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Metal-oxide varistor manufactured by Siemens & Halske AG. Modern varistor schematic symbol, which is the same as a thermistor symbol [1]. A varistor (a.k.a. voltage-dependent resistor (VDR)) is a surge protecting electronic component with an electrical resistance that varies with the applied voltage. [2]
Surge Protection Device (SPD) for installation in a low-voltage distribution board. A surge protector (or spike suppressor, surge suppressor, surge diverter, [1] surge protection device (SPD), transient voltage suppressor (TVS) or transient voltage surge suppressor (TVSS)) is an appliance or device intended to protect electrical devices in alternating current (AC) circuits from voltage spikes ...
In certain materials like ferric oxide (Fe 2 O 3) with titanium (Ti) doping an n-type semiconductor is formed and the charge carriers are electrons. In materials such as nickel oxide (NiO) with lithium (Li) doping a p-type semiconductor is created, where holes are the charge carriers. [14] This is described in the formula
Metal oxide varistors typically have lower resistance as they heat up; if connected directly across a power bus, for protection against voltage spikes, a varistor with a lowered trigger voltage can slide into catastrophic thermal runaway and sometimes a small explosion or fire. [23]
These are designed to tolerate large surge currents for the suppression of overvoltage transients. In many applications this function is now served by metal oxide varistors (MOVs), particularly for trapping voltage transients on the power mains.
In some DC circuits, a varistor made of inexpensive metal oxide, called a metal oxide varistor (MOV) is used. They may be unipolar or bipolar, like two inverse-series silicon Zener diodes, but are prone to wear out after about a dozen max-rated joules of energy absorption such as lightning protection, but are suitable for lower energy.
Metal-oxide varistor (MOV) + Up to 70 000 Amps surge + Lifetime @ 100 Amps, 8x20 uS pulse shape: 1000 surges - Shunt capacitance >500 pF - Leakage approximately 10 micro amps Avalanche diode + Lifetime @ 50 Amps, 8x20 uS pulse shape: infinite + Shunt capacitance: 50 pF - Low surge capability: 50 Amps @ 8x20 uS pulse shape - Leakage ...
A transient-voltage-suppression diode can respond to over-voltages faster than other common over-voltage protection components such as varistors or gas discharge tubes. The actual clamping occurs in roughly one picosecond, but in a practical circuit the inductance of the wires leading to the device imposes a higher limit. This makes transient ...