In the given OP-AMP circuit on the side: a. Find the feedback resistor (Rf) required to obtain the specified output voltage. b. If R1 = R2 = 2.2 kΩ and Rf = 18 kΩ, calculate the output voltage (VOUT).

by musethor
June 18, 2023

For an ideal OpAmp, the point where the inputs resistor and Rf meet all together, in this configuration, is at 0 volt (since the other input of the OpAmp is at the ground),

giving the current from R1 equals to 200mV / R1, and the current from R2 is also 200mV / R2.

For an ideal OpAmp, no current enters in the OpAmp through the inputs, so the incoming current coming from R1 et R2 has to exit through Rf.

The current through Rf is thus 0.200/R1 + 0.200/R2 [Amp],

so the voltage on the output side of Rf is

Rf * (0.200/R1 + 0.200/R2)

= 18000 * (0.2/2200 + 0.2/2200)

= 3.27 volt. Negative.

You should be able to solve the first part using a similar train of thought.

by vanderghast
June 18, 2023

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