Short version: if I needed to drive a MOSFET from mains AC, that will be switching (PWMing) mains AC as well, and needed to do this "fast and often"* how should I derive the power to drive it's gate from the same mains AC?
- Fast = turning the MOSFET on or off as fast as it allows = sourcing/sinking as much current to/from gate as is it reasonable = 1+ amp per mosfet (IRF830).
- Often = PWM frequency of in the range of 20-30kHz.
Long version: I am making a kind of sine wave dimmer for incandescent bulbs and for this I need to drive two MOSFETs (gates and sources tied together) that will PWM-switch mains AC. Everything will be packed tightly in a closed box, so I figured that switching MOSFETs on/off as fast as possible should keep them as cool as possible. I also thought I must use gate driver because my attiny (PWM source) cannot source/sink as much current as the MOSFETs are ready to accept. The only power supply that I got is mains AC and I need to step it down to ~12V to drive the gates and provide reasonable current so I can switch them "fast and often" in 20-30 kHz.
Initially I was thinking about capacitive PSU, but all schematics that I've seen were for very low currents. I didn't take chances designing my own, as I wasn't sure if it is feasible at all (for much higher currents that is).
Then I tried it with SR087, but the 100ma that it provides wasn't enough.
Now I am thinking of getting a open-PCB-type SMPS that gives me 500ma and use it to drive the gates. Something like this, for example. What I am not sure, is can I connect it's ground to the rectified ground from mains AC. I suppose I could, as the SMPS output is floating, but I guess there's only one way to find out. Here's a rough diagram:
It does not include optoisolated UART to attiny and filters that I have yet to figure out how to design. And 1k gate resistor is not neccesary 1k, I'll try to keep is as low as possible with the final choice of gate drive PSU.
Or is there any other way to drive MOSFETs from mains AC @10V+ and at least several hundreds of miliamps?
Thanks a lot in advance!
General info: I have very basic and limited knowledge in electronics and circuit design and no formal education. I do, however, understand all the risks associated with mains AC and take it with a healthy level of paranoia.