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Application Notes are Helpful However Power Electronics Has Quirks that Require More In Depth Coverage

In my series of blogs I have been covering power electronics online design tools. In this blog I want to diverge from that topic. I am doing this because power electronics are physical circuits with quirks that result from the parasitics.

When a circuit becomes highly physical and spreads across FR4 real estate, parasitics result. Add in voltage and current switched at high frequency and you have issues. Furthering this mystique is the way in which topologies have their own little hidden nuances such as the right half plane zero and/or the moving zero due to capacitor ESR that changes over temperature along with the capacitance itself. Modelling only goes so far in terms of addressing these anomalies. Similarly, application notes and data sheets might address a specific application yet they fall short of the reality in which some circuits settle into as a result of the space left over in a product after the sexier electronics are implemented. In other words, final products don’t always have the luxury of laying out a circuit like you did. Beyond that, power is mostly custom so design modifications are almost always a part of the game.

So where do you turn for this information? I started by searching for the top power management companies. Then I visited their websites for more information. It was a scary journey as I found some of my material still existed; scary in the fact that I realized how much I’ve forgotten over the years. It was enough to make Curly grimace and say, “Ngraa!”

In terms of relevance, there is a lot of older material that still has an impact today. Even after a graduate stint at Virginia Tech, I find myself still pulling out the old Unitrode material when I want to brush up on topics. It’s getting harder and harder to find buried among the Texas Instruments website however I’m still very grateful for the hard work put in by Lloyd Dixon, Bob Mammano, and Bill Andrecyk. Here’s a somewhat usable directory to this information at Unitrode. I’m not putting TI down here as they have a really good directory on power electronics at http://www.ti.com/lsds/ti/analog/powermanagement/technical-documents.page

Fairchild is another company that addresses the fringe occurrences in power electronics. They have these subjects in terms of presentations at Fairchild Power Seminars as well as a blog on subjects at: Fairchild blogs.

Linear Tech is a power player known for establishing niche areas in upcoming markets. I took the technology route when investigating their offerings and came up with this website from youtube Linear Technology on YouTube. In addition to addressing educational subjects, there are several videos on company history that took me down nostalgia row. After 30 years in this industry I can foresee a future blog on the history of power electronics and how it has evolved.

I’ve touched on a few of the power management companies yet none of them is a “tweener” like Power Integrations. To me a “tweener” is in between a power management IC and a power semiconductor. Power Integrations invented this hybrid product with a guerilla tactic of entering an established market that was overlooking the obvious. Others soon followed. Although it took a bit of tab clicking, I found this website on Design Support to contain some useful information: Power Integrations Design Support.

This blog could go on and on as there are so many solutions out there for power management. But then again, it’s a blog which is supposed to quickly address a subject rather than turn it into a full length report. An industry editor once told me that subjects revolve every eight months based on readership. If you’re company was not addressed here, there will be a future opportunity for exposure. Depending on demand, it may not be eight months.

At the very least, I hope my articles convince Microsoft Word that parasitics is in fact an acceptable spelling in the English language. The red line you continuously put under the word parasitics gives me uncomfortable flashbacks to the grading techniques of my physics professor Dr. Kinsey. That’s not the least of my Bill “Hates”.

18 comments on “Application Notes are Helpful However Power Electronics Has Quirks that Require More In Depth Coverage

  1. Ken.Coffman
    June 2, 2015

    Thanks for the shout out to Fairchild, Scott. To close the loop, as a Fairchild engineer, I too often reach for the Unitrode books when I'm trying to understand something and I really enjoy working with the Untirode/TI team in New Hampshire we hired en masse many years ago. They are very sharp engineers. I vividly remember a conversation I had with Bill Andrecyk while wandering the halls of a hotel in China, he was a character. But, the end of his life was not so positive. May he rest in peace. Wouldn't it be a wonderful world if the duty cycle equation told you everything you needed to know about a converter? Well, maybe not, because the business wouldn't need us. As always, the devil is in the details.

  2. Effective-Technical-Writing dot com
    June 2, 2015

    I'm glad you liked the article Ken.  I encourage others to post useful sites in these responses.  As I said, it could have gone from a blog to a full length report.  Still I hoped some save time navigating the endless wealth of information on power electronics.  I often find myself discovering material that gets me close but not close enough to a solution to my problem.  

    There are so many that contributed to power electronics over the years.  I realized this and wanted to write a blog dedicated to the 30 years I have observed.  I remember when Unitrode first started the roving seminar series.  I was mesmorized by the allure of travelling and presenting material to a point where I became an applications engineer doing just that.  Lloyd Dixon made a comment that he created a lot of material at home while in his bath robe.  That appealed to me over the sentence of a daily commute.  Now here I sit in the Rockies doing just that as deer and elk pass within feet of me.  I'm not done writing about Lloyd.  He wrote a very impactful control loop application note that I will be addressing in a future blog.  There might also be a note on the trials and tribulations of life as an applications engineer.  I could address trying to sell transistors combined with your own company's control ICs while having to team up with competitors in areas where you didn't make controllers.  That's a conflict of interest that resulted in me having to do some 'splainin, Lucy.

