The varistor is a voltage-limiting protection device that utilizes the nonlinear characteristics of the varistor. When an overvoltage occurs at its two poles, the varistor can clamp the voltage to a relatively fixed voltage value, thus achieving Protection of the stage circuit. A significant role of varistors is in transient overvoltage protection in circuits. Although its flow capacity is large, its energy capacity is not large. In addition, because its maximum inrush current pulse width is much smaller than the actual pulse current width of large and medium power semiconductor systems, short circuit or burnout and failure will occur frequently.
The varistor commonly used on the market today is a varistor of (ZnO) zinc oxide, which is mainly caused by the following reasons.
a. insufficient pressure
This is a good understanding. If a product has a working voltage of 220V and your varistor is 180V or less, it will definitely break down and damage.
b. Current and surge are too large
The current passed by MYG05K is 0.1mA. The nominal voltage of MYG07K, MYG10K, MYG14K, and MYG20K refers to the voltage across the varistor when passing 1mA DC current. The use of the device in the product, especially the device that needs to be plugged and unplugged, will cause the varistor to be damaged more quickly, because the surge of the product during plugging and unplugging is relatively large (the device at both ends is not supplied to the ground), and the pressure sensitive withstand voltage will cause The product itself and TVS protection are weakened and the damage rate is high.
Several varistor overheat protection technologies:
(1) Using a spring to pull the low melting point solder technology
(2) Potting technology.
(3) Isolation technology.