Research On Single-stage Isolated Electrolytic Capacitor-less LED Driver

The light emitting diode(LED)has a series of advantages,such as high luminous efficiency,longer service life and low destructiveness on the environment.LED has become the main way of lighting.Due to the characteristics of LED,it needs constant current LED driver.When the input is AC 220 V,two times of the power frequency pulsation exists because of the difference between the input and output power of the LED driver,which needs electrolytic capacitors to absorb.The short service life of electrolytic capacitors greatly restrict the service life of LED driver.Therefore,the ways of eliminating the electrolytic capacitor and increasing the life of the LED driver have become a hot topic in the research of LED driver.Firstly,the research on the efficiency of traditional two stage electrolytic capacitor-less LED driver is described.Paper proposes a single-stage electrolytic capacitor-less LED driver based on interleaving parallel technology and the principle of reducing capacitance.Then,the conducting modes and characteristics of the main circuit are analyzed.Secondly,because of all input power is absorbed by the energy storage capacitor of the single stage electrolytic capacitor-less LED driver,the peak voltage of capacitor becomes relatively high,which leads to the potential safety problem and high voltage stress.A single stage isolated electrolytic capacitor-less LED driver is proposed to solve these problems,which pluses an auxiliary winding in the transformer and structure the energy storage circuit to Flyback converter.The signal of output current is often used to regulate the isolated LED driver.However,the existence of photo-coupler,which is necessary device in the secondary side current feedback control circuit,leads to the larger size and higher cost of the LED driver.The primary side regulation can solve these problems successfully.A control strategy based on the primary side regulation is proposed,and the control circuit is designed.Finally,the experimental prototype of the proposed single stage isolated electrolytic capacitor-less is designed.The turn number of transformer and the voltage and currentstress of the main circuit device are analyzed and calculated.Beside,the choice of switch devices is given.A prototype has been built and tested to prove the correctness of the theoretical analysis.