Now consider a resistor at the output of the operational amplifier as shown here

Question

Now consider a resistor at the output of the operational amplifier as shown here. Again assume an ideal amplifier. Draw the circuit again and show how you use the ideal op amp properties plus KCL, KVL. and Ohm's law to find the following if Rc = 1 k ohm. i1? i2? i3? v0? i0? i4? Calculate the input power delivered by the voltage source vs. Calculate the output power absorbed in the resistor Rc. Determine the power gain Pout/Pin . How can there be more power out than going in - where does the extra energy come from? Suppose the circuit schematic in question 2 is built with a model LM741 op amp According to the tables in Rizzoni on pages 469- 472, the maximum absolute value of i4 that a 741 can provide is about 25 mA. If Ra = 1 k ohm, Rb = 3 k ohm, and vs - 0.3 v. determine the minimum value allowed for Rc.

Explanation / Answer

i2 =vs/RA ::::::::::::::::::::; i3 =- V0/RB :::::::::::::::::::i1 = 0 (from common ground concept) ::: i4 = 0 , beacuse no current flow through opamp ::::::::::: io = Vo/Rc b) input power =pin = Vs^2/RA ::::::::::::::::::::; po = out put power = Vo^2/Rc ,,,,, where Vo =-RB*Vs/RA Po = [-RB*Vs/RA]^2/Rc power gain =Po/pin = Rb^2/(RA*Rc)

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