Analysis And Design Of LED Constant Current Driving Power Control Chip With High Power Factor

The driving power source plays an important role in improving the stability of the LED light emission and its efficiency and life.The high power factor can eliminate the harmonic pollution of the driving power supply to the power grid and improve the power utilization rate;the high-precision constant current drive can improve the stability of LED emission and extend its life.Therefore,the study of LED constant current driving power control chip with high power factor has important theoretical significance and engineering application value.By analyzing the principle and control method of power factor correction,the expression of input voltage and input current of system and on-time under CRM is deduced,a scheme to achieve high power factor by using a constant on-time to control the CRM flyback converter is proposed.Through the analysis of the traditional LED constant current principle,it is concluded that the traditional constant current scheme can not achieve high power factor,so a scheme that can achieve LED constant current drive and can improve the power factor by controlling the turn-off delay time of the switch is proposed,the relationship between the turn-off delay time and the LED output current is deduced.A constant current and constant on-time control PFC circuit is designed,to ensure that the product of the peak current of the switching transistor and the ratio of the off-time and the period is a constant value when of the flyback converter operating in the CRM,thereby realizing constant current and high power factor.The key modules of the chip are designed,including internal power generation,zero current detection,leading-edge blanking,logic driving circuit and undervoltage lockout,VCC over-voltage,output over-voltage and peak current limiting of the chip,and completed a LED constant current driving power control chip with high power factor.Based on the 0.35?m 5V/40V BCD simulation library,Cadence and Hspice software are used to simulate and analyze the key circuit modules in the chip.Based on the primary side control flyback converter,the chip system simulation platform is built,and the chip application system circuit is simulated and analyzed.The simulation results show that the feasibility of the designed chip.Based on the 0.35?m 5V/40V BCD design rule file,the layout of the whole circuit is completed by using Cadence software.The circuit and its parasitic parameters of the designed layout are extracted and used to verify after verification.The simulation results show that the feasibility of the designed chip and layout.