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i want to limit the current through a MOSFET (high side) as simple as possible. The MOSFET will switch 600V and approx. 150mA for 1-2 seconds. The focus really lies on simplicity. I know that i can control the drain-souce current through gate voltage. But is this reliable?

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  • \$\begingroup\$ you'll want a floating high side control circuit to bring the gate from 600V to ~585V or whatever seems reasonable for your Vgs threshold of the MOSFET you use. \$\endgroup\$ – KyranF Nov 13 '15 at 18:56
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    \$\begingroup\$ DESAT circuit for MOSFET/IGBT \$\endgroup\$ – Marko Buršič Nov 13 '15 at 18:59
  • \$\begingroup\$ See electronics.stackexchange.com/questions/94185/… which is closely related to Marko's answer. \$\endgroup\$ – Fizz Nov 13 '15 at 19:17
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    \$\begingroup\$ If you are trying to build a current source, just use a simple current source circuit with a sense resistor and BJT. Mind you, if the output is short circuited, the MOSFET wil experience 600V * .15A = 90 Watts for 1-2 seconds. Make sure that either can't happen or doesn't blow it up. \$\endgroup\$ – mkeith Nov 13 '15 at 19:24
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    \$\begingroup\$ The newer power mosfets are not so good in analog mode due to current crowding which can lead to hotspotting and device failure despite calculated junction temp being well within acceptable limits .This horrible effect is worse at high voltages .You could consider series connected devices or a simple buck convertor. \$\endgroup\$ – Autistic Nov 13 '15 at 20:12
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Here is my basic idea. Please note that I don't normally design high voltage or high power electronics. And I am not even sure the OP is using PMOS. So just let this be a point of discussion rather than an endorsed solution. Note that dissipation in R4 needs to be considered. Also, @Autistic made that comment about hot-spotting.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Might need some tweaks. I get 174mA when I simulate that. \$\endgroup\$ – Fizz Nov 13 '15 at 22:35
  • \$\begingroup\$ Thank you for the suggestion. I need to clarify myself: I want to discharge a capacitor. The actual design is a MOSFET with a resistor. My idea was to drop the resistor and limit the maximum current. However, it seems that a current limiting with a MOSFET is way more complex than simply putting a resistor behind it. \$\endgroup\$ – BertBaker Nov 13 '15 at 22:56
  • \$\begingroup\$ Don't give up yet. Draining a cap with a current source will probably bring the voltage down more quickly. Is there some reason why you can't put the circuit on the low side? \$\endgroup\$ – mkeith Nov 13 '15 at 23:14
  • \$\begingroup\$ @mkeith .Have you managed to buy 600V P channel mosfets? \$\endgroup\$ – Autistic May 5 '17 at 11:07
  • \$\begingroup\$ @Autistic, no, I have not. \$\endgroup\$ – mkeith May 6 '17 at 3:40
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You might not be able to source a p-channel MOSFET easily. You can invert that whole circuit and use a n-channel FET (and an NPN). The calculations would be approximately the same.

Note that at 600 V and 150 mA for 1-2 s, that's a power of 90 W, or about 135 J. Be sure your FET can handle that.

600 V, 150 mA 1-2 s corresponds to a capacitor of C=I.T/V = 375 uF. Is that correct ?

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