Study On A Resonant LED Driver And Its Thermal Design

Due to the advantages of long life, high light-efficiency, energy saving, no flicker,etc., traditional light sources are gradually replaced by LED light source in the field offamily lighting. More and more attentions are payed on the research and developmentof LED drivers for researchers of power electronics.Reliability issue is a key factoraffecting the lighting quality and life of LED lighting system. Improvement inefficiency and thermal analysis on LED drivers are particularly important inimproving its reliability.Based on high efficiency and application in a few watt power families lightingsystem, a tapped-inductor quasi-resonant step-down converter was built in this paper.Working principle and detailed analysis of soft-switching process on the converterwere introduced; the losses on various components of the converter were calculateddetailedly; the histogram of losses in various components was given. In this paper, athermal simulation model of a LED driver was established. The thermal field andthermal stress analysis of the driver was done by using the software EFD Pro8.2, andthe temperature rise from various parts and the temperature field distribution of thePCB were obtained. By analyzing the reasons leading to overheating and unideal heatdistribution, corresponding thermal simulation using an improved model was carriedout. Finally, the comparison and analysis of experimental measurement results andsimulation results were given.In this paper，a new type of tapped-inductor quasi-resonant converter prototypewas designed and set up. The detailed design process and methods of the majorparameters of the circuit components were given，including the design of tapped-inductor, of resonant capacitor, selection of MOSFET, of output rectifier diode andoutput filter capacitor. The main parameters of the prototype were: input voltage176-265Vac, output voltage4-7V, and constant output current700mA. Experimentalmeasuring results showed that the efficiency of the prototype was full compliant withthe designed requirements, and the efficiency was up to85%at full load.