1&2
Course Number and Title: Voltage-Current (I-V) Characteristics of Diodes – Experiments
ECENG2084 – Applied Electronics-I Laboratory
Instructor: [Instructor Name]
Lab Assistant: [Lab Assistant Name]
Name of Student(s):
Biruk
Date:
08 May 2025
I. Objectives
• Experiment 1 – Testing a Diode:
To determine the diode’s health using the digital multimeter’s (DMM) diode test function. A
properly working diode is expected to show a low forward voltage drop (typically around 0.66–
0.70 V) when forward-biased and display a high (open-circuit) reading in reverse bias.
• Experiment 2 – I-V Characteristics of a Diode:
To study the relationship between the applied voltage and the current through a diode by
constructing a series circuit (diode with a 1 kΩ resistor) and recording voltage drops (across
both resistor and diode) as the applied voltage is varied from negative (reverse bias) to positive
(forward bias).
II. Background Theory (Introduction)
Diodes are semiconductor devices that allow current to flow primarily in one direction. When
forward biased (anode more positive than cathode), a silicon diode typically exhibits a voltage
drop around 0.7 V. In reverse bias, ideally no conduction occurs except for a negligible leakage
current. This inherent one-way conduction makes diodes essential for rectification, signal
clipping, and protection applications.
In Experiment 1, we use the DMM’s diode test function to assess the diode’s health by checking
that it has a low forward voltage drop and high reverse resistance. In Experiment 2, by applying
a range of input voltages to a series circuit (diode plus resistor), we can observe that the diode’s
forward conduction begins after a “knee” voltage (approximately 0.7 V), while reverse bias
maintains nearly full voltage across the diode with negligible current flow. These behaviors
underpin the fundamental non-linear characteristics of diodes, which are exploited in many
electronic circuits.
III. Materials / Components and Equipment
Used
For Experiment 1:
Digital Multimeter (with diode test and ohmmeter functions)
Diode (e.g., 1N3064 or equivalent)
Connecting probes
For Experiment 2: Variable DC Voltage Source (capable of providing from approximately –2 V to
+2 V)
Typical Diode
1 kΩ resistor (R₁)
Breadboard and connecting wires
Oscilloscope and/or additional DMM for voltage measurements
IV. Experimental Methods or Procedures
Experiment 1: Testing a Diode
1, Setup:
Set the DMM to the diode test function. Verify that the meter supplies an internal forward-bias
voltage (typically between 2.5 V to 3.5 V).
Connect the red (positive) lead to the diode’s anode and the black (negative) lead to its cathode.
2, Measurement:
Record the voltage reading (expected around 0.5–0.9 V, typically 0.7 V) when forward biased.
Reverse the leads to test in reverse bias; the meter should display “OL” or the internal voltage
reading—indicating extremely high reverse resistance.
3, Evaluation:
Compare the readings to the expected behavior; a properly functioning diode should show low
forward resistance (and a characteristic voltage drop) and negligible conduction in reverse bias.
Experiment 2: Voltage-Current Characteristics of a Diode
1, Circuit Construction
Construct the circuit with the diode (D₁) in series with a 1kΩ resistor (R₁). Connect the series
arrangement to a variable DC voltage source. As shown below:
2, Measurements:
Vary the applied voltage (Vi) from –2 V to +2 V.
Measure the voltage drop across R₁ (VR₁) and across the diode (VD₁).
Calculate the diode current (ID₁) using Ohm’s law:
VR1
ID1= (with R1=1kΩ)
R1
3, Data Recording:
Record the result in a table.
4, Analysis:
Plot the I-V characteristics from the table.
Compare the diode’s behavior in forward bias (where conduction begins and VD₁ stabilizes
around 0.7 V) with its reverse bias (where nearly the full applied voltage appears across the
diode and current remains minimal).
V. Observations, Data, Findings and Results
Vi(V) VR1(V) VD1 ID1
-2.0V 0.0V -2V -0.04mA
-1.0V 0.0V -1.01V -0.02mA
-0.7V 0.0V -0.7V -0.015mA
-0.5V 0.0V -0.49V -0.01mA
0.0V 0.0V 0V 0V
0.5V 0.33V 0.67V 0.01mA
0.7V 1.27V 0.72V 0.015mA
1.0V 0.08V 0.6V 0.012mA
2.0v 0.01V 0.49V 0.01mA
Note: In the reverse bias region (negative Vi), nearly all of the applied voltage appears across
the diode with negligible current (ID₁ ≈ 0). In the forward bias region beyond the conduction
threshold (around 0.7 V), the diode voltage remains approximately constant while additional
voltage appears across the resistor, resulting in increased current
VI. Data Discussion or Analysis
The data from Experiment 1 confirm the intrinsic characteristics of a diode. The forward-biased
test produced a voltage drop in the expected range (around 0.7 V), while the reverse-biased
condition yielded a very high resistance (displayed as “OL” on the meter), indicating no (or
negligible) conduction. This verifies that the diode is functioning properly.
In Experiment 2, the I-V characteristic reveals two distinct regions:
Reverse Bias (Vi: –2 V to 0 V): Since the diode is reverse biased, almost no current flows, and the
entire applied voltage appears across the diode.
Forward Bias (Vi: 0.5 V to 2 V): The onset of conduction occurs near 0.7 V. Once the threshold is
reached, even as the applied voltage increases, the diode clamps its voltage drop to around 0.7
V, and the extra voltage is dropped across the series resistor. This leads to a nearly exponential
increase in current—as calculated by I = (Vi – 0.7 V)/R₁.
The observed “knee” in the I-V plot clearly demonstrates the non-linear conduction property of
a semiconductor diode, validating the theory discussed.
VII. Conclusions
Experiment 1: The diode test using the DMM clearly shows a normal forward voltage drop and
high reverse resistance, confirming the diode’s proper operation.
Experiment 2: The measured I-V characteristics illustrate that a diode remains non-conductive in
reverse bias and begins substantial current conduction only after the forward threshold is met
(around 0.7 V). The nearly constant voltage across the diode in forward bias also confirms its
rectifying behavior.
Overall, both experiments successfully demonstrate the fundamental properties of diodes. The
results are consistent with theoretical expectations—underscoring the diode’s ability to allow
current flow in one direction while blocking it in the opposite direction.
