Hello everyone! Today, I'm going to give you a thorough overview of Zener Diode. This blog is the continuous blog of the series of Diodes so if you wish to read about any other diodes or basic's of diode then you may visit our website. In this blog, we will be discussing the Definition, Symbol, Construction, Zener Diode IV-Characteristics, Advantages of the Zener diode, How to choose a perfect Zener diode, Functions of Zener Diode, Applications, Zener Diode's no. and so on.
A Zener diode allows current to flow not just from anode to cathode, but also in the opposite direction when the Zener voltage is reached. Zener diodes are the most widely used semiconductor diodes because of this feature. Zener diodes are used for voltage regulation, as reference elements, surge suppressors, and in switching applications and clipper circuits Let us learn about the role of Zener diodes, as well as their operation, and more, in this blog.
When ordinary silicon diodes are reverse biased, they block all current and are damaged if the reverse voltage is too high. As a result, these diodes are never used in the failure region.
Zener diodes, on the other hand, are unique. They are specifically intended to perform without fail in the breakdown region.
Zener diodes are used as voltage regulators, and circuits that keep the load voltage almost constant despite large fluctuations in line voltage and load resistance. A Zener Diode also called a Breakdown Diode, is a severely doped semiconductor device that operates in the reverse direction. The junction breaks down and the current flows in the opposite direction when the voltage across the terminals of a Zener diode is reversed and the potential exceeds the Zener Voltage (knee voltage). This effect is known as Zener Effect.
There are several packages available in Zener diode. Some are employed for high levels of power dissipation and the rest are contained with surface mount forms. A tiny glass encapsulation surrounds the most popular form of Zener diode. The cathode side of the diode is marked by a band around one end.
The lines of the symbol resemble a "Z," which stands for "Zener."
How does a Zener Diode work in reverse bias?
When forward-biased, a Zener diode behaves just like a regular diode. When the diode is connected in reverse - bias state, however, a small leakage current flows through it. The current begins to flow through the diode when the reverse voltage reaches the predetermined breakdown value (Vz). After reaching a maximum defined by the series resistor, the current stabilizes and remains constant throughout a wide range of applied voltage.
There are two types of breakdowns for a Zener Diode:
- Avalanche Breakdown
- Zener Breakdown
Zener Breakdown in Zener Diode
A very intense electric field appears across a narrow depletion region when a reverse voltage is given to a Zener diode. The electric field is strong enough to break the covalent bonds of some valence electrons, allowing them to move into the conduction band. These electrons then become free electrons that can conduct electricity. The Zener effect is said to have occurred breakdown because a large number of such free electrons create a large reverse current across the Zener diode.
Avalanche Breakdown in Zener Diode
At high reverse voltage, avalanche breakdown occurs in both normal and Zener diodes. When the free charge carrier collides with other atoms, more electrons and holes are created. The reverse bias current develops when these free electrons begin to move across the circuit. The junction is completely destroyed by the reverse bias current. And once the junction breaks down, it's impossible to get it back to its original place. The saturation current in reverse bias causes the avalanche breakdown. As a result, if we increase the reverse voltage, the electric field will also increase.
V-I Characteristics of Zener Diode
When reverse-biased voltage is applied to the Zener diode, it allows only a small amount of leakage current until the voltage is less than Zener voltage.
The V-I characteristics of a Zener diode can be divided into two parts:
(i) Forward Characteristics
(ii) Reverse Characteristics
APPLICATION OF ZENER DIODE
Following are the applications of Zener diode
For regulating voltage across small loads, a Zener diode is employed as a voltage regulator. To reverse bias the load, a Zener diode is connected parallel to it, and after the Zener diode exceeds knee voltage, the voltage across the load becomes constant. The Zener diode is connected across the load RL in this example. The voltage across the load must be adjusted so that it does not exceed Vz. Choose a Zener diode with a Zener breakdown voltage that is close to the voltage we need across the load. In a reverse bias state, connect the Zener diode. A large amount of current flows through the diode when the voltage across it reaches the Zener breakdown voltage. The voltage drop across the load is equal to the Zener breakdown voltage since the load is in parallel with the diode. The Zener diode creates a route for current to pass, which protects the load from excessive currents.
The voltage across the resistor lowers when the input voltage exceeds the Zener breaking voltage, resulting in a short circuit. The Zener diode can be used to avoid this.
By limiting the portions of either one or both half cycles of an AC waveform, the Zener diode is used to change AC waveform clipping circuits.
Zener diode specifications
Zener diodes vary in specifications such as maximum reverse current, nominal working voltage, power dissipation, maximum reverse current, and packaging. Some commonly used specifications include
- Voltage Vz: The reverse breakdown voltage—2.4 V to around 200 V; can go up to 1 kV, while the maximum for the surface-mounted device (SMD) is about 47 V
- Current Iz (max.): Maximum current at the rated Zener voltage Vz—200 uA to 200 A).
- Current Iz (min.): Minimum current required for the diode to break down—5 mA and 10 mA.
- Power rating: The product of the voltage across the diode and the current passing through determines the maximum power that the Zener diode can dissipate. 400 mW, 500 mW, 1 W, and 5 W are usual values; for surface mounted, 200 mW, 350 mW, 500 mW, and 1 W are typical values
- Voltage tolerance: Typically ±5%.
- Package: Leaded devices and the surface mount either as discrete devices or within integrated circuits.
- Zener resistance (Rz): The diode exhibits some resistance as evident from the IV characteristics.
Some Popular Zener diode
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Zener Diode Standard Zener Voltages
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