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How do I regulate the output coming from a 50V transformer? At the filter's output, the transformer has 50*1.4142=70.7 volts. But this voltage of course drops as a load is applied, since the filter capacitor doesn't get a chance to charge fully.

70 volts is still manageable, as there are devices able to work at that voltage. But what if I want to do 60V DC. 80 V DC? Things start getting complicated there.

I think a 3-pin regulator is no longer suited for this. Probably a discrete zener diode + power transistor would work, but the regulation is not as good as a 3-pin device. Though, I don't mind this, as this is the supply for a closed-loop audio amplifier, which has good PSRR.

What if I wanted to do this with a buck converter? I'm familiar with the TPS40061. This device works with inputs 10 to 55V. Can a device like this be used with an auxiliary power supply, and regulate higher voltages?

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    \$\begingroup\$ Why not use a transformer with multiple secondaries so that you can get a voltage to drive a control chip for the switcher? \$\endgroup\$ – Ignacio Vazquez-Abrams Sep 8 '14 at 1:10
  • \$\begingroup\$ @IgnacioVazquez-Abrams well, that's one of my ideas but I haven't found a chip that states explicitly that it will woork with an auxiliary supply. \$\endgroup\$ – hjf Sep 8 '14 at 1:40
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    \$\begingroup\$ You probably won't. Use something like a TL494. \$\endgroup\$ – Ignacio Vazquez-Abrams Sep 8 '14 at 1:45
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You can use a controller chip rather than a one-chip regulator.

Edit: For example, the NCP1034

You can use a boutique high voltage switching regulator chip such as the LTC3639, or a similarly 'special' high voltage linear regulator such as a TL783 (if the power requirements are minimal).

You could make a pre-regulator/voltage limiter with discrete parts.

You may be able to use an off-line style flyback regulator with a DC input (be careful the UVLO circuitry does not interfere with your relatively low input voltage requirement). Or use an isolated off-line supply directly.

If you're after a regulator for a high power audio amplifier (50V+ implies hundreds of watts output) you could use this impressively expensive and sophisticated boutique chip (LT8705). 80V max in and buck/boost. 71V is a bit too close for comfort to 80V but maybe you could get a lower voltage transformer since it's a buck-boost regulator.

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  • \$\begingroup\$ Interesting parts. I like that word, boutique, to describe Linear parts. I usually steer clear from LT as they're ridiculousy expensive for "general" usage. I think the controller alternative would be the best. I still have to find one that explicitly says you can use an external (auxiliary) supply to power it. \$\endgroup\$ – hjf Sep 8 '14 at 3:56
  • \$\begingroup\$ Not an aux supply type, but see edit above. \$\endgroup\$ – Spehro Pefhany Sep 8 '14 at 4:21

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