| In recent years, people have been committed to the development and design of new lighting source. With its high efficiency, energy saving and environmental protection, long life, high reliability and many other advantages, LED (Light Emitting Diode)is recognized as the most valuable "green" light source in the21st century and will become the dominant product in lighting market by replacing incandescent and fluorescent lamps. The drive power supply with high efficiency, low cost, high power factor and a long life is the key to ensure the light quality of LED and its overall performance. On the issue that the LED drive power supply mismatches the service life of LED light source, this paper mainly studies LED driver power supply without electrolytic capacitor.LED drive power supply is a power converter which transforms AC voltage to stable DC voltage and then supplies it for the LED light source. Since the input power of LED drive power supply is fluctuating, in order to ensure that the output power is constant, the storage capacitor with large-capacity energy is required to balance the instantaneous input power and output power and in general, electrolytic capacitors with large capacity are used as the energy storage capacitors. However, the life of electrolytic capacitors, only a few thousand hours, is much shorter than the LED life (>50000hours), which makes LED drive power supply mismatch with LED long service life. In order to prolong the service life of power, the electrolytic capacitors in the power supply must be reduced or even eliminated, or replaced by other types of capacitors. This article aims to employ Fairchild semiconductor (Fairchild Semicondutor) FL7701intelligent isolation step-down LED drive to achieve the design and research of LED driver power supply without electrolytic capacitor, thus to improve the whole lifespan of LED lighting source on the condition of meeting the energy efficiency standards and the harmonic requirements.This paper first introduces the new development and trend of LED drive power supply and proposes a new way to design LED driver power supply without electrolytic capacitor. In this paper, FL7701intelligent isolation step-down LED driver is used in control chips. Meanwhile, this paper expounds the operating principle of LED driver power supply without electrolytic capacitor composed of buck converters, and gives a detailed analysis of the design of power supply circuit and the selection of its key components, and the optimization design of the periphery circuit and the output inductance is finished, which make LED drive power supply without electrolytic capacitor true. The digital technology which employs control chips to automatically detect the condition of the AC input voltage can construct the internal reference signal to achieve high power factor (PF>0.9) and lower total harmonic distortion (THD). In LED lighting applications, due to the conversion efficiency, the traditional technology of transformer will cause additional loss of transformer. Through the control chips directly connected with the DC or AC line input, the traditional method with the low efficiency can be replaced to realize the high efficiency. At the same time, this paper also analyses the overall efficiency of power supply and the source of electromagnetic interference and puts forward some ways to improve the efficiency and to restrain electromagnetic interference.By making an experimental prototype, the correctness and feasibility of the theoretical analysis is verified. It is showed that the circuit has strong practicality and superiority and can be applied to the LED bulbs or spotlights, reflector lamps and MR lamps of PAR lamps as well as indoor lights. The analysis of the experimental data demonstrates that this type of without electrolytic capacitor has the characteristics of high power factor, high efficiency, high reliability and flicker free and can also meet the requirements of energy conservation and environmental protection and the standards of EMC test. |
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