Title: Demystifying Switching Power Supplies
Author: Raymond A. Mack, Jr.
Publishers: Elsevier, Inc., Imprinted by Newnes
List Price: $49.95
ISBN: 0-7506-7445-8
Publication Date: 2005
Number of Pages: 344
The latest in the Newnes Demystifying Technology Series is Raymond
Mack’s Demystifying Switching Power Supplies. Self described
as “The Essential Guide to the Theory, Design, and Applications
of Switching Power Supplies”, this book does not disappoint.
Although not written specifically for electromagnetic compatibility
engineers, this book has great value in understanding the styles
of switched mode power supplies (SMPS), their advantages and disadvantages,
as well as solving design problems from control to component selection.
The concept of the book was to provide a “crash course”
in switched mode power supplies, from the theory and concepts,
through to a variety of designs. Although the author supplies
all the information on making unique and original designs, he
also supplies information on the use of Off the Shelf power supplies
and modules. All this is done with very clear and basic mathematical
solutions, and a clear concise writing style that makes the book
an easy read.
Mr. Mack starts by giving an overview of the various styles of
SMPS: Boost, Buck, Inverted Boost, Boost-Buck, Transformer Isolated
of various styles, Synchronous Rectification, and Charge Pumps
of various styles. Each design is accompanied by a clear “Idealized”
diagram showing current flows and explaining why the converter
works. A description of applications and efficiencies is also
included in the text.
Now that the styles of SMPS are understood, we step up to Control
Circuits in Chapter 2. There is a basic overview of control circuits
and error amplifiers, as well as an eight-step process for testing
a control circuit, transcribed from Linear Technology application
notes. Voltage mode and current mode pulse width modulation controllers
are examined, as well as multiple phase and resonant mode controllers.
The statement highlights the need for more advanced control circuits,
“A typical Pentium 4 power supply must supply 1.4 Volts at
65 Amps”. Ten years ago, we didn’t use this type of
language.
Now comes an interesting Chapter, Chapter 3, The Input Power Supply.
Here Mr. Mack addresses AC to DC converters in the world of safety
and regulatory requirements. In a very basic overview, he discusses
EMI regulations including ground fault issues for medical devices,
safety agency issues, especially concerning the use of various
types of capacitors, well as power factor correction and inrush
current issues. Hold Up Time calculations and explanations are
given in simple forms, as well as input rectifier considerations.
Do not look for EMC design considerations beyond the basic P filter
given in the text.
In Chapters four and five, we find guidelines for Non-Isolated
Circuits and Transformer Isolated Circuits, in that order. Covering
30% of the book, here we find the greatest amount of detailed
analysis and mathematical solutions given so far. For the power
supply designer, this will be the meat of the book. In the non-isolated
section, we mainly see buck and boost converter designs, inverting
and charge pump designs. In the transformer-isolated section,
the book covers flyback circuit styles and designs, forward converter
styles and designs, as well as push-pull, half bridge, and full
bridge designs. Again, you will not find much help in the control
of EMC. Even a statement about magnetic coupling appears at the
end of Chapter 4 could too easily be overlooked or ignored.
At this point we address Passive Component Selection in Chapter
6. Specifically, capacitor and resistor styles are addressed.
A good discussion is given on the equivalent series inductance
and resistance of capacitors, including some discussion on dissipation
and power factors. Here is found a good groundwork of capacitor
construction, application, and failures. Again, this is a text-based
discussion, not one with much mathematics or diagrams. There is
only one graph of impedance verses frequency, and that is for
a comparison of a ceramic capacitor to a tantalum capacitor. There
is a good explanation on ceramic capacitors and their dielectric
temperature codes. An overview of resistor styles and characteristics
is also included.
Chapter 7 covers Semiconductor Selection. This starts with diode
characteristics and selection, which includes their strengths
and weaknesses. Bipolar transistors are described in a basic but
complete manner, with several graphs showing turn on/turn off
and bias waveforms, and the author explains why they should be
considered over MOSFETs. Of course, this leads to the section
on Power MOSFETs and an extended description of Gate Drive. This
section has a good explanation of MOSFET design and characteristics,
clear and full of figures and graphs. To complete the section
are discussions on Safe Operating Area and Avalanche Rating, Synchronous
Rectification, Sense FETs, and Insulated Gate Bipolar Transistors.
Chapter 8 was my favorite, Inductor Selection. Of course, this
came from my EMC background. Starting with basics again, the author
covers core geometries, wire gauge capacity, and core properties.
He does a good job describing B-H curves, magnetic properties
such as permeability, eddy currents and the like, as well as the
magnetic materials powdered iron and ferrite. Although the graphs
may be confusing to the uninitiated, and inadequate for the experienced
user, they do supply a foundation from which further research
can be made. The author also gives a good explanation of powdered
iron core design in a basic, textual manner that is both simple
and clear, and even covers the most important aspects.
Transformer Selection is the topic of Chapter 9. There is a good
overview of design considerations from winding capacitance and
leakage inductance, to creepage and clearance issues, and winding
stackup. Assistance is given on selecting a transformer core and
obtaining additional information online. Safety issues are addressed
and equations are supplied to assist in choosing the right transformer
core.
Chapter 10 and 11 cover design examples. Chapter 10 deals with
A “True Sine Wave” Inverter using several different
designs. It is pointed out that these are used typically for uninterruptible
power supplies and that “true sine wave” means less
than 20 % total harmonic distortion. The final Chapter covers
A PC Off-Line Supply, showing the steps to creating a 220-watt
power supply. The sections include choosing inductors, capacitors,
diodes, and transistors. Fairly complete calculations are included
for the reader. A warning is given stating, “The intent is
to show the steps necessary to start from paper and go into the
lab to finish the design.”
This is a good book to learn the basic design of switch mode power
supplies and design. It is not intended to be a complete dissertation
or analysis of the topic. It does not include significant EMC
design or address troubleshooting issues. It is described by the
publisher as “Intended for readers who need to quickly understand
the key points of switching power supplies, this book covers the
20% of the topic that engineers use 80% of the time”. From
this point, it does this very well. The language is clear, the
topics addressed are covered completely, and the layout of the
book is very well done.
About the author of this article: Patrick G. André received
his physics degree in 1982 from Seattle University. He has worked
in the Electromagnetic Compatibility (EMC) field for 22 years.
He is a NARTE Certified Engineer in both EMC and ESD (Electrostatic
Discharge). He has worked in the military and aerospace environment
for the entire time, and worked in the commercial electronics
environment for the last ten. Patrick has a strong ability in
the test and measurement area of EMC. He is president of André
Consulting, Incorporated. Patrick has been a member of the IEEE
EMC Society for 21 years, serving as chairman, vice chairman and
arrangements chairman of the Puget Sound Section. He also works
for the Seattle Gilbert and Sullivan Society and Pro A/V Incorporated
as a Sound Design Engineer. He may be reached at pat@andreconsulting.com.
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