Research And Design Of A Buck LED Drive System With Low EMI Dual Mode Dimming

With the gradual development of LED driving equipment,there are higher requirements for its function and performance.How to realize intelligent dimming and effectively resist electromagnetic interference has become the research direction of LED driving system.However,compared with linear regulator and charge pump,switching power supply is more suitable as the driving control core of LED equipment because of its wide input and output range,low cost and high conversion efficiency.Therefore,this paper designs a low EMI dualmode dimming buck LED drive system.In this paper,firstly,the topology and working mode of switching power supply are analyzed and compared,and thus the buck topological structure under the continuous conduction mode is selected.Then,as PWM modulation is more efficient than PFM and less harmonic noise,it is easy to design,so PWM modulation method is adopted in this paper.In addition,the voltage mode loop control and current mode loop control are studied and analyzed.Finally,the peak current mode loop control is adopted to improve the response speed and simplify the loop compensation.In this paper,when designing the system,firstly,considering the stability of the system loop,the small signal model of the main switch loop and peak current mode control loop is built,and the small signal model of the whole system is established by combining the main switch loop and the control loop,and the simulation verification and analysis are carried out based on MATLAB software;secondly,due to the low integration and low efficiency of traditional dimming structure,a dual-mode hybrid dimming structure is proposed,which uses external PWM multiplexing pin and inputs different frequency and adjustable duty ratio to study the relationship between duty ratio and LED current intensity in different modes,and increases the dimming range,so as to realize the adjustment of LED light.Then,in order to reduce the electromagnetic interference of LED driving system,a low EMI circuit based on triangular wave frequency modulation method is proposed.This circuit can expand the frequency of oscillator by generating periodic modulated charge discharge current,so that the switching frequency and the peak energy of high-order harmonic are distributed in a wider frequency band,effectively reducing the electromagnetic interference.Finally,the whole system characteristics are verified and analyzed by simulation,and all the simulation results meet the circuit design performance index requirements.The low EMI dual-mode dimming buck LED drive system designed in this paper adopts 0.18 μ m BCD technology,which can realize the random switching between PWM dimming and analog dimming,and effectively reduce the electromagnetic interference of LED drive system.