Assuming I have an 'ideal' op-amp.
If I have an Rf and Rin with a voltage into the inverting input and the non-inverting is grounded: my basic formulas is (-Rf/Rin) * Vin
What if I put a voltage directly into the non-inverting input with the above conditions?
I understand everything except getting my signs correct. To use real numbers:
Rf 10k Rin 5k Vin1 2 volts Vin2 1 volts (this is the voltage on the non-inverting input).
My calculations will be:
The current across Rin will be the difference between 2 volts and 1 volt because the op-amp will make the inverting equal to the non-inverting input (in this case 1 volt).
This difference in voltage is divided by Rin to get the current
The current is then multiplied by Rf to get the voltage drop across Rf.
Now my problem is: I have all the correct voltages and currents, however, my signs get confusing and I'm not sure what to get for the op-amp's outptu voltage especially when I start changing the input voltages (i.e. making one higher than the other, making one negative, and one positive, vice versa, etc..)
Is there is an easier way to do this, a formula, or am I not thinking about it correctly?