  3. mohaankris
    June 3, 2015

    yeah nice article

  4. Scott Elder
    June 3, 2015

    For all but the largest supplies (i.e. >250W), I suspect the requirements for multiple engineers designing great supplies–and writing great app notes–will diminish in much the same way it has for radios.  It seems there is less and less of a need outside of a few companies.

    The most recent wifi and bluetooth chips (RF-another tough design problem) solve about 98% of the RF problem for less than $1.00.  Same thing for high resolution data converters.  I think this is all good and necessary so that the next generation can spend their time working at the next higher level.

    A few great power supply designers will still need to stay behind designing the sub-250W-modules–and reading all those application notes you write about– just like some engineers have to stay behind writing assembly code.

    I've been studying planar power recently and it is amazing how much offline power can be designed inside an area 1/4th the size of an old iphone for a few bucks.  TI has 100,000 customers for their ICs.  How many of those need a Bob-Mamano-Class App note?

    The future power supply appnotes will probably classify power using letters (i.e. Class A module can be powered by a Class Z source and drive 4 Class A4 loads).  There will be no need for the majority of tomorrow's power engineers to understand Volts, Amps, Volt-seconds, or Power in much the same way that today's digital IC designers don't need to know how a transistor works.

    This is all good for those that stay behind and those that are moving electronic design further up the food chain.

     

  5. Effective-Technical-Writing dot com
    June 3, 2015

    Scott,

    Thanks for responding.  The industry is moving more towards canned solutions however, power remains custom in a lot of applications.  In addition, there isn't always board space left to transfer gerbers over from an application note based design.  As for the internet, more and more information appears daily.  This means that there are solutions posted.  Finding them can be a challenge.  Sometimes, more isn't better.  That was the gist of my article.

    As for how many engineers will be searching, I don't really deal in marketing numbers.  That seems to be the theme of your response.  Many companies are assessing the market in order to allocate resources accordingly.  In general, many companies have met their demise when thinking they know what engineers and customers want instead of understanding it.  We won't go into that further other than to focus on the theme of the original blog which was: how do you solve your problem when the physical circuit is implemented?  Like it or not, many engineers still struggle with that.  Many companies could care unless of course the run rate is 10k per month or more.  That's what blogs are for, directing struggling engineers in the absence of applications support.  

    I've heard the argument for the future of standardized power for 30 years and to date, it has failed to materialize.  There are specific applications that phones and processors dictate power solutions for.  However, power remains custom rather than categorized.  So do the engineers.  I remember an application engineer coming in (won't say from which company) and saying, “I only do DC.”  Then his boss said, “We have thee best power engineers.”  hmmmm.  Why are you here then?  You don't have an AC solution yet your engineers know more than I do.  Why am I here then?  The lesson learned here is that addressing the customer's needs is the best option over telling them what they need.

    Scott

  6. Scott Elder
    June 3, 2015

    My comments about your blog were addressing the need for quality, deeper, application notes.  I'm simply remarking that the need is diminishing outside of a few areas.  So doesn't it make sense that fewer people will invest their time in that endeavor?

    At this stage in my career, I always think marketing numbers during a design.  I suppose that's because I work in the integrated world rather than discrete.

    Don't you think though at some point–and again for <250W supplies--that the price point for a module solution will eventually be the only viable (read: reasonable) solution?  Engineers salaries continue to rise, electronics cost continue to fall.  It seems the curves have to cross at some point for all 30-year-old approaches.  Just like with data converters.  Just like with radios.  And just like programming.  What makes sub-250W power so special that it is immune to the ingenuity of tomorrow's engineers to accellerate the crossover I wrote about?

     

  7. Effective-Technical-Writing dot com
    June 3, 2015

    Scott,

    I am very happy with the application notes that are here and now.  Navigating them is the issue.  Finding the information is crucial in this time constrained world.  I was pointing out directories that help you to find this information.  My reference to Unitrode was based on their tendency to explain the entire system rather than be product specific.  It became my own personal comfort zone as I knew I had read it in the past and I knew where to find it.  Furthermore a lot of their material was written back when computer simulations weren't as proficient as today.  Therefore one had to have a feel for the system operation.  Not only did these guys have a feel for it, they were able to put it into words.  

    Application notes have changed with the ability to simulate as well as include graphics and simulations.  Here is an example.  

    In today's application notes, control loops are designed from a derivation of equations that you assume are correct or derive yourself.  Then a Bode plot is presented.  The plot, combined with the derived poles and zeros give you a feel for the system.  The plot however is data driven and asymtotic with rounded corners.  This leaves some ambiguity about the feel for the systems.

