Patent ID: 7446512

Claim:
A resonant switching power supply device comprising: a power supply circuit for outputting a DC power, a switching circuit having multiple switching elements, to which the DC power of said power supply circuit is input, for carrying out switching operations complementarily, a resonance circuit, to which the output of said switching circuit is input, having series-connected devices comprising a first resonance capacitor and a resonance coil, a switching transformer, and a second resonance capacitor connected in parallel with the primary winding of said switching transformer, a rectifying/smoothing circuit to which the secondary output of said switching transformer is input and in which the input is rectified and smoothed and then output, a current detection circuit comprising a detection transformer having a primary winding in which a current substantially identical to the current flowing in the primary winding of said switching transformer flows, a rectifying circuit for rectifying the secondary output of said detection transformer, and a current-voltage conversion circuit for converting the output of said rectifying circuit into a voltage, a control circuit, to which the outputs of said power supply circuit, said rectifying/smoothing circuit and said current detection circuit are input, for controlling the switching operations of said switching elements in said switching circuit, and a first load device connected to the output side of said rectifying/smoothing circuit, wherein the load value of said first load device is adjusted depending on the output of said resonant switching power supply device using said control circuit.