Research On A Low Output Ripple Electrolytic Capacitor-less LED Driver

Light Emitting Diodes(LEDs)have advantages such as high efficiency,long lifespan,environmental friendliness,and dimmability,which have gradually replaced incandescent lamps and fluorescent lamps as light sources.However,the input current of the LED driver fluctuates with the input voltage in a sine wave,and the phase difference between them reduces the power factor.Moreover,the input current fluctuates in the form of double frequency,resulting in power pulsation difference.Therefore,to balance the power pulsation difference,a larger capacitance electrolytic capacitor is generally chosen.However,the lifespan of the electrolytic capacitor is short,and the output current contains a larger ripple,which easily causes flicker.Therefore,it is meaningful to develop an LED driver power supply with low output ripple and no electrolytic capacitors.Firstly,This article introduces and analyzes in detail the traditional topology of electrolytic capacitor-free LED driver power supply,including various operating modes,waveforms,and electrical characteristics.The article derives formulas to achieve high power factor and no electrolytic capacitors,and gives appropriate simulation parameters,simulation waveforms,and result analysis based on this theory.Secondly,a low output ripple,electrolytic capacitor-free LED driver is proposed to address the shortcomings of the traditional topology,including high bridge rectifier circuit losses,no energy exchange during the transformer’s switch tube conduction period,and large output current ripple.The new topology designs the resonant part into a positive-negative resonance working mode,provides theoretical analysis of corresponding operating modes,and derives formulas for circuit operating characteristics.Simulation analysis is conducted,and the results are compared with the traditional LED driver power supply topology,verifying that the new topology achieves low output ripple while maintaining the high power factor advantage of the original topology and improving the utilization of the transformer.Furthermore,replacing the bridge structure with a non-bridge structure reduces the overall driver losses.Finally,two control methods are applied to further verify the feasibility of this topology.Using state space averaging method,the function of the entire system is analyzed,and a 60 W experimental prototype is designed and experimentally studied based on the above theory.The results prove that the proposed topology achieves low output ripple and high efficiency,demonstrating its superiority.