Ideal Opamp Analysis: Determine Vout for Vin = 2V & Vs = 15V

[joel amos]

Given this ideal op-amp, determine V_out if V_in = 2V and V_s = 15 V.

So I know that the ideal op-amp has infinite gain. As the difference between V+ and V- is substantial (2V), wouldn't that mean the output would theoretically by infinitely large but instead max out at V_s? Am I understanding correctly, or am I way off?

 

[LvW]

Yes - you are right. Each application of opamps as linear amplifiers requires dc feedback. This allows a suitable dc operating point in the mddle region between the supply voltages as well as an amplification factor that is determined by the feedback resistors only.
Otherwise, even very small input voltages cannot be amplified (in case of REAL opamps) because an always present offset voltage will drive the output into saturation.

 

[joel amos]

Okay, that makes sense. Thanks for the response!

 

[analogdesign]

The way it is drawn the output would be pinned at the -Vs rail, not Vs. The inverting input (-) is higher than the non-inverting input (+) here.

 

[joel amos]

So it should be -15 V?

 

[berkeman]

So it should be -15 V?

Depends on the opamp. Some can drive their output to the rails, and others saturate somewhere close to the rails (within a volt or two). If you are to assume it is an ideal opamp, what do you think?

BTW, is this from a schoolwork assignment? What is the context of the question?