I am asked to calculate the voltage at the non-inverting input of the op-amp if v1=4.78V and v2=0v.
I thought that the answer would be zero, as the voltage at the non-inverting input must be approximately equal to the voltage at the inverting input, and the inverting input is connected to ground. However, this is incorrect.
I would appreciate it if you could help me understand what is happening here. I have gone through some practice questions relating to op-amps with circuits constructed similar to this using the assumption that the voltage at the input equals that at the output, however, i am getting this question wrong.
Thank you very much for your time,
Best Answer
The inverting input is not connected to ground- rather it is connected to a voltage divider between the op-amp output and ground. The output voltage is thus quite easy to find, given the voltage at the inverting input. But you don't know that voltage yet.
When the op-amp is balanced, the voltage at the two inputs is equal. Ideally, the inputs don't affect the voltages. Ideally the output voltage is driven to whatever voltage balances the op-amp, assuming negative feedback and infinite gain.
The voltage at the non-inverting input is just the mid-point of another voltage divider and the instructor has made it easier on you by setting one end to zero.