I'm currently designing a product that will have a PIC running of
four 1.5V penlight cells.   There is also a 12bit A/D and pressure sensor
on the circuit which both demands very accurate 5V supply.

This sounds like a fairly simple problem to solve, but I would still
be interested to hear how other people would tackle the same problem.
The full  requirements to be met are:

1. Stable 5V supply over the entire battery life
2.  Software ON/OFF control of the supply voltage
3. Automatic wake up of the micro every 10 minutes or so.

I was planning to use a MAX860 to double the voltage and then just
use a low dropout fixed 5V regulator like the LM2936-5 to regulate it
down to 5V.  My circuit only draws about 20mA, so the efficiency of
the MAX860 should be more than 90%.   The MAX860 also provides a
shutdown function, which should make it possible for the micro to shut
down its own supply.

How do the rest of you guys out there that makes battery operated
equipment ensure a solid 5V over the entire life of the batteries?
Is this proposed method that I want to use an acceptable way of doing
this, or is there a better way to skin the cat?

Another question : What is the best way to switch the 5V supply to
other parts of the circuit.   I suppose it would be a MOSFET, but
what I really want to know is the part number of a good general
purpose MOSFET that is widely available.  Every time I try to order
one from my databook, I get told that I need to buy a minimum of
10 000 and that it would take 8 weeks to deliver.  This is very
frustrating when you only need a couple for prototyping.  Where do
you guys get your MOSFETS from?  (Especially you fellow South
Africans)


Rgds
Werner
FOR SALE: Parachute. Only used once, never opened, small stain.

--
Werner Terreblanche     http://users.iafrica.com/w/we/wernerte/index.htm
wterreb@plessey.co.za (work)  OR  wernerte@iafrica.com  (home)
Plessey SA, PO Box 30451,Tokai 7966, Cape Town, South Africa
or at home : Suite 251, PostNet X5061, Stellenbosch, 7599
Tel +27 21 7102251  Fax +27 21 7102886  Home +27 21 8872196
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