Electronics > Beginners
Need help understanding this OpAmp behavior.
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L_Euler:
Are you sure the reference voltage pot is turned to 5V and not zero.
David Hess:
The 324/358 is subject to phase reversal if the negative common mode limit is exceeded:

If either input or both inputs are lower than –0.3 V with respect to the negative supply, excessive input current can flow and the output may display phase reversal, also called inversion.

http://www.ti.com/lit/an/sloa277/sloa277.pdf
Wigo:

--- Quote from: David Hess on July 10, 2019, 03:10:22 am ---The 324/358 is subject to phase reversal if the negative common mode limit is exceeded:

If either input or both inputs are lower than –0.3 V with respect to the negative supply, excessive input current can flow and the output may display phase reversal, also called inversion.

http://www.ti.com/lit/an/sloa277/sloa277.pdf

--- End quote ---

Thanks a lot. So all runs down to RTFM 😉 i should have known.
Rerouter:
The clipped circuit I posted earlier will still work with both types of op amps. If your sensitivity is still too high you can use a resistor divider to the op amp input.
David Hess:

--- Quote from: Wigo on July 10, 2019, 05:03:12 am ---Thanks a lot. So all runs down to RTFM i should have known.
--- End quote ---

Most early JFET operational amplifiers also suffer from the same problem.

Like the susceptibility of a General Products hull to damage from antimatter, the phase reversal "feature" was not widely advertised.
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