2.5V Lithium 'AA' sized batteries: Where to find?

Eric Smith eric at brouhaha.com
Sun Mar 6 13:43:07 CST 2005

Joe wrote:
> Then why don't you squeeze in a LDO 5 regulator and install two standard
> 3 volt Lithium batteries?

Unlike normal linear regulators, LDOs are very finicky.  They are picky
about both the value and the ESR of their filter capacitors, and the
requirements vary considerably between different LDOs.  They not only
have maximum ESR requirements, they have minimums as well!  Pay very
close attention to the data sheet.

I recommend not using LDOs unless you're really experienced with these
issues, and even then you can still sometimes run into trouble.

For running 5V circuits from a pair of 3V lithium batteries, you
might be better off just using a normal silicon diode in series,
for a nominal 0.7V drop.  However, the voltage drop decreases at
low currents, so this may not be adequate for a low power circuit.

That said, I've had pretty good results with the National Semiconductor
LM1117 LDO regulator when used in accordance with the design guidelines
in its data sheet.  They are available in TO220 and various SMT packages,
with fixed or adjustable voltage, are fairly inexpensive, and are
available from Digikey.



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