Auto Detect Supply with P-channel FET

Discussion in 'General Electronics Chat' started by nethanger1, Aug 19, 2013.

  1. nethanger1

    Thread Starter New Member

    Aug 19, 2013
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    I have a battery pack (12V) and a brick supply (12V) and I want to use a P-channel FET to switch between the two and create feedback to a uC in the process. How would I go about doing that?
     
  2. ScottWang

    Moderator

    Aug 23, 2012
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    How about the current of two 12V?

    What's the load of two 12V? (current of load?)

    What do you mean of feedback to a uC, does it means that to indicate which 12V is using?

    If you want to switch between two 12V then you should using two P channel not only one.
     
    Last edited: Aug 19, 2013
  3. nethanger1

    Thread Starter New Member

    Aug 19, 2013
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    So V1 is a brick power supply and V2 is a battery. With this input circuit, the p-channel mosfet would be closed when the brick is not plugged in. When the brick is plugged in, the fet opens the battery circuit drawing only from the brick now. The Vin signal goes to a two buck converters, one bucking down to 5V and another bucking down to 7.3V (only when the brick is plugged in).

    [​IMG]
     
  4. ScottWang

    Moderator

    Aug 23, 2012
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    If you want to using P MOSFET, have you ever considering about the sat voltage of Vgs when you using logical level its needs 4.5V, and normally its needs 10V?

    Or you can using power plug and jack to do the job?
     
  5. Sensacell

    Well-Known Member

    Jun 19, 2012
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    How about using just two diodes? You could monitor the power supply input with a resistor divider before the diode, unplugged = 0 volts.
     
  6. nethanger1

    Thread Starter New Member

    Aug 19, 2013
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  7. LDC3

    Active Member

    Apr 27, 2013
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  8. nethanger1

    Thread Starter New Member

    Aug 19, 2013
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    Then wouldn't I be shorting out the internal battery when I want to open the circuit with the battery connects.
     
  9. LDC3

    Active Member

    Apr 27, 2013
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    No, because the battery is disconnected from the circuit when the plug is inserted into the jack (which has your external power).
     
  10. ScottWang

    Moderator

    Aug 23, 2012
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    The plug and jack what mentioned at 4#, if you know the functions of plug and jack, maybe you will try it.

    [​IMG]
     
  11. nethanger1

    Thread Starter New Member

    Aug 19, 2013
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    Ah, okay, I understand. The only jacks I've used previously were for guitar pedals which are used to disconnect the battery when the guitar cable isn't plugged in. Thanks, I'll try it.
     
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