Best way to detect what power source is connected?

[Harald Kapp]

I'm planning on using resettable fuses on each input. Do you think another one of the main bus is also required?

Principally not a bad idea but...
However if you put fuses in series, you need to observe some rule (see e.g. here, page 10).
In your setup I would not put a fuse on the main bus.

 

[(*steve*)]

You've fine to the effort of having "perfect diodes", adding the fuses will put back some of that voltage drop.

This is even worse if you're considering polyfuses.

 

[KiwiSteve]

One more question if I may...

Would using a op-amp or comparator on the FET gate work just as well? I'm needing to send the signal to a micro-controller so it doesn't need to be driving current.

Steve

 

[(*steve*)]

It's a tricky problem because the gate voltage is driven higher than any supply rail in the circuit

 

[KiwiSteve]

Not sure what is meant by "sky rail", that's a term I've not heard before. Couldn't I use a voltage divider?

 

[(*steve*)]

Sky == Supply when you get but by autocorrect.

And but == hit

Aaaaagh!

A voltage divider will load down the voltage which is supplied by a low current boost circuit. Not a good idea in this case.

I'm thinking a P Channel jfet might be the answer.