Patent ID: 8787042

Claim:
A DC power supply comprising: a DC power source; a power conversion circuit capable of generating an alternate current from a direct current; a primary winding of a transformer, the primary winding being connected to an output of the power conversion circuit; a secondary winding of the transformer; a rectifier diode bridge circuit connected to the secondary winding; and a filter circuit including a filter reactor and a filter capacitor, the filter circuit being connected to an output side of the rectifier diode bridge circuit, wherein a resonance reactor is provided on an output side of the secondary winding, and wherein a resonant switch circuit including a parallel circuit comprised of a diode and a semiconductor switch, configured for resonant circuit control, and further including a resonant capacitor is connected to the output side of the rectifier diode bridge circuit in parallel to the rectifier diode bridge circuit, whereby a serial resonant circuit comprised of the resonance reactor and the resonant capacitor in the resonant switch circuit is formed, wherein an orientation of the diode comprising the resonant switch circuit is a forward direction in an orientation from negative to positive of the rectifier diode bridge circuit being connected in parallel, the DC power supply further comprising a snubber circuit that includes a snubber diode and a diode for discharging a snubber capacitor connected in series and is connected in parallel to the filter capacitor in the filter circuit, wherein the snubber capacitor is connected to an output point of the rectifier diode bridge circuit via a midpoint between the snubber diode and the diode for discharging the snubber capacitor connected in series, wherein, when the semiconductor switch for controlling the serial resonant circuit of the resonant switch circuit is turned on, the discharging of the snubber capacitor and a charging of the resonant capacitor are started, and thereafter, the charging and discharging of the resonant capacitor is continued even after the discharging of the snubber diode is terminated, a semiconductor switch of the power conversion circuit on a primary side of the transformer is turned off, when a discharge current of the resonant capacitor becomes equal to a load current, and a snubber current for charging is made to flow to the snubber capacitor, via the snubber capacitor and the snubber diode, when a free-wheeling current of a secondary side of the transformer becomes zero.