Troubleshooting Switching Power Converters: A Hands-on Guide 1st Edition by Sanjaya Maniktala.
Preface by Sanjaya Maniktala:
A few weeks ago, I found myself groping for some sorely needed inspiration. I was even questioning the very need for a book on this particular subject. So despite spending fi ve years in the general vicinity of the legend behind it, I fi nally went and bought myself the “other” book—Troubleshooting Analog Circuits by Robert Pease. I am glad I did, because it ended up fulfi lling both my requirements—I not only learned that his book is truly is an inspiring resource (certainly something to chuckle your way through coach class with pretzels and coffee in hand), but also that it isn’t about Power Conversion. Take, for example, that famous picture on its cover. The hopelessly entangled object you see there (the creation, not the creator) apparently served as a historic V-F (voltage-to-frequency) converter circuit. But really, it would never pass muster as even a basic switching converter. Breadboards, for one, are kryptonite to switching converters. If you really think about it, all that that picture so aptly conveys is exactly what you shouldn’t ever be attempting to do in power. Reassuringly, even that book itself recognizes that “switch-mode regulators [are] a whole new ball-game.”
So it was surprising for me to learn that the analog troubleshooting book was originally intended to be just a single chapter of a much larger volume on the topic of switching power converters. Maybe that project just slipped through the cracks of time. Perhaps it was too diffi cult a venture to undertake—a hypothesis somewhat supported by the fact that there is still virtually no other book out there on this topic (cheers to the book you’re holding, by the way!). But I also tend to believe that if it were published in the format it seems to have been originally conceived in, it could well have turned out to be quite misleading—for reasons very similar to that on the cover of the analog book. For a while, that had me seriously thinking: “whose bright idea was that?” Then I realized that back in those days, Power Conversion was still in its infancy. Who knew what lay ahead? In the early 1970s, the Intel 8080 microprocessor was dazzling engineers around the world with its blazing computational speed of 2MHz! “Digital” became the anthem for a new generation of EE graduates. Virtually every prospective hire our company interviewed in that decade (and the next), when asked what he or she would like to do for the company, said without a blink—“Microprocessor!” I think I probably got to do Power only because I was not considered good enough for all the really “good stuff.” Though a little later I think things must have soured for some of the laggards involved in this digital race, individuals and companies alike. And in the resulting reverse pileup, somehow everything non-digital suddenly got crowned “analog.”
I wonder how that happened. Catchy phrases such as “the power of analog” may have tickled the collective imagination, but at best they were just oxymorons (quite appropriately with a “moron” in it!). Because, despite all their apparent familiarity and similarity, “Analog” and “Power” are actually strange bedfellows. You just can’t club them together in one grand compendium titled “Everything you didn’t want to know about digital circuits . . . and weren’t afraid to ask.” Yes, though both analog and power have certain commonalities, in that they are both essentially “non-digital,” the similarity ends right there. The distinguishing characteristic of modern switching power converters is that their sharp edges of current and voltage, driven by an almost mystically endowed inductor, generate so much high-frequency content that all the hitherto painfully learned rules of the game tumble helplessly to the ground (quite literally so).
“Analog or Power, what’s in a name?” you may well ask. One practical problem arising from that lack of dichotomy is that in many companies, senior managers suddenly arrive almost unheralded on the scene, possessed with the driving vision and unfettered desire to steer the huge switcher business to new heights—based solely on the credentials that they know everything about op-amps. In a recent case inside a major analog company based in Santa Clara, California, the newly appointed senior VP of the two successful product lines “Power Management” and “Portable Power” pulled aside his staff to ask almost incredulously, “Why do you call our switchers ‘simple?’ ” He was convinced that somehow this totally degraded the product—maybe like simple burgers, or simple minds. Notwithstanding the glaringly obvious fact that that had in fact been the most recognized brand name of the company for the last ten years. Should we call them “Performance Switchers?” Or “Blazing Switchers?” How about “Complex Switchers?” Or maybe “Fiery Switchers?” (Now that would make engineers run to buy ’em!) I was told a hush fell in the conference room right after. A few careerists were still nodding their heads in unbridled awe, but no one there was going to be the one to tell the Emperor that he really needed a (good) tailor now.
