EMI Prediction Of A Flyback Converter

Switching mode power supply has become the most popular power supply because of its smaller size,higher efficiency.Compared with the traditional switching power supply the small size means the power density is higher,switching frequency is higher,placement of components is more complicated,and all the factors may bring Electro-Magnetic Interference problems.The fast voltage and current translation and many copuler capacitors are the source of the noise,they can be reflected in the electromagnetic interference test.How to control electromagnetic interference is an important step in the design phase of switching power supply.If the relationship between single component and the electromagnetic interference of power supply can be found,and electromagnetic interference of power supply can be controlled with the parameter,then the development cycle will be shorten,cost of development will be reduced,production efficiency of production line will be increased,cost of waste by electromagnetic interference will be reduced.In this paper,the flyback switching mode power supply is the analysis sample,simplified the model of transformer,created the model of conducted electromagnetic interference test,set up the test circuit of transformer to control the electromagnetic interference of the power supply,and got experimental verification.The main contents are as following:Taking the small flyback switching mode power supply as the research object,analyzed the high frequency switching behavior of switch components and their influence on electromagnetic interference,analyzed the emission mechanism of electromagnetic interference from conducted interference and radiated interference.Simplified the model of transformer,analyzed the relationship between transformer and electromagnetic interference with the coupler capacitors of transformer,created the test model of conducted interference testing,simulated the conducted interference testing,proposed the method to control conducted interference and common mode noise interference via control the transformer.Summarized and analyzed the relationship between parameters of transformer and conducted interference and common mode noise interference with the experiment data,presented the evaluation of transformer in the early design phase,set up the test circuit of transformer.At the same time,analyzed the influence of electromagnetic interference with structure of transformer,differential mode inductor,common mode inductor and ferrite bead.Took different solutions of flyback switching mode power supply for verification and analysis,summarized the experimental data to verify the feasibility of the EMI prediction method.The content of this paper is helpful for the design and production of small power flyback switching mode power supply,can achieve the prediction of electromagnetic interference via control the transformer.