[sdiy] multiple dc from a single ac supply

[Jim Patchell]

    Voltage doubling is OK for certain applications.  I have used it myself.
The problem is that the more current drain, the bigger the caps need to be, so,
generally, voltage doubling is really only viable where low currents are
involved.  For a little box that is very limited in what it has in it, this is a
great solution.  However, to power your modular, it is not.

    -Jim

Lincoln Fong wrote:

> While looking inside a broken Alesis Midiverb 3 yesterday I noticed that
> from a single 9V ac wallwart (probably no more than 500mA) they had produced
> plus/minus 12V dc reg (just for the audio I presume) as well as 5V regulated
> driving all the logic and 3X  7 segment LED displays. The highest DC voltage
> I measured was nearly 20V unregulated! I guess by voltage doubling and cap
> isolation. Why don't people use these methods more often? It seems sensible.
>
> Having said that can anyone point me to a schematic? The power is fine but
> all the LEDs/displays are dead and it phuts on the output.
>
> Lincoln