# Bipolar switched-mode power supply

I'm looking to design a power supply that, given 24V input, can deliver +/- 0-12V output at 3A. It will be used to drive a Peltier module in either heating or cooling mode, which is why it must be bipolar. Here's an example of a commercial device that does this (but I don't know what circuit they used).

Is there a specific circuit that is known to be good for this application? Can/should I just feed the output of a standard buck converter into an H-bridge to allow inverting the voltage?

• How many units per year? Or is this just a one-off? Also, can you afford any overhead voltage? (In other words, can it be $\pm\:0-10\:\text{V}$ instead?)
– jonk
Oct 2 '18 at 19:07
• Why build what you can buy for $25 USD? In a small PCB mount package as well. – user105652 Oct 2 '18 at 21:13 • @jonk about 200 units per year, and +/- 0-10V should be fine also Oct 3 '18 at 1:07 • @Sparky256 i'm not sure what you're referring to? I'd be happy to buy something for$25. The one i linked is 256 CHF ~= $250 Oct 3 '18 at 1:09 • @zplizzi. Could not find an exact match. Best was Digikey +/- 12V at 2.5A for$100. To keep cost down look for an "open-frame" style instead of PCB mnt.
– user105652
Oct 3 '18 at 2:05

Go with a commercial IC. TI and (what was) Linear do controllers for TECs. Search for application notes. Easy, have development boards and PCB layouts. And they are small.

• Do they have ones that heat as well as cool? Oct 3 '18 at 16:29
• This chip is kinda pricey but looks like it would do the job! Oct 3 '18 at 21:20
• @zplizzi I used this before, works well and you don't use all your brain power reinventing the wheel. Oct 14 '18 at 11:08

I assume by your willingness to use an H-bridge that the Peltier device is electrically isolated; i.e. you don't have to have one end grounded.

If you know how to implement the slow H bridge that may be easiest. Beware of strange switchover distortion effects if you're trying to go from heating to cooling (or visa versa) on the fly.

In theory, the most direct, least-component way to do it would be to drive that H bridge with a suitable pair of PWMs, and either control the output voltage or limit the duty cycles such that you stay within 12V. But it'd probably have to be a BIG Peltier module for that to make sense.

If they're still made, an analog-input class D amplifier chip would work.

• PWM may be ok for OP's application, but it is not the best way to drive peltiers. Oct 2 '18 at 21:30
• I was leaving the choice of the obligatory inductors as an exercise for the reader. Really. Honest. Oct 2 '18 at 23:57
• By slow H bridge do you mean slow decay mode as described here? Oct 3 '18 at 1:23
• @TimWescott I believe you. The problem is efficiency, which is the biggest fly in the ointment for novices using peltiers. An adjustable current supply works best. Possibly controlled by a PID loop. ;-D Oct 3 '18 at 16:10
• @evildemonic: Yes -- I think a buck running through a slow H bridge would be best, unless there are Peltier controller chips that heat as well as cool. Oct 3 '18 at 16:28