Page 189 - Op Amps Design, Applications, and Troubleshooting

172 VOLTAGE COMPARATORS

REVIEW QUESTIONS

1. Refer to Figure 3.7. Which components) is (are) used to determine the threshold
voltages?
2. Refer to Figure 3.9. If resistor RI develops a short circuit, describe the effect on circuit
operation. Will there still be a rectangular wave on the output pin?
3. Refer to Figure 3.9. If resistor R F is reduced in value, describe the relative effect on the
circuit hysteresis.
4. Refer to Figure 3.7. If resistor Rj is changed to 68 kilohms, what is the value for the
upper threshold voltage? Does this resistor change affect the circuit hysteresis (V SAT =
10FJ?
5. Refer to Figure 3.14. If resistor R 1 is reduced in value (and no components are
damaged), what is the effect on the negative threshold (assume ideal zeners)?
6. Refer to Figure 3.14. If diode D 3 becomes open, describe the effect on circuit operation.
7. Refer to Figure 3.15. Describe the effect on circuit operation if diode Dj develops a
short circuit.
8. Refer to Figure 3.17. What is the purpose of R$? Will the circuit still appear to operate
correctly if R$ is reduced to one-half its original value as long as no components are
damaged? Explain.
9. Sketch a simple graph of voltage versus time that illustrates the relationship between
the voltages at the following points in Figure 3.17: v jf %, and the output pin of the op
amp. Be sure to indicate relative voltage amplitudes and phase relationships.
10. Refer to Figure 3.19. What is me effect on circuit operation if R s is returned to a +20-
volt supply instead of the +15-volt source shown in the figure?