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Best way to detect what power source is connected?

Discussion in 'General Electronics Discussion' started by KiwiSteve, Dec 30, 2016.

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  1. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    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.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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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.
     
  3. KiwiSteve

    KiwiSteve

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    Apr 11, 2014
    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
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It's a tricky problem because the gate voltage is driven higher than any supply rail in the circuit
     
    Last edited: Jan 14, 2017
  5. KiwiSteve

    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?
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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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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