Project Analog - February 2009 - (Page 18) thermal management of dc/dc Power modules By carl schramm Recom Power New York, NY http://www.recom-power.com Contents Viewpoint Selecting the Right dc/dc Converter losses in the transistors, rectification losses, core losses in the transformer, and resistive losses in the windings and tracks. The maximum allowable internal temperature is determined by the Curie temperature of the transformer core material, the maximum junction temperature in the switching transistors and rectification diodes and the maximum operating temperature of the capacitors. To achieve an optimal internal thermal environment, Recom converters are fully potted with a thermally conductive epoxy so that the concentrated sources of heat are conducted evenly throughout the converter. It is possible to further lower the thermal resistance to ambient by fitting an external heat sink. Recom states the minimum and maximum ambient operating temperatures because they are easiest for the end user to measure and to monitor. The advantage is that true ambient temperature can be measured in the actual application and it need not be theoretically calculated, plus the results are valid for both sealed and Get the best thermal management results from power modules T he laws of thermodynamics state that heat energy can only flow from a warmer to a colder environment. To dissipate heat from a dc/dc converter module, the ambient temperature must always be lower than the maximum allowable internal temperature. The smaller the difference, the less heat energy will be lost and thus the converter will warm up even more. TemPeraTure sPecs You should consider the operating temperature range with or without derating and the maximum case temperature. Some manufacturers say that these two values are the same. The case (surface) temperature of dc/dc modules are typically given as 100° or 105°C. This value appears at first to be very high; however this figure includes the self-warming through internal losses and the ambient temperature. The internal losses occur mainly through switching Selecting the Right Battery System Understanding the Buck Switchmode Power Converter Analog news Microchip analog page Sample center microchipDIRECT Reference designs/ app notes Technical training 18 · PRojeCt ANAlog · VolUme 3 / NUmBeR 1 http://www.recom-power.com http://www.microchip.com http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=79&redirects=analog http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=79&redirects=analog http://sample.microchip.com/Default.aspx?testCookies=true http://www.microchipdirect.com/catalogselection.aspx?returnURL=default.aspx http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1469&filter1=function&redirects=appnotes http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1469&filter1=function&redirects=appnotes http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1423
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