DC selector circuit

[dist]

I wanna build a DC selector circuit for the powersupply part of my pedals. A circuit that selects the highest of two Vsources. Battery and adaptor. So that if the V from the adaptor drops lower than V from the battery it switches to battery psu.

This would be usefull for several reasons. I can use DC jacks without the battery switch, and, if the adaptor fails, the pedal will run on its battery, whitout having to unplug the adaptor.

Most likely there is lots of info on this on the www, but as my English suck, and i don't know the right terminology for this type of circuit i have no clue of what to search for?

Anyone have Any info that might help me find some info I'd be very gratefull

[Andre]

You could use something like this:



But  you will need some additional power switch to prevent battery drainage when you unplug the power supply and don't use your pedals.
Excuse for the bad dwawing.

André

EDIT: already added the power switch

[Sir H C]

Often done with "diode ORing".  Just have a diode from both supplies to the DC in on the pedal, and whichever voltage is higher will have that diode conducting.  If they are about the same, both will conduct though.

[dist]

Thanks. Il di some thinking.

[Paul Perry (Frostwave)]

If you are doing the two diode thing, note that you lose .6V or so in the diode drop, or .3 with schottky diodes.
The good thing is, you won't damage the battery, because the current can't run back into it.