- #1
AdkinsJr
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Homework Statement
Write output voltage in terms of input voltages for the circuit drawn.
I drew the circuit and then feed back loop.
Homework Equations
Ohms Law V=IR
Basic Properties of Op Amps (ideal), voltages are assumed equal at both inputs...
The Attempt at a Solution
The difficulty is that there should be two currents that need defining, but I'm not sure how to eliminate both of them. I wrote two equations for the current through the feedback loop and then equated to write Vout in temrs of the resistances and Va.
[tex]I_a = \frac{V_{out}-V_a}{R_2} [/tex]
[tex]I_a = \frac{V_a-V_{out}}{R_1}[/tex]
[tex]V_{out}=\frac{V_a-V_{in}}{R_1}R_2 +V_a[/tex]
I can't figure out how to write Va in terms of Vin and the resistances at this point. The only other relationships between Va and other quantities come from the fact that [tex]V_b=I_bR_3[/tex] which means that [tex]V_a=I_bR_3[/tex] also, but I still need to get rid of the current Ib now, so that doesn't help much. I can't figure out what I'm missing. Any help would be great.