Electrical – In a non-inverting op-amp, why is it R1/(R1+R2) instead of R2/(R1+R2) in this circuit


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So, why is r1 used in the above formula instead of R2?

Best Answer

If I redraw the circuit slightly...


simulate this circuit – Schematic created using CircuitLab

This is essentially what is around the OPAMP, a typical voltage divider circuit. V- is the voltage across R1 thus:

\$V- = V_o \frac{R1}{R1+R2}\$

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