Patent ID: 8873257

Claim:
A switching power supply apparatus, comprising: a DC power supply including a high-side terminal and a low-side terminal; a first switching element and a second switching element, connected in series between the high-side terminal and the low-side terminal of the DC power supply; a resonance inductor and a resonance capacitor, connected in series to an connection point for the first and second switching elements; an output circuit configured to supply power to a load based on a resonance current provided by the resonance inductor and the resonance capacitor; a current detection unit configured to detect a resonance current passing through at least one of the first switching element and the second switching element; and a control circuit configured to generate a drive control signal at levels at which the first switching element and the second switching element are alternately turned on or off, to control a cycle of the drive control signal according to the detection signal from the current detection unit so that the output power from the output circuit is maintained constant, to perform at least one of detecting whether or not the resonance current detected by the current detection unit is beyond a first detection level over a predetermined time period, and detecting, in a case of detecting that the resonance current is beyond the first detection level over the predetermined time period, that the resonance current falls below a second detection level, and detecting whether or not the resonance current detected by the current detection unit is below a first detection level over a predetermined time period, and detecting, in a case of detecting that the resonance current is below the first detection level over the predetermined time period, that the resonance current exceeds a second detection level, and to invert, in a case of detecting that the resonance current falls below or exceeds the second detection level, the levels of the drive control signal at which the first switching element and the second switching element are turned on or off.