piclist 1999\02\10\115943a >
Thread: battery/wall xfmr switching
face BY : Mark Willis email (remove spam text)

erik wrote:
> Hello,
> I'm finishing up my first (?real?) PIC project. A chess clock. I'd like
> to power it with either a 9V battery or a little wall transformer.
> I'm guessing there is an IC out there to switch between supplies. Or
> maybe there is some other trivial way to do this.
> Any help would be much appreciated.
> Thanks,
> Erik

 One way would be to use diode "Or"-ing (use a power supply that has
over 9V output - which would include most 9V wall warts!) - Common
cathodes, an anode to +9V and +WallWartIn, and the system picks the
higher voltage automagically.  Cheap, too.  (Do lose a diode drop's
worth of power - an FET or BJT circuit might be better if switching
between 2 battery sources.)  One project used this with a bridge
rectifier they had scads of, as a reverse voltage protection/spike
protector (connect the common anodes to ground, though Battery & Wall
Wart then need to share grounds.)  "Think Devious" <G>


<36C1BAA4.F37B27D4@nwlink.com> 7bit

See also: www.piclist.com/techref/power/batterys.htm?key=battery
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