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simple power switching circuit

Discussion in 'Electronic Basics' started by none1, Nov 11, 2007.

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  1. none1

    none1 Guest

    Hello,

    I am working on a small project using a pic microcontroller that
    I want to have run for months at a time. I can put the pic to sleep
    to conserve power but I would also like to remove power to the
    peripherals I am adding (i2c eeprom, etc). What I want to do is
    use one of the pic output pins (high) to power up the devices when
    I need to use them. This seems like it should be pretty easy, can
    anybody point me to a simple circuit to do this or recommend a good
    way to do this.

    thanks !
     
  2. Jamie

    Jamie Guest

    Look for a logic Mosfet transistor that can be gate driven via
    an output of the PIC.
    A high side P-channel config should do it. That would be the
    S (Source) to the + rail, G (gate) via a parasitic resistor
    to an output of the pic. (D) drain will supply the peripherals.
    The pic's output will have to go low to turn on the fet.
    Select a fet that has full turn on at 50% or less of the rail
    voltage you're using..
    That's about the drift of it..
    P.S.
    Make sure you have the output of the pic programmed for pull up.
     
  3. none1

    none1 Guest

    Thank you.

    Is there a mosfet which will do the same thing you describe except with
    the gate being pulled high to turn on ? All the pins on the pic will powerdown I
    think when I put it to sleep, plus I would like a circuit that draws no
    power when the pic is sleeping. I'm not sure how much power the mosfet
    draws when 'turned off' with the pull up resister.
     
  4. Eeyore

    Eeyore Guest

    Yes, it's very practical. What kind of peripheral (voltage/current) do you need
    to power up/down ? That will influence the design.

    Graham
     
  5. Eeyore

    Eeyore Guest

    If using a mosfet to switch the load I'd suggest an n-channel type with a high side
    driver chip. IR do lots of high side drivers and I think Microchip even has some.

    Graham
     
  6. Nobody

    Nobody Guest

    Out of curiosity, what's the advantage of using an n-channel type?
     
  7. ian field

    ian field Guest

    It helps the manufacturer sell an extra high-side driver chip.
     
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