However, there are differences between real opamps and theoretical ones.įirst, make sure this opamp can run properly from 10V of supply. If everything is set up right, you should get -1.28V on the output from the circuit as shown. This webpage seems to indicate the 741 doesn't suffer from phase-reversal - the ones that do are JFETS - so maybe it is just your chip that's busted - but I'd use the LM358 instead.
There are plenty of cheap and good op-amps that have much better performance specs than the 741. Which is one of several reasons why my tongue-in-cheek comment ("basic 741 opamp answer: there's always a better op-amp to use") is good advice. Modern op-amps are carefully designed to not have this problem, because it's confusing and nasty to debug. Outside that range, it used to be common for the output gain to sometimes reverse sign, causing positive feedback rather than negative feedback and the output to saturate at the rail until it came back into its valid input range. In the case of an LM741 (datasheet from the +/- 15V supply range yields a guaranteed +/- 12V common-mode input range. Op-amps have a valid common-mode input range. If they both do the same thing, then this smells like a case of phase-reversal. If you have another chip, try that to make sure this one is not blown.
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