Designing automatic power source selection circuit. Help.

I'm trying to design a simple, low cost circuit that can automatically select (using logic) a voltage source.

I have a product that has a pic on board along with a battery connector (goes to 5V reg) and a programming port that is also able to supply voltage. The combined sources (for unknown reasons because the reg should be able to handle it) causes the pic to stop functioning.

I'd like to eliminate the problem by having circuitry decide to use the battery only if the programming port voltage is not present. The logic is easy -- the part selection is not. I could definitely use a bit of help here.

Any ideas and advice would be greatly appreciated.


I should have mentioned that this product is fairly old school and uses 9V batteries or a 9V (14V unloaded) wall adapter for the two voltage sources in question.

Re: Designing automatic power source selection circuit. Help

try one of these

Autoswitching Power Mux

https://focus.ti.com/docs/prod/folders/print/tps2113a.html

Re: Designing automatic power source selection circuit. Help

punishermoose said:

I should have mentioned that this product is fairly old school and uses 9V batteries or a 9V (14V unloaded) wall adapter for the two voltage sources in question.

Click to expand...

Can't you simply use 2 Schottky Silicon Diodes? Anode to + of each power supply, cathodes connected together, providing the highest voltage from both sources minus .5V