Saturday, December 22, 2012

Learning SMPS the hard way

SMPS is the toughest section in Power Electronics. Tremendous knowledge is required for choosing active and passive parts for use in SMPS circuits. Special parts are often required specifically for use in SMPS. Many components that can be used for low frequency applications in Power Electronics may fail if used in SMPS circuits.

When I started learning Power electronics in 2008, I placed emphasis on SMPS. Regarding SMPS, nothing was available here. I had to collect and gain everything piecemeal- knowledge, literature, active and passive parts, testing equipment etc. The main drawback was the lack of knowledge in this field. In my country, SMPS is not taught in detail in any engineering university. So, teachers are not readily available. Additionally, relevant books were also not available.

So, my father chalked out a deliberate and detailed plan for me to learn SMPS:

Detailed Plan for learning SMPS at home

Step 1   – Collecting knowledge by collecting required books from abroad.
Step 2   – Gathering SMPS related knowledge from internet.
Step 3   – Collecting test equipment.
Step 4   – Collecting minimum required parts.
Step 5   – Learning and collecting different types of Ferrite Cores and knowing in detail regarding winding of Ferrite Cores in different Topologies.
Step 6   – Learning how to design PCBs using design software and making the PCBs.
Step 7   – Collecting and practicing SMPS in hardware and in simulation software.
Step 8   – Testing the test circuits on verroboard.
Step 9   – Assembling the circuits on PCB and testing in detail.
Step 10 – Finding drawbacks and making necessary corrections.

Accordingly, I collected numerous SMPS-related books.

The first book with which I started to learn SMPS was “Power Electronics Demystified” by Chandra Shekhar Roy, which was collected from Kolkata, India. For beginners it is a very good book.

These are some of the important books I collected:

  • Power Supply Cookbook -- Marty Brown.
  • Practical Switching Power Supply Design -- Marty Brown.
  • Power Sources and Supplies -- Marty Brown editor.
  • Switching Power Supply Design -- Abraham I Pressmen.
  • High Frequency Switching Power Supplies-Theory and Design -- George Chryssis.
  • Demystifying Switching Power Supplies -- Raymond A. Mack,Jr.
  • Practical Design of Power Supplies -- Ron Lenk.
  • Regulated Power Supplies -- Irving M. Gottleb.
  • Switching Converters Medium and High-power -- Dorin O Neacsu.
  • Principles and Elements of Power electronics -- Barry William
  • Switch mode Power Converters Design & Analysis -- Keng C Wu.
  • Switch mode Power Supply Handbook -- Keith H. Billings.
  • Power Electronics Handbook – Industrial Electronics Series -- Edited by Timothy L. Skvarinina of Purdue University.
  • Power Mosfets –Theory and Application -- Duncan A Grant and John Gower.
  • Digital Power Electronics and Applications -- Fang Lin Luo, Hong Ye, Muhammad Rashid.
  • Switching Power Supplies A to Z -- Sanjaya Maniktala

Most of the test equipment including oscilloscope were collected from the  local market. For initial test circuits, good quality parts were collected. However one very annoying thing was that in the test circuits capacitors occasionally leaked and got destroyed. With a lot of effort, I found that in high frequency circuits, low ESR capacitors are to be used - many of the widely available regular capacitors cannot be used as they have rather high ESR. Now there was a problem. How would I know which capacitors have low ESR and which don't? I procured an ESR meter from Portugal through my aunt who lives in Vienna, Austria. With the help of the ESR meter, low ESR capacitors were collected from local market. Same thing happened with regular rectifier diodes also and I came to know ultimately that for high frequency SMPS circuits, ultrafast or schottky diodes needed to be used instead of the regular rectifier diodes (because of the reverse recovery time).

Next problem was with Ferrite core. In local market, required ferrite cores were not available. After quite a lot of searching, some ETD39 type ferrite cores made by Chinese manufacturers were found. These were available as spares for flyback transformers used in Chinese non-brand television sets available in local market. I collected some, unwound them and split them into 2 halves. I rewound the bobbin by hand to use in test circuits. Initially I faced problems due to the large air gap these cores had (intentionally provided as they were meant for use in flyback topology) and could not be used in an optimum way in other topologies where large air gap is not to be used. Problem was also there regarding use of required size of wire in different frequencies and those problems could be overcome by gaining knowledge regarding the phenomenon of “Skin Effect” in high frequency circuits. With the passage of time, I gathered knowledge regarding different type of cores – like EE, EC, EI, ETD, Toroidal – and their applications in different SMPS topologies and winding speciality. I collected some from China with the help of local suppliers.

To collect the required active and passive parts for SMPS circuits, one has to have detailed knowledge regarding SMPS. I had to work extremely hard to gain sufficient pertinent knowledge, for hundreds of hours had to be spent reading books, surfing net, going through forum contents and reading datasheets, application notes, design tips, etc. After gaining the minimum knowledge required, it became easier to collect required parts for test circuits from home and abroad. One of my aunts lives in USA and I have collected lots of parts from USA through her.

