What are varistors used for?
What are varistors used for?
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. A capacitor may be installed across the signal lines. However, this capacitor cannot suppress voltage surges.
How does MOV work?
The term MOV stands for “Metal Oxide Varistor”. As the name Varistor suggests, it is a variable resistor. But unlike a potentiometer, the resistance of the MOV changes automatically based on the voltage across. If the voltage across it increases the resistance decreases and vice versa.
What is the difference between varistor and thermistor?
A thermistor is one that changes value with temperature. One is voltage sensitive the other temperature sensitive. A varistor is resistor that changes resistance with applied voltage. A thermistor is one that changes value with temperature.
How do I read varistor code?
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.
Do varistors 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 are varistors rated?
Multi-layer varistor (MLV) devices provide electrostatic discharge protection to electronic circuits from low to medium energy transients in sensitive equipment operating at 0-120 volts dc. They have peak current ratings from about 20 to 500 amperes, and peak energy ratings from 0.05 to 2.5 joules.
What are varistors made of?
The most common modern type of varistor is the metal-oxide varistor (MOV). This type contains a ceramic mass of zinc oxide grains, in a matrix of other metal oxides, such as small amounts of bismuth, cobalt, manganese oxides, sandwiched between two metal plates, which constitute the electrodes of the device.
What is the difference between MOV and NTC?
Varistor belongs to metal oxide varistor (MOV), which is a non-linear resistance element with zinc oxide (ZnO) as the main component. NTC thermistor is a temperature-sensitive resistor made of negative temperature coefficient (NTC) and special semiconductor ceramic materials.
What is varistor thermistor?
Thermistors are electrical resistors whose value is dependent on the temperature of their material. Varistors are electrical resistors whose value depends on the voltage applied across them. This voltage-dependent characteristic is used for protection of devices and circuits against overvoltage.
How do varistors fail?
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.
Are varistors directional?
Modern varistors are primarily based on sintered ceramic metal oxide materials which exhibit directional behavior only on a microscopic scale. Varistors are used as control or compensation elements in circuits either to provide optimal operating conditions or to protect against excessive transient voltages.
What happens when a varistor fails?
