This is a simple circuit which can provide an adjustable voltage source of 0 to 330 Volt. The supply is short-ciruit proof. the current is limited to about 100mA.
TR1 is a 1:1 mains transformer; it is included for safety.
The mains voltage from TR1 is rectified with bridge D1 (1Amp / 500V) and large elcap C1.
T1 is switched as a source follower: the source of T1 will follow the voltage of the wiper of R3. D2 is included to protect the gate of T1; although in theory not necessary I strongly recommend to include it!
T2 and shunt resistor R2 build the current limiter. When the output current becomes too high, T2 will discharge the gate of T1. This will prevent the current to become too high. The value of R3 has been determined experimentally; it depends also on the Hfe of T2 so you may need to tune the value of R2.
Note that T1 needs a large heatsink: in worst case T1 will dissipate 330V x 100mA = 33Watt! Instead of a BUZ 326 (400V/10.5Amp) you can also use an IRF740 (400V/10Amp). The output impedance of the power supply is determined by the beta of T1, so the larger the MOSFET the lower the output impedance!
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