Research On Electromagnetic Radiation Prediction And Its Characteristic Of Vhf Switching Power Supply

Due to the complexity of the structure and electromagnetic radiation mechanism of switching power supply,far-field radiation interference of switching power supply is still a difficult problem.GaN has been widely used in switching power supply due to its wide bandwidth and high performance.The development of GaN and VHF(very high frequency power supply)has also brought greater challenges to EMC design.In this paper,the 30 MHz VHF(very high frequency power supply)boost power supply is taken as the research object,and the prediction and characteristic analysis of far-field radiation are the main targets of this paper.The analytical model and equivalent antenna simulation model of far-field radiation of VHF power supply are established.The far-field radiation of VHF switching power supply is predicted,and the radiation characteristics of VHF switching power supply are analyzed according to the prediction results of the model.The contents of this paper are as follows.In order to obtain the common-mode excitation source in VHF Boost circuit accurately,a common-mode voltage representation method is deduced from the view of charge by introducing a common-mode voltage contribution coefficient to characterize the contribution of conductors to common-mode voltage.The mutation of common-mode voltage along the conductor direction can be regarded as the result of a common-mode excitation source.Common-mode excitation source is used to build a common-mode radiation emission model,and the common-mode current distribution and far-field radiation characteristics are verified by simulation.To study the radiation mechanism of VHF switching power supply,a 30 MHz VHF Boost power supply is designed,and its PCB layout is optimized.The high frequency model of the circuit is established and simulated.According to the generation mechanism of common mode source proposed in this paper,the commonmode excitation source of Boost power supply is extracted,and the radiation structure of the circuit is analyzed and simplified.After that the equivalent common-mode radiation model of the circuit is established.Based on this radiation model,an analytical algorithm of radiation field is given,and the far field radiation of boost circuit is calculated using this algorithm.In order to verify the radiation model and analytical algorithm,a 30 MHz Boost circuit with attached cables are constructed for experimental verification.Th e circuits are tested in a 10-meter semi-anechoic chamber.The far-field radiation obtained by analysis model,common-mode antenna simulation model and practical test is compared and analyzed.The effectiveness and practicability of the generation mechanism of common-mode source and the equivalent common-mode antenna model in the far-field radiation prediction of VHF switching power supply are verified.The radiation pattern of the two circuit can be obtained by simulating the commonmode radiation model.By using the radiation pattern,the distribution character of radiation field has also been analyzed.The main significance of the study is to analyze the generation mechanism of common-mode excitation source in the circuit,and apply this mechanism to the radiation field prediction of VHF switching power supply.It provides a feasible method for the analysis of the far-field radiation of VHF switching power supply.