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Old 4th Aug 2020, 2:50 pm   #98
dave cox
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Join Date: Jan 2009
Location: Bristol, UK.
Posts: 2,059
Default Re: High voltage regulator circuit.

Andy,
Regulation is usually measure against ...
(1) Time - as things warm up from cold and after a change in output voltage (settling time)
(2) Changes to input voltage
(3) Changes in load current (repeated at different output voltages ?)

If you are seeing regulation that is not so good, it would be interesting to know how much the gate voltage is moving so I can try and match it up to the spice model. Obviously, once its hitting the current limit its much less interesting as it is not operating as a regulator!

The startup under load issue you see is typical of a 'foldback' current limit. I think I have set the limits too low in the first design (the spice model tops out at ~100mA @400V and 15mA @ 0V) so as you suggest the values need adjusting

R1, on its own, sets the short circuit current. I think your change is safe, it will give something like 30mA into a short (?) but it's the MOSFET that has to do the heavy lifting, so check you are still in the SOA at the voltage across it (and watch the heat!)

R4/R5 I will need to spice if they don't give a sensible uplift in max current as the voltage goes up (40 years ago I could do it in my head but not now ).

dc
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