Study Of LED Power Supply In Automotive Headlamp System

As one of the vehicle essential safety components, automotive headlamp plays avital role on automotive safety. With the advent of high-power white light-emittingdiode（LED）, LED has begun to enter the lighting field and leads a new revolution inlighting field last20years. Because of its many advantages, LED gains more and moreattention in the industry of automotive headlamps and becomes the development trendof the headlamp accompanying with AFS and other advanced headlight technology.Due to LED’s unique electrical characteristics, it requires specialized driver powersupply. Switch power supply is usually the first choice to drive high-power LED atpresent. The large capacity electrolytic capacitor is mostly employed to filter the outputripple voltage in traditional switch power supply, which has became the shortslab inLED lighting systems because it does not match the LED’s reliability and service life.And, the filter capacitor’s own factor renders the residual output ripple, which affectsthe LED luminous efficiency and depreciation. In addition, the electrolytic capacitorblocks the miniaturization, integration and the overall layout of drive power. Theseshortcomings in the automotive environment (automotive-grade temperature, and spacerequirements) may become more serious.For the above-mentioned problems，and directing at the condition of the automoti-ve lighting system, a novel circuit topology, which based on Buck converter andemployed an active ripple compensation circuit to replace the electrolytic capacitor, wasproposed in this paper. The new circuit combined switching power supply with linearpower supply, which utilized switching power supply to achieve the high energyefficiency and took advantage of the linear power supply to restrain circuit output ripple.This power supply had a smaller output ripple and higher reliability. Besides, it hadgreat advantage on circuit miniaturization and integration.Firstly, the active ripple compensation circuit was proposed based on the traditionalBuck converter. Secondly，The working principle of new topological structure wasintroduced, and its small signal model was built. Then, the steady state and dynamicperformance of the main circuit was studied by the numbers. Lastly, the applicability ofthe compensation circuit and its power loss were discussed.Taking many factors into consideration of the automotive headlamp, the hysteresiscurrent control model which tracking inductor current was proposed. Finally, the active ripple compensation Buck LED driver power circuit was simulated and the experimentcircuit was designed and debugged.This Study Showed that the active ripple compensation circuit could compensatethe inductance ripple current completely, and the circuit output current is DC in theory,which was proved by the simulation and experiment results. Hysteresis current controlmodel had excellent response and robustness which could overcome car battery voltagefluctuations and maintain the LED working stability. Because there was not a largecapacity electrolytic capacitor, the power supply’s reliability and service life could begreatly enhanced. This study on the novel LED drive power had some significance onthe development of the headlamp.