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  1. I'm aware of that, yes. I guess i'll just make some tests, try to re-design it, and if it turns out all wrong, i can always put some voltage regulator for regulator part, while pre-regulation will take care of power transistor. I didn't intend to go so high, but i made a mistake when ordering toroid and now i'm stuck with too high voltage, and i don't want to waste 225 VA toroid... Thanks for your help!
  2. pre-regulation will be switching type, with mosfet, so no dissipation will be on that part (schematic was published in elektor magazine years ago, i already tested it and works great). I'll put 65V to opamps, while collector of power NPN will be via this switching pre-regulator. I know i'll have to recalculate some parts, especially some resistors, i think. I just wondered if you ever tried it with such high voltage. After all, that's why i've got OPA445. I tried with MC34074 and other schematic (which works for years with Ucc 30V and LM324), but they are not precise enough, since i couldn't get voltage less than 3-4 volts.
  3. OH, i forgot to mention that i'll be using pre-regulation circuit, so input will be appr. 5-7 V higher than output
  4. I intend to replace transistors Q2 and Q4 with single TIP142, which is darlington type. I hope it's OK? Should this still work flawless? I've got OPA445 opamps and with transformer 45V i'll have input voltage of 65V, and i'll set max. output to 50V. i'll use AVR instead of potentiometer for voltage control. is there anything else i should be carefull about (except all parts must be for such high voltage, of course)?
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