Last modified: July 2015
Hello all, I have finished my next book dedicated to Fast Analytical Techniques applied to determining linear circuits transfer functions. You will learn how to analyze simple to complex linear circuits by determining the circuit's time constants in different configurations. The idea is to split a complex circuit into small sketches and solve them independently. Then assemble the results to form the complete transfer function. The book is under review and first comments are extremely positive. Each chapter is offering 10 fully-documented problems so that you can check if you have acquired the skill. I hope to have the book published for APEC in March 2016.
Switch-Mode Power Supplies: SPICE Simulations and Practical Designs, second edition is now completed and the book has been sent to the printer. It took me a while to clean all typos, errors and bad drawings that you, readers friends, have been kind enough to report. The final listing for the 1st edition is posted here. So, what do we have in this second edition? Well, some chapters have been expanded, some simply cleaned up. Here we go for the detailed list:
Chapter 1: the complete derivation of all rms currents in CCM or in DCM for the power switch, the inductor, the diode and the input/output capacitors is now fully documented. All formulas have been tested and several Mathcad files will be available on the editor site to let you calculate these data depending on your design. Not only rms currents are calculated, but also the various time durations in DCM for instance. Convenient tables summarize constraints at the end of each subsection.
Chapter 2: on top of the classical PWM gain derivation, a feedforward small-signal block has now been described. The complete small-signal model of the PWM switch operated in current mode has been added and simulated. Duty ratio factories have been described to show how you can get the ac response of a DCM or a CCM current mode converter with a voltage-mode model by adding a single in-line equation to the existing model. Sub-harmonic instabilities are not predicted but low-frequency response for both modes perfectly agrees with that of higher order models. For those interested in small-signal modeling, I added an appendix in which I derive the ac response of a voltage-mode boost converter operated in DCM. You will see that despite previous SSA prediction, DCM converters are still second-order systems whose quality factor is simply much lower than in CCM.
Chapter 3: the compensator section has been expanded with OTA transfer functions for type 1 and 2. A complete TL431 bipolar-based model has now been included in this new edition
Chapter 4: some new SPICE blocks have been described and in particular, a corrected D flip-flop which is now more robust to forbidden input states.
Chapter 5: clean-up of the existing section mainly
Chapter 6: I have included a complete small-signal analysis of a BCM PFC stage when operated in current or voltage mode control. I also added a section letting you predict what the bulk minimum voltage will be when you have selected a normalized capacitor. This is important to know this bulk valley voltage as the converter will have to pass 100% of the power while in this input range.
Chapter 7: this chapter now includes a complete explanation of the over power phenomenon in flyback converters operated in CCM, DCM or in quasi-resonance (QR). Over power protection or OPP, is an important part of the flyback design. It is there to compensate the extra output power (hence current) a flyback converter will deliver when supplied from its highest input voltage. If no precautions are taken, risks of fire or destruction exist. This new section explains the origin of this output power runaway and how to compensate it. Small-signal has not been left aside and a small-signal model of the QR flyback converter in current mode is presented. A section showing how to account for the nonlinear variation of the Coss capacitor has been added as well as a simple laboratory circuit to check for transformer saturation.
Chapter 8: the complete transfer function of the active clamp forward converter operated in voltage mode has been added with step by step derivation as well as tests a against prototype response. Compensation details for a 30-A dc-dc are also offered. The coupled inductor small-signal response has also been revamped thanks to comments from a sharp reader.
There is no CDROM in this new edition, most of the files will now be available on line from the McGraw-Hill site. These files, together with a chapter sample are available through the dedicated landing page, here: http://www.mhprofessional.com/product.php?isbn=0071823468
The book distributors
Comments, feedback and corrections: I keep a correction file in which I compile your findings and comments. The file is here and will be updated when needed.
Designing Control Loops for Linear and Switching Power Supplies: a Tutorial Guide is now available for sale. This new book took me three years of work, every night. It first started in 2009, I wanted to write an exhaustive text on how to design compensators for power supplies. Operational amplifiers (op amps) were first on the list, but I then realized that there was many other types of active elements that could be used to perform this function: TL431, operational transconductance amplifiers (OTA) and shunt regulators like in the TOPSwitch (Power Integrations) series. If literature abounds on op amps, there are few documents on TL431, OTAs and TOPSwitches, but all scattered in application notes sometimes difficult to find. I have dedicated an entire chapter for each of them, even detailing TL431 internals. Of course, there are non-isolated and isolated versions with an optocoupler.
