I want n 12V 1A supply for a project. I want a transformer-less topology.

I was reading and experimenting with readily available traic based dimmers. They use phase control to cut the input voltage to a load. So I thought it might be used to provide a stepped down voltage.

Here's what I have done so far:

  • Connected a simple dimmer to the phase line, set it to minimum (which is about 20% I guess), rectified it and connected a filtering capacitor to the positive and negative terminals of the bridge. The output voltage was still 220v.
  • Next, I connected a 10k resistor to the between the positive and negative terminals. The voltage dropped significantly.

Now, the the output voltage was dependant on two things.

  1. The output voltage increased as I increased the phase from the dimmer which was as expected.
  2. The output voltage also depended in the load resistor. If I increase the load resistor, the output voltage increased. Now, this was something that I think will cause problems depending on the type of load I connect in the future.

The scope of the project is not just limited to the 12W requirement. Ih I can convert 220vac to 30vdc, then I can connect a buck-converter to this and use it as a variable power supply.

Please help me complete this.

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  • 3
    \$\begingroup\$ Why does everyone seem to want a transformerless everything? It is inappropriate and dangerous for use in a bench supply. \$\endgroup\$ – DKNguyen Jul 19 '19 at 14:54
  • \$\begingroup\$ @DKNguyen Because they haven't found a local shop making transformers and they think they cost a fortune. \$\endgroup\$ – Marko Buršič Jul 19 '19 at 15:27
  • 2
    \$\begingroup\$ Your circuit is showing mains earth symbols for the DC side. Since your neutral is earthed at the supply you will have a short-circuit between the top of the bridge and the left corner of it as soon as the top line goes negative. The rectifier will be smoke. The circuit has no mains isolation. It's just a bad idea. Nobody does it this way. \$\endgroup\$ – Transistor Jul 19 '19 at 18:26
  • \$\begingroup\$ Like DKNguyen and Transistor said this is dangerous. Standard safety requirements (for example UL requirements) typically require transformer isolation from the mains. For your own safety, don't do this. For academic purposes only, this approach probably wouldn't work well anyway because of the triacs. A triac is typically very tricky to control with a reactive load, and dimmers are typically designed to work well with light bulbs and nothing else. Your capacitor will likely mess things up, and your idea won't really work without the capacitor. \$\endgroup\$ – Mr. Snrub Jul 19 '19 at 20:02

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