How to analyze a circuit like this two-op amplifier

[HelloManner]

In TINA, the measured VOUT is 15V, what analysis method can analyze the voltage of VOUT

 

[KlausST]

Hi,

you simply DON´T do this in real world.
You short circuit the outputs of two OPAMPs .. so they are figthing against each other. Always.
Most probably resulting in overheat and at leat one OPAMP to be killed.

Klaus

 

[crutschow]

What is the supposed purpose of this op amp killer circuit.

 

[barry]

What is the supposed purpose of this op amp killer circuit.

Smoke Generator

 

[FvM]

Even if we assume short circuit proof general purpose OP, feeding 20 V to an input with +/- 15V supply will kill most OPs. The behaviour of outputs shorted against each other is generally undefined and no useful object of circuit analysis.

 

[danadakk]

Just curious, were the 100 ohms R's supposed to be in series with OpAmp
outputs, then tied together ? Eg. your schematic drawn in error ?

Like this :

 

[D.A.(Tony)Stewart]

5.798 out is not a good outcome as well showing that the output inverted the expected result to be higher than the lowest input.

 

[FvM]

@danadakk
I presume you are trying to read sense into post #1 schematic, e.g. by assuming +/- 20 V supply voltage. But that's beyond +/-18 V maximum ratings and TL072 can't source 50 mA that would be required to maintain 10 V output voltage difference into 200 ohm load.

 

[danadakk]

Actually was my intent to do it with idealized OpAmp models to avoid
real limitations, simply forgot to update the OpAmp models used.

Old age, and an IQ in the single digits will do it every time.

@FvM, TL072 DS I was looking at -

But I was not paying attention to current....

 

[HelloManner]

Sorry, I didn't consider The actual op amp model, about the source of the circuit, when I was looking at The Art of Electionics, I got the rules for analyzing the op amp, and I noticed that it was an analysis rule in the case of negative feedback, so I designed something so that when the op amp was connected to the load, it would break its negative feedback state. I wanted to know how they should be analyzed, so I designed this circuit,.

 

[KlausST]

Hi,

in case of two OPAMPs with connected outputs .. and this output feedbacked to each OPAMP, then
usually one OPAMP likes to drive it´s output fully HIGH and the other fully LOW.

Now usually the OPAMP output stage design is not perfectly matching symmetric. Thus usually one output "wins" above the other.
Thus - depending on OPAMP type - I expect the output to be stalled close to either power supply rail (never centered) .. independent of the OPAMP inputs (as long as within specified input voltage range). So leat´s say >15V or <-15V on a +/- 20V supplied OPAMP.

.. Until the OPAMPs get destroyed.

Klaus

 

[crutschow]

I designed something so that when the op amp was connected to the load, it would break its negative feedback state. I wanted to know how they should be analyzed, so I designed this circuit,.

It makes little sense to design a circuit the purposely doesn't work.

 

[danadakk]

@OP, if you break the fdbk loop a simple model to use for analysis is :

In fact you can, for base purposes, let Rid = infinity, R0 = 0. Avol is, for many
OpAmps to day, > 1,000,000.

Then you can write node/loop equations and analyze. But keep in mind Vout
cannot exceed supply rails of the OpAmp, so any answer you get exceeding
those values is meaningless.

Note by doing open loop you are leaving behind the great aspects a super
high G differential amplifier with fdbk provides. You basically degenerate the
OpAmp into a comparator. Here by the way many comparator circuits have
+ fdbk, to implement hysteresis, which provides noise rejection.

Regards, Dana.