Download Lab 9-1a: Op-Amp limitation – slew rate (p200)

Week 4: Op-Amp Applications
This week lab is a bit longer than usual. You are advice to try answering what you
would expect from each circuit before coming to the lab. To speed things up, you can
also build two circuits on the breadboard (especially for 9.1a).
Lab 9-1a: Op-Amp limitation – slew rate (p200)
Read pages 184-195 on departures from ideal op-amp behavior in the lab manual.
We are only doing part (a) of 9-1, but note that you need to do everything Op-Amp
Op-Amp twice: first with the 411 Op-Amp, and then with the (older and less
capable) 741 Op-Amp.
Answer the following questions in your report for each Op-Amp (you can put your
answers side-by-side):
1) Sketch the input and output waveforms when you drive your op-amp follower
with a 1 kHz square wave (chose the amplitude to avoid clipping).
2) Measure the "slew rate" for rising and falling signals. Describe your method and
show your calculations.
3) Repeat the last 2 steps using a non-clipped sine-wave input. To measure the slew
rate, measure the frequency at which the output waveform begins to distort (this
is roughly the frequency at which amplitude begins to drop, as well). Do the slew
rates that you measure with square and sine inputs agree?
4) Summarize the differences between the 741 and 411 that you observe.
Lab 9-2: Integrator (p202)
Answer the following questions in your report:
1) Sketch the input and output waveforms with a 1 kHz square wave input. Choose
your amplitude to avoid clipping. You may need to adjust the signal generator's
DC offset if your output is saturating, as described in the lab manual.
2) From the component values, predict the output of a 2V p-p 500 Hz square wave
input. Show your calculations and sketch your prediction. Confirm (and update if
necessary) your prediction with a measurement.
3) Try removing the 10M resistor in parallel with the feedback capacitor. What
happens? Why do think it was included in the original circuit?
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Lab 9-3: Differentiator (p203)
Answer the following questions in your report:
1) Sketch the input and output waveforms with a 1kHz triangle wave input
(depending on your function generator, you’ll need to use a 50% symmetry).
Explain why the output makes sense for a "differentiator". Show your
calculations.
2) Sketch the input and output waveforms with a 1kHz sine wave input. Explain
why the output makes sense for a "differentiator". Show your calculations. (Note
that we don't use the "Krohn-Hite generators" mentioned in the text.)
Lab 10-1: Two comparators (p234)
Read pages 207-221 on comparators and oscillators.
Answer the following questions in your report:
1) Sketch the input and output waveforms with 100 kHz sine wave input to the 411
open-loop circuit. Explain why the output should ideally be a square wave. Why
doesn't it actually look very square?
2) Replace the 411 with a 311 to build the circuit in Fig. L10.2 (and note that pins 2
and 3 are swapped!). Sketch the input and output waveforms with the same 100
kHz sine wave input. In what way is the 311 better than the 411?
3) Try to get your 311 circuit to oscillate, as described in the lab manual. Sketch an
example of your input and output waveforms with oscillation.
4) Add the positive feedback resistor to construct the circuit of Fig. L10.3. Sketch
input and output waveforms with 100 kHz sine wave input.
5) Predict the thresholds for this circuit, and then confirm (and update if
necessary) your predictions by reducing the input signal's amplitude.
6) Measure the circuit's "hysteresis", describing your method and showing your
calculations.
7) Connect the open-collector "ground" (pin 1) to -15V instead of the circuit
ground. How does this change the output waveforms? When might this be
useful?
Lab 10-2: RC oscillator (p236)
Answer the following questions in your report:
1) Predict the oscillation frequency that you expect for this circuit. Show your
calculations.
2) Sketch the output waveform you actually observe.
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Lab 12-2: Three terminal fixed regulator (p275)
Read pages 267-73 on voltage regulators.
Hook up the circuit in Fig. L12.4 with two modifications: first, do not use the fixed
15V supply (just use the variable supply which can go up to 21V) and, second, add
your multimeter (configured for measuring current) in series with the input to the
78L05 regulator so you can measure its power consumption (as voltage times
current).
Answer the following questions in your report:
1) Record the input current and output voltage for the following input voltages (in
volts): 3, 4, 5, 6, 7, 15, 16, 17, 18, 19, 20, 21. Do not leave your circuit with more
than 15V input for too long and be careful since the regulator (and anything it
touches) will become hot above 15V.
2) Make a graph of output voltage versus input voltage. Explain why the output
voltage is not the desired 5V at each end of the range.
3) Make a graph of the power consumed by the regulator versus the input voltage.
You can calculate this power as the difference between the power provided by
the variable supply and the power consumed in the pair of parallel 120 ohm
resistors. What happens to this power?
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