Laboratory 1
Diodes
Stefano Gregori
1
Information
1.1
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
Count
DC power supply, Keysight EDU36311A
1
Function generator, Keysight EDU33212A 20 MHz
1
Oscilloscope, Tektronix MSO 2024B
1
Multimeter, Amprobe 37XR-A
1
Solderless breadboard and wire kit
1
1.3
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
Pre-laboratory theory
2.1
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 of the semiconductor diode, and
Fig. 1b shows the corresponding package with the polarity indicator.
1
Laboratory 1, Diodes, © Stefano Gregori
2
A
I
V
K
(a) Symbol.
(b) Package.
Figure 1: Semiconductor diode.
I
V
(a) Symbol.
(b) Package.
Figure 2: Zener diode.
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
VT
(1)
I = IS e − 1 ,
where IS is the reverse saturation current (or scale current), which is constant for a given diode at
a given temperature, and where
kT
VT =
,
(2)
q
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].
Laboratory 1, Diodes, © Stefano Gregori
2.2
3
Zener diode
A diode manufactured to operate in the reverse breakdown region is called zener diode. Zener
diodes are often used in limiter circuits and 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.
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 4.13 on page 197 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 encapsulates 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.
2.4
Photovoltaic cell
Photovoltaic cells (or solar cells) and photodiodes are semiconductor devices that convert light into
electrical energy. They are diodes that use the photovoltaic effect to produce a current proportional
to the intensity of the incident light. The photodiode is the key device of optoelectronics and it is
typically operated in reverse bias. The photovoltaic cell is operated without a reverse bias and it is
often made of polycrystalline semiconductor, which is cost-effective for manufacturing large-surface
I
epoxy lens
LED chip
wire bond
reflector
V
flat
A
(a) Symbol.
K
(b) Package.
Figure 3: Light-emitting diode (LED).
Laboratory 1, Diodes, © Stefano Gregori
4
I
V
(a) Symbol.
(b) Package.
Figure 4: Photovoltaic (PV) cell.
devices. On the light-facing side of a photovoltaic cell, 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 utilizes the nonlinear characteristics of a 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 dc power supplies and battery chargers using ac outlets. Rectifiers
also work 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 be 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.
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
vI
vO
Figure 5: Half-wave rectifier.
Laboratory 1, Diodes, © Stefano Gregori
5
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.
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 −5 V to +5 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 voltage of channel 2 of the dc power supply to 2 V with a current limit of 100 mA.
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 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 to 6, as you set the dc power supply output voltage from −5 V to +5 V in 1-V
increments. Hint: To obtain a negative voltage switch the terminals connected to the power
Laboratory 1, Diodes, © Stefano Gregori
6
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 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 or 0.2 V).
3.1.2
Questions
1. Finalize the table by calculating the currents I, and plot the i-v characteristic curve of the
diode onto a 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-bias 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-bias 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). Using the data collected and the piecewise-linear model of the i-v
characteristic
(
0
VD ≤ VD0
(4)
I=
(VD − VD0 )/rD VD ≥ VD0
determine the parameters VD0 and rD by linear regression.
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. Zener diode. If you use the 1N4733 zener diode [3], use a voltage range from −10 V to
+10 V. In the forward-bias 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 reverse-bias
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. Photovoltaic cell. 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
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 in indoor
illumination conditions?
Laboratory 1, Diodes, © Stefano Gregori
7
R
VS
I
R
V
VD
VS
(a) Zener diode.
I
VD
V
(b) Photovoltaic cell.
R
VS
I
VD
red
green
V
(c) Polarity indicator with red and green LEDs.
Figure 7: Circuits for measuring the static i-v characteristics.
3. Light-emitting diodes. 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 and peak 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—Half-wave rectifier
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 a 6 V peak-to-peak sinusoidal wave
at 500 Hz (to obtain a 6-V p–p sinusoid, the function generator, which is typically expected
to be terminated into a 50 Ω load, must be set for a high-Z or high-impedance output load
Laboratory 1, Diodes, © Stefano Gregori
ch1
8
vI
vO
ch2
R
(a) Without capacitor.
ch1
vI
vO
R
C
ch2
(b) With capacitor (peak rectifier).
Figure 8: Half-wave rectifier.
since you are using a 10-kΩ resistor). Note: Use the oscilloscope to determine the peak-topeak 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 and make sure that both channels have the same scale and are
coupled in dc. Measure the maximum and minimum of both waveforms. Take some time to
consider what you are seeing and observe how the two waveforms differ. Doing so will help
you to understand the behaviour of the diode in this circuit. Note: You will need to take a
photo of your breadboard with this circuit to be included on the first page of the report.
3.2.2
Questions
1. Using one of the oscilloscope screenshots you captured, highlight the regions on the image
where the diode is conducting (allowing current) and where it is non-conducting (blocking
current). What happens if the diode is reversed?
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? Measure this voltage difference using the cursors and explain how
it relates to the diode cut-in voltage.
3.2.3
Procedure—Peak rectifier
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
Laboratory 1, Diodes, © Stefano Gregori
9
the previous configuration.
