I came a cross a design problem which I need your suggestions in it.
I have 3 power sources, Main Supply which is 9-32DC, a battery pack 12VDC, and PoE Module, all are connecte to tripel output 12, 3.3, 5VDC voltage regurlators, and finally a microcontroller.
I would like to detect a power failure on the three of them, and also use one of them on power failure.
I thought about first the user must use the Main Supply first, then the uC use its ADC to check for the voltage on the battery pack, use a voltage divider to lower the voltage then measure the value and check if its lower than a value, however this method is also I want to use it for charging the batteries it self!. The same scenario I will do with the main supply and the PoE, but the problem with the resistors that they must have high power, the current that can be drawn I assume its more than 9A. I'm also not sure which VRef should I feed the microcontroller with, it's very problematic issue too. Do you guys havae an opinion or suggestion for better design ?