EDC Lab (EE-300) | Lab 2: Zener Diode Characteristics
LAB REPORT
Electronic Devices and Circuits (EE-300)
Lab 2: Zener Diode Characteristics
Name Reg. No.
Class / Sec Group No.
Instructor Date
1. AIM
1. To observe and draw the I-V characteristics of a Zener diode.
2. To find the voltage regulation of a given Zener diode.
2. EQUIPMENT
• Zener diode (1)
• Regulated DC power supply, 0–30 V (1)
• Voltmeter, 0–20 V (1)
• Ammeter, 0–20 mA (1)
• Resistor, 1 kΩ
• Breadboard and connecting wires
• Proteus simulation software (for the simulation part)
3. THEORY
A Zener diode is a heavily doped p-n junction diode designed to work in the reverse
breakdown region. Under forward bias it behaves like an ordinary silicon diode and starts
conducting at about 0.6 to 0.7 V. Under reverse bias it blocks current until the reverse voltage
reaches the Zener voltage (VZ). At that point the current rises very sharply while the voltage
across the diode stays almost constant. This near-constant voltage is what makes the Zener
diode useful as a voltage regulator.
The value of VZ is set by the doping level: heavier doping gives a narrower depletion region
and a lower breakdown voltage. Two mechanisms cause breakdown. The Zener effect (field-
induced tunnelling) dominates below about 5 V, and the avalanche effect (impact ionisation)
dominates above about 6 to 7 V.
The current in breakdown must be limited, or the diode will overheat and be damaged. The
maximum safe current is IZ(max) = PZ / VZ. For example, a 1 W, 10 V Zener can carry at
most 0.1 A (100 mA). For this reason a resistor is always connected in series with the diode,
here 1 kΩ.
The quality of regulation is measured by the percentage regulation, which compares the diode
voltage with no load (VNL) and with a load connected (VFL):
% Regulation = (VNL − VFL) / VFL × 100
Page 1
, EDC Lab (EE-300) | Lab 2: Zener Diode Characteristics
4. PROCEDURE
1. Connect the power supply, voltmeter and ammeter with the Zener diode for reverse
bias, as in the circuit diagram (the Zener cathode toward the positive terminal).
2. Increase the supply voltage from 0 V to 20 V in the steps given in the observation
table.
3. At each step, measure the voltage across the diode and the current through it, and
record them in the table.
4. Reverse the polarity of the supply to obtain forward bias and repeat the readings.
5. For regulation, record the diode voltage with no load (VNL), then connect the load
resistor RL and record the diode voltage (VFL) and current (IFL).
6. Plot the forward and reverse characteristics on one graph and calculate the percentage
regulation.
7. Build the same circuits in Proteus, run the simulation and compare the results with the
hardware readings.
Page 2
LAB REPORT
Electronic Devices and Circuits (EE-300)
Lab 2: Zener Diode Characteristics
Name Reg. No.
Class / Sec Group No.
Instructor Date
1. AIM
1. To observe and draw the I-V characteristics of a Zener diode.
2. To find the voltage regulation of a given Zener diode.
2. EQUIPMENT
• Zener diode (1)
• Regulated DC power supply, 0–30 V (1)
• Voltmeter, 0–20 V (1)
• Ammeter, 0–20 mA (1)
• Resistor, 1 kΩ
• Breadboard and connecting wires
• Proteus simulation software (for the simulation part)
3. THEORY
A Zener diode is a heavily doped p-n junction diode designed to work in the reverse
breakdown region. Under forward bias it behaves like an ordinary silicon diode and starts
conducting at about 0.6 to 0.7 V. Under reverse bias it blocks current until the reverse voltage
reaches the Zener voltage (VZ). At that point the current rises very sharply while the voltage
across the diode stays almost constant. This near-constant voltage is what makes the Zener
diode useful as a voltage regulator.
The value of VZ is set by the doping level: heavier doping gives a narrower depletion region
and a lower breakdown voltage. Two mechanisms cause breakdown. The Zener effect (field-
induced tunnelling) dominates below about 5 V, and the avalanche effect (impact ionisation)
dominates above about 6 to 7 V.
The current in breakdown must be limited, or the diode will overheat and be damaged. The
maximum safe current is IZ(max) = PZ / VZ. For example, a 1 W, 10 V Zener can carry at
most 0.1 A (100 mA). For this reason a resistor is always connected in series with the diode,
here 1 kΩ.
The quality of regulation is measured by the percentage regulation, which compares the diode
voltage with no load (VNL) and with a load connected (VFL):
% Regulation = (VNL − VFL) / VFL × 100
Page 1
, EDC Lab (EE-300) | Lab 2: Zener Diode Characteristics
4. PROCEDURE
1. Connect the power supply, voltmeter and ammeter with the Zener diode for reverse
bias, as in the circuit diagram (the Zener cathode toward the positive terminal).
2. Increase the supply voltage from 0 V to 20 V in the steps given in the observation
table.
3. At each step, measure the voltage across the diode and the current through it, and
record them in the table.
4. Reverse the polarity of the supply to obtain forward bias and repeat the readings.
5. For regulation, record the diode voltage with no load (VNL), then connect the load
resistor RL and record the diode voltage (VFL) and current (IFL).
6. Plot the forward and reverse characteristics on one graph and calculate the percentage
regulation.
7. Build the same circuits in Proteus, run the simulation and compare the results with the
hardware readings.
Page 2
