Feedback Current Matches Input Current

This feedback-current-matches-input-current lesson uses KCL at the ideal inverting node: with zero input-pin current, resistor current in must match feedback current out. The 1 A input and 1 A feedback row is exact only for the stated ideal virtual-ground and zero-bias-current assumptions. Real circuits include input bias, finite open-loop gain, offset, resistor tolerance, bandwidth limits, noise, finite precision, and measurement uncertainty.

The output sign is the direction needed to balance current at the inverting node. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

The input pin current is zero

The input pin takes zero current, so the node balance is resistor-in equals feedback-out.

I_{\text{pin}} = 0\ \text{A}

The checked current is 1 ampere in and 1 ampere back through feedback.

I_{\text{in}} = I_{\text{feedback}} = 1\ \text{A}