An input resistor suppresses noise and stray pickup developed across the high input impedance of the op amp.

Transcription

1 When you have completed this exercise, you will be able to operate a voltage follower using dc voltages. You will verify your results with a multimeter. O I The polarity of V O is identical to the polarity of V I. An input resistor suppresses noise and stray pickup developed across the high input impedance of the op amp. FACET by Lab-Volt 109

2 Op Amp Fundamentals O If V I I from 0 V. As V moves away from 0 V, the op amp responds by changing its output voltage. Since V O is fed back, the change of output voltage continues until V is restored to 0 V. When V equals 0 V, additional voltage change is not required. The new output voltage is stabilized. 110 FACET by Lab-Volt

3 If V I is increased from 2 Vdc to 6 Vdc, V O must change by a. 8 Vdc. b. 6 Vdc. c. 4 Vdc. d. 2 Vdc. If V I change by a. b. c. d. Locate the VOLTAGE FOLLOWER circuit block, and connect the circuit shown. Use a two-post connector to complete the feedback path. Use your voltmeter to measure the circuit dc output offset voltage. Your circuit does not use a trim or nulling adjustment. V O = Recall Value 1 FACET by Lab-Volt 111

4 Op Amp Fundamentals the input voltage to your VOLTAGE FOLLOWER circuit block. voltage setting resolution. Monitor the circuit input voltage with your voltmeter. Adjust V I to mv. Be precise. O I and V O. Based on your result, the a. difference, if any, equals the offset error voltage of the op amp. b. circuit cannot operate unless a trim adjust is added. 112 FACET by Lab-Volt

5 Adjust V I Based on a comparison between the circuit input and output voltages, the voltage follower a. I. b. I. c. has an effective unity gain and does not invert the polarity of V I. d. inverts the polarity of V I. Based on your observation, a. U1 is not saturated. b. V is correct and should remain nearly 0 V. c. since V is 0 V, V I and V O are essentially equal. d. All of the above. As you monitor V from end to end. Based on V, a. U1 is driven into saturation. b. U1 is not driven into saturation. c. V I and V O d. None of the above. As you monitor V O from end to end. Based on V O, a. the circuit output duplicates the input voltage. b. the polarities of V I and V O are identical. c. All of the above. d. None of the above. FACET by Lab-Volt 113

6 Op Amp Fundamentals Monitor the circuit output voltage as you remove the two-post connector located in the U1 feedback loop. Based on your observation, a. U1 operation is not affected by the open feedback path. b. the circuit output voltage does not follow the circuit input voltage. c. the circuit no longer has an output voltage. d. The inherent output offset voltage of the LF441 op amp is very low. The op amp feedback voltage maintains the input differential voltage at nearly 0 V. An open feedback path results in op amp saturation. 1. A voltage follower circuit a. has a gain of 1. b. has unity gain. c. does not invert the polarity of its input voltage. d. All of the above. 2. Typically, voltage follower circuits are used as a. impedance matching devices. b. c. sinusoidal generators. d. 3. a. b. it is low in value. c. the follower requires high levels of input voltage. d. All of the above. 114 FACET by Lab-Volt

7 4. a. output and noninverting terminals of the op amp. b. output and inverting terminals of the op amp. c. noninverting and inverting terminals of the op amp. d. noninverting terminal and circuit common. 5. Which statement about a voltage follower is false? a. The output voltage tracks the circuit input voltage. b. Input voltage polarity is not inverted. c. The ratio between the circuit feedback and input resistors must equal 1. d. A voltage follower has unity gain. FACET by Lab-Volt 115