LABORATORY MANUAL
Electronic Devices
ENGG*3450
Fall semester 2022
Instructor:
Dr. Stefano Gregori
Laboratory 1
1
1.1
Information
Purpose
The purpose of this laboratory is to study the diodes. In this laboratory, you will measure
the current-voltage characteristics of diodes, test a photovoltaic cell, detect voltage polarity
with LEDs, and build rectifier circuits.
1.2
Equipment
Equipment
DC power supply, BK Precision 1672
Function generator, BK Precision 4017A 10 MHz
Oscilloscope, Tektronix MSO 2024B
Multimeter, Amprobe 37XR-A
Solderless breadboard and wire kit
1.3
Count
1
1
1
1
1
Components
Part
Count
1N4004 diode
1
1N4733 zener diode
1
Red LED
1
Green LED
1
5-V 100-mA solar cell
1
1 kΩ resistor
1
10 kΩ resistor
1
1 µF capacitor
1
22 µF capacitor
1
2
2.1
Pre-laboratory theory
Semiconductor diode
A semiconductor diode allows current in one direction only, like in an electronic check valve
or in a one-way street for electrons. Because of this unidirectional behaviour, you have to
distinguish between the terminal in which current can enter and the terminal in which it
cannot. Therefore one terminal is labelled with + and called the anode (A); while the other
terminal is labelled with − and called the cathode (K). Fig. 1a shows the schematic symbol
1
A
I
V
K
(a) Symbol.
(b) Package.
Figure 1: Semiconductor diode.
of the semiconductor diode, and Fig. 1b shows the corresponding package with the polarity
indicator.
A positive current can enter the anode, when the anode is biased positively with respect
to the cathode (i.e. in Fig. 1a, if V > 0, then I > 0). The diode is on or in forward bias.
The current increases rapidly when the voltage exceeds a certain cut-in (or turn-on) voltage
(e.g. around 0.4 V).
When the voltage is applied with reverse polarity, the current cannot flow through the
device (i.e. in Fig. 1a, if V < 0, then I ' 0). The diode is off or in reverse bias. If the reverse
voltage exceeds a critical breakdown value VZK , then the reverse current increases rapidly.
In forward bias, the relation between I and V is modelled by (Shockley)
V
I = IS e VT − 1 ,
(1)
where IS is the reverse saturation current (or scale current), which is constant for a given
diode at a given temperature, and where
VT =
kT
,
q
(2)
is the thermal voltage, with k = 1.38 · 10−23 J/K the Boltzmann’s constant, q = 1.60 · 10−19
C the elementary charge, and T the absolute temperature (in K). For example, at T = 300
K (i.e. 27°C), VT = 25.9 mV; at T = 293 K (i.e. 20°C), VT = 25.3 mV.
In reverse bias, the exponential term in (1) becomes small compared to unity, and the
current can be approximated as
I ' −IS .
(3)
Manufacturers usually specify the maximum ratings for forward current (IF ) and reverse
voltage (VR ), the diode forward currents (IF ) at given forward voltages (VF ), and the diode
reverse currents (IR ) at given reverse voltages (VR ). The current-voltage characteristic of a
typical semiconductor diode is shown in figure 4.8 on page 185 of the textbook [1], and the
parameters of a specific device are provided on the corresponding data sheet [2].
2.2
Zener diode
A diode manufactured to operate in the reverse breakdown region is called zener diode. Zener
diodes are often used as voltage regulators because of the steep current-voltage characteristic
in the reverse breakdown region, which provides an almost-constant voltage for a range of
currents.
2
I
V
(a) Symbol.
(b) Package.
Figure 2: Zener diode.
Fig. 2a shows the schematic symbol of the zener diode, and Fig. 2b shows the corresponding package with the polarity indicator. With the reference polarity in Fig. 2a, I and
V are positive in forward bias. It is preferable to avoid using the terms anode and cathode
for zener diodes, because the current can have both directions.
When the reverse voltage exceeds a breakdown value VZK , the reverse current increases
more rapidly for a given voltage increment than in forward bias. Manufacturers usually
specify the diode voltages at given test currents (e.g. VZ = 5.1 V at IZT 1 = 49 mA) and
the dynamic resistance rz = ∆V /∆I at specified test currents (e.g. rz = 7 Ω at IZT 1 = 49
mA) that indicates the slope of the current-voltage characteristic (i.e. slope = 1/rz ). The
characteristic of a typical zener diode is shown in figure 4.19 on page 203 of the textbook
[1], and the parameters of a specific device are provided on the corresponding data sheet [3].
