A Study Of Multi-Channel LED Driver Based On DC Current Distributed Power System Structure

In light-emitting diode?LED?color mixing applications such as LED landscape lighting,LCD display,RGB LED colorful environment decoration,etc.LED driver is required to control independently each output current to ensure the normal operation of colorful LED.The DC current distributed power system structure is charactered with high flexibility,high reliability,modular design,etc.Therefore,a two-stage multi-channel constant current LED driver based on the DC current distributed power system structure is proposed,which consists of front-stage converter and back-stage converter.Firstly,the circuit topology is chosen,then the quantitative parameter of main circuit and controller of the two-stage multi-channel constant current LED driver is analyzed and designed in detail.Finally,the stability of the system is analyzed and verified,and the experimental research is carried out.The main research contents and results of this thesis are as follows:Firstly,according to the functions of the front-stage converter and back-stage converter,and the characteristics of various circuit topologies,the Flyback converter operating in discontinuous current mode?DCM?is chosen as the front-stage converter,which achieves power factor correction?PFC?and electrical isolation functions;The current-type Buck converter operating in continuous capacitor voltage mode?CCVM?is chosen as the back-stage converter.The input ports of all the current-type Buck converters are series connected to make their input current be same and reduce their switch voltage stresses.The current-type Buck converters regulate the corresponding output current and all the output currents can be controlled independently.Then,the main circuit and controller of the front-stage Flyback converter and the back-stage current type Buck converter are analyzed and designed in detail.According to the working principle of the front-stage Flyback converter and the back-stage current type Buck converter,the design method of the main circuit is obtained.Combined with the design example,the quantitative design of the main circuit parameters is completed;By analyzing the switching mode and the main working waveform of the front-stage Flyback converter and the back-stage current type Buck converter,the small signal model can be obtained respectively,and the design of the current loop PI controller of the front-stage Flyback converter and the back-stage current type Buck converter is completed;The simulation and verification of the analysis and design above were carried out by PSIM and MATLAB simulation software.The results verified the correctness of the analysis and design method above.Finally,the stability analysis and experimental verification of the two-stage multi-channel constant current LED driver composed of the front-stage Flyback converter and the back-stage current type Buck converter are completed.According to the equivalent loop gain Z_inc-L/Z_outc-Sutc-S of the DC current cascade system,that is,the ratio of the closed-loop input impedance of the back-stage current type Buck converter to the closed-loop output impedance of the the front-stage Flyback converter,it's determined that the stability of the cascade system by using the Nyquist criterion;According to the analysis and design above,a experimental prototype of 60W two-stage three-channel constant current LED driver is built.The experimental results verify the correctness of the analysis and design above,and the highest efficiency is 88.4%.