I tried out Russell's circuit, mainly out of curiosity.  It works quite
well, but aside from the novelty, I did not need a method to light an LED
from a single cell.  But it *is* interesting...

The best LED drive seems to be to connect the LED from the output to the
supply, as Russell mentioned.  Also, since NPN's are typically faster than
PNP's, I reversed the topology and achieved faster switching times. This
improves efficiency slightly and I think allows for higher voltages to be
produced.

So if you have a handful of old alkaline batteries sitting around waiting
to be disposed of, you can squeeze every last electron out them and have a
bunch of blinking LEDs decorating your lab in the dark.

In practical terms, aside from LED's, there is a good use for this circuit.
 There have been several requests on the piclist for power supply circuits
so if you want one to play with, this is a good one as it is very low power
and won't likely let out the magic smoke from inside the parts.  And it's a
lot safer than, say, offline switchers.

Finally, if one needs to power up a pic circuit from a single cell (key fob
transmitter, rtc, etc.), you could do a lot worse than to try this out.
With the led removed, it's not too hard to get 5 or 6 volts out of it. And
since pic's can be made to run down to around 3 volts, it should do nicely
to power them.

Tom M.

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads