School of Mechanical & Manufacturing Engineering

(SMME)

National University of Science and Technology (NUST)

ELECTRONICS ENGINEERING (EE – 227)

ASSIGNMENT NO.1

ZENER DIODE

Program: BE-Aerospace Semester: 4th

Session: Spring 2025 Course Code: EE-227

NAME: Ali Tawasal

455925
AE-01

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DEFINITION
Zener diodes are semiconductor devices that allow current to flow in both directions but
specialize in current flowing in reverse. Also known as breakdown diodes, Zener diodes are
the most common electronic components used as stable voltage references for electronic
circuits.

HISTORY
American physicist, Dr. Clarence Melvin Zener, first described the electronic properties of
Zener diodes while researching the breakdown mechanisms of semiconductor materials. As a
theoretical physicist at Bell Labs in New Jersey, he wrote a research paper later published in
1934, identifying a type of electrical breakdown later known as the Zener effect. These
specific processes were named after him in the years afterward in his honour.

ZENER DIODE INFOGRAPHIC

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FUNCTIONALITY
Current going across the terminals in reverse bias (backward) is called the Zener
effect. When voltage potential is met, this causes the Zener voltage (Vz)/breakdown voltage.
Zener diodes uniquely consist of a heavily doped P-N junction that allows current to flow in
reverse when reaching Vz. A well-defined Vz can conduct current continuously in reverse
bias without getting damaged. Current then increases to a maximum level determined by a
series resistor and stabilizes, remaining constant over a range of applied voltages. Therefore,
Zener diodes are applicable for use as voltage regulators.
A Zener diode operates within the normal range of forward bias, with a turn-on voltage
between 0.3V and 0.7V. When connected in reverse bias, the current flows backward, thus
causing a small leakage of current to flow. As the reverse voltage increases to the arranged
Vz, current flows throughout the diode. Current increases to a maximum decided by the
series resistor and then stabilizes to remain constant over a range of applied voltages.
Zener diodes have two breakdown effects. Knowing these two effects help with
understanding their functionality. First is the Zener effect, prevalent in voltages below 5.5V
and involves a tunneling effect to cause the breakdown. The second is the avalanche
breakdown or impact ionization which occurs in voltages above 5.5V. These breakdowns
both result in the same behavior, and they do not require different circuitry, but each does
have a different temperature coefficient. The Zener effect has an anode (negative) terminal
temperature coefficient, while the avalanche has a cathode (positive) terminal temperature
coefficient. Both temperature effects are almost equal to 5.5V. They cancel each other out,
making Zener diodes rated at around 5.5V and stable over a wide range of temperature
requirements.
Think of a Zener diode like two diodes in parallel, facing opposite directions. The voltage
that's forward bias in a Zener diode has a voltage drop of 1V needed for the diode to turn on
for the current to flow. The forward voltage is forward biased. The current flowing backward
is considered the Zener voltage or reversed biased due to its properties. An example of the
Zener voltage is 3.3V. For the current to flow across the diode, the current must maintain at
least a minimum of this voltage. Having a predictable voltage drop makes Zener diodes not
only useful as voltage regulators, but a correctly set Zener diode may limit the voltage of
other devices.

COMMON SPECIFICATIONS
 Current Iz (max): Maximum current at the rated Zener Voltage (Vz – 200μA to
200A).

 Current Iz (min): Minimum current value required for a diode to break down.

 Forward Bias: Voltage going across a diode that allows the current to flow easily in
one direction.

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  Power Rating: Denotes the maximum power the Zener diode can dissipate and is a
product of the diode voltage/current flowing through it.

 Reverse Bias/Zener Effect: Voltage going across a diode in the opposite direction of
forward bias, this particular voltage doesn't cause any detectable current to flow,
changes AC to DC current, and manipulates other electronic signals.

 Temperature Stability: Diodes around 5V have the best stability.

 Voltage Tolerance: Typically ±5%

 Zener/Breakdown Voltage (Vz): This is the minimum voltage that causes a portion
of an insulator to experience a breakdown and become electrically conductive.
Voltage ranges from 2.4V to 200V and can go up to 1kV, while the maximum for the
surface-mounted device is 47V.

 Zener Resistance (Rz): The resistance exhibited to the Zener diode.

KEY TERMS
 Avalanche Breakdown: Occurs when a high reverse bias voltage increases the
electric field and further expands up the depletion region.

 Diodes: A two-terminal electronic component that conducts current in one

asymmetrical direction with a low resistance of zero and a high infinite resistance in
the other.

 Doping: The process of adding certain chemical elements which contain small
impurities to a semiconductor to change its electric conductivity.

 Electrical Breakdown: This process occurs when insulated electrical materials

exposed to high voltage become an electrical conductor and electric current flows
through it. It's also known as a dielectric breakdown.

 Impact Ionization: The process in a material by which one energetic charge carrier
can lose energy by the creation of other charge carriers.

 P-N Junction: A boundary or interface between two types of semiconductor

materials, p-type (positive), and the other is n-type (negative), which are both inside a
single crystal of semiconductor. The "p" side contains an excess of holes, while the
"n" side contains an excess of electrons in the outer shells of the “n” side’s electrically
neutral atoms.

 Semiconductors: A material product with an electrical conductivity value falling

between a conductor such as a metallic copper and an insulator, such as glass.

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  Tunneling: A purely quantum-mechanical process in which a microscopic particle
can penetrate a potential barrier even when the energy of the incident particle is lower
than the height of the barrier.

CHARACTERISTIC CURVE

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EXAMPLES AND APPLICATIONS
Surge Suppressor: An electrical device, also known as a surge protector, that is used to
protect equipment against power surges and voltage spikes while blocking voltage over a
safe threshold of approximately 120V.

Switching Signals: An output signal switching device (or OSSD) is an electronic device in a
machine's safety system that provides a coded signal that, when interrupted due to a safety
event, signals the machine to shut down. This helps avoid a stray signal operating a machine
during unsafe conditions.

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Voltage Reference: An electrical device that produces a fixed (constant) voltage regardless
of the loading on the device, power supply variations, temperature changes, and the passage
of time.

Voltage Regulator: When the load voltage equals the Zener voltage of the diode, the series-
connected resistors limit the current through the diode. This serves to regulate voltage when
there is an excess amount of voltage while the diode is conducting. The diode generates
noise which can be suppressed by adding a large value decoupling capacitor across the
diode.

Voltage Shifter: When applied to a circuit with a resistor, Zener diodes act as voltage
shifters. The circuit lowers the output voltage equal to the diodes’ Zener voltage.

Waveform Clipper: Reshapes a signal and prevents voltage spikes from affecting circuits
connected to a power supply.

Zener diodes applied to an electronic circuit board

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Power strips are used as surge protectors

Smartphones contain voltage regulators

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Application examples that utilize Zener diodes are smartphones which contain voltage,
voltage reference devices like digital multimeters, and power strips which are surge
suppressors. Electronic circuit boards contain Zener diodes and are used to shift voltage, be a
waveform clipper, and switch signals in a variety of devices involving Bluetooth technology,
televisions, transmitters that produce radio waves, and more.

CONCLUSION
Some notable manufacturers of Zener diodes include Nexperia, Vishay, ROHM, and
Toshiba. These manufacturers produce Zener diodes for use in a variety of electronic
components specializing in industries like consumer electronics, automotive,
telecommunications, computing, industrial, and more. Zener diodes are small components
that play a big role in the devices that serve industry professionals and everyday consumers,
and they will continue to do so for years to come.

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