Electrical – How to build the simplest 12V 2A switching power supply


The problem:
I need to learn to build the simplest switching mode power supply. If I succeed, I hope I'll be able to work my way up and make more advanced SMPSs for other applications.

I did my research:
I've been searching everywhere for a tutorial on how to build a simple switching mode power supply, however, the tutorials and solutions I found look super complicated for me. So far I have looked at a few articles and have used the PI Expert and the Power Stage Designer Tool (from Texas Instruments) to get familiar with designing the circuit. I know how an SMPS works, but I'm afraid I need to learn how to set up the "switching" part (i.e. how to set up the IC that is in charge of controlling the MOSFETs).

My Stash:
Includes 5-PC-power-supplies worth of scavenged components, and I was wondering if I can actually build a smaller PCB that only outputs 12V 2A.

The applications:
The simplest one is that I need to supply constant 12V to two fans, mounted on the heatsinks of two 50W LEDs, which are powered by a 100W LED driver. Linear regulation isn't a good idea for obvious reasons.

I would appreciate any help.

Best Answer

First things first - a SMPS is not a simple circuit, and they just get more and more sophisticated. So one option you have is to start with a toy implementation with an inductor, a BJT, a capacitor and a microcontroller to drive the BJT. You wont get 2A out of it on your first go, and you'll probably fry a few BJTs, but you'll learn a lot.

But if you're keen on building something useful, then you need to pick an IC. It's hard to find much simpler than TI's Simple Switcher series. The LMZ14202H would probably meet your needs.

Both the inductor and the switcher are integrated, so you only have to concentrate on the feedback circuit. Follow their application notes very carefully and you should have something running fairly quickly. The LMZ14202H only comes in an SMD package though, so you'll probably want to get a 0.05" breakout board too for prototyping.

Trying to re-use components from existing power supplies is unlikely to be a fruitful path - those components are likely to be quite specialised, chosen to suit a specific design, and reverse-engineering a commercial power supply design is harder than building one from scratch.