What is a Varistor? How its protect our devices.


Hey, guys, if you ever open any type of electronic device like a TV, sound system, stabilizer, etc., you will definitely notice that there are many types of small components embedded in it. These components may be a diode, transistor, resister, MOSFET, inductor, capacitor, varistor, etc. And all these components work differently in different conditions. However, in this post, we will look at varistor. In this post, I will discuss what varistor is and its working principle. And what is the use of this device?

What is a varistor?

Varistor is a type of resister whose resistance varies at different voltage levels. It means the resistance of this device depends on the supply voltage. That’s why we call it a VDR (voltage-dependent resistor). Varistor characteristics include nonlinear and nonlinear ohmic. which is a diode-type characteristic.

What is a varistor
image credit : wikipedia

This device decreases resistance when high voltage passes through it. and make a short circuit. It means that, in the case of high voltage, current can flow through this device. But in the case of resistors, this does not happen. Resister behaves consistently in all circumstances.

Generally, this devices are made from two types of materials: copper oxide and germanium oxide.


Its symbol is just like a resistor, but a line crosses the resistor symbol. which shows the variable resistor, and this symbol presents a varistor. The varistor’s symbol is shown below.

Varistor Symbol
Resister Symbol

What materials are used in Varistor: –

In general, two types of materials are used in this device. Which are metal oxide and silicone oxide. However, the metal oxide type is the most common varistor. It’s known as the MOV.

Uses of this device:

As we know, it is an electronic device. And it’s likely that we use it in every electronic device. This device is used in electronic devices for protection purposes.

This device saves our devices from excessive transient voltage. This excessive transient voltage occurs when a high load disconnects from the supply. And in this case, other connected devices can get a high surge of voltage. and can get burned.

To solve this problem, we use this device. This device is used in various types of devices like TVs, display boards, extension boards, mobile chargers, tube lights, LED lights, etc.


What is the proximity effect? How to mitigate it?

What is the Ferranti effect and how to mitigate it?

A varistor works as follows:

Suppose that a load is connected to the supply. And use the variator in parallel with the load. As we can see in the figure below, and our supply voltage is 250 volts.

That’s why we will also use a 250-volt varistor. when the excessive transient voltage occurs in a circuit that is higher than 250 volts. In this case, the varistor senses the high voltage and works like a good conductor.

As a result, this device allowed all of the excessive transient voltage to pass through itself. and make a short circuit. Due to this effect, overvoltage can’t reach the connected load. A fuse will be burned and the circuit breaker will trip when the varistor makes a short circuit. Thus, our connected load will be safe.

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