SWITCHING POWER SUPPLY APPARATUS

PROBLEM TO BE SOLVED: To provide a switching power supply apparatus with constant-current characteristics that has a structure in which an inductance of an inductor configuring a resonance circuit can be adjusted.SOLUTION: A switching power supply apparatus includes: a transformer 4 that supplies an output current of a switching power supply part 1 to a primary coil via a series resonance circuit 2 and a parallel resonance circuit 3; a rectifying and smoothing circuit 5 that rectifies and smooths an inductive voltage of a secondary coil of the transformer 4 to supply the rectified and smoothed inductive voltage to a load 8; a current detection part 6 that detects a current supplied from the rectifying and smoothing circuit 5 to the load 8, such as a relay apparatus for a submarine cable or the like; and a controller 7 that controls the switching power supply part 1 depending on a detection signal from the current detection part 6. An inductance of an inductor L2 connected in parallel to a capacitor C1 configuring the parallel resonance circuit 3 can be varied by adjusting a core gap to obtain desired resonance characteristics.