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I really hope someone can help me with this difficult issue:

I want to generate a PWM signal from a 170V DC input.

ok, so far I have an arduino that can generate a PWM signal and drive a MOSFET that is in a Buck converter circuit. Just a coil and capacitor, giving me the voltage I want for my load. This is my main objective, run my load using the 170V DC. I have no found a Buck converter that can take in ~200V DC and also I need a high power. So I have decided to build my own. Everything is working fine, except.... how do I run the arduino? Same issue, I need ~200V down to 5-10V.

So I need a way to generate a PWM signal, with 170~200V dc input.

After reading a bit I found I need to build a triangle wave generator and then use a comparator to get the PWM signal. But how do I build a triangle wave generator or a comparator? And again the issue with the high voltage. Most of the Op-amps (used as comparators) cannot handle high voltages. I do not want this circuit to over heat either and want to keep the power low.

Can I build a simple oscillator circuit that can take high voltages and low power? somehow control its duty cycle?

any help is appreciated. thank you!

enter image description here

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    \$\begingroup\$ Take a look at fully isolated gate drivers, i.e. Si8234. Also, where do you get your 170V from? I hope you're not trying to roll your own off-line power supply. Most off-the-shelf power supplies are also rated to operate with a DC input voltage, by the way. \$\endgroup\$ Dec 23, 2021 at 1:56
  • \$\begingroup\$ can i build my own gate driver? \$\endgroup\$
    – Sander Mez
    Dec 23, 2021 at 1:57
  • \$\begingroup\$ Not really. The closest you'd get is a gate drive transformer but these have a lot of drawbacks. If you can, avoid working with such high voltages. It could be the last thing you'll ever do. \$\endgroup\$ Dec 23, 2021 at 1:59
  • \$\begingroup\$ @SanderMez You can but you probably don't want to for high side drive. An alternative approach to the transformer mentioned by Jonathan is a low side style driver running off an isolated converter with opto coupling. \$\endgroup\$
    – DKNguyen
    Dec 23, 2021 at 1:59
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    \$\begingroup\$ If you can't or won't change the motor, search on offline switching supplies. They take AC at the line voltage, rectify it into something around your design voltage, then convert it down. If you don't want to use something off the shelf, you can at least learn from established techniques -- there's no need to reinvent the wheel. \$\endgroup\$
    – TimWescott
    Dec 23, 2021 at 3:34

2 Answers 2

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"But how do I build a triangle wave generator or a comparator? And again the issue with the high voltage."

High voltage has nothing to do with these parts. These are just timer components to trigger the PWM. You just derive power for them anyway you can. It doesn't matter if it is inefficient because it is so low compared to the overall power. Such as zeners or high-voltage linear regulators (they exist and obviously run hot and can only support several mA). Designs also exist where these are only used to bootstrap the system to get a switching regulator started which then takes over to power the logic.

Feedback is a different story. You do need to use a comparator or opamp with high voltage there. You can step voltages down with a divider for processing. And placing a capacitive divider in parallel with the resistor divider eliminates high frequency phasing.

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Given a high DC voltage, a resistor/capacitor generates a ramp up, and a breakover device (such as a PUT==programmable unijunction transistor) can abruptly switch and pull down, generating the up-and-down phases of a crude triangle wave.

The utility of this in creating a 24V output is small, however; one generally uses 24V when electric shock hazards are to be avoided, and an isolation barrier in addition to voltage transformation is necessary to achieve that goal.

That is because rectified 120 VAC is connected to NEUTRAL and (when rectifiers are conducting) to LINE, while a safe-to-touch system just connects to GROUND (the non-powered pin of the three), or (in "double-insulated" devices) doesn't even connect to that.

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