There are many different kinds of surge protectors. Surge protectors installed on power lines don’t absorb or otherwise diminish damaging power surges. Their primary function is to divert these destructive forces away from your sensitive circuitry.
There are four basic kinds of surge protectors: metal oxide varistors (MOVs), avalanche diodes, filters, and gas tubes.
Metal oxide varistors (MOVs) are a common choice. The word varistor is a combination of two words: variable resistor. As these words imply, an MOV is a highly resistive device that triggers during an AC power surge and diverts the excess voltage, preventing it from reaching your expensive computer equipment.
MOVs are designed to accommodate surge levels up to a specified breakdown voltage. When this limit is exceeded, the MOV varies from a highly resistive state to a state of low resistance. The excess energy is “clipped” from the power line and sent to ground.
Surges occurring at the peak of a sine wave are clipped by the MOV, but high-voltage spikes may still occur (though they’ll eventually be clipped), and the MOV response times can range up to 500 picoseconds. This is the primary weakness of an MOV, but it’s usually overcome by the inclusion of some other suppression technique within the surge protector.
Avalanche diodes, also known as Zener diodes, are semiconductor devices similar to MOVs, but they feature much faster response times (usually less than one picosecond). Avalanche diodes are available in a wider range of sizes to provide accurate and repeatable voltage clamping. However, they have limited ability to withstand large surges, which means they should be combined with other devices to make them useful for lightning surge protection.
Filters are also usually built into surge protectors, along with other suppression devices, to offer enhanced levels of protection. They’re made up of discrete coils, called chocks, and capacitors that are designed to filter noise occurring within specific frequency ranges on AC power lines. Continue reading
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