With the increasingly severe energy crisis and climate change, energy conservation has become a topic of global concern. Lighting is an important aspect of human energy consumption, accounting for about 20% of the world's total energy consumption. Therefore, research and development of green and energy-saving lighting technologies have been increasingly valued. High power LED street lights are a new type of lighting method that uses DC voltage to light up high-power LED groups to meet lighting needs. Therefore, traditional power sources used to drive incandescent lamps, fluorescent lamps, energy-saving lamps, sodium lamps, and other light sources are not suitable for directly driving high-power LEDs. Based on the working characteristics (V-I characteristics) of high-power LEDs and the driving requirements of LED street lights, this article designs a quasi resonant high-voltage constant current LED street light driving power supply using power electronics technology and PWM integrated control chip within a universal wide input voltage range (90-265 V), simplifying the circuit structure and improving the power supply's working efficiency.

For traditional hard switch flyback converters, parasitic capacitance will oscillate with the primary leakage inductance of the transformer. The voltage value on the parasitic capacitance is generally large. When the MOSFET in the next clock cycle conducts again, the parasitic capacitance will discharge through the MOSFET and generate a large current peak. Due to the high voltage between the MOSFET drain and source at this time, the current spike will generate switching losses, and at the same time, the current spike contains a large amount of harmonic content, which will also generate EMI. After considering the above factors, if the detection circuit can effectively identify the valley value of the MOSFET drain source voltage and turn on the MOSFET at this time, the voltage on the parasitic capacitor will be minimized, and the current peak during conduction will also be minimized. This working mode is often referred to as quasi resonant switch [3]. Therefore, the basic principle of quasi resonant technology is to utilize the resonance generated by the capacitance (parasitic capacitance or external capacitance) at both ends of the MOSFET and the leakage inductance of the transformer's primary side. By real-time detection of the valley voltage at both ends of the switching device, the approximate zero voltage turn-on of the switching tube is controlled, reducing the switching loss of the MOSFET and improving the efficiency of the converter. In addition, softer switching characteristics reduce the EMI noise of the power supply, allowing designers to reduce the number of filters used and thus lower costs. The entire circuit structure is simple, with high full load efficiency and low no-load loss.

1. Design requirements for drive power supply

LED is a current driven component, and its brightness depends on its forward current [4]. Therefore, using a constant current power supply to drive LED is the best method. A constant current source can avoid output current fluctuations caused by input voltage fluctuations, thereby keeping the brightness of the LED constant. For the constant current driving method, the series driving connection method is also the best choice for LED. Considering that the series connection method may cause the problem of high output voltage, 40 1 W LEDs are selected for series connection in this example, which requires the design of a power supply with a rated power of 40 W to match it. According to the actual lighting requirements of street lamps, only a 40 W power supply needs to be used as a basic module for corresponding power expansion. The specific design requirements for a 40 W power supply are as follows: (1) Input voltage is 90~265 V; (2) Rated output voltage 132 V; (3) Rated output current 330 mA; (4) Power efficiency η=90%.

2. Design of Quasi Resonant Circuit Based on FAN6300

FAN6300 is a highly integrated PWM control chip launched by Feizhao Company, and Osram is also considering using FAN6300 for its 12W to 60W LED driver products. The internal valley voltage detector of FAN6300 ensures that the power system operates in a near resonant state over a wide range of household power and under any load conditions, and reduces switching losses to minimize the switching voltage on the MOSFET drain. FAN6300 also has multiple protection functions, such as pulse by pulse current limiting function, which can provide short circuit and open circuit protection for the system, enhancing the reliability of the power supply. Therefore, adopting FAN6300 can significantly improve the performance of flyback converters. The main circuit of the power supply in this article adopts a single ended flyback topology structure.