# Ideal Op Amp With Inductor

#### Theman99

Joined Nov 8, 2011
2
Here is an image of the circuit in question. My only question is how exactly I relate the voltage of inductor to that of the ideal op amps V+
Im guessing I do KVL at the point right out of the inductor.
But im not really sure. Just wondering how to set up this, thanks.

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#### steveb

Joined Jul 3, 2008
2,436
Here is an image of the circuit in question. My only question is how exactly I relate the voltage of inductor to that of the ideal op amps V+
Im guessing I do KVL at the point right out of the inductor.
But im not really sure. Just wondering how to set up this, thanks.
Since the OPAMP is ideal, you can assume that the connection of the + terminal of the opamp to the RL combination has no effect on the voltage across the inductor. Hence, you can simply calculate the first order response of the coil voltage to the input squarewave, and then treat this as an input to the noninverting amplifier, based on the opamp and two gain control resistors on top.

#### Theman99

Joined Nov 8, 2011
2
For this though are you saying that you calculate the voltage across the inductor and that is equal to V+, which you then use with KCL to find the vout?

#### steveb

Joined Jul 3, 2008
2,436
For this though are you saying that you calculate the voltage across the inductor and that is equal to V+, which you then use with KCL to find the vout?
Once you say you have an ideal opamp, I think you really don't need KCL because the current into the + terminal is zero. The input RL circuit is then effectively isolated and behaves like a voltage source. It is really KVL that applies to the RL series circuit. So, the problem reduces to calculating the output voltage of a simple RL circuit and then multiplying that voltage by a gain as determined by the noninverting amplifier.