# What is a varistor diode?

## What is a varistor diode?

A varistor is an electronic component with an electrical resistance that varies with the applied voltage. Also known as a voltage-dependent resistor (VDR), it has a nonlinear, non-ohmic current–voltage characteristic that is similar to that of a diode. The name varistor is a portmanteau of varying resistor.

## What is the difference between diode and varistor?

The ability to protect sensitive circuit parts from high transient voltages is the same function a TVS diode provides. Varistors are bidirectional components suitable for both AC and DC circuits. They come in different design packages.

What happens when a varistor fails?

Under different current conditions, failure modes include electrical puncture (see Figure 4), physical cracking (see Figure 5), and thermal runaway. Cracking happens because varistors are basically a ceramic material, and hitting them with a sharp high-amplitude surge is like hitting a dinner plate with a hammer.

### How do I choose a varistor?

Consider the maximum continuous voltage that will be applied to the varistor including any high line conditions (i.e., 110% or more of nominal voltage). Ratings are given for continuous sinusoidal AC and DC voltages. If a nonsinusoidal waveform is applied, the recurrent peak voltage should be limited to √2x VM(AC).

### How is varistor measured?

How do you test for varistor? Touch one meter probe to the free varistor lead and the other probe to the connected lead. Read the resistance on the meter. If it reads nearly infinite resistance, the varistor is still good.

How many types of varistor are there?

There are two main types of Varistors available in market namely the silicon carbide and metal oxide Varistors.

## How is varistor value calculated?

The simplest ways of determining the current duration are simulation or measurement (τ = t*r). The time constant can also be calculated to an approximation with equation 13. Here the varistor resistance of voltage class K20 is calculated for 1 A.

## Does a varistor have polarity?

Does a varistor have polarity? In the case of metal oxide varistor, a zinc-oxide layer is basically sandwiched between two metal electrodes. As a result, there is no polarity.

How do I know if my varistor is bad?

Touch one meter probe to the free varistor lead and the other probe to the connected lead. Read the resistance on the meter. If it reads nearly infinite resistance, the varistor is still good. If it reads very low resistance, the varistor is blown.

### Can I remove varistor from circuit?

Metal-oxide varistors (MOVs) are the most widely used device for protecting sensitive electronics from damaging overvoltage transients. To date, most consider MOVs to be sacrificial devices, expected to disconnect (open) in the event of a failure. Unfortunately, this is not the case.

### How does varistor protection circuit?

Varistors are used to protect a circuit from high voltage surges. When a high voltage surge is applied to a circuit, the outcome is usually catastrophic to the circuit. When a voltage surge exceeding a specified voltage (varistor voltage) is applied, the varistor suppresses the voltage to protect the circuit.

How can you tell a good varistor?