Hi,
Living rural we annually have a few grid power cuts. I am planning a power backup system for Arduino fingerprint doorlock and indoor lightning.

When blackout and 3S Lipo-battery backup kicks in for the doorlock, a led strip would light up too not to be left in the dark. Normally led off.

This could easily be constructed with a switching relay (pic). But as a hobby i would prefer a more sophisticated solution without mechanical components. Yet not unnecessary complicated. Common electronics component inventory is up to date.

How would you design it? Thanks.

 

hi pocale,
Have you considered two Schottky diodes?
E

 

Thanks for reply. I found with a diode at each power supply and the backup having lower voltage will do smooth and simple backup system. Thit is a good idea. I am looking something like that. However, how would then the LED-strip be powered only with battery supply, goes beyond my circuit design capability. Thanks.

 

how would then the LED-strip be powered only with battery supply

Here's one approach using two Schottky diodes and a P-MOSFET:
M1 is off when the AC powered V2 is high, and conducts when V2 is off.