EMI Simulation And Characteristic Analysis Based On Switching Mode Power Supply Module

Switching mode power supply is widely used in many fields due to its high efficiency,and small size.However,the high frequency on and off of MOSFET will cause a large transient voltage/current,which will generate conducted and radiated EMI.With the development trend of higher frequency,miniaturization and modularization of switching mode power supply,its EMI problem becomes more and more serious,which not only affects its normal work,but also pollutes the surrounding electromagnetic environment.Therefore,how to accurately predict and inhibit the EMI of switching mode power supply and improve the EMC performance of system are key points and difficulties of study.In this paper,we take DC/DC switching mode power supply module and its combined switching mode power supply board as objects of study,study the conducted and radiated EMI of switching mode power supply and analysis its EMI characteristics through theoretical analysis,simulation and experimental test.First of all,we analysis the EMI mechanism of switching mode power supply based on its circuit structure and working principle from the perspective of EMC three elements,including EMI sources and propagation paths.On the basis of the fact that DC/DC switching mode power supply module usually operate in combined state and internal details are difficult to obtain,we propose a new method to analysis its EMI.Firstly,extracting the key information by experimental test to establish the model of DC/DC switching mode power supply module according to the circuit topology.And packaging basic units in the software to form the model library based on the idea of behavior level modeling,so as to realize the EMI simulation of switching mode power supply board.At the same time,we introduce the EMI experimental test method and basic principle of switching mode power supply.In this paper,we simulate and analysis the conducted EMI of various DC/DC switching mode power supply module and different combination types of switching power supply board.Through the comparison of simulation and experimental test results,the accuracy of simulation method is verified,and summarizing its conducted EMI characteristics,including EMI frequency,amplitude and variation trend.In addition,the influence of transformer`s leakage inductance and parasitic capacitance between MOSFET and radiator on conducted EMI is investigated on the basis of the simulation model of DC/DC switching power module.By means of "field-path" combination and PCB parasitic parameters extraction,we establish radiated EMI model of switching mode power supply board.Then the far-field and near-field radiated EMI and resonance simulation are carried out in turn.According to the simulation results,the radiation region,radiation magnitude,resonance frequency and resonance mode of PCB are predicted and analyzed.And we find that the radiated EMI in the input area of switching mode power supply board is particularly serious.Then,the cosimulation of switching mode power supply board and equipment structure is carried out,we investigate the distribution and leakage of radiated field under different layout structures.It is beneficial to the optimization of system layout and the improvement of EMC performance.