Feedback Forces Equal Inputs - Electronic Circuits VI: Op-Amp Feedback and Exact Gain Networks Step by Step

An ideal op-amp in negative feedback is modeled as an exact equal-input contract. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Negative feedback checks equal input voltages

In the linear ideal model, feedback drives the two input pins to 0 volts together.

V_+ = V_- = 0\ \text{V}

The output is still inside the rails

The output is 0 volts, between the dual rails.

-12\ \text{V} \le 0\ \text{V} \le 12\ \text{V}