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Encyclopedia > Varistor

A varistor is an electronic component with a significant non-ohmic current-voltage characteristic. The name is a portmanteau of variable resistor. Varistors are often used to protect circuits against excessive transient voltages. A varistor is also known as Voltage Dependent Resistor or VDR. The ohm (symbol: Ω) is the SI unit of electric resistance. ... In electricity, current refers to electric current, which is the flow of electric charge. ... This article may be too technical for most readers to understand. ... Look up Portmanteau in Wiktionary, the free dictionary. ... Resistor symbols A resistor is a two-terminal electrical or electronic component that passes a current that is proportional to the potential difference between its terminals in accordance with Ohms law. ... An electrical network or electrical circuit is an interconnection of electrical elements such as resistors, inductors, capacitors, diodes, switches and transistors. ... This article may be too technical for most readers to understand. ...


Metal oxide varistor

A metal oxide varistor for high voltage (385 V)
A metal oxide varistor for high voltage (385 V)

The most common type of varistor is the Metal Oxide Varistor (MOV). This contains a mass of zinc oxide grains, in a matrix of other metal oxides, sandwiched between two metal plates (the electrodes). The boundary between each grain and its neighbour forms a diode junction, which allows current to flow in only one direction. The mass of randomly oriented grains is electrically equivalent to a network of back-to-back diode pairs, each pair in parallel with many other pairs. When a small or moderate voltage is applied across the electrodes, only a tiny current flows, caused by reverse leakage through the diode junctions. When a large voltage is applied, the diode junctions break down because of the avalanche effect, and a large current flows. The result of this behaviour is a highly nonlinear current-voltage characteristic, in which the MOV has a high resistance at low voltages and a low resistance at high voltages. ImageMetadata File history File links Download high resolution version (1485x1980, 374 KB) Summary Description: Varistor (voltage dependent resistor). ... ImageMetadata File history File links Download high resolution version (1485x1980, 374 KB) Summary Description: Varistor (voltage dependent resistor). ... Hot metal work from a blacksmith In chemistry, a metal (Greek: Metallon) is an element that readily forms ions (cations) and has metallic bonds, and metals are sometimes described as a lattice of positive ions (cations) in a cloud of electrons. ... An oxide is a chemical compound of oxygen with other chemical elements. ... General Name, Symbol, Number zinc, Zn, 30 Chemical series transition metals Group, Period, Block 12, 4, d Appearance bluish pale gray Atomic mass 65. ... Types of diodes In electronics, a diode is a component that restricts the direction of movement of charge carriers. ... An avalanche diode is a silicon diode that is designed to break down and conduct at a specified reverse bias voltage. ...


If the size of the transient pulse (often measured in joules) is too high, the device may melt, burn, vaporize, or otherwise be damaged or destroyed. For example, a nearby lightning strike may permanently damage a varistor. The joule (symbol: J) is the SI unit of energy, or work. ... Lightning over Pentagon City in Arlington County, Virginia Cloud to cloud lightning Lightning is a powerful natural electrostatic discharge produced during a thunderstorm. ...


Important parameters for varistors are response time (how long it takes the varistor to break down), maximum current and a well-defined breakdown voltage. When varistors are used to protect communications lines (such as phone lines used for modems), their capacitance is also important because high capacitance would absorb high-frequency signals, thereby reducing the available bandwidth of the line being protected. A parameter is a measurement or value on which something else depends. ... The term communications is used in a number of disciplines: Communications, also known as communication studies is the academic discipline which studies communication. ... Within phonetics, a phone is a speech sound or gesture considered as a physical event without regard to its place in the phonology of a language. ... A modem (a portmanteau word constructed from modulator and demodulator) is a device that modulates a carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. ... Capacitance is a measure of the amount of electric charge stored (or separated) for a given electric potential. ... Bandwidth is a measure of frequency range. ...


Varistors compared to other transient-suppressors

Another method for suppressing voltage spikes is the transient voltage suppression diode (TVS). There are two significant differences between a varistor and a TVS: A transient voltage suppression diode is a device used to protect sensitive electronics from voltage spikes induced on connected wires. ...

  • Varistors typically have an order of magnitude more leakage current, that is, they will drain a battery 10 times faster.
  • Varistors degrade over time. This shows up after repeated transient events.

Another transient voltage suppression device is the gas discharge tube which, unfortunately, has a much higher breakdown voltage, but also a very much higher current capacity, and can withstand multiple high-voltage hits (for example, from lightning) without significant degradation. Lightning over Pentagon City in Arlington County, Virginia Cloud to cloud lightning Lightning is a powerful natural electrostatic discharge produced during a thunderstorm. ...


*Note: only non-ohmic variable resistors are usually called varistors. Other, ohmic types of variable resistor include the potentiometer and the rheostat. schematic symbol for a potentiometer Originally the term potentiometer was used to describe an apparatus used to measure the potential (or voltage) in a circuit by tapping off a portion of a known voltage from a resistive slide wire and comparing it with the unknown voltage by means of a... schematic symbol for a potentiometer In this article: Rheostat and potentiometer. ...


See also

  • http://www.radioradar.net/docs/varistor.php some info in russian.

  Results from FactBites:
 
Varistor - Wikipedia, the free encyclopedia (422 words)
A varistor is an electronic component with a significant non-ohmic current-voltage characteristic.
Varistors are often used to protect circuits against excessive transient voltages.
When varistors are used to protect communications lines (such as phone lines used for modems), their capacitance is also important because high capacitance would absorb high-frequency signals, thereby reducing the available bandwidth of the line being protected.
Varistor - definition of Varistor in Encyclopedia (435 words)
A varistor is a type of resistor with a significantly non-ohmic current-voltage characteristic.
Varistors are often used to protect circuits against excessive voltage by acting as a spark gap.
Varistors typically have an order of magnitude more leakage current, ie they will drain a battery 10 times faster.
  More results at FactBites »

 
 

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