Walking through the streets of big cities such as Shenzhen and Beijing, you can already see the cool white LED street lights on both sides of the road. The exchange of AC and solar-powered LED street lights will certainly become an irreversible technological development trend in the next few years, not only because of the reliability and energy saving of high-brightness LED lamps, but also because of its very low maintenance costs. The challenge for designers now is how to design a highly efficient auto-dimmable LED streetlight solution with unstable mains input. The Arrow AC/DC LED street light solution described below can provide a useful idea.
LED street lights generally require more than 25W of power, depending on the range of lighting required and the height of the installation. Arrow's LED streetlight solution based on AC mains input selected CREE 's lighting-grade XLamp MC-E LED, NXP's PFC controller and flyback controller SSL1750, and TI's DC/DC constant current controller TPS40211. The XLamp XR-E LED is a lighting-grade multi-chip module with a lumen count of 107 per watt. Cree currently offers 5W to 9W XLamp XR-E LED modules with a typical thermal resistance of 8Â°C/ W.
NXP's SSL1750 is a switching power supply (SMPS) controller IC suitable for driving 25W to 250W LED lighting applications. For applications with power requirements below 25W, the SSL152x series and SSL1623PH are more suitable.
The SSL1750 integrates a PFC (Power Factor Correction) controller and a flyback controller that enables cost-effective LED drive power with a small number of external components. At all output power levels, its special green features ensure high efficiency. This applies to quasi-resonant operation at high power levels and down-conversion at lower power levels. At low power levels, the PFC transitions to burst mode to maintain high efficiency. In burst mode, soft start and soft stop functions have also been added to eliminate audible noise. At low power, the flyback controller switches to the down mode and limits the peak current to 25% of the maximum. This ensures high efficiency at low power while minimizing transformer audio noise. The SSL1750 makes AC/DC conversion more than 90% efficient.
The TPS40211 is a wide input (4.5V to 52V), non-synchronous boost controller with a maximum output current of 700mA, allowing dimming via PWM with an output voltage from 20V to 37V. It has an efficiency of 90% or more at 8-18V input. It is suitable for applications that require a source-grounded N-channel FET topology (such as boost, flyback, and SEPIC) and a variety of LED driver applications. Its main features include: programmable soft-start, overcurrent protection, automatic retry, and programmable oscillator frequency. Current mode control provides improved transient response and simplified loop compensation.
Arrow also offers optical lens and optical solutions for LED street lights. The ARR1-R60120-L1 is an optical lens specifically designed for LED streetlight applications. It features high efficiency, single beam pattern and consistent effects. When designing LED street lights, designers should also consider the following questions: the number of lumens covered by LED lights under the street, the height of the LED lamp post (4-6 meters for parking lot lighting, 8-12 for highway lighting) m), thermal constraints, and the following standards (IP23 for outdoor products, IEC60598 for AC mains, IEC1000-4-5 for arc and surge current, IEC68-2-Fc and EMC/CISPR for mechanical properties) 15).
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