I agree that its wasteful to use a linear regulator to run your pic on 5
volts especially with the LDO consideration. Also the efficiency close
to 50% if using a 9 volt battery. Wasteful! Three AA's work sufficiently
but not in all cases. Bulky too.

I just stumbled on some really nifty SMR's (switched mode regulators) in
smt and dips. The MAXIM MAX761 and MAX738A.
http://pdfserv.maxim-ic.com/arpdf/MAX761-MAX762.pdf
http://pdfserv.maxim-ic.com/arpdf/MAX1684-MAX1685.pdf

Also the Linear Tech devices are also a good choice.
http://www.linear-tech.com/prod/prod_home.html?product_family=power

With efficiency between 92% and 96%, this may be a reasonable
alternative. Quiescent currents about 150ua and shutdown about 1ua. The
only drawback is the possibility of noise generated by the switcher and
the higher parts count.

One nice thing is that most of them will take voltages from 3 to 16+
volts to achieve a 5 volt output.

I will be throwing together some prototypes to see if they will meet my
needs and post my results here if I feel there may be some interest. My
goal is something that won't exceed the real estate of a TO220 pkg, and
continue to squeeze all I can get out of a dying battery.

Rick

Matt Pobursky wrote:

> Yeah, that was just an "off the top of my head" suggestion as I'd
> used that family of parts in the past. I believe that Maxim has
> some LDO's that use significantly less quiescent current. Toko
> would also be a good source to explore. As I recall, the reason
> we used the T.I. part was that the Iq was not a problem (we were
> shutting down the regulator and when it was running the load
> current was ~20mA, so the Iq was a negligible percent) and it was
> cheaper than anything else available at the time.
>
> There are some very good parts out there these days specifically
> targetted at extending battery life. I'll bet you can find a good
> one that will fit your operating current requirements. Good luck
> in your search.
>
> Matt Pobursky
> Maximum Performance Systems
>
> On Thu, 21 Feb 2002 08:43:41 +1300, Paul Gaastra wrote:
> >
> >I liked Matt Pobursky's
> >suggestion of that TI TPS7250 low drop out regulator except that
> >its quiescent current is 180uA.  My circuit draws 290uA on
> >average so I think the two diodes would waste less energy
> >(haven't done the sums).  I see that it has a 0.5uA sleep state
> >so maybe I could work out something
> >there.
>
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