OP-AMPS II

Purpose: See the effect of changing the feedback resistor and input resistances.

Introduction:

We need to calculate the resistances necessary to get a gain of -10 and what the current coming out of the op amp would be if Vs were 1V:

 

Experiment:
We then build the circuit setting the Vs to 0.25 and vary it while recording the voltages across the input and output resistors. A voltage divider was used to get Vs .

The circuit was then built with a 1K Ohm load according to the following schematic:

The same data was recorded with this set up.

\Data:

    Inverting Op-Amp

     

Vin Desire(V)	V_IN Actual(V)	V_Out Measured(V)	V_Rf Measured(V)	I_op Calculated(mA)
0.25	0.26	-2.59	2.58	0.026
0.5	0.52	-5.18	5.18	0.052
1	1.01	-10.11	9.94	0.101

       For V_IN = 1V

       Measured I_cc = 0.867 mA
                Calculated P_cc = 12*0.867 mP = 10.404 mP
       Measured I_ee = -0.979 mA 

                 Calculated P_ee = 12*0.979 mP = 11.748 mP

       I_cc + I_ee = 0.112 mA
       The percent error is 12% therefore, it is consistent with KCL.

 

      Circuit with 1k Ohms load

    

Vin Desire(V)	V_Out Measured(V)	V_Rf Measured(V)	I_op Calculated(mA)	I_cc Measured(mA)	I_ee Measured(mA)
1	-10.02	9.77	0.1	0.877	-0.984

    For V_IN = 1V

    Measured I_cc = 0.877 mA
            Calculated P_cc = 12*0.877 mP = 10.524 mP
    Measured I_ee = -0.984 mA
             Calculated P_ee = 12*0.984 mP = 11.808 mP
     I_cc + I_ee = 0.107 mA
     The percent error is 07% therefore, it is consistent with KCL.

Conclusion:

    With percent errors of 12% and 7% this experiment is considered a success and obeys Kirchhoff's Current Law. We saw that the gain depends directly on Rf/Ri.