Gavin-
    If this is for a one-off you might consider a monolithic DC-DC converter
such as a Power Convertibles HPR118. This is spec'd to drop 24V to 5V and is
all in a nice convenient, potted package suitable for breadboarding. Just
supply 24V and out comes 5V. It is not, if I remember correctly, regulated
however. And you might run into some minimum load requirements (page 2 of my
datasheet shows 8 mA.) But once you start looking at this option you might
find others along the same lines from different companies. It will save you
a lot of effort in magnetics design. Not cheap though!
    Another idea- National Semiconductor 'simple switcher' family. I've got
a 'pitch pack' from them which includes the entire supply (one 8 pin SO, two
caps, a low profile inductor, and a diode) all on a convenient PCboard. Part
# is LM2594M-5.0.
    Yet another idea- For such a low current, you might be able to get away
with a hefty charge pump IC. Maxim has a selection I believe.

    For all the ideas: be sure and pay good attention to power supply
decoupling whenever you *intentionally* start imposing high frequency noise
on your supply lines.

Brian

-----Original Message-----
From: Gavin Jackson <vulcan@IHUG.CO.NZ>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Friday, March 13, 1998 6:43 PM
Subject: Power Supply


>Hi there
>
>I'm looking for a DC-DC converter that can
>step 24V down to 5V. It's for a PIC I have
>onboard a boat. It only needs to be able
>to supply 5mA max and have as few
>external components as possible.
>I have a zener, but that's just using
>too much batter power.
>
>I've been looking at the MAXIM IC's but I
>can't find any that will do, although I'm
>sure I've seen one before.
>
>Please suggest any that you may used
>before.
>
>Regards
>
>Gavin
>--------------------------
>vulcan@ihug.co.nz
>http://www.geocities.com/TheTropics/Cabana/2625
>--------------------------