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Discussion in 'Electronic Design' started by CeeRox, Nov 9, 2007.

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  1. CeeRox

    CeeRox Guest


    Does anyone have an easy solotion on how to overvoltage protect some
    digital in- and outputs?
    Im going to have 5V digital inputs and outputs from an uControler.
    These signals shall withstand that someone connects +12V to them. On
    the inputs i can use a series resistor with a zenerdiode. But how
    about the outputs..?
    Any suggestions on how to solve that in an easy way? Some kind of
    buffer solution?
  2. Guest

    The usual solution for buffering and protecting the outputs is an open-
    collector or open drain buffer.

    The classical open collector inverting buffer is the SN7406, which can
    take up to 30V across the collector

    It is a very old device - I first used it back in 1971 - and while
    Farnell still stocks it, there are many similar devices available.
  3. An old trick is to use a crow-bar circuit.
    When an over-voltage occurs, an SCR conducts
    from Vcc to ground and blows the fuse, or trips
    the breaker.
  4. default

    default Guest

    It is called an open collector non-inverting buffer - you supply a
    pull up resistor to the +12 V source for an output or put your load
    between +12 V and the OC if it can be driven with the current the
    buffer is rated at.

    Some controllers, and many digital logic IC's do offer OC outputs for
    that reason.
  5. Ralph in NH

    Ralph in NH Guest

    Here's another immortal chip from the 70s, one of my all-time favorites -

    Best regards,
    Ralph in NH
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