Overview

Understanding the fundamental operation of switching power supplies is an introduction into the dark arts of engineering. On paper, they are no more than the introductory college courses of electronics, but when you add in the parasitic behaviors of the components, then the challenge becomes much greater. For me, it is exciting.

I remember the first switching power supply I ever attempted. It was a 30-kHz flyback supply. I designed the control section using an NE556 and wound my own transformer on an MPP torroid core. When I powered it up, I made a shocking discovery. I had made a wonderful 3-MHz, AM modulated RF transmitter. At which I said, "Oh my (fill in your preferred deity). I need to do a lot more learning."

To do a thorough design and analysis of a switching power supply you will need a new set of instruments, such as: oscilloscope voltage and current probes, a spectrum analyzer and a network analyzer. Welcome to a world where few engineers have ventured.

Switchmode power supplies first became practical in the 1970s, where one used improvised control circuits, bipolar transistors and slow diodes. They operated at less than 50 kHz. The first power MOSFETs emerged in the late 1970s. They were easier to drive and switched much faster than bipolar transistors. This allowed the switchmode power supplies to now exceed 100 kHz and even go as high as 300 500 kHz. Today, with the much improved diode performances, better magnetic materials, resonant techniques, and...