Research On Highly Accuracy LED Driver IC With High Power Factor And Reliability

Due to the advantages of high efficiency,energy saving,long life,small size,environmental protection,easy dimming and rich colors,LED lighting has developed rapidly in recent two decades,and its penetration rate has increased rapidly.By the end of 2020,the penetration rate of LED lighting in the field of lamps and lanterns reached 80%.As a current-mode device,LED needs to be equipped with a constant-current power driver.At present,LED drivers still have some problems,such as low constant current accuracy(greater than ±3%),low power factor(lower than 0.95),large total harmonic distortion(greater than 15%)and low driver reliability.In view of the above-mentioned problems of LED driver,this paper focuses on the research of output current accuracy,power factor and reliability of LED driver,and the main innovative research results are as follows:1.Aiming at the problems that the existing LED constant current mechanism is sensitive to the deviation of production process and the constant current precision and consistency are not high,a high precision constant current control algorithm is proposed.The algorithm chooses to detect the demagnetization time of transformer from the primary winding,and adjusts the switching frequency according to the demagnetization time.Because the inductance variable is eliminated and input compensation correction and output compensation correction are introduced in the high-precision constant current control algorithm,the output current accuracy is not affected by the difference of transformer primary inductance value,input line voltage fluctuation and load switching,and the current error can be controlled within ±2.5%.2.In view of the high cost and complex structure of the existing output current detection topology,a demagnetization detection topology based on drain sampling of power MOS is proposed,and the resonance signal sampling and processing algorithm and circuit are designed.This topology simplifies the application system structure,reduces the system volume,improves the robustness of the system and the efficiency of chip design process transplantation,and promotes the commercial application of the system.3.A high power factor constant current control mode based on single-stage converter is proposed.In this mode,the switch mode with constant on-time and internal integrator are used to control the input current to follow the input voltage waveform,so as to realize high power factor constant current;At the same time,under different input and load conditions,the demagnetization duty ratio is adjusted to realize high-precision output current control.This mode adapts single-stage controling,so that small system size and high cost-performance ratio is archived,and power factor can reach above 0.995 and THD is less than 15%.4.A set of LED constant current chip design process and implementation scheme to achieve high reliability and high integration is proposed.In this paper,the reliability problems in the current LED driver design are studied,and the chip circuit reliability and chip package reliability are designed respectively.A LGA system-level multi-chip packaged LED driver chip with multiple failure protection mechanisms is developed,and its reliability is verified.The chip has achieved 750 V withstand voltage and passed many reliability tests such as JESD22 standard and J-STD-02 D standard.On the basis of the above four researches,based on Hua Hong HHG 0.35μm 5V/40 V BCD process and Changjiang Electronics Technology LGA packaging process,a LED constant current driver chip with high power factor,high precision and high reliability was developed and mass production was realized.The test results show that the power factor reaches 0.98,the constant current precision reaches ±2.4%,and the withstand voltage exceeds 750 V when the AC input voltage is in the range of 85V～265V and the output power is 7～12 W.At the same time,the chip has passed many reliability tests such as JESD22 standard and J-STD-020 D standard,the failure rate is less than 80 ppm,and the constant current precision with high power factor and high reliability of the chip system are remarkable promoted.