Mains program dimming LED street light power supply solution

Since the Ministry of Science and Technology launched the "10 Cities, 10,000 Lamps" proposal, local governments have responded and made every effort to promote it. Most of them are to transform the existing high-pressure sodium lamps into LED street lamps, so the original AC power supply circuit is still there, and a batch of LED street lamps powered by mains are urgently needed. Although LED street lamps powered by mains generally use constant current power supplies, most of them do not have dimming functions. However, even if they are powered by mains, how to further save energy is still an important issue. For this reason, Shanghai Longmao Company and Hong Kong Weida Company have worked closely together to launch a series of power supply solutions for mains program dimming LED street lamps. Among them are various solutions of 80W (100W), 112W (150W), and 168W (200W) (the numbers in brackets represent the wattage of the constant voltage source used). All these solutions adopt the solution of constant voltage first and then constant current to achieve the highest performance.

Taking 112W LED street light as an example, its block diagram is shown below.

The AC/DC constant voltage source uses the VP28SA150U constant voltage source from Hong Kong Weida Company. Its maximum output power is 150W, the output voltage is 28V DC, and the maximum output current is 5.36A. Its efficiency is as high as 92%, and the power factor is as high as 0.99 or above. The appearance is shown in the photo.

The models and specifications of other wattage AC/DC constant voltage sources are shown in the following table:

The output voltage can be increased by 2-3V based on the maximum voltage required by the LED load, so that the subsequent constant current drive source works in buck mode to obtain the highest efficiency.

The dimmable step-down constant current source of Longmao Company is connected to the back, which can accept the dimming signal of pulse width modulation (PWM). Its efficiency is as high as over 97%. It is used here to drive 4x7 1W LEDs. A total of 4 such modules are used to drive a total of 112W LEDs. The dimming controller uses SLM4801 produced by Longmao Company. This dimming controller can set the brightness at different time periods according to the traffic flow in the area measured in advance. This controller can start timing and dimming when the entire street light is turned on. It can also measure light according to the built-in photosensitive element and automatically turn on the light when it gets dark. After using program dimming, energy can be saved by more than 60%.

These solutions have been adopted by relevant companies and are ready to be used in several street lamps.