Determine output voltage of inverting op amp

[stobbz]

**broken link removed**

So, I've worked out the closed loop gain with respect to the inverting input, but I can't get the correct answer for that of the non-inverting input.

The question asks to find the output voltage. By multiplying the input voltages with their respective closed loop gains and adding together, that should give the output voltage.

For the inverting input: Av = -5
What about at the non-inverting input? Answer works out to be -15v.

Any help appreciated

 

[MrAl]

Hello there,

I think the easiest way for you to do this is to use the superposition theorem. To use this you short out one input to ground, calculate the output, then put that input back to normal and short the other input to ground and calculate the output again. You then add the two output results and that is the total output.
For this circuit you could first short the -5 to ground and compute the output call it Vo1. Then put that one back and short the -3 to ground and compute the output and call that Vo2. Now you just add the two outputs.
BTW the gain of non inverting stage is 1+Rf/Rin which in this case is 1+10k/2k if that helps.

 

[stobbz]

That answers my question perfectly, makes sense now, thanks a lot.