As Regras de Ouro dos Amp-Op

The Op-amp Golden Rules

From Horowitz & Hill:

For an op-amp with external feedback

I. The output attempts to do whatever is necessary to make the voltage difference between the inputs zero.	The Voltage Rule
II. The inputs draw no current.	The Current Rule

Comments on 1: The voltage gain of a real op-amp is so high that a fraction of a millivolt input will swing the output over its full range. Practically, that amounts to rule 1.

Comments on 2: The input current is so low (0.08 microamps for the 741, picoamps for an FET-input op-amp) that rule 2 is practically correct.

The ideal op-amp