Research On Fly-back Transformer Loss Modeling And EMI Suppression Technology

The fly-back converter is widely adopted in low power applications due to its simple structure.With the ever trend of high switching frequency and high power density,the switching frequency is getting higher and higher,and the PCB layout is becoming more and more compact.Correspondingly,the design of fly-back transformers has also become more stringent.As a major power loss source of fly-back converter,improper design of the transformer will cause excessive heat to make its own temperature rise too high,as well as causing other components to have excessive temperature rise.In order to make a reasonable design of the fly-back transformer,this dissertation firstly analyzes the core loss of the fly-back transformer,and introduces the classical core loss calculation model.And an improved core loss calculation model based on the traditional core loss calculation model is presented for fly-back transformers.At the same time,the existing copper loss model is reviewed and summarized.The reason why these models cannot predict winding loss of fly-back transformer well is explained.A new copper loss model suitable for the fly-back circuit transformer is proposed.Based on this model,the optimization method of transformer winding wire diameter is proposed and verified by simulation and experimental results.In addition,this dissertation analyzes the principle and conduction path of common mode interference of fly-back circuit.By deriving the common mode noise current through the transformer,the conditions for achieving common mode noise cancellation are derived.Based on these,several common mode noise suppression methods are proposed.Finally,the experimental results verified the theoretical analysis.The loss models and the noise suppression strategies proposed in this paper have good performance on accuracy and is easy to follow,which is attractive for practical design applications.