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

Joe wrote: 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. http://www.national.com/pf/LM/LM1117.html Eric