The present invention expands the allowable range of input voltages in a current resonance DC-DC converter. One embodiment includes a drive circuit. The drive circuit, (a) in a first control mode, switches a first transistor ON/OFF at a drive frequency based on the output voltage or output current of a resonance circuit, and switches a third transistor to a state that is opposite to the first transistor at a timing that is approximately the same as the ON/OFF timing of the first transistor, and, (b) in a second control mode, switches the first transistor ON/OFF and switches the third transistor to a state that is opposite to the first transistor at a timing that is offset from the ON/OFF timing of the first transistor only by a phase shift amount based on the output voltage or output current of the resonance circuit.
