Contradictory closed-loop behaviour of TL051CP op-amp

Question

I tried to set up the TL051CP op amp as a current-voltage converter, but in a configuration somewhat different from the usual current-voltage converter setup with the non-inverting input simply connected to ground.

In my circuit the potential at the non-inverting input may vary. I now observed that at a voltage difference between inverting input and non-inverting input of about -0.3 V, where the TL051CP should be at positive saturation voltage, the TL051CP's output is not saturated.

When the same specimen of TL051CP is measured for open-loop behavior, there is no such anomaly: Its output is at positive saturation voltage for voltage differences between inverting input and non-inverting input in the range from near 0 to -0.4 V, thus also at -0.3 V.

The TL051CP specimen does not seem to be broken and I observed that behavior also with other specimens of the TL051CP but not yet with other types of op amps. Is this some constructive peculiarity of the TL051CP?

Answer 1

V.1, I cannot be more precise about the details of the circuit because this is supposed to enter into a patent application and spreading out the details before its filing will be lethal. I now have a hypothesis why the TL051CP behaves like this while other op amps don't. Being able to state that the setup would also work with the "general purpose" TL051 CP would be beneficial but apparenty this is not correct. For patenting purposes it is now essential for me to know which op amps do not work and to be able to exclude them from the scope of the claims, otherwise the patent would be invalid. I must find out what the general problem with op amps of the type TL051 CP is in my setup and be able to explain that in writing. You can close the post for the time. If I should overcome the problem and the patapp was filed I could revert in more detail and explain. Many thanks for your help.