN
preregulator circuit may be incorporated using the 2N6576 in con-
junction with a 30-V zener diode. This particular circuit outputs 48
V DC at a maximum current of 1 A.
Negative Fixed Configurations
Equivalent negative designs of the previous circuits are easily arrived
at by selecting a negative three-terminal regulator device. The basic
configuration for such a design is shown in Fig. 6. All other criteria
remain the same as in the discussion of the positive regulator basic
circuit. For output current boosting, the external transistors are sim-
ply changed to N-P-N devices, as shown in Fig. 7.
Three-terminal negative regulators are wired as shown in Fig. 8 to
provide a constant current sink. Again, this follows the same design
criteria as the positive regulators previously discussed.
Device IQ
MC79XX 1A
MC79LXX0.1A
C|N: required if regulator is located more than a few inches (*2" to 4") away from input supply
capacitor; for long input leads to regulator, up to IßF may be required. C|N should be a high
frequency type capacitor.
CQ: improves stability and transient response
XX: these two digits of the type number indicate nominal output voltage.
Fig. 6. Negative three-terminal configuration.