Learning SMPS the hard way

Learning SMPS the hard way

  December 22, 2012    Tahmid

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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.

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I edited this article from the article I had previously posted on www.edaboard.com on 17-02-12 - http://www.edaboard.com/entry1444.html .