US Patent 7872561 Composite transformer and insulated switching power source device

An E-shaped transformer core has a middle leg and one pair of outer legs and on opposite sides with respect to the middle leg. A first pair of coils including at least two coils are wound around the middle leg so that a power transmission transformer unit is formed. The outer leg is divided into two outer leg portions and with a space therebetween allowing coil wiring therebetween, and a second pair of coils including two coils are respectively wound around the respective two outer leg portions and so as to have mutually opposite winding directions, so that a signal transmission transformer unit is formed.