Patent ID: 6380836
Filing Date: 2002-04-30
Classification: H01F,H02M,H05K,Y02B

Abstract:
A switching power supply apparatus comprising a transformer for power transmission having a primary coil and a secondary coil, a main switch to control the current flowing from an input power supply into the primary coil, a rectifying and smoothing circuit which includes a choke coil and rectifies and smoothes an output of the secondary coil of the transformer for power transmission, and a control circuit to control the action of the main switch, wherein there is provided:a core having an intermediate leg and at least a pair of external legs arranged at equal intervals from the intermediate leg; a first printed coil provided on a first substrate which has an intermediate hole and a pair of external holes respectively inserted in the intermediate leg and the pair of external legs of the core, the first printed coil being wound around the intermediate hole; and a second printed coil provided on a second substrate which has an intermediate hole and a pair of external holes respectively inserted in the intermediate leg and the pair of external legs of the core, the second printed coil including a pair of external printed coils which are connected in series and are respectively wound around the pair of the external holes and each having the same number of turns but wound in opposite directions; wherein the pair of external printed coils of the second printed coil generate magnetic fields in opposite directions to each other in the intermediate leg such that the magnetic fields in the intermediate leg cancel each other and induce no induction voltage in the first printed coil, and induction voltages induced in the external printed coils of the second printed coil by magnetic flux generated by the first printed coil are substantially canceled, whereby the first printed coil and the second printed coil form separate inductors which are not magnetically coupled, further comprising a third printed coil provided on a third substrate which has an intermediate hole and a pair of external holes respectively inserted in the intermediate leg and the pair of external legs of the core, the third printed coil being wound around the intermediate hole, whereby the first printed coil is magnetically coupled with the third printed coil to form a first transformer; and further wherein the transformer for power transmission comprises the first transformer.