Improvements in performance and reliability for segmented linear LED drivers

Several improvements have been made to the conventional segmented linear light-emitting diode (LED) driver topology to enhance the performance and reliability of the system. A compensation technology is proposed to adaptively adjust the impedance of the sensing circuit to keep the output luminance constant in case of line voltage variations. Based on the proposed technology, an active over temperature protection technique is presented to constrain the averaged LED current according to the junction temperature to prevent the driving IC from overheating. Otherwise, a pulse width modulation dimming circuitry which is compatible with input logic level ranging from 1.8 to 20 V is proposed. The proposed technologies are implemented in a 1.0 μ m 5/20/500 V BCD technology with three high voltage MOSFETs integrated on chip. The experimental results show that within 220±15% V, 50 Hz AC line-voltage variation, the output luminance is restrained to 4% in total. The output luminance can also be effectively controlled by the PWM dimming circuitry, and a dimming range of 95% is achieved with good linearity.