using mains TX in reverse

I have a small project maybe coming up - to build a one-off specilist PSU. it is actually a microphone power supply. It would need to provide +6VDC, 200VDC and 90VDC.All at low current (a few mA max).

Because it is an audio circuit, keeping in-band noise to a minimum is important. Previous experience with voltage doublers etc has not been great as they do throw out a lot of 50Hz harmonics.

I am thinking about the following approach:

A conventional low voltage supply, say 12V unregulated, with 6V derived from that with a linear regulator.

And then using a pair of sine wave oscillators at, say, 100kHz, 4V rms or so and using their outputs to drive a pair of low power mains isolation transformers operating in reverse. So, say it was a 230V/6V transformer, the 6V winding is driven, at about 4V rms, giving a secondary sine wave at 100kHz, about 160V rms, which is then revtified and smoothed. Then using feedback to control how hard the transformer is driven to regulate the output.

I am thinking that the transformer will be very efficient at HF, using sine waves means no harmonics to get rid of, just filter out the 100kHz fundamental and get nice clean high voltage DC with cheap commonly available components.

Is there any reason not to use a 5 buck mains transformer this way?


thanks

Daniel

Although your principles are correct in practice you may find that the 60Hz transformer will not work very well at 100KHz, the core may have very high losses. You may need to wind your own or get one specifically designed to handle that frequency.

It sounds as if you want to build a flyback converter, if you don't need isolation you may want to wind your own auto-transformer on a toroid core.

Hi John, thank you. Yes, I hadn't considered transformer losses.

Not exactly a flyback converter, as it would use an amplitude controlled sine wave rather than switching, but similar. Indeed, isolation is not important.

I hadn't considered winding inductors, and have never done that before, but will look into it. That would probably be smaller and lighter. Not sure about core materials and winding specification though.

Daniel