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Varistor
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<p>A varistor (a.k.a. voltage-dependent resistor (VDR)) is a <a href="/facts/Surge_protector/o3LqlVNv">surge protecting</a> <a href="/facts/Electronic_component/F3NBVv4Q">electronic component</a> with an <a href="/facts/Electrical_resistance/hxSt0UAj">electrical resistance</a> that varies with the applied voltage. It has a <a href="/facts/Nonlinear_system/4aYItALC">nonlinear</a>, non-<a href="/facts/Ohm%27s_law/PjfEyTgI">ohmic</a> <a href="/facts/Current%E2%80%93voltage_characteristic/wft425cq">current–voltage characteristic</a> that is similar to that of a <a href="/facts/Diode/JyaoyGnk">diode</a>. Unlike a diode however, it has the same characteristic for both directions of traversing current. Traditionally, varistors were constructed by connecting two <a href="/facts/Rectifier/me8XDxND">rectifiers</a>, such as the copper-oxide or germanium-oxide rectifier in <a href="/facts/Antiparallel_(electronics)/mGx0Rw2o">antiparallel</a> configuration. At low voltage the varistor has a high electrical resistance which decreases as the voltage is raised. Modern varistors are primarily based on sintered <a href="/facts/Ceramic/9JKudpqX">ceramic</a> metal-oxide materials which exhibit directional behavior only on a microscopic scale. This type is commonly known as the metal-oxide varistor (MOV). </p><p>Varistors are used as control or compensation elements in <a href="/facts/Electrical_network/zt94kTW0">circuits</a> either to provide optimal operating conditions or to protect against excessive transient <a href="/facts/Voltage/EN2po6N2">voltages</a>. When used as protection devices, they <a href="/facts/Shunt_(electrical)/EEBIeEdo">shunt</a> the current created by the excessive voltage away from sensitive components when triggered. </p><p>The name <i>varistor</i> is a <a href="/facts/Portmanteau/d124JEbz">portmanteau</a> of <i>varying resistor</i>. The term is only used for non-ohmic varying resistors. <a href="/facts/Resistor/JrsGReM6">Variable resistors</a>, such as the <a href="/facts/Potentiometer/UtTC1Nvj">potentiometer</a> and the <a href="/facts/Rheostat/UtTC1Nvj">rheostat</a>, have <a href="/facts/Ohm%27s_law/PjfEyTgI">ohmic</a> characteristics. </p>