Patent ID: 7855471

Claim:
A power supply device comprising: an auxiliary power supply unit configured to be charged with a direct-current electric power, the auxiliary power supply unit being a second capacitor; a constant-voltage power supply unit that includes a charging unit configured to convert an alternating-current electric power from an alternating-current power source into direct-current power, a third switch, and a first switching control unit configured to alternate a supply of converted direct-current power between a first load and the second capacitor via the third switch; a voltage converting unit configured to convert a first voltage of the auxiliary power supply unit into a second voltage, the voltage converting unit including a second switch, and a first capacitor, wherein the voltage converting unit is configured to control a soft-switching of the second switch that switches on and off a supply of electric power of a second voltage to the first capacitor, and generate voltage by the soft-switching of the second switch, the voltage converting unit stopping voltage generation when the second switch halts the soft-switching and becomes an open state; a voltage-conversion control unit configured to control the voltage converting unit; a voltage determining unit configured to determine whether the second voltage exceeds a predetermined threshold; a first switch that is arranged between the voltage converting unit and a second load, the first switch switching on and off a supply of an electric power of the second voltage to the second load; and a second switching control unit that controls the first switch, wherein when the voltage determining unit determines that the second voltage exceeds the predetermined threshold, the voltage-conversion control unit controls the voltage converting unit to stop converting the voltage, and then the second switching control unit controls the first switch to supply the electric power of the second voltage to the second load, wherein while an inrush current flows into a second load located in a subsequent stage of an output terminal through the voltage converting unit as a supply of the electric power, only an electric charge charged in the first capacitor flows into the second load, and as a result no high current flows through the voltage converting unit and power loss is reduced.