A Charge Pump Multi-channel Constant Current White Led Driver Design

With the development of technology, constant current white LED driver is used widely in portable products. Butthe majority of manufacturers of portable products favor the charge pump multi-channel constant current LED driver because of its obvious cost-effective advantages.The designing of the charge pump multi-channel constant current LED driver mainly focus on the charge pump efficiency and power MOS size optimizing, efficient and adaptive mutual conversion of 1x and 1.5x pattern, multi-channel current source and sink matching design.First of all, the system architecture is selected under definite performance criteria. Then the operation principle of capacitor is presented. After that, the equivalent resistance model of lx and 1.5x are calculated. Based on high-efficiency optimization, Lagrange multipliers is applied to optimize the size of the power MOS in 1.5x operation.Secondly, the thesis presents a new mode called switching method of digital threshold hysteresis, which compares the minimum cathode voltage with a given threshold in order to complete the mode control of lx and 1.5x by state machine. Then the detail analysis of the mode control in the PWM dimming time is shown.Next, based on current mirror-matching analysis and system requirements, current sink architecture is selected and a detailed analysis of the current sink loop parameters is derived including negative feedback compesation. Then, the negative feedback resistor is used to improve the current mirror matching in 6-channel current-source design. The simulation results show good performance.At last, the final validation is performed. The sub-circuits are descripted with the VERILOGA language for fast functional sytem verification. The sub-module parameters are adjusted at this phase. Then the simulation is carried out with the actual circuit. The final validation results meet the design requirements as presented.