Relying　on　the　advantages　of　small　size,　good　controllability,　and　consistency,　printed　circuit　board　(PCB)　inductors　are　being　widely　used.　For　PCB　inductors,　reducing　copper　loss　is　one　of　the　key　issues.　Although　some　research　works　focus　on　fringing　effect　in　PCB　planar　winding,　there　are　few　methods　to　reduce　proximity　loss　for　PCB　inductor.　Regarding　the　abovementioned　issues,　this　letter　first　improves　the　Ferreira＇s　1-D　copper　loss　model　to　accommodate　the　core　feature　of　PCB　winding:　variable　number　of　turns　per　layer.　With　this　model,　pyramid　theorem　is　proposed　that　putting　the　layer　with　fewer　turns　into　positions　farther　away　from　the　air　gaps　can　lower　the　total　winding　loss.　Based　on　the　theorem,　this　letter　proposes　a　novel　PCB　inductor-winding　structure　named　pyramid　winding,　which　has　fewer　(or　equal)　turns　on　layers　farther　from　air　gaps.　Pyramid　winding　has　less　copper　loss,　fewer　copper　layers,　smaller　size,　and　lower　cost.　In　the　experiment,　inductor　prototypes　with　the　same　six　turns　and　ferrite　pot　cores　but　different　PCB　winding　arrangements　are　built　for　a　300-kHz　2700-W　LLC　converter.　Tests　on　inductor　resistance　and　converter　efficiency　are　done,　and　the　pyramid　theorem　and　the　effectiveness　of　pyramid　winding　are　verified.　©　1986-2012　IEEE.