Op-Amp Non inverting mode

Question

I know how the non-inverting configuration actually looks but I wonder why it can't be identical to the inverting mode (regarding connection of resistors). The feedback is the major issue I can see here but just for mathematical calculation of gain, this modified circuit would still produce the gain same as that of the inverting mode(with negative sign of course).

Why is the non-inverting configuration producing inverted output like in inverted configuration? What are the factors that differentiate the non-inverting and inverting configuration of the op amp?

^{simulate this circuit – Schematic created using CircuitLab}

original image

Answer 1

The op amp is a pretty basic amplifier, it measures the difference between its inputs, and provides a correction on its output based on its gain, be it internal, or limited by external components,

With the 2 inputs, if you give a slightly more positive voltage different things happen, for the + input, the output will increase slightly, for the - input, it will decrease slightly, the device is amplifying this difference by up to 1,000,000 times, so only a tiny difference is needed for it to respond.

For what you have drawn, it will act more like a comparator with hysteresis, when the + input is slightly positive, the output will increase, but this just sums with the + input making it more positive until the output slams against its supply rail, where as the normal non inverting approach uses its feedback to stop the run away,

Answer 2

You've connected the feedback resistor to the noninverting input, which means that you now have positive feedback instead of negative feedback.

Remember, without feedback, the opamp has very high (theoretically infinite) gain. It is only the application of negative feedback that reduces the circuit gain to a definite value. That is why, even in the noninverting "mode", the feedback must still be negative — connected to the inverting input.