I need to design a circuit that will switch to a battery if the power feed goes out.
This is on a vehicle. The scenario is listed below.
Both feeds are 5v.
One feed is coming from the 12v car battery via an inverter.
The other feed is coming from a "AA" battery pack.
Basically we need to watch the first feed, if that feed stops it needs to switch to the second feed.
My first attempt was with a 7404 quad inverter. Basically if the first feed stopped the second feed would fire off
a power transistor because the 7404 can not sink the servo current.
Anyway the circuit worked but there was not enough power to control the servo. And I feel the circuit was MUCH more complicated than it needed to be.
My confusion is with the grounds. The battery pack is a power source in its own right while the first feed is using the chassis ground.
Do I need to switch power and grounds?
Anyone have a simple solution for me?