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I'm designing an interface PCB for an Advanced Energy Ultravolt E series high voltage power supply, which has a voltage set input and a current monitor output. Because of the possibility of arc discharge/sparking at these voltages, I want to be able to set a current limit. At minimum this would be an overcurrent shutoff, better would be to reduce the output voltage to the level where the current is equal to the current limit.

I immediately thought of the following circuit:

schematic

simulate this circuit – Schematic created using CircuitLab

(note that M1 is effectively inverting, which is why the feedback signal I_monitor goes to the positive input to OA1)

I assume that I could make R2 high resistance or make R3/R2 small to make this stable, but the former makes this slow to respond and the latter makes it less effective as a current limiter (ideal circuit has R3 open). I could also put a capacitor in parallel with R3, giving the same high-frequency roll-off as making R2 large. What would you recommend?

For the overcurrent shutoff, I imagine the same type of circuit with I_set and I_monitor going to a comparator instead of an op amp, so that for overvoltage the voltage set goes to zero instead of attempting to linearly limit the voltage.

Ben G.
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  • As drawn, M1 can become a dead short across the power supply. Regardless of R2 value this will not end well. If Imonitor exceeds Iset (voltages) M1 starts turning on, increasing current drawn from supply. This will not end well. –  Jun 10 '21 at 12:40
  • Please excuse if I drew the diagram unclearly, the + and - pins that I showed connected on the power supply are the voltage control inputs. So if the current on the high voltage side (shown disconnected from load) surpasses I_set, the control voltage should be reduced. – Ben G. Jun 11 '21 at 14:51

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