Research On Mechanism Model Of Common Mode Interference And Improvement Caused By Magnetic Coupling In DC/DC Switched Mode Power Supply

Switched mode power supply is becoming more and more high-frequency,its volume is decreasing,and its power density is also increasing.With the decrease of the distance between the components,it is more and more obvious that the effect of the electromagnetic coupling between them,it also brings more and more electromagnetic interference problems.In order to reduce the volume of some large current switched mode power supply,the common mode interference noise is suppressed only by Y capacitor instead of common mode inductor.In this research,it is found that the stray magnetic field of the toroidal inductor in some DC/DC switcher mode power supply has magnetic coupling with the common mode circuit between Y capacitor and metal enclosure,which has a great impact on the common mode interference emission.A Boost converter is taken as the research object in this dissertation,the magnetic coupling mechanism is analysed,the common mode interference model formed by magnetic coupling effect is established,and the design of corresponding suppression or improvement are proposed.The main contents of this dissertation are as follows:In order to research the influence of stray magnetic field coupling on common mode interference noise,a Boost converter is designed and manufactured in this dessertation.Through the main function measurement and simulation,the prototype function is verified to be normal.The new abnormal phenomenon of common mode interference in Boost converter is observed through interference test,and it is analyzed that it may be caused by magnetic coupling.In order to quantify the magnetic coupling phenomenon,the mechanism of magnetic coupling interference is analyzed in this dissertation first.The stray magnetic field distribution around the toroidal inductor is simulated and analyzed.It is found that the stray magnetic field is strong at the lead gap.The design of experimental shows that the toroidal inductor is the interference source,the common mode circuit between the Y capacitor and the metal enclosure is the sensitive body,and the magnetic field coupling plays a major role.Then,the circuit model of magnetic coupling is modeled,and the magnetic coupling coefficient is extracted by simulation and measurement.In order to verify the accuracy of the magnetic coupling model,the common mode interference mechanism model of Boost converter with magnetic coupling effect is established.Through the comparison of simulation and measurement,it is proved that the model is more accurate before 2 MHz.The magnetic coupling characteristics are analyzed.By changing the placement angle of the toroidal inductor,the minimum of the common mode interference noise is found at 90 degrees.With Y capacitor moving to the port,it is found that the change of common mode interference noise is not obvious.In order to suppress and improve the common mode interference,it is found that the stray magnetic field distribution of the toroidal inductor is affected by the lead gap size,winding inter turn spacing and density through simulation analysis first.Therefore,the inductors of EI and GU cores are used,the common mode interference noise is obviously reduced.The Y capacitor and the toroidal inductor are placed vertically or the height of PCB is changed to reduce the common mode interference noise.In this dissertation,a new magnetic coupling interference phenomenon in switched mode power supply is researched,and the coupling mechanism is analyzed and modeled.The results are in good agreement with the experimental results,which also provides a reference for the analysis and design of magnetic coupling in other switched mode power supply.