2. Adjust the time scale on the oscilloscope so that you have between 3 and 7 periods on the
screen. This will help you to better see what is happening. Take a screenshot 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 average
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 20 Hz, then repeat the
steps above.
6. Replace the 1 µF capacitor with the 22 µF instead. Caution: Observe the polarity of the
capacitor and connect the positive terminal to the output and the negative terminal to the
ground.
7. Repeat the steps above using waveform frequencies of 20 Hz and 200 Hz as before and measure
the voltage at vO .
3.2.4
Questions
1. If you keep the capacitance 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.
2. If you hold the frequency of the input signal constant, describe what happens to the peak-topeak voltage and to the average voltage of the output signal as the capacitance is increased.
3.2.5
Optional steps
If you have finished the mandatory experiments and you still have time, you can take the following
steps.
1. Double-anode zener. Connect the 10 kΩ resistor and the two zener diodes to make the
limiter circuit in Fig. 9. Apply a 20-V peak-to-peak sinusoidal wave with the frequency of
500 Hz as input. Adjust the time scale on the oscilloscope so that you have 3 to 7 periods on
the screen and measure the maximum and minimum values of the input and output signals.
This will help you to better see what is happening. After this step, take a screenshot of
the oscilloscope displaying both input (ch1) and output signal (ch2) together in one screen.
Indicate on the image which zener diode is in forward bias and which is in reverse bias in each
region. Describe the difference between the input and output signals. What happens if you
use only one zener diode?
2. Voltage-level indicator. In the circuit in Fig. 10, when the input voltage exceeds a certain
zener threshold, the corresponding LED turns on, indicating that the input has crossed that
level. Use R1 = 10 kΩ and R2 = R3 = 1 kΩ, and apply a voltage VS from 0 to 15 V. Explain
how the series resistors limits the current and protects the diodes and LEDs. Discuss how
to modify the indicated voltage levels. How would the circuit behaviour change if the zener
diodes were replaced with regular diodes?
Laboratory 1, Diodes, © Stefano Gregori
10
R
ch1
vI
ch2
vO
Figure 9: Double-anode zener limiter circuit.
VS
R1
R2
R3
Figure 10: Voltage level indicator.
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 designed to operate in the breakdown region, they are employed in limiter
circuits and voltage regulators.
• 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.
5
Writing the laboratory report
5.1
Report format
Provide answers to the experiment questions in a concise and professional manner. The report must
include the following components:
Laboratory 1, Diodes, © Stefano Gregori
11
• Cover page titled “Laboratory 1 Report” with a colour picture of the circuit built in experiment 2 (minimum resolution: 1280 × 720 pixels). This page should also report the course
title, instructor name, laboratory session number, date and time, as well as your full name
and student identification number.
• Documentation of experiments: Two pages for each experiment documenting your activity with the appropriate measurement results and graphs (four pages total). Answer the
questions and report the measurement conditions, the type and value of the components used,
and the instruments employed along with their settings.
• Optional components: Add one page per optional component, if applicable.
• Observations: 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.
Additional requirements:
• Include a clear schematic for each circuit built, with all component values, types, and other
relevant details clearly labeled.
• All graphs must be properly labeled with units, axis titles, and clearly marked scales to ensure
readability and accurate interpretation.
• Do not include any figures or material from external sources, including this manual or the
course textbook.
Please adhere strictly to the following formatting guidelines:
• The report must be submitted as a pdf file with a maximum size of 4 MB.
• The file must be named using the format: lab1[your last name].pdf (e.g. lab1gregori.pdf).
• Each page, figure, and table must be numbered; page numbers should appear in the top-right
corner, outside the set margins.
• Use white letter-sized paper (21.6 cm × 27.9 cm) in 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.
• Oscilloscope screenshots must be captured using a USB-A drive or the bench-top computer
via Tektronix OpenChoice Desktop. All screenshots must include the date and time they were
taken. If the oscilloscope’s date and time are incorrect, please ask the technician to adjust
them. Smartphone photos of the oscilloscope screen, or screenshots without a visible date and
time, will not be marked.
Important: Submissions that do not comply with these submission and formatting guidelines
may incur grade penalties or may not be marked, at the grader’s discretion.
Laboratory 1, Diodes, © Stefano Gregori
5.2
12
Timeline
The report must 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 Laboratory 1 report on the
course webpage. 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.
Important: Late submissions will incur in grade penalties or may not be marked, at the grader’s
discretion. Reports not submitted via the dropbox will not be marked and will receive a grade of
zero.
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 independent work, collected data, 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 text, data,
graphs, and other material related to the laboratory activity is allowed.
Please remember that copying text, data, or figures is plagiarism, even if you received the
material from a friend or a third-party service, if you found the material on the Internet (including
learning apps, answer-sharing platforms and LLMs), or if you are reusing material for which you
have previously received credit. 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, figures, 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. The instructor
will follow up on academic misconduct concerns as per University policy and out of respect to all
the students who are maintaining their academic integrity.
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.
6
Acknowledgements
The contributions of the teaching assistants, laboratory technician and students to this manual are
gratefully acknowledged.
Laboratory 1, Diodes, © Stefano Gregori
13
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