Patent ID: 6956748

Claim:
A switching power supply comprising an input power source; an input winding, a transformer comprising an intermediate winding which has an end being connected to the ground and a magnetic flux canceling winding that is connected to said intermediate winding in series; a coupling capacitor for coupling the other end of said intermediate winding; a main switch for switching an electric current being supplied from said input power source via said input winding and an electric current going through said intermediate winding via said coupling capacitor; a first rectifying switch for rectifying an electric current going through said intermediate winding and said magnetic flux canceling winding, which are connected together in series, during when said main switch is being OFF; a second rectifying switch for rectifying an electric current going through said magnetic flux canceling winding during when said main switch is being ON; and a smoothing capacitor for smoothing an electric current going through said magnetic flux canceling winding; wherein said magnetic flux canceling winding is provided in a direction which is opposite to a direction of magnetic flux generated by said input winding and said intermediate winding; wherein said apparatus is arranged such that a third rectifying switch is provided between said intermediate winding and said input power supply so that a current rectified by said third rectifying switch is recovered to an input current, or such that an intermediate tap is provided in said intermediate winding, and a fourth rectifying switch is provided between said intermediate tap and a load so that a current rectified by said fourth rectifying switch is outputted to said load.