V G wrote:
> I'm looking to build a simple, battery powered power supply for
> prototyping which provides multiple outputs, like -18V, -12V, -5V,
> -3.3V, 0V, 3.3V, 5V, 12V, 18V.

Do you really need all that?  It sounds like gross overkill.

Nowadays, circuits use negative supplies less than they used to.  Digital i=
s
all 0-3.3 or 0-5 volts.  About the only reason for a negative supply I have
had in recent years is so that the common mode range of opamps can go to
ground without weird effects and still have some output drive left too.
Usually a simple charge pump is good enough for this.

If this is just for bench testing, then you don't really need it to run fro=
m
batteries and it doesn't need to be all that efficient.  Having it isolated
is a good idea, but that can be achieved with even a dumb 60Hz tranformer
wall wart.

Whether you use batteries or a wall wart for power, it sounds like
efficiency isn't that big a deal.  You can make a switcher that regulates t=
o
one B-E drop above a 5V LDO.  That gives you a rough 5.6V and a clean 5.0V
supply.  Then linearly regulate the 5.6V down to 3.3V.  Anything that
produces regular pulses can run a charge pump to make about -2.4V.  This ca=
n
even be the Fosc/4 output of many PICs.

That would give you regulated 5.6, 5.0, 3.3, and -2.4 volts, which is going
to cover the vast majority of circuits you will likely want to mess with.
You still have the original raw battery or wall wart voltage for things tha=
t
need power.

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