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DC/DC BOOK OF
KNOWLEDGE
Practical tips for the User
By Steve Roberts M.Sc. B.Sc.
Technical Director, RECOM
DC/DC Book of Knowledge
Practical tips for the User
Steve Roberts, M.Sc. B.Sc.
Technical Director, RECOM
Third Edition
© 2016 All rights RECOM Engineering GmbH & Co KG, Austria
(hereafter RECOM)
The contents of this book or excerpts thereof may not be reproduced, duplicated or
distributed in any form without the written permission of RECOM.
The disclosure of the information contained in this book is correct to the best of the
knowledge of the author, but no responsibility can be accepted for any mistakes,
omissions or typographical errors. The diagrams illustrate typical applications and
are not necessarily complete.
Preface from RECOM Management
When we introduced our first DC/DC Converter more than 25 years ago, there were little pub-
lished technical material available and hardly any international standards to follow. There was
a pressing need to communicate practical application information to our customers, which
prompted us to add some simple Application Notes as an appendix to our first published prod-
uct catalogue. The content of these guidelines grew over the years as we gained more and
more expertise. Although they are still of a rudimentary nature, they are well received by our
customer base and today they have become an 70-page Application Note package available
for download from our website.
The advance of semiconductor technology and the shift towards highly integrated digital elec-
tronics has diminished the knowledge base of analogue techniques in many design labs, uni-
versities and technical colleges over the years. We often see a lack of practical know-how in
analogue circuit design, particularly with regard to applied techniques, test and measurement
and the understanding of filtering and noise suppression. Therefore, as experts in this arena,
we saw the need for a much more comprehensive technical handbook that could be used as
reference by hardware designers and students alike.
At the start of 2014, Steve Roberts, our Technical Director, started to invest his free time to
start documenting the extensive application knowledge on the design, test and application
of DC/DC converters available within the RECOM group. Despite all of the pressures of his
demanding job, along with new product development and the technical planning of our new
research and test labs, he has managed to complete this onerous task in time for Electronica
2014. Today, two years later, in the time for Electronica 2016 the third edition of the RECOM
DC/DC Book of Knowledge has been enlarged to include an additional chapter on magnetics.
Steve has presented us with a handbook that we are sure will greatly benefit the engineering
community and all those who are interested in DC/DC power conversion and its applications.
The handbook will initially be available as a printed version and PDF, not only in English but
also in German, Chinese and Japanese.
Board of Directors
Gmunden, 2016
RECOM Group
Preface from the Author
The function of any AC/DC or DC/DC converter module is to meet one or more of the following
requirements:
i:
ii:
iii:
iv:
to match the secondary load to the primary power supply
to provide isolation between primary and secondary circuits
to provide protection against the effects of faults, short circuit or over heating
to simplify compliance with safety, performance or EMC legislation.
There are a number of different techniques available to achieve these aims, starting at its
simplest with a linear regulator and going through to multi-stage, digitally controlled power
supplies. This book aims to explain the various DC/DC circuits and topologies available so
that users can better understand the advantages, limitations and operational boundaries of
each of these solutions. The language used is necessarily technical, but is kept as simple as
possible without trivialising the technology involved.
The author has many years of experience answering customers’ questions, helping with de-
sign-ins, presenting at seminars, writing articles and even making Youtube videos. Despite
this accumulated know-how, there is still something to learn new every day about this diverse
and wide-ranging subject. This book is subtitled “Practical tips for the User” because it hopes
to de-mystify the topic of power conversion, despite there being as many solutions as there
are applications. If it succeed in passing at least some of our expertise and knowledge on to
you, then it will have accomplished its goal.
The information given in this book is given in good faith and has been checked for veracity,
but if the reader finds any errors, omissions and inaccuracies, please feel free to inform me.
Steve Roberts
Technical Director
s.roberts@recom-power.com
RECOM
Gmunden, 2016
Contents
1.1
1.1.1
1.1.2
1.1.3
1.2
1.2.1
1.2.2
1.2.2.1
1.2.2.1.1
1.2.2.1.2
1.2.2.1.3
1.2.2.1.4
1.2.2.1.5
1.2.2.1.6
1.2.2.1.7
1.2.2.1.8
1.2.2.1.10
1.2.2.1.11
1.2.2.1.12
1.2.2.2
1.2.2.2.1
1.2.2.2.2
1.2.2.2.3
1.2.2.2.4
1.2.2.2.5
1.2.2.2.6
1.2.2.2.7
1.2.3
1.2.3.1
1.2.3.2
1.2.4
1.2.5
1.2.6
1.2.6.1
1.2.6.2
1.2.7
1.2.8
1.2.9
1.2.10
1.
Linear Regulators
Efficiency of a Linear Regulator
Other Properties of the Linear Regulator
LDO Linear Regulators
Switching Regulator
Switching Frequency and Inductor Size
Switching Regulator Topologies
Non-Isolated DC/DC Converter
Switching Transistors
Buck Converter
Buck Converter Applications
Boost Converter
Boost Converter Applications
Buck-Boost (Inverting) Converter
Buck/Boost Discontinuous and Continuous Mode
Synchronous and Asynchronous Conversion
w
e
er er
Two Stage Boost/Buck SEPIC Converter
Two Stage Boost/Buck ZETA Converter
Multiphase DC/DC Converters
Isolated DC/DC Converters
Flyback DC/DC Converter
Forward DC/DC Converter
Active Clamp Forward Converter
Push-Pull Converter
Half Bridge and Full Bridge Converters
Busconverter or Ratiometric Converter
Unregulated Push-Pull Converter
Parasitic Elements and their Effects
QR Converter
RM Converter
Efficiency of DC/DC Converters
PWM-Regulation Techniques
DC/DC Converter Regulation
Regulation of Multiple Outputs
Remote Sense
Limitations on the Input Voltage Range
Synchronous Rectification
Planar Transformers
Package Styles of DC/DC Converters
Introduction
1
3
4
4
6
7
7
8
8
10
12
13
15
15
17
18
21
23
24
26
26
28
30
31
34
35
36
39
42
43
45
46
49
49
52
54
56
57
59
1
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