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Nowadays, finding high voltage semiconductors is very easy and can be done at any electronic component shop. The components in use are very standard, the diodes being 1N4007, and the MOSFETs in the differential amplifier can be any HV low power MOSFETs like FQN1N60CTA. The NPN transistor is BC550 and the Power MOSFET is an IRF840 for instance. Basically you can use whatever components you want as long as they have a maximum voltage rating of no less than 400V. You should prepare the power MOSFET to dissipate around 15W in worst case scenario, with a sufficient heatsink to draw away the heat. A little tip. I strongly recommend the output capacitor, not to provide ripple rejection, but to provide local power supply when using it to supply class B amps, as they tend to have an average current rating of less than twice the peak rating, and we can't have the power supply sagging as the current limiter kicks in at every ,,attack''. The capacitor will provide the needed current for the short duration of the spike and the voltage will remain stable. Some of the specs are:
- Input Voltage - varies according to the transformer you have. Must be somewhere between 320-370V after rectification, and mustn't fall below 305-310V at full output loading.
- Output Voltage - 150V - 300V
- Output current - Average 90mA with the current limiter. Should be able to handle spikes of up to a few hundres mA (when testing class B amps for instance)
- Efficiency - Typical for linear regulators. Check the web for reference.
- Ripple suppression - Very good at -50dB. It shouldn't have more than a few mV of ripple at the output
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