Please check the announcement in different languages (English, French, German, Japanese, Mandarin, Simplified Chinese, Korean and Spanish). Thanks to all my friends world-wide for their kind help! (Bernie, Werner, Ken-san, Kelvin, Patrick, W.S. and Juanito)
You can download the Table of Content here.
The book starts to explain loop control theory in a very basic approach, "with the hands" as we say in French : ) Then, the following chapters go deeper into the theory you need to know as a power supply engineer. There is some mathematical content but there are a lot of examples that show how to put the theory at work. This is a strength of the book to my opinion: it bridges theory that you have learned at school with what you will face in your engineering challenges. For instance, we all learned how to build a compensator with an op amp (I still have my class documents) but how do you apply that knowledge to a TL431, a Transconductance Amplifier or a Shunt Regulator? And what if you add an optocoupler? Throughout the pages, you will learn where phase margin comes from, how to select crossover frequency, how to efficiently compensate a control system and much more! I hope you will enjoy this new work that took me 3 years to write. As usual, almost all the equations were derived by myself with all the steps so that you can follow...and correct me if I am wrong!
Chapter 1: this chapter is an incomplete introduction to control systems. I have tried to gather the very basic things you need to know about control systems and I introduced some of the tools you will need in the following chapters. This chapter is for people who have no notion of control systems at all and want to understand how such a system works. No complex diagrams or difficult equations, a step-by-step introduction. Of course, experts reading this chapter will smile but, again, this brief introduction is not for them, they can jump to chapter 2 immediately : ) Please note that the entire Chapter 1 is offered for download by Artech on its website.
Chapter 2: now we start the discussion about serious stuff. I am showing how to properly write transfer functions. You will discover that a transfer function can be derived in different ways. One of them uses brute-force algebra. The result is analytically correct but when you look at the result, it is almost impossible to say if there is gain, if there are poles and zeros and where they are hide. Re-write the same function the proper way and all these information clearly appear in the equation. Knowing how to write transfer functions this way is the key to fast analytical techniques and so-called low-entropy expressions. Learn how to get the poles and zeros just by looking at the electrical schematic!
Chapter 3: in this chapter, I explain where phase and gain margins come from. At school, I was told that "you need to have at least 45° of phase margin at crossover" and that was it! I never had a clue where this number was coming from and how to apply it. Learn how phase margin is linked to the quality factor of a second-order system. Check how to read these data on Bode but also on Nyquist plots. Learn what modulus and delay margins are. Understand the importance of output impedance and the way to shape it via the right crossover frequency.
Chapter 4: we now enter the world of compensation: how to shape the return path so that my control system be stable, fast and precise. PID configuration are explored and I reveal the link between coefficients and poles/zeros placement. Nothing new here, but this is done step by step so that you can follow the path. A few examples put the PID at work and show that in some cases where Bode says it will be stable, the system isn't. Learn why and how to properly compensate your product.
Chapter 5: this chapter covers compensators using operational amplifiers. You will find type 1, 2 and 3 structures, with and without optocouplers. You have all the equations, ready to use. I even re-wrote the k factor equations for those interested in the approach. All derivations steps are detailed and commented.
Chapter 6: transconductance amplifiers (OTAs) are popular among the IC designers community. They are easy to design and require less die area than they op amp cousins. However, the set of equations you have for op amps does not readily apply. I have re-derived all the design equations in this chapter. Even if you add an optocoupler, it is covered. Also, I explain why it is difficult to build a type 3 with an OTA and what are its limitations.
Chapter 7: the TL431 is the most popular elements found in todays power converters. Hosting a precise reference voltage and an open-collector op amp, it is a remarkably well-crafted device. Actually, op amp and reference make only one and the transistors arrangement was made by a genius designer! Check TL431 internals and learn how to use that component to build type 1, 2 and 3 compensators with an optocoupler.
Chapter 8: TOPSwitches from Power Integrations are very popular high-voltage switchers. Rather than hosting a voltage control input, these devices are sensitive to injected current as a means to control the duty ratio. Again, previous equations no longer fit and I have reworked them all for the classical compensator types.
