ECE 2205 Lab5
More Operational amplifier circuits
In this week’s lab, we will build more circuits using the 741 op amp.
Wire up each of the circuits shown below. Use power supply voltages of +15 V and –15 V for the
op amps. Also, be sure to measure the values of the resistors used in your circuits. Apply the
input voltages described in each section and perform the required measurements. Record your
data. Save a copy of the waveform traces to include in your lab report.
Bring a flash drive to lab for collecting scope traces or you can use your smart phone to take a
picture of the waveforms.
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ECE 2205 Lab5
Buffer amplifier and current output limit
a. Build the simple voltage divider shown in above at left. Measure the voltage across R2.
b. Place a unity-buffer amp between the two resistors and measure the voltage across R2
again.
c. Replace R2 with a 1-kΩ potentiometer, set so that the potentiometer resistance at the output
is 1 kΩ. While observing the output with the voltmeter, slowly decrease the resistance
until the voltage drops to 4.9 V. Remove the potentiometer and measure the resistance.
Use your measurements to calculate the output current.
d. Re-insert the potentiometer and decrease resistance until the voltage drops to 3.33 V.
Remove the potentiometer, measure the resistance, and calculate the current in this case.
e. Repeat the measurement of c & d, but with the resistance adjusted until the output is 1.67
V. The measurement of parts c, d, and e should give you a pretty good idea of the output
current limit of the 741 op amp.
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ECE 2205 Lab5
Digital-to-analog converter
17.6 k
D0
RF
8.8 k
D1
4.4 k
D2
D3
R6
1.1 k
–
+
R5
4.7 k
4.7 k
–
+
vo
2.2 k
The digital-to-analog converter (DAC) is one of the most important circuit in electronic systems.
A DAC takes digital information in the form of binary numbers and converts it into analog
voltages. The circuit shown is a very simplified version of a DAC that shows the basic
operation. You will learn more DACs (and their counterparts, analog-to-digital converters) in
subsequent classes.
Build the circuit. Include a 5-V supply node that can be used to provide the “1” inputs.
(The third source of the triple output DC supply can serve this purpose. Be sure to
connect all the required grounds.)
b. Calculate the expected output voltage for each of the sixteen different inputs.
c. Measure the output voltage for each of the inputs. Start at 0000 and work your way up to
1111. To make an input be "0" connect it ground and make it be a "1" connect it to 5 V.
a.
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ECE 2205 Lab5
D3 D2 D1 D0
0
0000
1
0001
2
0010
3
0011
4
0100
5
0101
6
0110
7
0111
8
1000
9
1001
10
1010
11
1011
12
1100
13
1101
14
1110
15
1111
vo (calculated)
vo (measured)
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ECE 2205 Lab5
Integrator
R2 68 k
C
0.1 µF
vs
R1 1 k
–
+
vo
a. Build the simple integrator circuit shown above.
b. Apply a 500-Hz square wave with a 1-V amplitude at the input. (The input should be at 1
V for 1 ms and then switch to -1 V for 1 ms.)
c. Before measuring the output, make a sketch of your prediction of the shape of the output.
d. Observe the input and output together on the oscilloscope. Save a copy of the oscilloscope
display to include in your report.
Clean up
When finished, be sure to turn off the equipment, put away all of your parts, return the wires to
the wire racks, clean off any debris from the lab benches, and return the op amps to the
instructors.
Report
Prepare a report that includes the calculations, measurements and oscilloscope traces for
each of the circuits, as described in the instructions.
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