Low offset OpAmps - why so easily damaged?

Discussion in 'General Electronics Chat' started by bloodybrick, Jun 12, 2014.

  1. bloodybrick

    Thread Starter New Member

    Jun 12, 2014
    I really need help to solve this problem as it is my teacher's question on final exam.

    In application note AN-1192, the Bridged-Paralel circuit of four LM3886 circuits. And there, in the schematics, are four servo circuits, which are integrators of DC voltage. It is DC offset protection. Those circuits needs LOW-OFFSET OpAmps like LF412, AD712, OPA2134 etc.

    But, when I made a ciruit od PCB, many times happended, that one of the OpAmp got destroyed, probably because of voltage-peak. Mostly it happened in inverting type of servo.

    When I changed LF412 or AD712 for cheap TL082 with input offset 3 mV, no problem occured and they (TL082) were worked properly. But while I put back AD712 after some test, it was destroyed.

    So why are those low-offset amps so sensitive? When I looked to datasheets, they look almost same inside.

    Thank you for suggestions
  2. crutschow


    Mar 14, 2008
    Hard to say. It's probably related to different input amplifier structures between the two devices. I doubt that it's related to whether they are low-offset types or not. You need to clamp whatever over-voltage is zapping the op amps.