    When Dixon wrote “Control Loop Design” (search slup098) he hit a milestone that I've never seen duplicated.  This is because he goes step by step in the design by telling you how each loop contributes to the overall Bode plot.  He includes advice on where to put the poles and zeros as well as commenting about limits of the components including charging the compensation caps or railing the amplifiers.  One of his best contributions are the STRAIGHT LINE Bode plots such as in Figure 4.  Not only does this place the poles and zeros in the right location, it goes a long way to explain how the system goes from a two pole LC based roll off to a single pole load/output cap based system when implementing current mode control.  I know of no other concise, easy to use, complete note than this.  I'm sure it's out there with the many contributions by applications engineers, university people, and wizards such as Ridley, Middlebrook, Erickson, Lee, and the many others who put knowledge into a keyboard. 

    As for my comments on the 10k per month run rate, I've experienced that twice at small companies in the last two months.  That wasn't a barb at how applications support is allocated.  I own my company and understand that you spend the time where the money is.  When I was an applications engineer there was a philosophy about working with the little guy as he someday might be a big guy.  If you don't believe me, all you have to do is look at the retrospec of companies that have come and gone over the last two decades.  Even the disties have to spend time wisely in applications support.  After all, there are only so many hours in the day and you can't boil the ocean.  You can however create impactful, useful, and informative application notes that provide a solution when your engineers aren't available to.  Conference papers don't really do this either as they are more focused on research and explaining things through a series of equations.  Dissertations and thesis (what's the plural for thesis?) may contain this however they are lengthy and somewhat hidden in the search engines.  And as for application notes, they are mainly designed to explain and promote a product.  They often have little references to the problems encountered and solutions imposed however they are not always focussed on a specific subject such as common mode noise or leakage inductance along with the associated havoc.  Some of the websites that I mentioned are focused on that.  One is in presentation format instead of a written report style.  For you aspiring authors, here's a simple method for becoming a writer.  Gather the data, draw the diagrams, create a presentation, fill the presentation with the spoken words that accompany it and wah-lah, you have an application note.    Again my blog was to direct readers to solutions, not to dis app notes.  I used the grand platform of Planet Analog as a method for communicating this to readers.  

    As for my comment on turning subjects every 8 months to get companies exposure, I'd suggest answering these blogs with responses to exposure your directory of power information IN GENERAL TERMS.  Although the responses are void of URLs, references to material that works such as slup098 go a long way with solving problems.  View it as having been screened by a neutral party such as myself who found the information useful and passed it along rather than sent you to a specific, narrowly focused website that commercializes a product.  In addition, there are many key words in this blog and responses that will help you find solutions.  I also mention experts that offer material.  It's like the balance in how an apps engineer spends their time in terms of how to respond.  Don't make it a commercial yet provide valuable information with a key to why it worked to solve your problem.  Give us  clue as to where the good stuff is.

    Scott

  8. joseph6
    June 4, 2015

    Yes buddy i absolutely agree with you !!

  9. upender19
    June 6, 2015

    nice post

  10. lhawrencee
    June 8, 2015

    I am very happy with the application notes that are here and now.  Navigating them is the issue.  Finding the information is crucial in this time constrained world.

  11. ramesh19
    June 8, 2015

    I am very happy with the application notes that are here and now.  Navigating them is the issue.  Finding the information is crucial in this time constrained world.

  12. ramesh19
    June 8, 2015

    I am very happy with the application notes that are here and now.  Navigating them is the issue.  Finding the information is crucial in this time constrained world.

  13. pawan17
    June 8, 2015

    Thanks for the shout out to Fairchild, Scott. To close the loop, as a Fairchild engineer, I too often reach for the Unitrode books when I'm trying to understand something and I really enjoy working with the Untirode/TI team in New Hampshire we hired en masse many years ago. They are very sharp engineers.

  14. ravi369
    June 8, 2015

    I'm glad you liked the article Ken.  I encourage others to post useful sites in these responses.  As I said, it could have gone from a blog to a full length report. 

  15. suriya08
    June 8, 2015

    This is all good for those that stay behind and those that are moving electronic design further up the food chain

  16. sachin002
    June 9, 2015

    Thanks for the shout out to Fairchild, Scott. To close the loop, as a Fairchild engineer, I too often reach for the Unitrode books when I'm trying to understand something and I really enjoy working with the Untirode/TI team in New Hampshire we hired en masse many years ago. They are very sharp engineers.

  17. nithin 78
    June 9, 2015

    I've been studying planar power recently and it is amazing how much offline power can be designed inside an area 1/4th the size of an old iphone for a few bucks

  18. D Feucht
    June 13, 2015

    Scott,

    You're clicking around the edges of one of my hot-buttons regarding power controller ICs. Too many of the specs tell how to use the part but not what it is. My message to power IC makers is

     

    Don't tell me how to use a part until after you tell me what it is !

    Telling me how to use it is fine – this is application data – but only after the part has been adequately specified. I have an article in the making on this so I'll not dwell on it here except to say that critical design parameters for PWM controllers are often not provided because there does not exist within the project or program at the IC company people with a sufficient depth of understanding to know that it should be included. A straightforward s -domain analysis of the outer voltage control loop of PWM ICs often cannot be done without some parameter guessing because design information has been neglected in the specifications.

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