LED lighting circuit protection elements:the varistor

The varistor is used to protect the LED lamp itself. It can be said that no matter what kind of power supply, switching power supply, linear power supply, the LED lamp needs this protection.It is used to protect the surge voltage that often occurs on the mains network.The so-called surge voltage is mainly caused by lightning strikes or the start and stop of high-power electrical equipment, and the short period of high voltage pulse.Lightning strikes are the main cause.Direct lightning strikes can be classified into direct lightning strikes and indirect lightning strikes. Direct lightning strikes the power supply network. This possibility is rare, and most large power grid systems have lightning protection measures.An indirect lightning strike is a surge triggered by lightning that travels over the power grid. Such a surge is highly likely because there are 1,800 thunderstorms at any one time around the world, and 600 lightning strikes per second.Each lightning strike induces a surge of voltage on a nearby power grid.The width of the surge pulse is usually only a few subtleties or less, and the amplitude of the pulse can be as high as several thousand volts.Mainly because of its high amplitude, it has the greatest impact on the damage of electronic equipment.All kinds of electronic equipment can be easily damaged if left unprotected.Fortunately, surge protection is as simple as adding an anti-surge varistor, usually in parallel with the rectifier.

The principle of this varistor is that there is a nonlinear resistance whose resistance is close to open circuit within a specified threshold, and whose resistance is immediately close to zero once the applied voltage exceeds the threshold.It's easy to absorb the surge.And the varistor is a recoverable device, surge absorption, it can then play a protective role.

Its main indicators are: 1) maximum continuous operating voltage (divided into AC and DC, for example, 415V), and 2) varistor voltage (threshold, for example, 510V), which refers to the starting voltage when the current is greater than 0.1mA.3) The maximum limiting voltage refers to the maximum peak voltage, Vp, above it at the peak current Ip that the varistor can withstand (e.g., 200A), e.g., 845V;In fact, since the surge is usually only a narrow pulse with a very small width (a few microseconds), its voltage and current relationship can no longer be described in terms of resistance because it is actually a nonlinear device.

In order to ensure continuous and stable light, the operating power of LED power supply is also increased, and the price of varistors that meet the high operating frequency is also increased.This is not conducive to reduce the cost of LED lights such high volume production of civilian products, in addition to the protection characteristics of ordinary varistors, can take into account the needs of power and size, and the price is not expensive, is the best choice of LED lamp circuit protection devices.

Coordinating editor AJX