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The most prominent features are:
- Current limiting - since I'll be using a vacuum tube rectifier i have to limit the current to 90mA so that's the 8ohm resistor at the output. Decreasing it will increase the current, but beware at 90mA and full voltage drop the MOSFET will dissipate around 30W
- Voltage regulation - the input filtering may not be critically dampened but the rising output is delayed by the 100nF capacitor so the ringing will not be present at the output, and the voltage drop will be lower. The 100nF capacitor is directly responsible for the output ripple. At 100nF the ripple is 1mV, and at 470nF the ripple is less than 500uV. Don't increase it too much, because the output will lag when varied.
- Rough and fine control of the output voltage.
Tips:
- The 330ohm resistor should be 2W but since the coil will have around 150ohm active resistance itself, you can go with 150ohm resistor at 1W.
- All other resistors and potentiometers can be 1/2 or even 1/4W.
- All capacitors should be 450V
- The MOSFET can be either IRF740, which will be cutting it close to the maximum voltage rating, or it can be 7N60 just to be sure. The BJT can be whatever you like. BC550 for instance. The diodes - 1N4007
- Mount the MOSFET on sufficiently large heatsink, especially if you plan on using it at lower voltages.
The Major Disadvantage is that the output will kneel under loading, because there is no zener to fixate the output. Anyway a slight adjustment on the voltage through the fine control will suffice
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