The current of LED increases due to various reasons in use. At this time, protective measures need to be taken to ensure that the LED will not be damaged because the increased current exceeds a certain time and amplitude. Using circuit protection devices is the most basic and economical protection measure. The most commonly used protection element for LED lamp circuit protection is varistor.

Varistor is used to protect LED lamps. It can be said that no matter what power supply, switching power supply and linear power supply are used for LED lamps, such protection is required. It is used to protect the surge voltage that often occurs on the municipal power network. The so-called surge voltage is mainly a short-time high-voltage pulse caused by lightning stroke or the start and stop of high-power electrical equipment. Lightning stroke is the main reason. Lightning strike can be divided into direct lightning strike and indirect lightning strike. Direct lightning strike means that lightning strikes the power supply network directly, which is rare, and most large power supply grid systems have lightning protection measures themselves. Indirect lightning stroke refers to the surge transmitted on the power grid induced by lightning. This surge is very likely to occur, because 1800 thunderstorms and 600 lightning flashes occur all over the world every moment. Each lightning strike will induce surge voltage on the nearby power grid. The width of surge pulse is usually only a few subtle or even shorter, and the amplitude of pulse may be as high as several thousand volts. Mainly because of its high amplitude, it has the greatest impact on the damage of electronic equipment. Without protection, all kinds of electronic equipment are easy to be damaged. Fortunately, surge protection is very simple. Just add an anti surge varistor, which is usually connected in parallel before the rectifier.

The principle of this varistor is as follows: there is a nonlinear resistor whose resistance is close to the open circuit within the specified threshold range, and once the applied voltage exceeds the threshold, its resistance is close to zero immediately. This makes it easy to absorb the surge. Moreover, varistor is a recoverable device. After surge absorption, it can then play a protective role.