I have designed a PCB. Now I am facing a issue that I want to use 12V PSU and 12V battery together so that if 12V PSU fails then 12V battery can supply power to PCB.Battery charging is not part of the project as i will remove battery when it is discharged and will attach to PCB after it is fully charged. Current requirement of my PCB is 3A. Now the issue is
How can I setup both power sources in my schematic that if PSU turns off then battery can supply power to whole PCB, Keeping in mind that my current requirement is 3A?
Basically, I need some switching circuit but with high current requirement.