Exploring Power Supplies with Multisim
Lab 3 Worksheet
P. C. Womble
Activity 1: (15 pts)
1. In the space below, calculate the output voltage of the transformer.
2. The output value of the multimeter when connected between the topmost and
bottommost leads of the transformer is ____________
V
3. Move the “+” lead of the multimeter to the center wire. What is the output
voltage? ____________ V
4. The center lead is called the “center tap” and should be half of the output voltage.
Is this true? YES or NO
5. Now, exchange the positions of the multimeter and the transformer as shown
below.
a. Calculate the expected voltage on the multimeter.
b. Write the Multisim calculated voltage. ____________________V
Activity 2: (15 pts)
1) Use the Grapher function of Multisim to graph the output of the transformer
before and after the addition of the diode. Print out and attach the graphs to the
work sheet.
2) Measure the period between two half-waves. If a capacitor was added to the 1 k
load, what capacitance would keep the voltage across the capacitor to ¾ of its
value for that period? Hint: calculate an RC time constant that is much longer
than the period between waves. Show work below.
3) Place the capacitor calculated in the last
question in the circuit diagram. Place
the leads of the oscilloscope in such a
position that you can see a waveform
similar to the one to the right. Print out
the circuit schematic and the waveform
and attach them to the worksheet.
4) Place the diode in such a manner that the half-wave rectification results in a
negative wave. Print out the circuit schematic and a graph of the resulting wave
form.
Activity 3: (15 pts)
1) Use the Grapher function of Multisim to graph after the addition of the second
diode. Print out and attach the graph to the work sheet.
2) Since the period between half-waves has changed, recalculate the size of the
capacitor necessary to keep the voltage across the capacitor to ¾ of its value for
that period.
3) Place the capacitor in the circuit such that you will simulate the waveform on the
previous page. Print out the circuit schematic and the graph.
Activity 4: (20 pts)
1) Use the Grapher function of Multisim to print out the waveform on the
oscilloscope of Circuit 4.
2) Place the oscilloscope leads at various points (for example between D2-D3 and
D4-D1) on the bridge and print out the waveforms. Do you see any practical
application for any of the wave forms? Describe below.
3) In Physics 260, you used a Wheatstone bridge. In the space below:
a. Sketch a circuit diagram of a Wheatstone bridge
b. Describe the purpose of a Wheatstone bridge
c. Describe the difference of the rectifier bridge to a Wheatstone bridge.
Activity 5: (15 pts)
1) The value of the capacitance which makes a smooth waveform is _______________
F.
2) Print out the circuit schematic and the waveform.
Activity 6: (20 pts)
1) Describe in the space below, the function of the LM7815 and LM7915 from the
notes in the component database.
7815--
7915--
2) Describe the outputs of Channel A and Channel B of the oscilloscope below.
What seems to be the purpose of this circuit?