Design And Application Of A Constant Current LED Driver IC Without Inductance

With the concept of energy saving and environmental protection in twenty-first Century,LED lighting source as a new type of energy saving and environmental protection electronic products,is more and more popular by the majority of consumers,the market size expanded year by year.At present,with the gradual introduction of thousands of households LED,high-voltage high-power LED lamps of 220V/50 Hz AC power supply as a direct power supply are ushered in the peak period of development.Although the high power AC-DC converter drive on the market a wide variety,excellent performance,but the general circuit complex,peripheral topological components,especially the large volume and high cost of inductance is one of the essential elements,which leads to high cost driver and large area defects of Power Supply Board.This paper from the driving high voltage LED lamp strand of the combination of theoretical research on discharge of electrolytic capacitor to load,then the proposed High voltage LED driver chip is designed without inductance transformer based on external energy storage capacitor.Because of the energy storage capacitor is a high voltage electrolytic capacitor,and the LED load voltage is high,so the load of LED can be directly plugged in electric supply with no other buck circuit.The peripheral topology of the chip is simple and contains fewer elements,at the same time as the topological component does not contain inductance of large volume and high cost,so the chip manufacturing cost is greatly reduced,reducing the LED drive power in the area.In this paper,the design of the chip uses the digital average current constant current technology,and combined with the digital analog hybrid circuit design,making the chip integration,chip area,and can be compatible with digital.The output power switch of the chip is made of high voltage LDMOS power transistor,which can meet the requirements of high voltage operation.The chip adopts PFM modulation mode,and the PFM control wave is generated by the digital constant current control logic module,which has strong anti-interference ability and high precision of constant current.The on-off of the power switch tube is controlled by the PFM wave with a certain duty cycle,then the external high voltage storage capacitor at certain frequency continuous charge and discharge,to make LED load current at a preset average current fluctuation,maintain a constant average output current.In this paper,the working mode,modulation mode and feedback control mode of the chip are studied,which provides a theoretical basis for the design of the chip.Based on the expected performance of the chip and the characteristics of the high voltage LED load,the framework and principle of the LED driver without inductance based on the energy storage capacitor are proposed.Then,according to the chip system framework,the chip system is divided into several large modules,and then the circuit design and simulation verification are carried out for each sub module under each large module,such as bandgap voltage reference module,OSC module,error amplifier,UVLO undervoltage lockout module etc..Finally,the overall circuit simulation and actual test results show that the chip can accept 220V/50 Hz mains input,output current 30 mA,output voltage at 213~227V,the conversion efficiency as high as 90%,can be realized on 7W high voltage LED lamp driver applications.The chip design based on 600 V BCD technology platform of Huarun China 0.5um,and using Altium Desiger software,realize the chip driver board design.