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Need help driving two IPS1031 Low-Side MOSFETs from a PIC

Discussion in 'Electronic Basics' started by [email protected], Aug 12, 2006.

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  1. Guest

    The IPS1031 is a Low-Side MOSFET Driver that drives its own MOSFET. I
    am planning on incorporating it into my design, but most of its spec
    sheet is total gibberish to me.
    I am driving two of them off of a single PIC output which can sink
    3.7-5V @ 25mA.
    The IPS1031 datasheet:
    http://www.irf.com/product-info/datasheets/data/ips1031.pdf

    Attached is a schem I used for its simulations purposes. Through the
    use of "OR" diodes, only two IPS1031s are on at any single time; Q2 is
    saturated when either Q1 or Q3 is saturated. S1 and S2 signafy two
    different PIC Outputs.
    Schematic is located at:
    http://www.myfilehut.com/userfiles/155002/Switch3.JPG
     
  2. Guest

    LMAO, I forgot to mention what it was that I needed help on. I was
    concerned about the required voltage to turn on the mosfet, and if in
    combination with the diode and the pic output, if it would even see
    this voltage.
     
  3. Chris

    Chris Guest

    Hi, Jed. The 1N5282 is a controlled forward voltage silicon diode, and
    will have a Vf of 0.55 to 0.6V at 1mA forward current. The IR Low Side
    Switch IC requires a minimum of 4.5V for guaranteed operation. If your
    power supply is 5.0V, and your PIC output was exactly 5.0V, that means
    the IN terminal will see 4.45V to 4.4V -- not quite enough for
    guaranteed operation. And there will be a voltage drop of a tenth of a
    volt or so at the PIC output with 1mA output.

    Of course, 4.4V or even 4.3V should be enough. But if you want to be
    sure, you might want to replace the 1N5282s with schottky diodes. That
    way, your diode "Wired-OR" configuration will be guaranteed to work.
    Schottkys have a typical forward voltage of less than 0.3V at low
    forward current.

    You might want to use standard transistors, though -- the PIC output
    pin can certainly source the current, and a 2N3904 will cost a lot less
    than your low side switch ICs (view in fixed font or M$ Notepad):

    |
    | .--------------------------------------o--------------.
    | | +12V +12V +12V | |
    | | | | | | |
    | | ~ V | | | |
    | | ~ - | | | V
    | | | | | | -
    | | .-. | - | |
    | | | | C| ^ .-. .-.
    | | | | C| | | | | |
    | | '-' C| | | | | |
    | | | | | '-' '-'
    | | '----o----' | |
    | | | | |
    | | _/ ___ |/ ___ |/ ___ |/
    | o--o/ o-o-|___|-o-| .--|___|-o-| .-|___|-o-|
    | | | 470 | |> | 2.2K | |> | 2.2K | |>
    | | D V .-. | | .-. | | .-. |
    | | - 4.7K| | | | 2.2K| | | | 2.2K| | |
    | | | | | === | | | === | | | ===
    | | o---. '-' GND | '-' GND | '-' GND
    | | | | | | | | |
    | | D - | === | === | ===
    | | ^ | GND | GND | GND
    | | _/ | '------------' |
    | o--o/ o-o -------------------------------'
    | |
    | |
    | +|
    | ---
    | -
    | |
    | ===
    | GND
    |
    (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

    With 2N3904s or other standard NPN small signal switching transistors
    and shottky diodes for D, this will work well for any 12V relay with a
    coil requiring less than 100mA.

    Good luck
    Chris
     
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