Book Review

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 EMC

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