I could not manage any useful software for SMPS hardware simulation. But for making PCB, I learnt and used PROTEUS ARES software. Since I required only a few pieces for each test circuit, professional PCB makers were usually unwilling to make the PCBs. Being in a real dilemma, using the internet, I learnt how to make PCBs and started making them at home with Ferric Chloride, Sticker paper, Laser printer and Iron.

Almost everything was sorted out but one crucial thing remained. Professional transformer winders of the local market were not familiar with Ferrite Core winding and hence I personally had to wind by hand all the transformers for different Topologies with different sizes of wire and also with Litz wire (self-made) in the initial test circuits.

In the first 2 years, for learning about the different stages and sorting out different problems at the different stages of the test circuits, I made almost 300 circuits. Though almost all of these circuits were unsuccessful for different drawbacks, I learnt valuable practical lessons from those failures. By correcting those drawbacks and learning lessons from those, I am now confident and by applying the gathered knowledge of SMPS with microcontroller, I started building some successful circuits of practical value.

I love reading SMPS books like reading novels. Making SMPS circuits is like playing games to me.

Learning SMPS is really difficult but one can learn it with passion, patience, hard work, dedication and relentless effort.

If any beginner in SMPS finds anything useful for his pursuit of learning, my effort of narrating my difficult journey in SMPS world will be worth the trouble.


I edited this article from the article I had previously posted on on 17-02-12 - .


  1. An amazing post. Your story inspires me, and many others, I am sure. I have decided to study SMPS circuits, and I stumbled upon your blog :-)


  2. Thanks.

    I wish you success in your endeavors.

  3. Wow what a effort!!! Thanks a lot for your tutorials they are helpfull and your story reminds me to myself. I also want to write some tutorials when I got my projects really working ! I love smps too. I keep watching for a good explaination about "compensation" I am sure you would be explain it perfect. Great blog!!! Thanks for your efforts Tahmid.

    Best Regards Timur

  4. What a great story. Finally, I found your page. I know about you Tahm1d since back on 2009 or 2010 at s**sivri forum. You have great post over there. But sadly to say, that I cannot join the forum since it is by invitation only. And now, I've found your blog, thanks God.
    Well, I love SMPS like you do. Because good power supply is needed in every electronic device. But, learning SMPS is not quite easy. So, by sharing experience with the expert in SMPS like you, will make my learning eazier.

  5. Tahmid i like to meet with u personally.ur tutorial and explanation method inspire me.i also love to design with mcu based system.right now i try to learn smps design and implementation.but the main problem is that i do need some guide line where to start first.this is may mail id: just knock me and let me know when ur free to meet with will be very helpful for me like a brother u stand side by side with me.

    Dhaka, Bangladesh

    1. I'm sorry. I can't meet you since I'm not in Dhaka anymore. If you need help, you can always find your answer using Google. For SMPS design, I recommend getting some of the books I mentioned and reading through them. That will be most helpful. Start with Marty Brown's "Power Supply Cookbook".

      Feel free to ask if you need help. Good luck!


  6. Very, very impressive, Tahmid, especially at your young age. It's also impressive that you've come so far with the resources you had. In my area (silicon valley, california), surplus electronic parts are plentiful, and I can get many of the parts you had to hunt for (MOSFETs, IGBTs, torroidial cores of any given type ferrite) either cheaply or free. Although I've had some experience with SMPS design in my formal job, I find that there is much I can learn from you, and will be visiting again.

    You write well, so I think you should collect your knowledge of SMPS into a book, and get it published!

  7. Hi
    i want to know that if you have build a fly-back topology based SMPS,which runs from 230V AC or any topology the voltage over mosfet will be higher than 300V and most oscilloscopes can measure up to 300V with standard probe. so do you use some differential probe or you estimate mosfet voltage by calculation .and never required to check voltage over mosfet.

    1. A lot of oscilloscopes have a 10:1 probe that can be used to detect higher voltages. The one I had at home (and it wasn't even a great oscilloscope) could read more than 500V easily.


  8. Hello Tahmid, your work is really impressive! You have really inspired me. I started learning electronics about a year ago and I have a real passion for it. I rarely go a day without learning something new. Anyway, did you learn most (85%) of what you know from the books you listed? I am buying them one by one because I really admire what you have accomplished. Do you think by the time I finish reading and understanding all the content in those books, I'll be in position to do what (or at least most) of what you have done? Do I need a lot of prior knowledge in electronics, or do the books pick up from nothing. I know all about DC passive circuits (chapter 1 of all about circuits), most of AC circuits from the same site, most chapter 3 (semi conductors), and I'm currently reading chapter 4 (Digital) circuits. I recently made a simple analog charge controller for a 6 volt 4.5 amp hour battery.
    Do you thin what I know is enough to get me started on reading the books?
    Thanks for you time, have a nice day.

