I have this schematic, which works well, using 9vac to a voltage doubler then rectification and +/- dc regulators:
http://psionicmedia.net/lyle/music/schem-detail.gif (http://psionicmedia.net/lyle/music/schem-detail.gif)
My question is, is there any way to get +/- 18vdc from a regulated 18vdc supply to feed into the positive and negative regulators, so I wouldn't have to use the 9vac supply?
QuoteMy question is, is there any way to get +/- 18vdc from a regulated 18vdc supply to feed into the positive and negative regulators, so I wouldn't have to use the 9vac supply?
Sure. With power supplies, as long as the power is available, there's always a way to change it around. But you may not like what you have to do to get there.
If you have DC that you want to convert, you either regulate it down (doesn't apply here) or chop it to AC and then do what you will.
In this case, the simplest way is to do what a charge pump converter chip does - fill up a cap with +18Vdc, then clamp the cap's + end to ground. The - end gets pushed to -18V, and that can then charge a cap on the negative side.
But you have to make an oscillator that does this, and then drive power devices to charge and pass the cap. The 7660/MAX1024, etc. do this automatically, but they're limited to under 10V in. There may be a chip that goes to 20V input. You'd have to look.
The other way is to charge up an inductor from the +18V supply, then to let it discharge to the - supply, a flyback voltage inverter. You'd have to arrange to regulate that. The CP converter makes whatever you put in.