Will a forward biased ESD protection diode power an op-amp?

Discussion in 'General Electronics Chat' started by Distort10n, Mar 5, 2008.

  1. Distort10n

    Thread Starter Active Member

    Dec 25, 2006
    429
    1
    Let us say we have the following conditions with our op-amp:

    Vcc = 0
    Vee = 0
    Vin = 1ms 5V pulse
    Internal ESD protection diodes to each rail

    Since my op-amp is unpowered, then the input signal is forward biasing the ESD diode from input to the positive power supply rail. Depending on the current from the signal source and perhaps the sinking ability of the positive power supply, wouldn't Vcc of the op-amp be connected to the Vin signal minus a diode drop thus providing power for a brief moment?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    I've seen some parasitic transistor circuits, so something inside the op amp might respond. The number of transistors makes it unlikely that you would see any output. Too many places needing current sources and so on.

    Got an o'scope? It would be easy to set up an experiment.
     
  3. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    It's not uncommon that components can be "backpowered" through the protection diodes. It can also happen with logic chips, especially those with FET outputs that inherently contain body diodes.
     
Loading...