Electronic – Converting universal AC to 3.3v DC @ 0.1A

3.3vacac-dcpower supplyswitch-mode-power-supply

There's a bunch of topics around this but i haven't found something that fits my requirements. I'd imagine this is a fairly common thing though so any pointers would be appreciated

Basically i want to design a circuit that can use mains power anywhere (85-265v AC) and power a simple system with max power consumption of around 100mA.


  • 85-265v AC input
  • 3.3v +-5% DC output
  • 10-100mA current
  • Size as small as possible
  • ~10mV ripple
  • Cheap (less than ~$10)

This is for a networked device and will be totally enclosed (no buttons etc) so i don't think it has to be isolated although it of course wouldn't hurt.

I've looked at existing PCB mount PSUs but the price is a bit too high. Also they can be fairly big (mostly tall) and provide much more current than i really need.
A simple solution with AC -> Transformer -> Diode bridge -> Voltage regulator would probably work but the transformer size becomes very big. Also i'm unclear how this will work with the universal voltage range.
Basically i probably want something similar to the 3rd solution here: https://electronics.stackexchange.com/a/41944/6809

The components from Power Integrations seem to be what i should be looking at but i'm slightly unsure where to start. Also very few of the examples give 3.3v out and usually at a much higher wattage than i need (= i'm thinking i can make something smaller/cheaper as i only need .1 Amp)

Best Answer

A device like the Power Integrations LinkSwitch-TN allows you to implement a simple buck converter that converts rectified mains voltage to a reasonably-well-regulated non-isolated low voltage with reasonably good efficiency.

If you need low ripple after the fact, you can put a linear regulator on the stepped-down output of the buck and minimize your resistive losses.

I've used these as primary-referenced control supplies and have had good success with them.

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