Look, in this circuit (
http://www.oocities.org/tjacodesign/300vsup/300vsup.html ) current is limited by T2, and in particular by the value of R2.
The rough formula for current limit in this circuit is:
I[limit] = U(be) / R2
Where:
Ube = Ube(T2) = 0.65V
R2 = (here) 3R3 = 3.3ohm
Just remember one thing: the power MOSFET has to be mounted on a decent heatsink, and another hint – you may try two, three (or even more) MOSFETS connected in parallel, as they behave like “controlled” resistors.
And another thing, with a load the unregulated voltage across R3 will drop and that means that the output voltage will also drop, so the regulation is not very good.
Here you may try to add, say, 50kohm resistor on top of the 500kohm pot and add 250V Zener diode in parallel with 500kohm pot. That will stabilize the reference voltage that is then divided and delivered to the gate(s) of the power MOSFET(s).
:wink:
IanP