Looking further “down” the food chain (or should I say “up”), till just a few years ago, Power was a niche market that most engineers didn’t want. Today it is a niche market that most can’t do. It has turned out to be one thing to write a brilliant paper on the subject, or even put together some heady course material for, quite another to get on the bench and really build a converter that works. Remember, you also need to make it exceedingly reliable, and it costs peanuts in the bargain. That’s the name of the game. At least one reason for this unfortunate situation is that very few engineering schools out there still teach any signifi cant amount of power electronics, especially about switch-mode power supplies (SMPS). It’s a double-E without the SMPS thrown in. Unfortunately, that is just not enough. Companies are scrambling to try and hire graduates from the handful of schools that specialize in power. The situation really needs to be rectifi ed quickly to cope with the steeply escalating demand for trained graduates.
The fi eld of Power has gotten not only critically important, but incredibly complex too. No longer can a wannabe expert get by based solely on the rather astute observation found deep within the Analog Troubleshooting book—“if you stand on a big soapbox and rant and holler, people will often think you know what you are talking about. They stop looking for mistakes . . . and that’s a mistake.” Yes, I do remember that thunderous pounding of the copy machine in Building D punctuated by some of the choicest epithets I have heard this side of the Pacifi c. That was truly unmistakable! Luckily, I have quickly learned from my own experiences that peers who help you fi nd mistakes before you make them, are your best friends in the business. Those who help you fi nd them after you make them are your well-wishers. And those who never say a word, before or after, are your real mistakes. Make no mistake about that!
In the scientifi c and engineering community of today, we are all becoming increasingly subject to the same level of critical examination and crosschecks as anyone else out there. No longer can we hide behind the mistakes of others, or rant and rail to misdirect attention away from our own mistakes. We must therefore learn to come clean whenever necessary, and also to do that as quickly as possible to avoid any signifi cant fallout from our erroneous actions or advice. For that is what will ultimately drive progress—ours and theirs. We must likewise also start demanding the same standards from everybody associated with the fi eld. No longer should we take shiny fl yers, media presentations, or slick online tools at face value. The bar must be raised, and very soon. Power happens to be so tricky an area that not only are there plenty of honest mistakes abounding (and I make my fair share everyday), but this fi eld also offers plenty of exotic buzzwords, scary equations, and impressivesounding “trade-off claims” to take refuge under—if that’s what you intended. Therefore, even vendors, for example, however high and mighty they may be, need to be subject to the same level of intense scrutiny that we are expecting to fall on ourselves. That is just engineering the way I understand it. If we don’t, I feel the costs will simply proliferate and grow for all concerned. The world is shrinking with every passing day, and in fact we are already deeply connected. Can we really afford to pretend otherwise?
Finally, it is time for me to say goodbye. Three books, you’ll agree, are enough! There just can’t be another one. This book was, therefore, my last chance to tell you some of the stories behind the experiences. I was also hoping to make it interesting and memorable in the process, make you feel like you lived through it yourself. Because that way, I fi gure, you are less likely to ever forget the technical learnings attached to the stories, either. So as I put my pen down once and for all, I thank you for your tremendous support always. I truly hope you not only learn from this book, but also enjoy it—as much as I did while writing it! I expect this one to be considered rather blunt in places, too, but I promised you the truth and this is it.
Chapter 1: Thinking Power
Chapter 2: High-Frequency Effects and the Importance of Input Decoupling
Chapter 3: Output Noise and Filtering
Chapter 4: Using Capacitors Wisely
Chapter 5: Maximizing the Effectiveness of the Ground Plane
Chapter 6: Printed Circuit Board Layout for AC-DC and DC-DC Converters
Chapter 7: Working without a Ground Plane
Chapter 8: Home-Grown Strategies in Troubleshooting
Chapter 9: Effective Bench Work
Chapter 10: Effi ciency Rules
Chapter 11: Magnetics, EMI, and Noise
Chapter 12: Discussion Forums, Datasheets, and Other Real-World Issues
⏩Author: Sanjaya Maniktala
⏩Puplication Date: September 14, 2007
⏩Size: 7.49 MB
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