Patent ID: 8274800

Claim:
A switching power supply apparatus comprising: a power factor correction converter including a rectifying circuit arranged to perform full-wave rectification on an AC input power supply, a switching circuit arranged to perform switching of a voltage output from the rectifying circuit, an inductor arranged to allow a current intermittently supplied from the switching circuit to flow, a rectifying/smoothing circuit arranged to rectify and smooth a voltage output from the inductor, and an average current control circuit arranged to control the switching circuit so that an average value of currents supplied to the inductor and a voltage signal supplied from the AC input power supply are in phase; and an isolated DC-DC converter including a transformer, a switching circuit which is connected to a primary winding of the transformer and arranged to perform switching of an output from the power factor correction converter, and a rectifying/smoothing circuit arranged to rectify and smooth an AC voltage generated in a secondary winding of the transformer due to turning on or off of the switching circuit and to output the AC voltage to an output terminal; wherein a digital control circuit which defines the average current control circuit is disposed on a secondary side of the transformer of the isolated DC-DC converter; a circuit arranged to transmit a switching control signal output from the digital control circuit to the switching circuit included in the power factor correction converter in an isolated state, a circuit arranged to transmit a signal used to detect a voltage output from the power factor correction converter to the digital control circuit in an isolated state, and a circuit arranged to transmit a value of a current supplied to the inductor included in the power factor correction converter to the digital control circuit in an isolated state are included; the circuit arranged to transmit a signal used to detect a voltage output from the power factor correction converter in an isolated state includes a pulse transformer connected to opposite terminals of the inductor included in the power factor correction converter; and the digital control circuit includes a calculating circuit arranged to detect a voltage applied to opposite sides of the inductor in accordance with a voltage output from a secondary side of the pulse transformer, and to calculate a voltage (Vo) output from the power factor correction converter in accordance with a voltage (Vbon) obtained when the switching circuit included in the power factor correction converter is in an on state and a voltage obtained when the switching circuit is in an off state, which are applied to the inductor.