Varistor knowledge

A varistor is an electronic component that prevents excessive voltage and protects the board from high voltage surges. The resistor material of the varistor is a semiconductor, and thus is also a type of semiconductor resistor. The zinc oxide varistor is now commonly used. There is a key parameter in the varistor parameters, the unit is Joule, and the excessive heat causes the varistor itself to rise too high and is damaged.

When the voltage applied at both ends is within the nominal rating, its resistance value is almost infinite, in a high-impedance state, and its leakage current varistor exceeds its operating voltage to generate current to clamp the overvoltage, and finally the electrical energy is Converted into heat. The varistor d has protective measures in the circuit, such as adding a fuse before the varistor. When the voltage is higher than the voltage of the varistor, the current in the varistor will be large, and the fuse will be blown to protect. Generally, overpressure will not burn the varistor in a short time, but if the pressure is too high in a short time, the varistor will burn out when the fuse is not blown (such as lightning strike).

When the voltage applied across the varistor is lower than the nominal rated voltage, the resistance of the varistor is close to infinity, and almost no current flows inside. When the voltage across the varistor is slightly higher than the nominal rated voltage, the varistor will quickly break through and change from a high-impedance state to a low-resistance state, and the operating current also increases sharply. When the voltage across it is lower than the nominal rated voltage, the varistor can return to a high impedance state. When the voltage across the varistor exceeds its limit voltage, the varistor will completely break down and burn out and cannot recover itself.