    1. I've learnt most of my SMPS from those books. If you finish reading them all and understand the content, you can probably do more than I can. There are a lot of difficult concepts in SMPS. I don't even understand some of those. However, if you understand most of it, and are willing to learn from practical experience (read: loads of mistakes, circuits going wrong, MOSFETs and drivers blowing up, etc) and learn from your mistakes, you'll make good progress quick.

      You do need prior knowledge in electronics. Grab some basic electronics books and start reading them as well - it might be better to do that before delving into SMPS.

      Feel free to ask if you have any more questions. Good luck!


  9. Hi
    thank you for your reply, can you give some good idea how to remove core from a transformer,if we get a transformer from a old pc power supply and want to re wind it. because it has glue or warnish over it due to which its not possible to easily remove core.

  10. hi tahmid
    we are designing flyback converter with following parameter:
    input voltage:230V
    output voltage:5v
    switch MOSFET:IRFP250N
    Diode: Fast Recovery Diode B860
    transformer: primary turns:88
    secondary turns:2
    problem is that switch or transformer get heated when we apply voltage above 90(at that time current is 0.95A).
    we intechange secondary terminal also.
    Increase Frequancy up to 120Khz to avoid core saturation.
    but nothing improvement.
    can you please help?
    My email ID is

  11. hello tahmid,

    I have designed a non inverting buck boost converter.
    I am having a problem with the snubber circuit. Can you post about the RCD turn off snubber circuits to supress the transients?
    I would really appreciate if u do.

    thank you in advance

  12. hi
    i have a general question when you make any power supply ,when you run it you directly apply it with 220V AC or you use some variable power source for first time ,and how do you keep noticing the temperature of mosfets is by some thermo-camera or just by touching it.
    Best Regards

    1. It's better to test on a current limited source first if possible to prevent damage. Unfortunately, I did not have a current limited high voltage power supply which is why I could not do that. So I just connected it to 220VAC with protection (fuses, current protection, etc).

      For the MOSFETs, I turn power supply off, let capacitors discharge and then feel the temperature.

  13. hello tahmid hope u will be fine. i want to design 22 Waat Led driver circuit which have input 190VAC to 240VAC and output is 20VDC to 40VDC and output current is 580 mA. and power factor is 90%.please tell IC and circuit which is used to design 22Watt LED driver circuit....

  14. Hello Tahmid! good blog, sounds lots of work behind...
    I'm working on a small inverter 200w. push pull bridge can feed 10Amps. But with no load i can reach 300-400Vac @60Khz.
    But I can't keep this voltage when a load is plugged i just can reach 60vac @ 30W...... My core is 2+2 primary 60 secondary.
    Could you tell me what kind of things can be responsible of this loss of power? i feed 8A@12VDC primary and i can just get merely 30W.... primary winding is 3X0.5mm² in parallel. Best regards. B.H@FRA

  15. hi,
    i am working on smps.I want to make 5V,1A using flyback ferrite core transformer. i am using viper22a ic i hope you r knowing that Ic.but the problem is i am not getting exact calculation of primary, auxiliary and secondary windings calculation.its frequancy is 60Khz.

  16. Hello Tahmid,

    This is really very nice blog for beginners....

    Dear All,

    If you require electronics components for SMPS design including Transformers, Inductors, Diodes, ICs then you can order us at (Only for India).
    We also do EMI EMC Consultation for clearing test like CE, RE, EFT, Overvoltage Hi-Pot Test etc...

    Rathy Electronics


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  20. I am trying to make boost converter, please suggest some PWM current ic including soft start up.

  21. what are effect magnetic field (from inductor) on Semiconductor Device such CMOS , Schottky diode , BJT , IGBTetc ?

  22. Yeah! Almost everything was sorted out but one crucial thing remained. Good explanation done for SMPS Power Electronics.

    SMPS Transformer Manufacturer in India | Toroidal transformer in India

  23. Sir
    I want to make a flyback transformer for converting 230v ac into 12v dc.
    please help me to design it.I need an out put current of 2A. I decided to use ee25 ferrite core.

  24. thank for sharing your view.
    there is Some helpful hint to boost your PC Speed.
    1. How to free up disk space.

  25. Nice work mate !

    Perhaps you might take a look at basic working of switch mode power supply. It's nice for those who are getting started.

  26. Nice Post! Good information you shared about SMPS circuits and it is so helpful to me and others also.Thanks for sharing.

    SMPS Transformer Manufacturer in India | Toroidal Transformer in India

  27. Nice Post! Awesome information you shared about special parts are often required specifically for use in SMPS. Thanks for sharing.

    SMPS Transformer Manufacturer in India | Toroidal Transformer in India