Thanks to all that replied, here is some more information:

This thing runs from six AA batteries. From this I need to generate
+3.3V, +5V,
+1.8V, +2.7V, and + /- 18V.

At the moment, every voltage is generated from the 3.3V supply. The +5V
is
'stepped up' from the 3.3V, and the +1.8V and +2.7V are generated by
small
linear regulators.

The reason everything is generated from the 3.3V was to get the 'most'
out of the
batteries. Since I have logged a discharge curve of the AA batteries, I
have noticed
that the time difference between the drop-out voltage of a 5V regulator
and a 3V
regulator is negligable, so I guess it might make more sense to generate
all the
voltages from the 5V supply. What do you think? Battery life is an
important issue.

On the subject of low noise, then really the answer is as low as
possible, as the
+ / - 18V has to be generated from the six AA batteries, and so has to
be some
sort of switcher.

Thanks for your comments

Graham


> On Mon, 18 Mar 2002, Graham North wrote:
>
> > Hi all,
> >
> > I need a +/- 18 Volt supply to power some Analogue circuitry, but I
> am
> > having difficulty finding DC to DC converters to generate the
> voltages
> > from a 3.3 Volt supply.
> >
> > As this is going to supply Analogue circuitry the outputs need to be
> > super clean, ultra low noise and well regulated. Oh and it would be
> > great if it was really efficient too!
> >
> > Does anyone have any recommendations?
> >
> > Thanks alot,
> >
> > Graham North
> >
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