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Best way to detect what power source is connected?

Harald Kapp

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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*)

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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

Apr 11, 2014
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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*)

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

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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*)

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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.
 
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