The Silent Guardian of Voltage Stability is the Zener diode. Small in size, giant in protection-meet the Zener diode. When voltage spikes, Zener strikes! Actually, precision and protection are essential in the electronics industry. When it comes to voltage regulation or surge protection in circuits, one component stands out: the Zener diode. It appears to be a conventional diode, but its behavior under reverse bias distinguishes it. In this article, we will look at the Zener diode symbol, how to do a Zener diode test, and how the Zener diode works as an overvoltage protection device in actual circuits.
What Is a Zener Diode?
A Zener diode is a
type of diode that allows current to flow in the opposite direction after a
specified reverse voltage (known as the Zener breakdown voltage) is reached. A
Zener diode, unlike normal diodes, is designed to withstand reverse voltage
without failure or damage. When forward-biased, it operates like a regular
diode. However, under reverse bias, it maintains a constant voltage after
breakdown, making it ideal for voltage regulation and protection.
Zener Diode Symbol
The Zener diode symbol is same as a regular diode, with a small but important difference in the cathode line:
 |
| Zener diode symbol Source:www.build-electronic-circuits.com |
It is represented by an arrow pointing in the direction of a crooked line. In schematics, the Zener diode symbol can be drawn in three different ways:
 |
| Zener diode representation type Source: www.build-electronic-circuits.com |
Circuit Diagram of Zener Diode
It functions as a single diode when placed in forward-biased conditions, but it is specifically made to operate in reverse-bias conditions. Even when a wide range of currents flow through it, the voltage stays constant when the reverse voltage is applied. It is also utilized in DC circuits as a voltage regulator because of this property. As a Zener Diode voltage regulator, maintaining a steady voltage is its main goal. To restrict the amount of current that can reach the diode, a series resistor is attached to the positive end of the DC circuit. It functions so that even under its breakdown conditions, the reverse-bias can still function. To restrict the amount of current that can reach the diode, a series resistor is attached to the positive end of the DC circuit. It functions so that even under its breakdown conditions, the reverse-bias can still function. Ordinary junction diodes are rarely used because reverse biasing above the breakdown voltage can quickly damage the low-power-rating diode. The Zener diode current should always be kept to a minimum when the maximum load current and the minimum input voltage are supplied to it. Selecting a Zener diode with a voltage that is almost equal to the load voltage which can be expressed as Vz=V becomes simpler when the input voltage and the necessary output voltages are known.
 |
| Circuit diagram of Zener diode Source:testbook.com |
How Does a Zener Diode Work?
A Zener diode operates in two modes:
 |
| Zener diode operation Source:testbook.com |
Forward Bias: If the anode is more positive than the
cathode, it acts like a normal diode and allows current- flow.
Reverse Bias:
Below the Zener
voltage: Very little current flows (just leakage current).
At or above the Zener
voltage: It starts conducting in reverse and maintains a constant
voltage across its terminals.
Here, reverse
voltage is useful in creating reference voltages and protecting
circuits from overvoltage.
According
to the working principle, it functions as a regular diode if the reverse bias
voltage is lower than the breakdown voltage or if it is forward biased. This
indicates that reverse bias prevents current from flowing while forward bias
permits it to do so. The diode then enters the Zener region, where it conducts
without suffering harm, when the voltage in reverse bias exceeds the breakdown
point. Although the current in this area is referred to as avalanche current,
it is also known as Zener current for a Zener diode. The diode retains its
non-conducting state and returns to its original characteristics when the
circuit's voltage drops. The extensive doping of the semiconductor material in
the Zener diode gives it the unique ability to perform in reverse bias and with
avalanche current. Additionally, by adjusting the semiconductor material's
doping level, the breakdown voltage and the thickness of the PN junction's
depletion region can be adjusted to any value based on the appliance's
requirements.
Avalanche
Breakdown
When
the reverse bias voltage is raised to a point where the electric field over the
depletion area is sufficiently powerful to knock electrons out of their valence
bonds and into the conduction band, a Zener diode experiences avalanche
breakdown. An avalanche is a chain reaction that occurs when these electrons
hit with other atoms, releasing additional electrons. The voltage across the
diode falls to a steady value known as the breakdown voltage as a result of the
abrupt surge in current caused by this electron avalanche.
Zener
Breakdown
When
a Zener diode has a narrow depletion area, a tunneling process known as Zener
breakdown takes place. Some of the valence electrons in the p-type material can
tunnel through the depletion region and into the conduction band of the n-type
material when the reverse bias voltage is raised to a level where the electric
field across the depletion region is sufficiently strong. The diode's current
abruptly increases as a result of the electron tunneling, and the breakdown
voltage—a fixed value—drops across the diode.
V-I Characteristics of Zener Diode
The V-I characteristics of a Zener diode are divided into forward and reverse characteristics.
 |
| V-I characteristics of Zener diode Source:testbook.com |
Applications of Zener Diode
- Voltage regulation
- Reference voltage generation
- Overvoltage protection
- Clipping and clamping circuits
- Switching applications
- Wave shaping circuits
Zener Diode Test: How to Check If It's Working
Zener Diode
Test: How to Check If It's Working
A Zener diode
test can determine whether the diode is functional and identify its Zener
breakdown behavior. There are two main ways to test a Zener diode:
1. Using a
Digital Multimeter (Basic Test): Multimeter
is firstly set to diode test mode. Then Red probe is connected to
anode and Black probe to cathode. A forward voltage (~0.6V to 0.8V) should be
displayed.
Reverse the
probes: Should show OL (open loop)
The test only
confirms basic diode behavior.
2. Zener
Breakdown Test (with Power Supply)
To test the Zener
breakdown voltage, we need:
- Variable DC power supply
- Series resistor (1kΩ typically)
- Voltmeter or multimeter
Steps
of Test: The Zener diode is connected in reverse bias: Anode is
connected to ground, cathode to resistor and power supply. The DC voltage is gradually
increased.
Measure
voltage across the Zener diode.
Results:
Before
breakdown: voltage is low.
At
breakdown: voltage stabilizes at the Zener voltage (e.g., 5.1V, 6.2V).
This is a complete
Zener diode test, verifying both direction and breakdown voltage.
Zener Diode as Overvoltage Protection
Zener Diode as
Overvoltage Protection
One of the most
important real-world uses of Zener diodes is protecting sensitive
electronics from voltage spikes. Most digital devices (like
microcontrollers or sensors) are sensitive to voltages above their rated
levels. When it gets over the Zener breakdown level. A Zener diode can shunt
excess voltage safely to ground.
- When voltage is below Zener
voltage → Zener does nothing.
- When voltage exceeds Zener
voltage → it conducts in reverse, keeping
voltage constant at the breakdown level.
Example:
To protect a 5V
device:
Use
a 5.1V Zener diode
Place
it across the input supply with a series resistor
If
input spikes to 12V, Zener conducts and clamps voltage to 5.1V
This is called a clamping
circuit, and it’s a common way to protect against:
- Lightning surges
- Switching transients
- Power supply glitches
Conclusion
Although the Zener diode symbol may not seem like much on paper, its inclusion in a circuit conveys a lot about protection, stability, and dependability. The Zener diode is your electronic bodyguard, whether you're protecting components from hazardous surges or controlling voltage in a precision circuit. The Zener diode is a vital component of contemporary electronic design because of its exceptional reverse voltage control capabilities, straightforward testing procedures, and potent overvoltage protective function.
0 Comments