DC-DC CONVERTER

PROBLEM TO BE SOLVED: To provide a primary phase shift type DC-DC converter that reduces a switching loss.SOLUTION: In the DC-DC converter having an inverter INV, a transformer Tr fed with a high frequency output of the inverter, a rectification circuit Rec for rectifying an output of the transformer, and a filter circuit F for removing a ripple from an output of the rectification circuit, a series circuit of capacitors C5 and C6 is connected between output terminals of the inverter and a junction of the capacitors C5 and C6 is connected to any input terminal of the inverter INV via a capacitance changeover switch Q5 that opens in a light load condition and closes in a heavy load condition, and the snubber capacitors C5, C6 are charged and discharged in the process of turning on/off switch elements Q1 and Q3 of upper arms of a reference phase leg 2 and a control phase leg 3 of the inverter and switch elements Q2 and Q4 of lower arms of the reference phase leg 2 and the control phase leg 3, to provide soft switching of each switch element.