2.3
Light-emitting diode
A light-emitting diode (LED) generates light when enough forward current passes through
the device. LEDs are made with direct band-gap semiconductors (e.g. Ga As, Ga N, Ga P,
Al In Ga P) and their current-voltage characteristics are similar to those of any semiconductor
diode, but they typically have a larger cut-in voltage (e.g. 1.6 to 5 V). The package is
also different (e.g. typically a transparent epoxy resin incapsulates the semiconductor chip
and forms a hemispherical lens). The parameters of specific devices are provided on the
corresponding data sheets [4, 5].
The schematic symbol of the LED is that of a semiconductor diode with two arrows
suggesting light emission as shown in Fig. 3a. The colour may be printed beside the symbol
if relevant. The cathode lead is the shortest of the two as shown in Fig. 3b. You may also
identify the cathode from the flat edge on the side of the package, or, if you peer through
the lens, the cathode is usually the one connected to the largest lead frame on which the
semiconductor chip is mounted.
I
epoxy lens
LED chip
wire bond
reflector
V
flat
A
(a) Symbol.
K
(b) Package.
Figure 3: Light-emitting diode (LED).
3
I
V
(a) Symbol.
(b) Package.
Figure 4: Photovoltaic (PV) cell.
2.4
Photovoltaic cell
A photovoltaic cell (or solar cell) is a semiconductor device that converts light into electrical
energy. It is a diode (Fig. 4a) that uses the photovoltaic effect to produce a current proportional to the intensity of the incident light. On the light-facing side, a layer of a transparent
material allows light to pass while protecting the semiconductor and the front contacts as
shown in Fig. 4b.
2.5
Half-wave rectifier
A common application that makes use of its nonlinear characteristic of the semiconductor
diode is the half-wave rectifier circuit. The purpose of a rectifier is to convert an ac signal
into dc. A waveform with a non-zero average (i.e. a dc component) is produced by allowing
only positive voltages to pass through. This is the basis for the dc power supplies using the
ac outlets. Rectifiers are also used as generators of harmonics, as signal-level detectors in
radio-frequency circuits, and as demodulator of amplitude-modulation (AM) radio signals.
The half-wave rectifier circuit shown in Fig. 5 consists of a diode connected in series with
a resistor. If the input voltage is a sinusoidal wave with zero average (i.e. no dc offset), the
diode is on during the positive half-cycle of the input, and the output voltage is almost equal
to the input voltage (assuming that the voltage drop over the diode is small). The diode is
off during the negative half-cycle, and the output voltage is zero. Therefore, while the input
voltage has a zero average value, the output voltage has positive average value.
3
Experiments
In this laboratory, you will conduct two experiments to examine the features of semiconductor diodes. In the first experiment, you observe and measure the static current-voltage
characteristics of a semiconductor diode in forward and reverse bias. In the second experiment, you will build a half-wave rectifier circuit and observe and measure the dynamic
behaviour of the output voltage when a sinusoidal input voltage is applied.
vI
vO
Figure 5: Half-wave rectifier.
4
R
I
VS
V
VD
Figure 6: Circuit for measuring the static i-v characteristics of a semiconductor diode.
Device
Rmeasured (kΩ)
VS (V)
VD (V)
I (mA)
..
.
..
.
..
.
Table 1: Example table for collecting the data points.
3.1
Experiment 1—Diode i-v characteristics
In this experiment, you will examine the static current-voltage (i-v) characteristic of the
1N4004 diode [2]. You will power the circuit with the dc supply and you will use the
multimeter to measure the voltage across the diode VD and across the source voltage VS .
You will use the measured voltage to calculate the current I through the diode. Based on
these values you will plot the i-v characteristic of the diode. You will apply supply voltages
from −10 V to +10 V and collect sufficient data points in order to generate suitable plots.
3.1.1
Procedure
1. Prepare a table similar to the example in Table 1 with at least 16 rows to collect the
data points.
2. Use the digital multimeter to measure the actual resistance of the 1 kΩ resistor (i.e. 1
kΩ is the nominal value, Rmeasured is the actual value). Write down this value as you
will need to use it in answering the report questions.
3. Using the 1N4004 diode [2] and the resistor R = 1 kΩ set up the circuit shown in Fig.
6 on the breadboard with the dc power supply as the voltage source VS .