Chapter 9: bench measurements are mandatory when you deal with control systems. It is important to verify that all hypothesis you made during the design phase lead to the expected phase and gain margins on the real prototype. And a prototype is a real piece of hardware, not a Simplis simulation bench, please! In this chapter, I explain the theory behind closed-loop measurements and where to be careful for reliable measurements. Then follow 5 design examples, putting theory at work.
There is no CDROM with that book but there are available simulation files that correspond to some of the book examples. These examples are simulated with Intusoft IsSpice and their demonstration version will certainly run a few of them. Didier Balocco was kind enough to translate some of these examples in LTSpice. These are beta versions. If you have the time to translate the remaining examples, I will be glad to post them in this webpage.
Yes, I know it for fact, there will be errors and typos in the 1500 equations I derived in this book. The term derived is correct because I really worked almost all these equations myself. First, because doing so let me identify obstacles that I could teach you how to avoid them when you follow my steps. Second, copy/pasting equations or pulling them out of thin air is not my writing style as an engineer. I apologize in advance if you find errors, mistakes or typos in these mathematical expressions. Given their number and despite the care I put in chasing them, this is unavoidable. Please, let me know where these errors are and I will maintain an errata list (1st print, 2nd print), giving credits to people who found these mistakes. Merci d'avance ! (Thanks in advance).
The book distributors:
Artech House offers a coupon to let you order the book from them directly with a 20% discount and free shipping! The flyer is here.
If you want to read my interview by EEWeb, please follow this link. I'm sure some of you will recognize the guy in the wall poster : )
Switch-Mode Power Supplies: SPICE Simulations and Practical Designs was released in 2008. Another book on power electronics you say? Not really. In the technical literature, you either have books that are purely academicals and offer in-depth analysis of converters, unfortunately without the essential links to the market reality. You also have purely practical books that pull equations out of thin air without any theoretical grounds. This book bridges both approaches and will hopefully please the power electronics student and the design engineer, both looking for analytical explanations but also for practical solutions when facing customer demands. This book is really about power supplies designs, with SPICE as a design companion. It covers dc-dc but also ac-dc converters. By the way, the ac-dc conversion in offline converters is made by the diodes bridge and the capacitor, the downstream converter is always a dc-dc, isn't it?
Press release for the book announcement in French, English, German, Mandarin and Japanese!!
(Xiè-xie to Patrick Wang and arigatô gozaimasu to Iguchi-san!)
The book is now available in simplified Chinese and Korean. Thank you to Mr Zhangde Lu who translated the whole book in a record time! Mr Lu is a teacher in Shaoxing university in China. The book is available from Publishing House China and Chinese links are posted below.
The book is organized in eight chapters covering the following subjects:
Chapter 1: this chapter starts with the basics of dc-dc conversion, step by step with linear regulators used to derive essential formulas such as closed-loop impedances or closed-loop input rejection. Then the classical buck, boost, buck-boost are analyzed in CCM/DCM and critical modes until an input filter is added. There, you will discover the effects of the filter insertion and learn how to compensate the converter while still attenuating the input noise (95 pages).
Chapter 2: small-signal modeling is really an important topic if you want to be serious about power supply designs. The chapter starts by showing what State Space Averaging is all about and how complicated it can be. Then, the PWM switch model is introduced and three new versions are derived: auto-toggling DCM/CCM voltage-mode and current-mode models, with sub harmonic prediction in CCM for the later. Of course, these models are large-signal ones and operate in dc, ac and transient analysis. Finally, a borderline model is derived, later used in PFC stages. This 100-page chapter really explains how these models were derived and how to use them for your studies (146 pages).
Chapter 3: loop control is always hard to understand for some new comers. I've strived to make things look simple, explaining how the k factor was derived and showing that, sometimes, it is not a panacea. I propose different equations to let you manually select the poles and zeros, crossing over at the exact desired frequency. Also, in most of the books, only op amps are used to illustrate compensation. In this book, I derived the transfer functions of TL431-based type 2 and 3 compensators and I showed how the optocoupler pole can affect the phase margin (100 pages).
Chapter 4: this is where you will learn how to build your basic subcircuit blocks and how to construct your new models, if necessary. For instance, how to model the error amp of the UC384X family. Understand the differences between syntaxes and learn how to write in-line equations. A section specifically details the derivation of a magnetic model, based on non-linear junctions. See how to wire generic PWM models in various configurations for the best simulation speed. Learn how to extract physical data from a transformer to later pass them to a subcircuit (66 pages).
