Please excuse what may be a stupid question, since I don't have access to test gear. I'm obviously no expert, and trying to learn the behavior of op amps.
What happens to an op amp (in my case, TL072) if the output is directly shorted to the input? (The red line in the attached diagram.) And does the behavior change whether it is inverting or non-inverting? I'm assuming that in both cases they reach saturation without damage to the chip.
This got me wondering how the amp would behave with a capacitor between input and output rather than a direct short. Can anyone advise? Thanks.
Electronic – Op-amp output and input shorted
operational-amplifiershort-circuit
Best Answer
Your circuit (without the short) appears to be a non-inverting amplifier and potentially might have a gain of 1 + R4/R3 but, as you don't show where R3 connects this can only be a best estimate on my part. So, shorting output to input will render the circuit with a gain of 1. This assumes that what you are feeding to pin 3 (the non-inverting input) is a voltage source of much lower output impedance than what the op-amp can muster.
In other words, a fairly useless circuit.
The only circuit I can think of (off the top of my head) that uses a capacitor from output to non-inverting input is one like this: -
Picture from this stack exchange question (a question and answer about schmitt trigger circuits). So does the link to the previous question provide enough insight into the circuit?
There is a significant difference; when the output feeds back to the inverting pin, the circuit behaves like a unity gain voltage buffer capable of buffering a high impedance signal.
Picture taken from here.