4. Set the dc supply voltage to +2 V.
5. Set the multimeter knob to dc voltage (V) and measure the voltage drop across the
voltage source (VS ) as shown in Fig. 6 by connecting the negative probe (black) to the
cathode of the diode (grounded) and the positive probe (red) to the positive terminal
of the voltage source. Record this value in the table.
6. Keeping the negative probe connected to the cathode terminal of the diode (grounded),
disconnect the positive probe from the voltage source and connect it to the anode
5
terminal of the diode to accurately measure the diode voltage (VD ). Record this value
in the table. Hint: Do not adjust, turn off, or disconnect the dc power supply during
this step.
7. Repeat steps 4 and 5, as you set the dc power supply output voltage from −10 V to +10
V in 2-V increments. Hint: To obtain a negative voltage switch the terminals connected
to the power supply so that positive goes to negative and vice versa. Note: you will use
the measured values of VS , VD , and Rmeasured to calculate the current through the diode
as I = (VS − VD ) /Rmeasured (i.e. you do not need to directly measure the current).
8. Take additional data points (i.e. at least 16 in total) in order to construct an accurate
i-v characteristic plot. Hint: In this experiment there are ranges of VS for which there
is little change in the current through the diode. Space your data points apart in
these regions (i.e. use large increments of voltage like 1 and 2 V). On the other hand,
there are ranges of VS for which the current through the diode changes rapidly and
significantly. Space your data points closer together in these regions (i.e. use small
voltage increments such as 0.1, 0.2, and 0.4 V).
3.1.2
Questions
1. Finalize the table by calculating the currents I, and plot the i-v characteristic curve
of each of the diodes onto a single graph. You can do this by creating a scatter plot
in a spreadsheet program, using for input data the values measured for VD and the
values calculated for I. Please plot VD onto the horizontal axis, using V as the unit of
measure. Please plot I onto the vertical axis, using mA as the unit of measure.
2. In the forward-biased region describe how the current through the diode changes as the
voltage across the diode is increased. Please formulate your answer in terms of change
in current per unit change in voltage (i.e. rf = ∆V /∆I). In the reverse-biased region
describe how the current through the diode changes as the magnitude of the voltage
across the diode is increased (i.e. in terms of rr = ∆V /∆I). What is the turn-on
voltage?
3.1.3
Optional steps
If you have finished the mandatory experiments and you still have time, you can repeat the
above procedure with one of the configurations in Fig. 7, with the following settings:
1. If you use the 1N4733 zener diode [3], use the same settings as for the 1N4004 diode.
In the forward-biased region describe how the current through the diode changes as
the voltage across the diode is increased (i.e. in terms of rf = ∆V /∆I). In the reversebiased region describe how the current through the diode changes as the magnitude
of the voltage across the diode is increased (i.e. in terms of rr = ∆V /∆I). In the
breakdown region describe how the current through the diode changes as the magnitude
of the voltage across the diode is increased (i.e. rz = ∆V /∆I). How does the slope of
the characteristic change from the forward-bias region, to the reverse-bias region, and
to the breakdown region?
2. If you use the photovoltaic cell, set the dc power supply output voltage from −5 V to
+5 V in 1-V increments. The first time, cover the cell or place it face down. Then
repeat the procedure with no shade and the cell facing up. Describe in which conditions
6
R
VS
I
R
V
VD
VS
(a) Zener diode.
I
VD
V
(b) Photovoltaic cell.
R
VS
I
VD
red
green
V
(c) Current polarity indicator with two LEDs.
Figure 7: Circuits for measuring the static i-v characteristics.
and in which region of its i-v characteristic it supplies power. Based on the collected
data, what is the maximum power that it can deliver and at what voltage and current?
3. If you use the red LED [4] and the green LED [5], you can connected them in parallel
with opposite polarities (anti-parallel configuration). A device that uses this configuration is the bi-colour LED which acts as a polarity indicator, giving a visual display
of the polarity of an applied voltage. Turn the power supply on and vary the supply
voltage from −10 V to +10 V. Observe the behaviour of the LEDs as you vary VS .
Specifically, you will want to write down the following:
• The ranges of VD and I across which each of the LEDs is lit up.
• The change in the intensity of the light emitted by each LED as VD and I vary.
• The value of VD and I at which the red LED just begins to emit light.
• The value of VD and I at which the green LED just begins to emit light.
3.2
Experiment 2—Half-wave rectifier
In this experiment you will build a half-wave rectifier that passes only the positive portion
of an input signal.
3.2.1
Procedure
1. Construct the circuit shown in Fig. 8a using the 1N4004 diode [2] and the 10-kΩ
resistor. Note: You are now using a different resistor than you did in the previous
experiments.
