Wierd ESD op-amp problem

Discussion in 'The Projects Forum' started by Ron R, Nov 21, 2009.

  1. Ron R

    Thread Starter New Member

    Nov 21, 2009
    7
    0
    Hello. I have a wierd ESD problem: I am using a OPA2344 in a two-stage circuit to convert 0-.33VAC 60Hz from a current transformer to 0-5VDC for an ADC. If I walk around a little to build up a tiny charge and touch the circuit input, the first stage inverting amplifier op-amp minus input jumps to a clean .5VDC-.7VDC voltage, and the output goes to the rail. This stays until the curciut is unpowered then powered-up again. It doesn't matter if there is a signal at the input or not. I never heard of such a thing, but I'm seeing it. Has anyone else seen this sort of thing? Is there a way to prevent this? (Humans touching the input terminals cannot be prevented.)
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Please post your circuit schematic, preferably in .png format.

    This will help to eliminate a lot of questions; a schematic is worth thousands of words.

    Without a schematic to refer to, it will be very difficult to divine what's going on, or to suggest a course of action to take to prevent this from occurring in the future.
     
  3. Ron R

    Thread Starter New Member

    Nov 21, 2009
    7
    0
    Thanks for the advice. I'm new to forums. I've attached a schematic. I've already tried to put 5.6v zener diodes or 20v transorbs on the input with no effect. Maybe not the right values. Does the OPA2344 or any op-amp go into a locked-up mode with a static charge?
     
    • ACC.png
      ACC.png
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  4. Darren Holdstock

    Active Member

    Feb 10, 2009
    262
    11
    RTFDS problem. The OPA2344 will latch up if an input exceeds the negative supply rail by more than 0.3 V. Clamp with a schottky diode, or use another op-amp.
     
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