Metal oxide varistors (MOV) vs VDR Ratings

Admin@AKR Technical


Metal Oxide Varistors ratings, and It is known as MOV. They are one of the most common types of varistors. They are voltage dependent, nonlinear devices that provide transient surge suppression. MOVs are makes primarily of zinc oxide, kobalt and other metal oxides.


Metal oxide varistors (MOV) Data sheet

What is Metal Oxide Varistor

Definition: A Metal Oxide Varistor (MOV) is a two-terminal semiconductor device. It is used in circuits to protect electrical and electronic equipment from excessive voltage transients. Its resistors are constructed based on the applied input voltage. These are the parts that are most commonly found on disk type on electronics boards.

The word varistor is formed by combining the two words variable resistor. This is also known as the Voltage Dependent Resistor (VDR). This is because the VDR's resistance automatically changes with the corresponding change in the voltage applied to it.

It seems to always be placed in the shunt when using tools for protection. It basically does this by protecting a circuit from surge voltages.

The image below shows the symbolic representation of a varistor:

These are basically to protect the circuit from switching surges and voltage fluctuations. These short-circuit when the voltage rises and blow the fuse in the circuit to protect the device.

Construction of Varistor

Varistors are made by pressing crystals of silicon carbide or metal oxide into a ceramic material.

Sintering is done after drying the material at high temperature. These are designed depending on the temperature and ambient conditions given by the electrical characteristics of the device.

To obtain good electrical contacts, the contacts of the material are metallized with silver or gold coating. The varistors are then furnished and coded by merging the leads into the contacts.

These are now commonly used in circuits as voltage clampers. These can also be used for a wide range of voltages. As it is a non-linear device the system absorbs destructive energy to prevent damage and dissipates it in the form of heat.

Usually, zinc oxide is used for its construction, hence it is also known as metal oxide varistor (MOV).

The image below shows the structure of the metal oxide varistor:

Here the varistor is made up of 90% zinc oxide and the remaining 10% is the junction filler material. In stark contrast to a typical silicon carbide metal oxide varistor, the MOV exhibits a low leakage current and accelerates its operation.

Fundamentals of MOV operation

As mentioned above, MOV is a non-linear device. This means that its characteristics do not change gradually, but rather the behavior changes rapidly when the voltage exceeds its parameters. It also features non-ohmic current-voltage characteristics similar to an MOV diode. However, unlike a diode, the current flowing through a MOV has the same behavior in both directions.

Function and behavior of the varistor

Before going into its mode of operation, one must first understand the relationship between voltage and the resistance of the varistors.

Metal oxide varistors (MOV) vs VDR Ratings
Varistor IV Curve 


Varistors exhibit unusual behavior when it comes to resistance. Their resistance comes to increase as the voltage decreases. But as the voltage rises above the rated voltage the resistance decreases rapidly.

Below is some MOV / VDR data for reference, look at it and select the required one.

                                                   Voltage Dependent Resistors (VDR) data sheet


Standard metal oxide varistors (MOV) data sheet



Conclusion
Metal oxide varistors (MOVs) are two-way and non-linear surge suppressor devices. They are widely used in various applications to limit voltage during voltage surges or temporary events. Highly reliable and powerful, these overvoltage protection surge protection MOVs are available in a wide variety of components and ranges. It is hoped that this article will help designers narrow down their search to help them choose the right MOV for their applications.

I hope you have learned from this article about Varistors. Thanks for reading this article to understand Metal Oxide Varistors (MOV) vs Voltage Dependent Resistors (VDR) Ratings.