Patent ID: 7542316

Claim:
A switching power supply unit comprising: a switching circuit converting a DC input voltage into an AC voltage; a transformer including a primary winding connected to the switching circuit, a first secondary winding, a second secondary winding, a third secondary winding, and a fourth secondary winding; a rectifier circuit including a first rectifier device, a second rectifier device, a first junction point and a second junction point, and outputting a rectifier voltage from the first junction point and the second junction point, the first rectifier device being inserted between the first secondary winding and the second secondary winding to form a series circuit therewith, the first junction point connecting the second secondary winding and the third secondary winding, the second junction point being commonly connected to a first end portion which is one end of the fourth secondary winding on a side opposite to the second rectifier device, and a second end portion which is one end of the first secondary winding on a side opposite to the first rectifier; and a smoothing circuit including a first input end, a second input end, a first output end and a second output end, the first input end being connected to the first junction point, the second input end being connected to the second junction point, the first output end and the second output end being each provided corresponding to the first input end and the second input end, respectively, and the smoothing circuit smoothing a rectifier voltage being input into the first input end and the second input end so as to output the rectifier voltage to the first output end and the second output end.