2. Connect the positive and negative terminals of the function generator to your circuit
as specified by vI in Fig. 8a. Set the function generator to produce an 6 V peak-to7
ch1
vI
vO
ch2
R
(a) Without capacitor.
ch1
vI
vO
R
C
ch2
(b) With capacitor.
Figure 8: Half-wave rectifier.
peak sinusoidal wave at 300 Hz (to obtain a 6-V p–p sinusoid, the function generator,
which is expected to be terminated into a 50 Ω load, must be set to output a 3-V p–p
sinusoid for the 10-kΩ load). Note: Use the oscilloscope to determine the peak-to-peak
voltage of the signal produced by the function generator (e.g. connect channel 1 of the
oscilloscope, ch1, as shown in Fig. 8a).
3. Connect channel 1 of the oscilloscope (ch1) to the input voltage vI and channel 2 (ch2)
to the output voltage vO (i.e. the voltage across the resistor). Adjust and set the
vertical scale for each channel to 1.0 V so that the oscilloscope can provide accurate
readings. Caution: Be careful with grounds. The ground of the oscilloscope must be
attached to the same node as the grounded terminal of the function generator (e.g.
you can connect it directly to the grounded terminal of the function generator if you
wish).
4. Using the oscilloscope, observe the waveforms of both the input voltage vI and the
output voltage vO . Adjust the vertical position on each channel so that both channels
have the same origin on the vertical axis. Take some time to consider what you are
seeing. Doing so will help you to understand the behaviour of the diode in this circuit.
3.2.2
Questions
1. Using one of the oscilloscope screen shots you took, indicate on the image the regions
where the diode is on (passing current) and the regions where it is off (blocking current).
2. Considering the circuit in Fig. 8a, can you predict what is the difference between the
peak value of vI and the peak value of vO , i.e. without measuring it and based only on
the measurements you took in experiment 1? How does this voltage difference relate
to the diode cut-in voltage?
3.2.3
Optional steps
If you have finished the mandatory experiments and you still have time, you can take the
following steps.
8
1. Connect the 1 µF capacitor as shown in Fig. 8b (the peak rectifier) and observe the
new waveforms. Note how the waveform on channel 2 (output voltage) has changed
compared to the previous step.
2. Adjust the time scale on the oscilloscope so that you have about 3 to 7 periods on the
screen. This will help you to better see what happening. Take a screen shot of the
oscilloscope display and save this image.
3. Use the multimeter to measure the dc voltage at vO . Record this value as well as the
voltage reported by the oscilloscope for vO in the previous step.
4. Adjust the function generator to change the waveform frequency to 200 Hz, then repeat
steps 2 and 3 above.
5. Adjust the function generator to change the waveform frequency to 600 Hz, then repeat
steps 2 and 3 above.
If you keep the capacitor constant, describe what happens to the peak-to-peak voltage and
to the average voltage of the output signal as the frequency of the input signal is increased.
Then remove the 1 µF capacitor and connect the 22 µF instead. Repeat the steps above
using waveform frequencies of 200 Hz, 300 Hz, and 600 Hz as before.
Caution: Observe the polarity of the capacitor and connect the positive terminal to the
output and the negative terminal to the ground. Note: You will need to take a photo of
your breadboard for this circuit to be included on the first page of the report.
If you hold the frequency of the input signal constant, describe what happens to the
peak-to-peak voltage and to the average voltage of the output signal as the capacitance is
increased.
4
Things to remember
• A semiconductor diode conducts a small current until the forward voltage is at least
0.4 V (cut-in voltage) and then the current increases rapidly.
• Beyond a certain value of reverse voltage, breakdown occurs, and current increases
rapidly with a small corresponding increase in voltage.
• Zener diodes are diodes designed to operate in the breakdown region, they are employed
in the design of voltage regulators whose function is to provide a constant dc voltage.
• LEDs have similar i-v characteristics as normal diodes and they emit light when forward
biased.
• Photovoltaic cells have similar i-v characteristics as normal diodes and they can supply
power when exposed to light.
• Rectifiers based on diodes and capacitors convert ac voltages into unipolar voltages.
9
5
Writing the laboratory report
5.1
Report format
In a concise and professional manner please provide answers to the experiment questions.
The report must include the following items:
• A cover page titled “Laboratory 1 Report” with a colour picture of the circuit built in
experiment 2 (with a resolution of at least 1280 × 720 pixels). This page should also
report the course and instructor names, the laboratory session number, date and time,
as well as your name and student identification number.
