Battery or external power detect circuit

[pacman22]

I need to come up with a design to detect if my board is being powered by battery or external DC power supply. How can I achieve this. The battery (VRLA battery, so no BMS) and the external power supply will be plugged in to the same 2 pin connector.

 

[KlausST]

Hi,

You say "the same 2 pin connector" ... so I guess there is no chance for some kind of "DC power line communication".
And I guess there is no chance for mechanical/optical (or similar) coding. Like: one connector activating a switch while the other does not.

Then you simply have voltage and current to work with.
If so: Your job is to specify both supplies and find a clear definition where they differ from each other.
* it could be simply the DC voltage range. Maybe the battery is 11V...14V .. while the DC power supply is >14.5V.
* it may be the voltage ripple .. lower on the battery than on the DC supply
* it may be the impedance that differs between them.

You have to understand that we can not know how to differentate between them. You need to know/give these informations.

Klaus