Chapter 5: in this chapter, we cover the design of dc-dc converters, the classical structures, in both voltage-mode and current mode configurations. There are small-signal analysis and transient studies in all cases The front-end filter section is also analyzed with input ripple specification targets (84 pages).
Chapter 6: rectifying the sinusoidal mains is a section common to all ac-dc converters. After all, the diode bridge and the capacitor are the elements that really perform the ac to dc conversion. The downstream converter is still a dc-dc, no? This chapter covers the classical diode bridge configuration then further introduces passive power factor correction, quickly followed by active power factor correction. The most popular topologies are covered and there are several design examples. An extensive usage of the average models is made here, leading to extremely short simulation times (88 pages).
Chapter 7: it is time to describe the isolated buck-boost also called the flyback converter. This chapter covers a lot of techniques pertinent to the flyback converter, what is the leakage inductor role, how it affects the drain voltage excursion and how you can use its presence in active clamp versions etc. The design section contains useful tricks to limit the converter power capability at high line for instance or to compensate the leakage spike on the auxiliary winding. There are three design examples, among which a multi-output borderline converter using the new BCM average model, also described in the book (160 pages).
Chapter 8: the forward converter is widely used in ATX power supplies (the so-called silver box) where the 2-switch configuration excels in 250 to 400-W applications. The chapter explores the various reset methods and introduces you to multi-output configurations through mag amps, or synchronous rectifiers. A complete design example is proposed at the end of the book (129 pages).
CDROM: the CDROM found with the book contains some of the most popular demonstration versions of currently available simulation softwares. I strived to give away almost all the examples of the book in OrCAD/PSpice and ICAPS/IsSpice formats. Some of the distributed versions also feature examples kindly translated by the software editors themselves. This is the case for uCap, TINA, Multisim, B2 Spice, 5Spice. Other demos include Power 4-5-6, Transim and TopSpice. I updated the Excel file dedicated to the k-factor to which TL431-based configurations have been added.
I purposely created specific application circuits that are not given away with the book. The library I am separately distributing includes the UC384X (UC3842/UC3843/UC3844/UC3845 SPICE models) precisely modeled and implemented in a lot of application examples. The same applies for Power Factor Correction circuits, ready to go on several platforms. The library and application circuits are available in different formats that are Micro Cap, TINA, OrCAD and IsSpice. You can download an application listing to check what is inside these libraries - also available for TINA and Micro Cap - OrCAD or IsSpice. Please drop me a line to my address: firstname.lastname@example.org ("SPICE library" as the subject ) to learn about this package and how to get it. I am currently setting up a distribution network for these files.
I also have participated to the development of a more comprehensive library file with AEi Systems. There are currently more than 200 PWM IC models in this file and you can obtain a detailed quotation and information via this link.
Yes, I know, there is place for more and there are subjects that I did not cover. However, this last book took me three years to finish and I felt I was writing a new never ending story... : ) I therefore kept interesting stuff for a next edition, in a few years from now. For instance, I will show where the phase margin value come from and how to analytically link the crossover frequency and the phase margin to the converter output impedance.
Please, forgive me in advance in case you find errors, mistakes or typos, despite all the efforts in trapping them, there might still be some left, even further to thorough corrections ran by numerous reviewers. I have maintained a list of collected remarks, with credits to authors that have found them! The corrections file for the first edition is here, compiling all errors and mistakes previously published.
The US IEEE Power Electronic Society has reviewed my book and published its comments in the PELS April newsletter.
An article has been published in Power Electronics Designs, written by Dr. Ray Ridley and published in the April 08 issue.
A review from Design/Analysis Consultants, Inc. where the book is recommended!
An excerpt has been published online in Power Management Design line.
The book appears in the "Best Power Supply Design Books" directory in SMPSTech webpage
Dr. Yan-Fei Liu from Queen's University (Canada) published a review in the Canadian section of IEEE.
The book was one of the best sales for technical books at ISSCC Conference 2009. Read this excerpt.
The book has been reviewed by Dennis Feucht in the EN Genius Network site. You can find the link here.
The book distributors:
There are several reviews you can read in the Amazon US website to learn about the book acceptance by engineers.
