Design Of LED Driver Chip Based On Average Current Mode

High brightness LEDs (HB-LEDs) is a kind of attractive light source, it has advantagesof energy-efficient, environmentally friendly, long service life, fast response, etc. As reducedthe production cost, HB-LEDs is gradually replace the traditional incandescent lamp andfluorescent lamp; Meanwhile, high-integration, high-accuracy and high-efficacy LED driverchip has become a hot current field.This paper presents a design of LED driver chip based on average current mode, thischip is applied to a LED driver with single-stage non-isolated Buck topology. In order toimprove the precision of LED current, compared with the intrinsic defects of peak-averagedifferences of the traditional peak current mode, this paper adopted the average current modewhich can precisely control the average inductor current of Buck structure; To improve thepower factor of the system, this paper analyzes and changes the slope to the PWM comparator,with the improved quadratic integral inductor current slope can reduce the total harmonicdistortion of system and improve system power factor. The architecture of LED driver chipprimarily contains Bandgap reference, linear regulator, CS converter, OTA, ramp generator,PWM comparator, oscillator. To improve the reliability of the chip, it also has under-voltagelockout, overvoltage protection, overcurrent protection and thermal protection.The LED driver chip is designed with CSMC0.5um BCD process in Cadence, the wholelayout area is800um×1200um. After tape out, the test results show that, when the inputvoltage is220Vac/50Hz,24LEDs series as the load, the average output current is194.4mA,THD is approximately28.1%, power factor reached96.2%and the system efficiency of91.1%; When the system input voltage with full voltage range of90Vac~264Vac/50Hz,24LEDs series as the load, the average output current is changes only4.4mA which mean thatmodulation precision of the chip is less than3%, power factor greater than91.7%, and systemefficiency is higher than88.1%, so the chip performance meet the design requirements.