A linear constant current LED driver with no off-chip inductor or capacitor

This paper presents a linear constant current LED driver with no off-chip inductor or capacitor. The proposed circuit consists of a main controller and constant current sources to drive the LED array. An improved control method is used for lighting the LED array step by step, shaping the output current in proportion to the input voltage. Each constant current source has functions of temperature compensation and over voltage protection. A prototype of a 7x7 LED array has been built to verify the control method. The chip is designed and implemented by using CSMC's 1 mu m 700V process. The post-layout simulation results indicate that under the 220V vertical bar rms 50Hz utility voltage, the system can realize a high power factor of 99.76% and a maximum power conversion efficiency of 90.68%.