release time：2020-05-16 source：Shenzhen TOFOLED Lighting Technology Co., Ltd.
As the energy crisis and climate warming become more and more serious, 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, so research and development of green energy-saving lighting technology has been paid more and more attention. High-power LED street lamps are a new type of lighting method that realizes the lighting needs by lighting high-power LED groups with DC voltage. Therefore, the traditional power supply used to drive incandescent lamps, fluorescent lamps, energy-saving lamps, sodium lamps and other light sources is not suitable for direct driving of large lamps. Power LED. In this paper, according to the operating characteristics (VI characteristics) of high-power LEDs and the driving requirements of LED street lamps, a quasi-resonant is designed using power electronics technology and PWM integrated control chip in a universal wide input voltage range (90~265 V) The high-voltage constant current LED street lamp driving power supply simplifies the circuit structure and improves the working efficiency of the power supply.
For traditional hard-switched flyback converters, the 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 is turned on again in the next clock cycle, the parasitic capacitance is discharged through the MOSFET and a large current spike is generated. Due to the high voltage between the drain and the source of the MOSFET, this current spike will cause switching losses, and 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 be used to effectively identify the valley of the drain-source voltage of the MOSFET and turn on the MOSFET at this time, since the voltage on the parasitic capacitance is the smallest at this time, the current spike during conduction will also be minimized. The operating mode is often referred to as a quasi-resonant switch . Therefore, the basic principle of quasi-resonance technology is to use the resonance between the capacitance (parasitic capacitance or external capacitance) at both ends of the MOSFET and the primary leakage inductance of the transformer to control the approximate zero voltage turn-on of the switching tube by detecting the valley voltage across the switching device in real time. The switching loss of the MOSFET is reduced, and the efficiency of the converter is improved. In addition, the softer switching characteristics reduce the EMI noise of the power supply, allowing designers to reduce the number of filters used, thereby reducing costs. The whole circuit structure is simple, full load efficiency is high, and no-load loss is small.
1. Design requirements for drive power
LED is a current-driven component, its brightness depends on its forward current , so it is the best way to drive LED with a constant current power supply. The constant current source can prevent the output current from fluctuating due to the fluctuation of the input voltage, so that the brightness of the LED remains constant. For the constant current drive method, the LED adopts the connection method of series drive is the best choice. Considering that the series connection will cause the problem of excessive output voltage, in this example, 40 1 W LEDs are selected for series connection. In this case, it is necessary to design a power supply with a rated power of 40 W to match it. According to the actual lighting requirements of street lamps, only the 40 W power supply needs to be used as a basic module for corresponding power expansion. The specific design requirements of the 40 W power supply are as follows: (1) The input voltage is 90~265 V; (2) The rated output voltage is 132 V; (3) The rated output current is 330 mA; (4) The power supply efficiency η=90%.
2. Quasi-resonant circuit design based on FAN6300
FAN6300 is a highly integrated PWM control chip launched by Fairchild. Osram is also considering using FAN6300 for its 12 W to 60 W LED driver products. The FAN6300's internal valley voltage detector ensures that the power system operates near resonance at a wide range of household power and any load conditions, and reduces switching losses to minimize the switching voltage on the drain of the MOSFET. FAN6300 also has a variety of protection functions, such as the pulse-by-pulse current limit function can provide short-circuit and open-circuit protection for the system, enhancing the reliability of the power supply. Therefore, the use of FAN6300 can greatly improve the performance of the flyback converter. In this paper, the main circuit of the power supply uses a single-ended flyback topology.
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