| Light-Emitting Diode(LED)has been considered as an ideal light source which has many favorable features such as environmental friendly,safe,high energy efficient and extremely long life of over fifty thousand hours.However in real applications,the lifetime,reliability and power efficiency are usually limited by the associated LED driver.To converting the mains AC voltage to a low-voltage DC for biasing the LED,being similar to most of the DC power supplies,large electrolytic capacitors(E-Caps)are used to buffer the varying input power.However,the typical lifetime of an E-Cap is only a few thousand hours and it may be even worse if it is operated in high-temperature ambient.This phenomenon leads to the lifetime mismatch between the LED chip and LED driver.The purpose of this work is extend the lifetime of AC/DC LED driver by eliminating the electrolytic capacitor or by reducing the capacitance value electrolytic capacitor so that it can be replaced with other kinds of capacitor which has a much longer lifetime.In this work,two approaches were proposed to reduce the capacitance value in the driver circuit.The first approach is a valley-fill circuit constituting by a series-parallel capacitive network at the input side of the circuit.This circuit does not only serve as a buffer for resolving the mismatch between input and output powers,it also reduces the high-voltage stress on the devices and improves the lifetime of the circuit.The second strategy is the introduction of the new control mechanism so that peak value of the output current can be reduced to close the averaged level.As a consequence,the rectifying can be done with smaller values of capacitors and inductors so as to remove the electrolytic capacitors.Modeling on the effects of these two approaches are developed.To validate the proposed methods,two prototypes with rating power of 15 W and 18 W were fabricated.High-performance in terms of power efficiencies,power factors and compactness were obtained. |
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