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Failure protection of varistor
Jan 17, 2019

Common resistance is varistor, lightning protection will be used in general. The failure mode of piezoresisors is mainly short circuit. If the short circuit time is too long, the peripheral parts will be damaged. There may also be openings.


When a higher power frequency temporarily overvoltage ACTS on the piezoresisor, it may cause the piezoresisor to instantaneously breakdown short circuit (low impedance short circuit), and the temperature fuse has not enough time to fuse, it may also cause a fire. In order to avoid this phenomenon, another shock resistance power frequency fuse can be connected in series on each varistor (single power frequency fuse may not fuse when aging failure). It can also be used in series with the varistor and the ceramic gas discharge tube, the ceramic gas discharge tube does not conduct when working normally, and the varistor has no leakage current, which can greatly extend the service life. Under surge impact, the ceramic gas discharge tube first breaks down, and then the surge voltage is limited by the piezoresisors. The total residual voltage is the sum of the two, which increases slightly (dozens of volts). After the shock, due to the current limitation of the varistor, the discharge tube can not maintain the conduction and extinguish the arc, and return to the normal working state; When the piezoresistive short circuit failure, because the ceramic gas discharge tube through a large power frequency current will soon fail, but its failure mode is mostly open, so it is not easy to cause fire.

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