Presentations and papers to download
APEC 2015, 3-hour professional seminar held in Charlotte, NC, C. Basso: this presentation capitalizes on what has been discussed during previous seminars and bridges theory with practical results. For instance, what is the impact of an op amp slew-rate and GBW product on phase margin for instance? How to ensure clean start-up sequences on isolated dc-dc converters? These are among the few topics I tackled during the session. Again, thank you all for attending!
Small Signal Modeling of the Boost Converter Operated in CM, C. Basso: this seminar shows how to derive the control-to-output transfer function of the boost converter operated in peak current mode control.
Active Clamp Forward in Current Mode, C. Basso: this short PPT shows the ac simulation results I was able to obtain with my voltage-mode model to which a duty ratio factory was added. Results are not far from what Simplis predicts.
Duty Ratio Factory Modeling in a CCM CM Buck Converter, C. Basso: this presentation shows how to independently model the control voltage Vc to duty ratio D block in a current mode converter. The presentation shows that by using a voltage mode stage to which a separately-modeled Vc-to-D is added, you obtain the complete control-to-output transfer function of the CCM CM buck converter.
APEC 2014, 3-hour professional seminar held in Fort Worth, TX, C. Basso: this presentation shows the PWM switch models at work in various converter structures. Fixed switching frequency in voltage and current mode is described but borderline conduction mode is also demonstrated. This presentation also introduces the small-signal model of the active clamp forward converter operated in voltage mode control. The model is then compared to bench measurements. The audience peaked to 150 people during the show, thank you all for attending!
Presentation skills, C. Basso: I have been teaching and speaking in front of an audience for a while now. My first speech, which goes back 20 years, was a complete disaster: trembling voice, shaky legs and so on. I made the obvious mistakes untrained people do and with time, I started to improve by learning from professionals. I also took several presentation skills classes (Decker training was excellent) and I improved over years. At least I hope I did : ) For those who need to present, I compiled most of the mistakes you must avoid to make your speech efficient and credible. I have one in French as well.
Small-signal analysis of the fixed current mode variable frequency flyback converter, C. Basso: this presentation teaches you how to derive the transfer function of a flyback converter operated in constant peak current while switching frequency is controlled. This technique is now widely used in converters implementing frequency foldback in light-load conditions.
APEC 2013, 3-hour professional seminar held in Long Beach, CA, C. Basso: this presentation teaches step by step how to derive large and small-signal models of switching converters. The presentation starts by showing how to linearize non-linear equations and then describes models for voltage-mode and current-mode CCM/DCM converters. It extensively makes usage of the PWM switch model. A model of a QR flyback model is also presented. Merci to my friend Chris Warin for kindly taking the below pictures!
Introduction by Mrs Chen, chairman of the conference Agenda of what I am about to present There we go, the audience peaked to 200 people which is very rewarding, thank you all!
Genuine type 2 compensator with the TL431, C. Basso: this short document shows you that a real type 2 built with a TL431 and involving two lanes is not wired as a type 2 with an op amp: a single capacitor is enough across the TL431. Adding an extra RC is useless.
APEC 2012, 3-hour professional seminar held in Orlando, FL, C. Basso: this presentation teaches you some less known aspects of loop control theory applied to switching and linear converters. Things like delay margins, modulus margin or how a PID converts to a type 3 compensator. They were in this new seminar entitled "The Dark Side of Loop Control Theory".
This is me, together with Franki Poon from the PowerEsim website!
APEC 2011, 3-hour professional seminar held in Fort Worth, TX, C. Basso: this presentation teaches you the untaught aspects of the flyback converter. Things like Over Power Protection (OPP) or Quasi-Resonant small-signal compensation are rarely included in seminars. They were in this one, entitled "The Dark Side of Flyback Converters".
These are the covered subjects in the 3-hour time. The RHPZ presence in both CCM and DCM was explained to the students.
Calculating the bulk capacitor parameters in an offline converter, C. Basso: this paper updates the current book content by improving the formulas used to derive the bulk capacitor value in a front-end rectifying section. Nothing spectacular here but I realized that these results could help the design community to calculate the right value.
APEC 2010, 3-hour professional seminar held in Palm Springs, CA, C. Basso: this presentation teaches you how to design compensators based on TL431, op amps or OTAs. This seminar associated with that of 2009 represent the subject of my new book on loop control.
This is me, teaching how to derive the full analysis equations for a type 2 compensator with an op amp. There were more than 100 students in the room.
