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I/O Protection

Discussion in 'Electronic Design' started by M Ihsan Baig, Feb 10, 2007.

  1. M Ihsan Baig

    M Ihsan Baig Guest

    I am designing a data acquisition circuit. The I/O's are TTL
    compatible, the I/O's get damaged when ever a high voltage spike(50 V,
    100us) hits the I/O's. Is there any any I/O protection circuit which I
    could use to guard against high voltage spikes.
    Thanks,
    Beg
     
  2. Several exist for example:
    Optocoupler.
    Transorb.
     
  3. Digital or analog? A series resistor and a clamp into a CMOS input
    will take care of some really severe transients on digital lines. If
    you like living dangerously, just the series resistor might be okay
    (probably you'll want a pullup or pulldown on the input in either
    case).


    Best regards,
    Spehro Pefhany
     
  4. Eeyore

    Eeyore Guest

    Lots of possibilities. Diode clamps to the supply rails is the most obvious and
    simplest one.

    Graham
     
  5. whit3rd

    whit3rd Guest

    For modest spikes, MC1489A is a common Schmitt trigger inverter
    that has no problem with +/- 20V input (and responds to TTL levels).
    That's about as robust as a cheap IC gets, you can add discrete
    components
    to go to higher tolerances (diode clamp to ground, transzorb or
    zener, even fuses and spark gaps).
     
  6. Rich Grise

    Rich Grise Guest

    I've always just used reverse-biased diodes to the rails, with optionally
    a small (maybe 100 ohms) resistor or a small choke.

    That's how they do it in video games, and I've never seen one fail at the
    inputs. (I used to fix video games.)

    Cheers!
    Rich
     
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