By Syed Tahmid Mahbub, EDAboard.com forum member

SMPS is the toughest section in power electronics. For this subject, you require additional knowledge for choosing the active and passive parts used in SMPS circuits. The special type of parts often required in power electronics (i.e. for low-frequency applications) may not be suitable in the case of SMPS.

When I started learning power electronics, I emphasized SMPS. But there was little information around SMPS where I lived. I had to find everything piecemeal — knowledge, literature, active and passive parts, testing equipment, etc. And there was also no engineering university in my country that taught SMPS in detail.

So, my father chalked out a deliberate and detailed plan for my SMPS education:

Detail step-by-step for learning SMPS at home

✓ 1 – Collecting knowledge by collecting required books from abroad.
✓ 2 – Surfing internet for SMPS related knowledge.
✓ 3 – Collecting test equipment.
✓ 4 – Collecting minimum required parts.
✓ 5 – Learning and collecting different types of ferrite cores and learning about winding of ferrite cores in different topologies.
✓ 6 – Learning PCB making software and making PCBs.
✓ 7 – Collecting and practicing SMPS in hardware and in simulation software.
✓ 8 – Testing the test circuits on Vero board.
✓ 9 – Assembling the circuits on PCB and testing in detail.
✓ 10 – Finding out drawbacks and making necessary corrections.

Accordingly, I collected a lot of books related to SMPS. My first book on power electronics and SMPS was, “Power Electronics Demystified” by Chandra Shekhar Roy. That is a very good book for starters.

Some of the important books I collected are as follows:
Power Supply Cookbook, by Marty Brown
Practical Switching Power Supply Design by 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, 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 my oscilloscope, were purchased locally. For initial test circuits, I collected good quality parts. But one thing was very irritating. Whenever I made a test circuit, the capacitors occasionally leaked and were destroyed. With a lot of effort, I found that in high-frequency circuits, you do not use normal capacitors. You use low ESR type capacitors instead. How did I discover which capacitors were low ESR? I procured an  ESR meter from abroad and with that meter and was able to find low ESR capacitors locally. The same thing happened with normal diodes. I eventually discovered that for high-frequency SMPS circuits, you must use ultrafast or Schottky diodes and not the normal diodes.

The next problem was with the ferrite core. I could not find ferrite cores locally. After a lot of searching, a found a few ETD39-type ferrite cores made by Chinese manufacturers which were available as spares for flyback transformers used in Chinese non-branded television sets available in the local market. I purchased some, unwound and split them into 2 parts, and rewound the bobbin by hand to use in test circuits. Initially, I faced a problem as those cores had a big air gap because they were meant for flyback topology and could not be used in an optimum way in other topologies where an air gap is not required. Another challenge was the wire size requirements for different frequencies. To overcome that, I  learned about the phenomenon of the “Skin Effect” in high-frequency circuits.

Another challenge was the wire size requirements for different frequencies. To overcome that, I  learned about the phenomenon of the “Skin Effect” in high-frequency circuits. With the passage of time, I learned about different type of cores — like EE, EC, EI, ETD, Toroidal — and their applications in different SMPS topologies. To buy the required active and passive parts for SMPS circuits, I had to study those in detail and did so over hundreds of hours spent reading books and surfing the Internet, going through forum content, reading datasheets, and more. After acquiring the bare minimum knowledge, it became easier to find required parts for test circuits from home and abroad.

I could not manage any useful software for SMPS hardware simulation. In order to make a PCB, I learned and used PROTEUS ARES software. I required only a a few pieces for each test circuit, so professional PCB makers were usually unwilling to make my PCB. Therefore, I learned online how to make a PCB and started at home with Ferric Chloride, sticker paper, a laser printer, and an iron.

Almost everything was sorted out but one crucial thing remained. Professional transformer winders locally were not acquainted with ferrite core winding and, therefore, 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 three years, I made almost 300 circuits in different stages. Although almost all of those circuits were unsuccessful for different reasons, I learned valuable practical lessons from those failures. By correcting those drawbacks and learning lessons from them, I am now confident. And, by applying my acquired knowledge of SMPS with a microcontroller, I began building some successful circuits of practical value.

Reading SMPS books is like reading novels. I love it and, to me, making SMPS circuits is like playing games. Learning SMPS is quite difficult but with passion, patience, hard work, dedication, and relentless effort, you can do it.

I hope the narrations of my difficult journey in the SMPS world is useful for those of you new to SMPS.

 

About the author
A native of Dhaka, Bangladesh, Syed Tahmid Mahbub completed his Bachelor’s degree from Cornell University, majoring in Electrical and Computer Engineering. His primary interests in electronics are embedded systems, power systems, and analog circuits. Outside of work, he keeps himself busy with projects involving microcontrollers, robotics and power systems, and writing on his blog www.tahmidmc.blogspot.com. Beyond electronics, he loves watching soccer and cricket. He also played cricket for the Cornell University club cricket team. Tahmid is a hardware engineer at Apple and has been an active member on EDAboard.com for almost 10 years.