Study On Conducted EMI In AC/DC Switching Converter Based On Chaotic Spread Spectrum

Electromagnetic interference(EMI)noise is excited by the high frequency current and voltage generated by the switchmode power supply(SMPS)due to its rapid switching action.The switching power supply for various electronic equipment must meet the corresponding EMC standards.This paper takes AC/DC switching converter as the main object of research,deeply studies the modeling,simulation and prediction of conducted EMI by flyback converter,and develops the first power management chip with chaotic spread spectrum function.Firstly,according to the topology characteristics of AC/DC switching converter and the test principle of conducted EMI,Saber was used to establish a complete conducted EMI simulation model.The equivalent model of high frequency transformer is obtained by theoretical calculation and experimental measurement.The high frequency equivalent model of MOSFET and diode was obtained by using the modeling tool in Saber.Impedance analyzer is used to measure the high-frequency characteristics of capacitance and inductance in the circuit.The propagation path of EMI noise between flyback converter and LISN is analyzed deeply,from which the DM mode propagation path and CM mode propagation path are obtained,and the DM transfer function and CM transfer function are also obtained.Secondly,the voltage between the MOSFET drain and the source was extracted from the Saber as the interference source,and the simulation results of conducted EMI in frequency domain were calculated in Matlab.The conducted EMI test platform was built in the laboratory,and it was verified that the simulation curve was consistent with the experimental results,with an error of about 5d B?V.Thirdly,the chaos attractor with the best EMI suppression effect on flyback converter is selected from Chua's,Lorenz,Liu chaotic attractors,and its hardware circuit is simplified.The chaos circuit and power management chip are encapsulated together by using wafers,and a power management chip with chaotic spread spectrum function is developed.Through the efficiency,voltage regulation,load regulation and ripple test,the working state and performance of the same prototype under three different conditions of fixed frequency,periodic spread spectrum and chaotic spread spectrum are compared.Finally,conducted EMI test is preceded and concluded that chaotic spread spectrum has the best conducted EMI inhibition effect without affecting the normal work of the prototype.