If I have an op amp configured as an integrator, with a capacitor from the output to inverting input and non-inverting input grounded, and connect the inverting input through a resistor to the negative supply, the output should ramp up linearly. My question is how the op amp does this? The analysis assumes that the negative input is at virtual ground, but with only a capacitor in the feedback loop and a DC voltage applied at the input how does the output cause the inverting input to stay at virtual ground? Thanks for any insight.

 

Are you familiar with the behaviour of a capacitor when it is charged from a constant current source?

This is the key to your opamp question.

hgmjr

 

Also keep in mind that there is no current flow into the inverting and non-inverting inputs of an ideal op amp. As a result, the constant current flows into the capacitor.

Please review the following link:

http://www.electronics-tutorials.ws/opamp/opamp_6.html:

http://www.electronics-tutorials.ws/opamp/opamp_6.html