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I am dealing with a system that requires me to drive a capacitive load at 120V-175Vrms, AC square/sine wave at two frequencies: 50Hz and 2000 Hz @ Ipeak = 100mA. I am currently trying to find the best way to achieve this.

I had originally used a HV driver chip that had a supply of 300V, modulate the output to create a 0-300V square wave, high pass filter it, and finally send it to my load. The issue with it was how I generated my power supply. I had used a voltage doubler + voltage divider to obtain 300V from 120VAC in. As you all know, voltage dividers are terrible for usage a power supply from a variable load.

My next plan was to instead use a high voltage op-amp with square wave input, and configure it like a comparator to create a AC square wave, which would drive my load. The issue is that again the power. Here I tried to implement a SMPS from 12V to 175V, but the problem was the efficiency was terrible and thus I could not find any economical 12V power supplies to adequately drive my load.

So my question to all of you: is there a better way to generate an AC sine/square wave of 120-175Vrms @I=100mA? Or is there easy solutions to the problems I have faced in my implementations?

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  • \$\begingroup\$ Do you have a transformer you could use to step 120VAC up to feed your HV driver? \$\endgroup\$
    – Dave
    Commented Oct 2, 2014 at 19:41
  • \$\begingroup\$ They still make linear supplies that go to 200V @0.1A. Buy a bunch of 48V wall warts and put them in series? Get a 48V supply and step it up. Make a lower voltage and step up the output with a transformer. \$\endgroup\$
    – George Herold
    Commented Oct 2, 2014 at 20:11
  • \$\begingroup\$ Is this a one-off project, or something that you need to be able to produce in quantity? For a one-off, I would just feed the output of a laboratory function generator into a medium-sized (e.g., about 50W) audio power amplifier, and connect its output to a 1:10 power transformer (AKA 12.6 V filament transformer, used in reverse). \$\endgroup\$
    – Dave Tweed
    Commented Oct 2, 2014 at 23:11
  • \$\begingroup\$ @DaveTweed, I do like the output transformer solution. (Keep everything at cheap ~30V. @~1A) But how does a 60Hz AC transformer respond at 2k Hz... I'm guessing there are better and worse. \$\endgroup\$
    – George Herold
    Commented Oct 2, 2014 at 23:46
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    \$\begingroup\$ @GeorgeHerold: It'll be kind of lossy, but remember, transformers with laminated cores are widely used in audio applications (20 Hz - 20 kHz). The better ones will have thinner laminations, of course. If you can liberate a suitable output transformer from an old tube amplifier, it'll probably work somewhat better than a generic power transformer. \$\endgroup\$
    – Dave Tweed
    Commented Oct 3, 2014 at 4:34

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