Varistor facts for kids
A varistor, VDR, (voltage dependent resistor) is a type of resistor. It controls the current depending on the voltage.
In these devices resistance drops sharply at a certain threshold voltage. Once the voltage across the device reaches the threshold, there is a breakdown of the electrical structure in the vicinity of the grain boundaries, which results in its electrical resistance dropping from several megohms down to a few hundred ohms. The major advantage of these is that they can dissipate a lot of energy, and they self reset–after the voltage across the device drops below the threshold, its resistance returns to being high.
This makes them ideal for surge-protection applications. As there is control over the threshold voltage and energy tolerance, they find use in all sorts of applications. The best demonstration of their ability can be found in electrical substations, where they are employed to protect the infrastructure from lightning strikes. They have rapid response, are low maintenance, and do not appreciably degrade from use, making them virtually ideal devices for this application.
They can be used to protect electronics from voltages that could damage components.
Images for kids
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Modern varistor schematic symbol.
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Varistor current vs voltage for zinc oxide (ZnO) and silicon carbide (SiC) devices
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High voltage varistor
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Plug assembly with surge protector circuitry
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Western Electric 3B varistor made in 1952 for use as click suppressor in telephone sets
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Circuit of the traditional construction of varistors used as click suppressors in telephony
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Western Electric Type 44A varistor manufactured in 1958, mounted on a U1 telephone receiver element for click suppression.
See also
In Spanish: Varistor para niños
