SWITCHING POWER SUPPLY

PROBLEM TO BE SOLVED: To provide a novel switching power supply capable of reducing loss caused by a recovery current of diodes Da-Dd and the like.SOLUTION: An inductor 14 is formed to a secondary side of a transformer T. In the case that no voltage is applied to a primary side coil w1 prior to that a polarity of an applied voltage of the primary side coil w1 is inverted, the inductor 14 continuously flows a current that has been flowing in a secondary side coil w2 immediately before the voltage is no longer applied. In such a configuration, an electrostatic capacitance Cs of a capacitor 18 is set to a value by which a current can be continuously applied to a smoothing inductor 16 over a time period from when charging of the capacitor 18 is terminated to when the time period in which no voltage is applied to the primary side coil w1 is terminated. Thereby, a current flowing in the secondary side coil w2 can be made be zero within the time period in which no voltage is applied to the primary side coil w1, which can avoid a recovery current from flowing in diodes Da-Dd.