Op-amp output voltage

[crazyjim30]

I came across this question. Our resources suck so badly that I can't even guess at the proper formula. Nothing in my notes, our slides, or the crappy ebook has been any help at all. [emoji35]   An Op-amp has an open-loop gain of 90,000. Vsat = +/- 13V. A differential voltage of 0.1 V p-p is applied between the inputs. The output voltage is what?

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[retrolefty]

I came across this question. Our resources suck so badly that I can't even guess at the proper formula. Nothing in my notes, our slides, or the crappy ebook has been any help at all. [emoji35]   An Op-amp has an open-loop gain of 90,000. Vsat = +/- 13V. A differential voltage of 0.1 V p-p is applied between the inputs. The output voltage is what?

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If differential input voltage is DC then .1 X 90,000 = 9,000 volts but Vsat limits max exertion to Vsat so = 13V

[crazyjim30]

Ah ha! Now it makes sense. Thanks.

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[danadak]

One normally does not use an OpAmp open loop, because its Aol
varies dramatically one part to another, very temp sensitive, and
noise considerations when dealing with very high G circuits.

The beauty of all that Aol is using it in a - feedback loop to set
what is termed closed loop gain. There is a Rome church sized
library worth of research and application notes written on OpAmps,
just google OpAmps or Operational Amplifiers. Go to TI, Analog Devices,
Linear Technology websites, reams of info.

Simulate one in Mathcad or alike and look at what happens with
various stimuli and feedback factors. Lots of fun. OpAmps are like
Resistors and Capacitors in usefulness, its their G and differential
mode, that create so many usefull circuits.

Regards, Dana.