Sunday, 10 March 2019

operational amplifier - Op-Amp damage from floating input


I have an op-amp circuit that has a block of dip switches that can be used to configure the gain of the circuit. We have had an unusual failure in the circuit that appears to be related to changing dip switches while the unit is powered on. This failure only seems to occur on occasion.


My suspicion is that the issues is caused by the switches being set they pass through a state such that no switch is turned on but have no evidence at this. In addition I would that expect that if all switches are left open this is effectively becomes a voltage follower and should try to drive the voltage to zero volts.


This is a simplified version of my schematic OPA1 is supplied from +- 15V rails, Input voltage is +-10v In- is connected to zero volts in a separate section of my circuit. The output load is a second amplifier stage and would present a load of approximately 100k


schematic



simulate this circuit – Schematic created using CircuitLab


Is there anything that adjusting these switches could do to destroy my op-amp to the extent it releases the magic smoke and leave a small crater in the surface of the op-amp.




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