Research Of Characteristics Of Conducted And Radiated Emission Of Flyback Switched Mode Power Supply

Switched mode power supply(SMPS) is widely used in many fields such as telecommunications, military equipment, transport facilities, etc. Because the switching speeds of electronic devices have been increased rapidly, electromagnetic interference(EMI) now cause a big problem so that it has been considered in order to meet the electromagnetic compatibility(EMC) standards. The flyback switched mode power supply is easy to realize buck, boost or buck-boost, and it often fails in the EMC measurement caused by conducted and radiated EMI. However, the compliance measurement of the conducted and radiated EMI cost very strict environments and expensive facilities, so the prediction of EMI becomes more important. According to reasons listed above, a series of research work have done in this thesis, the main contributions are summarized as follows:Firstly, the mechanism and route of conducted EMI has been analyzed, a time domain simulation method has presented to predict the conducted EMI. The models of active and passive components have been adopted by SPICE macro-model methods and the equivalent high frequency circuit simulation model, respectively. The CST PCB Studio has been utilized to extract parasitic parameters for a printed circuit board(PCB) based on the 2D field solver, and has performed a total circuit simulation. The experimental results has been validated the presented modeling method, and it has shown that the method is efficient and fast to predict and evaluate the conducted EMI;Secondly, the SMPS is a typical model of a PCB board with attached cables, the change rates of the large voltage and the current, dv / dt, di / dt, generated by the rapid switching of switch in the SMPS are the major radiation sources on the PCB board, also the attached cable can radiate energy coupled from the board to enhance the radiation, and it becomes prominent problem. A simplified model of radiated emission from flyback SMPS can be predicted rapidly based on the conducted and radiated emission mechanism, and a experimental result of the radiated emission at 3m away from a 20 W flyback SMPS has been used to verify to the simulation model;Finally, a series of the inhibiting SMPS conducted and radiated interference have been studied. The circuit and the field methods have been utilized to approach the inhibition of both conducted and radiated EMI. Obviously, it is necessary that to prediction of the conducted and radiated EMI and using some measures during the design stage are very useful to reduce the cost of the products.