Michael Watterson wrote:
> But I'd mentally think of that as a comparator, implementing a Schmitt
> trigger.

Right.  That's the point.  Too many EE candidates apply the linear circuit
rules without thinking whether they actually have a linear circuit.  Even
worse, some don't realize that their rule only applies to a limited set of
circuits and just blindly follow the inapplicable rule.

> An op-amp is only an op-amp if it has predominantly negative  feedback
> that  gives  a closed loop  gain a tiny fraction of open loop gain.

No, that's just one way to use a opamp.  A opamp is merely a circuit
building block that (in the ideal case) does:

  Out = Gain(PosIn - NegIn)

The rest is how you use that basic capability within your circuit.  The
basic opamp building block, however, remains just that.  It works the same
way regardless how the external circuit utilizes its capabilities.


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