03-06-2024, 01:13 PM
I found even with a -48V PSU that "short circuit proof" was tricky. Off the shelf solutions seem only reliable up to about +/- 30V
A series regulator that's short proof with up to 650V or more instant HT across it is possible. There are 200W 1200V FETs. It's not simple.
Also I'll see how useful manual adjustment of FET bias to adjust HT is. Plan B would be a comparator and feedback. But unless using an off the shelf solution oscillation is a risk. Again an open loop "shunt regulator" is simpler than series for HT, because of shorts.
A more complex solution (and now more common) is a low voltage supply and a boost regulator (a similar concept to a Line Output stage). These are conceptually simple and there are controller ICs. You might need a custom inductor and RFI can be an issue. The Cûk version of a SMPSU is easier to filter. I've built one for +90V using a reed switch for on/off. A custom coil on the reed was in series with the filament supply (regulated 1.35V or 6.8V, or D cells). The battery valve sets are so seldom used that replica battery packs make more sense.
This HT PSU is for bench tests, not building into equipment, which would use fixed HT.
A series regulator that's short proof with up to 650V or more instant HT across it is possible. There are 200W 1200V FETs. It's not simple.
Also I'll see how useful manual adjustment of FET bias to adjust HT is. Plan B would be a comparator and feedback. But unless using an off the shelf solution oscillation is a risk. Again an open loop "shunt regulator" is simpler than series for HT, because of shorts.
A more complex solution (and now more common) is a low voltage supply and a boost regulator (a similar concept to a Line Output stage). These are conceptually simple and there are controller ICs. You might need a custom inductor and RFI can be an issue. The Cûk version of a SMPSU is easier to filter. I've built one for +90V using a reed switch for on/off. A custom coil on the reed was in series with the filament supply (regulated 1.35V or 6.8V, or D cells). The battery valve sets are so seldom used that replica battery packs make more sense.
This HT PSU is for bench tests, not building into equipment, which would use fixed HT.
