Sorry,

The analogue circuitry doesn't need +5V, but is is used elsewhere! Doh!

Graham

> -----Original Message-----
> From: Graham North [SMTP:grahamnorth@CASTLEGROUP.CO.UK]
> Sent: Wednesday, March 20, 2002 10:55 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [ee]: +/-18 Volt Supply
>
> Oh, and now I don't need the +5V, he is going to use the +3.3V
> instead.
>
> So thats: +3.3V, +1.8V, +2.7V and + / - 18V from six AA batteries
> in series (~9V).
>
> Graham
>
> > -----Original Message-----
> > From: Dave Dilatush [SMTP:dilatush@COMCAST.NET]
> > Sent: Tuesday, March 19, 2002 10:49 PM
> > To:   PICLIST@MITVMA.MIT.EDU
> > Subject:      Re: [ee]: +/-18 Volt Supply
> >
> > Graham North wrote...
> >
> > >This is a hand held device, and thus space is tight so a custom
> > >transformer is out of the question i'm afraid.
> >
> > Hmmm.  OK, but a custom transformer need not be any bigger than
> > whatever off-the-shelf inductor or transformer you would have to
> > use anyway.  I've had custom transformers done that measured
> > barely 1 cm. on a side.
> >
> > >Ok, the noise. I will be measuring AC signals in the 10's of mV's
> > >range (I think) from a precision microphone.
> >
> > Ahhh.  This may not be so bad, after all.
> >
> > Switching regulator controller chips have been tending toward
> > higher and higher operating frequencies over the last several
> > years, largely propelled by the huge market for small handheld
> > devices like cellphones, PDAs and digital cameras.  Whereas
> > switching frequencies in the 20-50 KHz range were common five to
> > ten years ago, frequencies of several hundred KHz to well over a
> > MHz are common now.
> >
> > This means that if you're processing signals in the audio band,
> > or at least not too much above it, you might not have much
> > difficulty keeping your switching regulator from unduly
> > interfering with the analog stuff, with no more than reasonably
> > aggressive filtering.
> >
> > >I must admit that I am
> > >not designing the analogue circuitry, so will contact the person
> who
> > >is and ask how much (or little) noise he would like to see on the
> > >supplies.
> >
> > This offers the opportunity to change this problem from a Type A
> > Problem to a Type B Problem.  A Type A Problem is "your" problem,
> > whereas a Type B Problem is "the other guy's" problem.  In other
> > words, instead of asking him what he would like to see, tell him
> > what he's going to get--and let him deal with it.
> >
> > I'm being flippant, of course, but there is an element of
> > reasonableness in this: there are things he can no doubt do in
> > his analog subsystem that will make it less susceptible to
> > interference from your switcher, and he should be willing to work
> > with you on a compromise that will leave neither of you with an
> > impossible design task.
> >
> > Dave
> >
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