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Re: gEDA-user: ideal op amps in gschem



so just for fun, now that we're on the topic of silly op-amp tricks....
Here's a circuit which I came across inside some commercially sold equipment. The unit was not cheap (in terms of cost) and was not for the consumer market.


This is a little circuit with only an op-amp and 3 passives. Can't get more simple than that right? Turns out that the designers of it had some troubles understanding it.

The answers (to an accurate enough degree for engineering calculations) can be had in about 3 lines of hand analysis but I think it illustrates nicely how one must be careful with those "ideal" op-amps. It's also a good case of where one shouldn't substitute a simulator (with a model which may not capture important details) for thinking!

Have fun.

-Dan


p.s. hint: The pin on the schematic is the only connection (other than power and ground) to the rest of the circuit that this little gem was found in.

In case anyone wants a bigger hint, here is the context in which that op-amp circuit was found.


-Dan

Attachment: opamp2.pdf
Description: Adobe PDF document