Integrated　magnetics　has　been　popularly　used　to　improve　the　power　density,　but　the　winding　loss　mechanism　becomes　more　complex　and　hard　to　understand　for　its　versatile　magnetic　functions.　Therefore,　a　novel　ac　winding　resistance　model　of　integrated　magnetics　in　switched-mode　power　supply　is　presented　in　this　paper.　It　will　be　more　intuitive　and　suitable　to　reveal　the　winding　loss　mechanism　of　the　integrated　magnetics　which　have　both　transformer　and　inductor　functions.　The　model　is　illustrated　with　the　integrated　magnetics　in　forward-type　converter　and　the　coupled　inductor　in　voltage　regulator.　With　the　understanding　of　the　proposed　resistance　model,　the　measures　to　reduce　the　ac　winding　loss　of　integrated　transformer　can　be　taken　by　balancing　the　transformer　component　winding　loss　and　the　inductor　component　winding　loss.　©　2010　IEEE.