An average model for the phase shifted converter, C. Basso: this document shows how I built an auto-toggling average model for the phase shifted converter. The model exists in IsSpice but also in PSpice. Both average and generic cycle-by-cycle models are available in ready-to-use templates describing a 12-V/25-A power converter. They are part of the distributed library files.
APEC 2009, 3-hour professional seminar held in Washington DC, C. Basso: this presentation teaches you where phase margin and crossover frequency come from and guides through the stabilization process of a dc-dc converter.
I am on the left, on the ON Semiconductor booth at APEC 2009. The other fellow is my friend Larry Jenck.
Dealing with low-current optocouplers, C. Basso: this is an article I wrote in 2009 that describes how an optocoupler works and why you should always characterize its inherent pole. A method is offered to extract it quickly through a simple test fixture.
The TL431 in loop control, C. Basso: the TL431 is never studied as a part of the compensator in control theory books. However, this is a market reality, op amps are rarely used! Go through this new series of articles and learn how the TL431 works and how you can use it in a variety of configurations.
Selecting the cross-over frequency in relationship to the converter output impedance, C. Basso: this paper teaches how the cross-over frequency affects the output impedance of the converter you want to stabilize.
The link between the open-loop phase margin and the closed-loop quality coefficient , C. Basso: this paper explains the relationship between the open-loop phase margin you select and the resulting transient response you can obtain.
The PWM switch operated in Borderline Conduction, current-mode, C. Basso: this paper shows how to get the small-signal model of a flyback converter operated in the so-called quasi-resonant mode.
The RHPZ, a two-way control path, C. Basso: the Right-Half-Plane-Zero plagues the flyback or the boost converters operated in CCM. This paper explores the origins of the RHPZ.
Stability Analysis in multiple loop systems, S. Conseil, N. Cyr, C. Basso: a TL431 combines a fast and a slow lane. How to measure the total loop gain combining both lanes is the object of this paper.
"The PWM switch in transitioning models": this document was presented in PCIM 2005 and covers the history of SPICE models.
"The PWM switch concept...", PCIM 2005: this is the paper published in the PCIM proceedings.
"the forward converter small-signal gains": a short PowerPoint which shows how my new models match calculations in both VM and CM for a forward converter.
New models to download
TL431 models discussion: an interesting discussion on the TL431 and the performance of several available models.
New LTSpice models: Didier Balocco has come up with a new series of LTSpice circuits implementing the PWM Switch model in voltage and current modes. There are plenty of examples plus a quick installation guide. The files are here. Merci Didier !
LTSpice models: Charles Denton has been kind enough to translate the PWM switch models in LTSpice. Yes, it is obvious, you need a good book to understand how to use them... ;-)
It has been reported that parameter "K" could be mixed by LTSpice with the Boltzman constant. To avoid this, please change "K" into "Kf" and it should work. Kindly pointed out by Dennis in March 2015.
VerilogA models: the PWM switch model working in VerilogA, nicely translated by Nico Cyr from ON Semi.
VerilogA models: the PWM switch model working in VerilogA, a new model contributed by Rainer Krenzke from Dialog Semiconductor.
Flyback current-mode automated calculation spreadsheet: this is a new automated software which calculates the TL431 elements to stabilize of a flyback converter operated in peak current mode control. The software includes mode transition, sub harmonic poles and optocoupler pole contribution. Check it out!
Switch Mode Power Supply Cookbook - download files
SPICE editors links
SPICE sites and power supply sites:
YouSPICE : a community for electronic design and simulation.
EE Web : an electronics forum where technical people answer technical questions.
PowerEsim : if you want to design your power supply online, this is the link to follow.
How2Power : a site maintained by David Morrison, former PET editor, which deals with power electronics
About SPICE.com: a site dedicated to SPICE users worldwide with news etc.
LTSpice group users: the user group of Linear Technology free SPICE simulator, LTSpice
AEi Systems: a consulting engineering firm on SPICE modeling and worse case analysis
Design/Analysis Consultants: a consulting firm specialized in worst-case analysis and design robustness
Power Electronics links with papers to download
Order PCB: a marketplace where engineer and board houses connect and collaborate to create the world's newest ideas a one-stop-shop for board ordering.
Xploreengineering: a useful site gathering a lot of interesting links to personal and professional pages in electronics and other engineering fields.
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