Electrolytic Capacitor-less AC/DC LED Driver

High efficiency,long lasting,small size and environmental protection make LED lighting products the most promising new generation of green light source.While the quality of driver chip which is the vital part of LED lighting system determines the performance of the entire system.To improve the reliability and durability of driver chip,the electrolytic capacitor must be replaced by other types of capacitors such as film capacitors,even just remove the electrolytic capacitor in the circuit.Hence,it becomes an important research direction to develop a long lasting LED drive chip.Aiming at reducing the energy storage capacitor of LED driving power and improving the life of LED driving power supply,an AC/DC LED driving circuit with no flicker electrolytic capacitor is designed.In this paper,the design of the drive circuit using Boost-Buck cascade topology,in a frequency cycle,it will use the change in conduction time Ton to make input current occurs distorted and reduce the instantaneous power difference between input and output,so that the value of storage capacitor is reduced and electrolytic capacitor is replaced by film capacitors to extended the life of LED drive power.The circuit uses a set of control circuit to achieve PFC and output voltage conversion function,not only simplifies the circuit structure,but also reduces the design costs.The inductor current of the Buck converter operates in the critical current continuous mode and uses the average current control mode to achieve constant output current by controlling the current peak of the Buck converter.The circuit uses a line voltage compensation technologyby,sampling the voltage of the CS pin,to result to a compensation current proportional to the input voltage,to maintain the peak voltage constant,to avoid the power transistor shut down delay caused by the peak current overshot problem,thus ensuring a high output constant current accuracy.The control IC is fabricated in TSMC 0.35?m 5V/650V CMOS/LDMOS process,and verified in a 72V/150mA circuit prototype.The test results show that when the range of input voltage in 175?264Vac,the efficiency of the system is 83%,the voltage linear regulation is± 1%,the load regulation is ± 0.5%,and the electrolytic capacitor is replaced by 470nF CBB capacitor under condition that satisfy the power factor above 0.7.Therefore,the design of the control chip in the LED lighting has a very good application prospects.