Patent ID: 7292126

Claim:
A planar transformer for reducing common mode noise comprising: at least four printed circuit board (PCB) layers; a primary winding having first and second terminals and a plurality of coil turns therebetween formed by said at least four PCB layers sandwiched together; each said PCB layer having at least one of said coil turns formed thereon, wherein the coils turns on said PCB layers are connected in a predetermined way to form said primary winding; wherein said at least four PCB layers are arranged in a stack which forms said primary winding, wherein a first one of said PCB layers is positioned at the top of said stack and said second one of said PCB layers is positioned at the bottom of said stack; wherein said first terminal is connected to a coil turn on said first PCB layer and said second terminal is connected to a coil turn on said second PCB layer; and a secondary winding positioned adjacent to a selected one of said PCB layers that is in a position in said stack at a point that is substantially midway between said first and second PCB layers, wherein at least one of said PCB layers in said stack is positioned between said secondary winding and said first PCB layer in said stack, and wherein at least one other of said PCB layers in said stack is positioned between said secondary winding and said second PCB layer in said stack, such that common mode noise coupling from said primary winding to said secondary winding is minimized.