Patent ID: 8891255

Claim:
A switching power supply apparatus comprising: a series circuit that is connected to a power receiving unit into which a direct current input voltage is input and that includes a first switching element and a second switching element; a transformer in which at least a primary winding and a secondary winding are magnetically coupled to each other; a series resonant circuit connected in parallel to the first switching element or the second switching element, in which the primary winding in the transformer, an inductor, and a capacitor are connected in series to each other; a first rectifier smoothing circuit that rectifies and smoothes a voltage occurring at the secondary winding in the transformer during an on period of the first switching element to extract a first output voltage; a second rectifier smoothing circuit that rectifies and smoothes a voltage occurring at the secondary winding in the transformer during an on period of the second switching element to extract a second output voltage; a switching control circuit that drives the first switching element and the second switching element so that the first switching element and the second switching element complementarily repeat turning on-off, controls an on time of the first switching element and an on time of the second switching element based on the first output voltage and the second output voltage, respectively, and controls the first output voltage and the second output voltage; a first output voltage detection circuit that detects the first output voltage; and a second output voltage detection circuit that detects the second output voltage; wherein during the on period of the first switching element, a first power is supplied to the first rectifier smoothing circuit and a second power to be supplied to the second rectifier smoothing circuit is charged in the capacitor of the series resonant circuit; during the on period of the second switching element, the second power charged in the capacitor of the series resonant circuit is discharged and supplied to the second rectifier smoothing circuit; and the switching control circuit performs multivariable feedback control to the on time of the first switching element and the on time of the second switching element so that the first output voltage and the second output voltage are equal to certain voltage values based on a detection signal detected by the first output voltage detection circuit and a detection signal detected by the second output voltage detection circuit in the following relationship: Formula ⁢ ⁢ 5 L ⁡ [ ( T on ⁢ ⁢ 1 T on ⁢ ⁢ 2 ) ] = ( A B C D ) ⁢ L ⁡ [ ( V ref ⁢ ⁢ 1 - V o ⁢ ⁢ 1 V ref ⁢ ⁢ 2 - V o ⁢ ⁢ 2 ) ] ( 5 ) where, in Formula 5, A, B, C, and D denote transfer functions and L[] denotes a Laplace transform, V o1 denotes the first output voltage, V o2 denotes the second output voltage, T on1 denotes the on time of the first switching element, T on2 denotes the on time of the second switching element, V ref1 denotes a first reference voltage, and V ref2 denotes a second reference voltage.