Operational Amplifiers

In this lab we had the problems of wanting a voltage source varying  0-1V while having 0-10V of output. In this case we used an inverting amplifier to obtain a gain of -10. 6V battery supplies powered the op amp.

We first calc. the smallest Ri value for input resistance using Ohm's law (V = IR)         Ri = 1000Ω.

Afterwards, nodal analysis was used to calculate a value of Rf, the resistor between the inverting input and output of the op amp., that would satisfy a gain of -10.          Rf = 10000Ω.

For the  variable source (Rx) to vary 0-1V, a resistor Rx was placed, acting as a voltage divider. Assuming worst case scenario, where Ry = 0Ω, we calc. Rx = 283Ω. However, closest resistor available was 360Ω.

We determined Ry using KCL, measuring  5.95V from power supply and asuming V=1V for Ry.    
Ry = 72.72Ω.   Actual R used: 75Ω.

After calculations, we built the breadboard, switching the +/- terminals of one battery to have both
+ and - 5.95V power supplies. We then measured different Voltage values at 0-1Vin, as followed:

VIN          Vout  (V            Gain              VRi (V)            IRi  (mA)            VRf  (V)
                                      (Calculated)                              (Calculated) 
0.0V            0.02                  0                       0                       0.00                  0.03       
0.25V          2.62                  10.08                0.26                  0.26                  2.62
0.50V          4.06                  9.90                  0.41                  0.41                  4.17
0.75V          4.06                  9.44                  0.43                  0.43                  4.39
1.00V          4.06                  9.02                  0.45                  0.45                  4.62

With VIN = 1.00V, we measured the current from the power supplies:

(+Vcc) IV1 = 0.03 mA
(-Vcc)  IV2 = 0.76 mA

The gain was consistent, although it decreased as the voltage increased, and the current did not pass 1mA.