• About two pages for each experiment documenting your activity with the appropriate
measurement conditions, measurements and graphs (four pages total).
• A brief final page with your interpretations, observations, and comments on the results. You should include a paragraph for each experiment describing what you should
remember from the activity you have completed.
Please include a clear schematic for each circuit that you have built, labelled with component values, types and other pertinent information. Label carefully all the graphs and use
the correct units of measurement. Make sure that the graphs are clearly visible, including
the scales and titles of the axes. This is needed for anyone to be able to interpret what you
have done (including the grader, your colleagues, and yourself at a later time).
The guidelines to prepare your report are the following:
• The maximum number of pages allowed is six, the required file format is pdf, and the
maximum file size is 2 MB.
• The file name must be lab1[your last name].pdf, where your last name is your
last name (e.g. lab1gregori.pdf).
• Each page, figure, and table must be numbered; number each page at the top right
corner outside the set margins.
• Use white paper, letter format (21.6 cm × 27.9 cm), portrait orientation, single column,
margins at 2 cm minimum all around.
• The text must be in black ink, single-spaced (no more than six lines per inch), in a
font not smaller than Times New Roman regular 12 pts.
• Capture screenshots from the oscilloscope with the bench-top computer (using Tektronix OpenChoice Desktop) or a USB drive; photos of the oscilloscope screen will not
be marked.
Submissions that do not meet the format and the guidelines above will not
be marked and will receive a grade of zero.
10
5.2
Timeline
The report is intended to be submitted within a week from completing your activity in
the laboratory. You are asked to submit your report in pdf format using the dropbox Lab
1 report on the course webpage. The deadline is Friday, 30 September 2022 at 23:59.
Submissions that do not meet the deadline or that are not submitted via the
dropbox will not be marked and will receive a grade of zero.
Please verify that the uploaded file can be opened and is the one you intended to submit,
and keep a back-up copy of your report.
5.3
Evaluation criteria
The following aspects will be considered:
• Proper experiment set up and use of the tools.
• Precise data collection and correct answers.
• Correct interpretation of the results and relevant observations.
• Quality of the report (clarity, accurate documentation of the results, appropriate labelling, use of the units of measurement).
• Conciseness, complying with the report guidelines, and meeting the deadline.
5.4
Plagiarism
Your report must be the result of your own work, measurements, and self-expression. You
may discuss about components, tools, methods, and requirements, and ask questions to the
instructor, teaching assistants, and laboratory technician. However, you are responsible for
your own laboratory activity and the report must be written by you alone. No exchange
of graphs, measurements, and other material related to the laboratory activity is allowed
between students.
Please remember that copying text, data, or figures is plagiarism, even if you received
the material from a friend, if you found the material on the Internet (including learning apps
and answer-sharing platforms), or if you are reusing material that you have previously submitted elsewhere. Letting other students use your work, completing work for other students,
engaging in contract cheating or making answers available to others are also not allowed.
Therefore, please keep your reports, files, plots, and measurement data in a secure location.
If you are in any doubt as to whether an action on your part could be construed as an
academic offence, you are encouraged to consult with the instructor before submitting your
report. By submitting the report under your name, you are acknowledging that the content
of the report is entirely your own work, completed this term for this course.
Electronic means of detection, including Turnitin, will be used to identify possible plagiarism, unauthorized collaboration or copying as part of the ongoing efforts to maintain
academic integrity at the University of Guelph. All submitted assignments will be included
as source documents in the Turnitin.com reference database solely for the purpose of detecting plagiarism of such papers. The use of the Turnitin.com service is subject to the Usage
Policy posted on the Turnitin.com site.
11
6
Acknowledgements
Contributions of the laboratory technician, teaching assistants and students to this manual
are gratefully acknowledged.
References
[1] A. S. Sedra, K. C. Smith, T. C. Carusone and V. Gaudet, Microelectronic circuits, Oxford,
8th ed., 2020.
[2] 1N4000 series diodes data sheet:
http://www.onsemi.com/pub/Collateral/1N4001-D.PDF
[3] 1N4700 series silicon voltage-regulator diodes data sheet:
http://www.vishay.com/docs/85816/1n4728a.pdf
[4] HLMP-Cx08 red LED data sheet:
http://www.farnell.com/datasheets/1922527.pdf
[5] HLMP-3507 green LED data sheet:
http://www.farnell.com/datasheets/1918235.pdf
12