Op Amps II

Objective

 

    The purpose of the lab is explore the effects of a varying input voltages, and feedback resistors on the output voltage on an inverting Op Amp.

                            The following circuit was required to build in this experiment

 

Gain=-10=-Rf/R1

we know R1=10k

so Rf =100k

 

 

A measured voltage of 0.24 V obtained from the voltage divider in this experiment.

 The circuit was built and connected according to lab manual

 

 

      An 1k resistor was connected across the op-amp output.

 

    

 Data Table

V_in (Desired)	V_in (Actual)	V_out (Measured)	V_RF (Measured)	I_op (Calculated)
0.25 V	0.24 V	-2.41 V	2.46 V	-0.0246 mA
0.5 V	0.50 V	-4.90 V	4.87 V	-0.0502 mA
1.0 V	1.00 V	-10.04 V	9.86 V	-0.1028 mA

I_cc = 0.874 mA
I_ee = -0.981 mA
I_cc + I_ee = -0.107 mA
P_cc = V*I = 10.488 mW
P_ee = 11.772 mW

 

 

     Extra Credit

 

     R_f was replaced to obtain a gain of -5, and the determined value of R_f was 49.9k Ohms.

 

      

      Data was measured when V_IN = 1 V

 

 

The gain becomes -5 when R_f = 50 kΩ

Measured R_f = 49.9 kΩ

V_in (Desired)	V_out (Measured)	V_RF (Measured)	I_op (Calculated)	I_cc (Measured)	I_ee (Measured)
1.0 V	-5.03 V	4.99 V	-0.101 mA	0.885 mA	-0.985 mA

I_ee + I_cc = -0.1 mA

 

 

Conclusion

 

     We learned how to explore the effects of a varying input voltages, and feedback resistors on the output voltage on an inverting Op Amp. This experiment was very successful. The measured result is close to expected values, and it is consistent with Kirchhoff's Current Law. The results are as expected because the ratio of the feedback resistors gives a gain of -10. V_in does not change the gain, only the resistors. KCL held, so the experiment was a success. To get a gain of 5, the ratio of R_i:R_f had to be 1:5, therefore R_f = 50 kΩ. The gain of an inverting Op Amp is always equal to -Rf/Rin. If the gain is -5, the ratio of Rf/Rin has to be 5. As the same time, the current at the operating point is equal to the sum of the two rails coming into the op amp, and the KCL always holds correct.