| High power density DC/DC power supply modules are widely used in missiles,radar and other defense military and aerospace,medical and other civilian fields,in order to meet the demand,the power density of the power supply module is increasing,while the heat dissipation problem has become more and more serious,the temperature is too high,some internal devices may be damaged by heat,which makes the power supply equipment can not be used normally and reliability decreases,so the heat dissipation problem should draw our attention.In addition,the application environment of power supply modules is also very complex,and high reliability requires that they can work properly in various extreme environments without failure.Research results from various research institutions show that one of the important factors in determining reliability is the ambient temperature.In this paper,thermal design is studied based on a two-stage DC/DC power circuit topology;for other reliability,such as electromagnetic compatibility,electromagnetic interference noise is significantly reduced by designing EMI filters,and tests show that the power module studied in this paper has high reliability.Firstly,based on the analysis of circuit topologies of similar products at home and abroad,a main circuit topology with excellent soft switching characteristics is selected,i.e.,front-stage LLC transformer primary-side series-side parallel + back-stage Buck circuit staggered parallel topology,and the working principle of the circuit topology is introduced,and the effect of the difference of excitation inductance on the mean current degree and heat distribution in the actual circuit is analyzed.Three ways of heat dissipation are introduced,namely thermal conduction,convective heat transfer and radiation heat transfer,which leads to the concept of thermal resistance and derives the differential equation of thermal conduction.Secondly,the thermal design of this project is introduced from three aspects:device level,PCB board level and power module system level.The main idea of strengthening heat dissipation is heat source and heat path,i.e.,reducing heat generation from heat source and reducing thermal resistance on the heat path.Based on the initial selection of devices,the losses of the front and rear stage circuits are analyzed and calculated,which is the basis of thermal simulation.The thermal resistance model of the MOS tube,the heat dissipation model of the core and the heat transfer path on the PCB are established to calculate the theoretical temperature rise of the key devices.The thermal simulation is designed to obtain the simulated temperature of the device so that the uniformity of the heat distribution can be observed and subsequent optimization can improve the hot spot heat dissipation problem,and then the thermal test verifies the reliability of the overall thermal design.The efficiency-temperature curve shows that the prototype of this project still has high efficiency under high temperature environment.Finally,the common electromagnetic interference in the power module prototype is introduced,the electromagnetic interference noise sources and coupling paths are analyzed,including the differential mode and common mode noise coupling paths,and the designed EMI power filter can significantly reduce the electromagnetic interference noise.The prototype can still work normally after high and low temperature cycles,salt spray,vibration,shock and low air pressure tests,and the test results meet the requirements of relevant standards. |
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