In the field of lighting, LED lighting products are sought after by the market because of their energy saving, environmental protection, long life and maintenance-free advantages. Similarly, LED street lights are now fully occupied in the field of road lighting. The main function of the common street light LED driving power supply is to convert the AC input into a constant current output, and at the same time complete the matching with the voltage and current of the LED according to the requirements of the LED device.


Zhang Zhicheng, chief engineer of Jiansen Technology, pointed out that in addition to meeting safety requirements, LED street lamp driving power supply should have three basic functions:

First, keep the constant current characteristics as much as possible, especially when the input voltage changes, it should still be able to keep the output current within a very small range. That is to say, the LED street lamp needs to use constant current drive. The main reason is to avoid the drive current exceeding the maximum rated value and affect its reliability. At the same time, it must obtain the expected brightness requirement and ensure the brightness and chromaticity of each LED module.

Second, the driver circuit should maintain its own low power consumption, so that the system efficiency of the LED can be kept at a high level.

The third is the ability to use in abnormal power supply environments such as lightning strikes and surges.

For the description of the first and second basic functions, we will not discuss too much. Below we focus on the third point, that is, the protection of lightning strikes and surges by LED streetlight drivers.

There are currently statistics, there are about 40,000 thunderstorm centers around the world, and there are more than 8 million lightning strikes per day. In the rainy season, an average person is hit by lightning every 6 minutes. Including the rear-end collisions of the D301 and D3115 trains on the Shenzhen-Hangzhou line on July 23, 2011, all caused by lightning strikes.

Precious electronic equipment must increase the lightning protection circuit in the power input circuit. Of course, the lightning protection of electronic equipment is mainly secondary lightning protection, which is the protection of induced voltage (also called surge) generated by lightning.

Surge is a spike that has a high rate of rise and a short duration. There are many reasons for this, such as: secondary lightning strike, grid overvoltage, switch ignition, power supply reversal, static electricity, motor/power noise.

It is estimated that 75% of electronic product failures are caused by transients and surges. Voltage transients and surges are everywhere, power grids, lightning strikes, blasting, and even people walking on carpets can generate tens of thousands of volts of static-induced voltage, which are invisible killers of electronic products.

Jian Zhi Technology Chief Engineer Zhang Zhicheng highlighted that there are three main methods for current major surge (secondary lightning strike) protection:

1: Switch type: Its working principle is to exhibit high impedance when there is no instantaneous overvoltage. When responding to lightning transient overvoltage, its impedance will suddenly change to a low value, allowing lightning current to pass. When used as such a device, the device has: a discharge gap, a gas discharge tube, a thyristor, and the like.

2: Voltage limiting type: Its working principle is high impedance when there is no transient overvoltage, but its impedance will decrease continuously with the increase of surge current and voltage, and its current and voltage characteristics are strongly nonlinear. Devices used as such devices are: zinc oxide, varistors, suppression diodes, avalanche diodes, and the like.

3: split type or turbulent type

Shunt type: Parallel to the protected device, exhibiting a low impedance to the lightning pulse and a high impedance to the normal operating frequency.

Turbulent type: In series with the protected device, it exhibits a high impedance to the lightning pulse and a low impedance to the normal operating frequency. Devices used as such devices are: choke coils, high pass filters, low pass filters, quarter wave shorts, and the like.

In summary, Xin Mingfeng, chairman of Jiansen Technology, suggested that everyone should add a reasonable lightning surge protection circuit to the drive power supply, which will effectively reduce the damage probability and damage degree of street lamps and other electrical equipment.

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