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AD822 Output on Multisim Simulator

Question asked by MOS.6502 on Jul 3, 2017
Latest reply on Aug 13, 2017 by MOS.6502

Hi!

My name is Claudio, I'm a hobbyist and this is the first time I'm writing in this forum.
I have realized with a simulation program (Multisim) a circuit that uses an operation amplifier AD822. I was trying to get a circuit that would have this output:
VCC (+5V) when the difference between inputs exceeds + 20mV
VEE (-5V) when the input difference is less than -20mV
0V when the difference between the inputs is between -20mV and + 20mV
I would like to make a comparator with three states.
Playing with the values of feedback and input resistances, I managed to get my purpose on the simulator.
When the input difference is between a few mV, output is almost zero volt.
On the simulator this work well (You see in the oscilloscope the central part between 15mS and 30ms where the output assumes a value close to zero).
Is it a valid configuration?
I built the circuit.
The condition in which the output should be close to zero volt however does not work; I get a fast and continuous variation between + 5V and -5V.

What am I doing wrong? Is it possible that the simulation is not true?

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