Patent ID: 8848398

Claim:
A direct-current power supply device that converts energy obtained from an alternating-current power supply into direct-current energy, the device comprising: a rectifier that converts alternating-current voltage of the alternating-current power supply into direct-current voltage; a transformer that includes a primary winding, which includes a tap at a connection point where a first primary winding and a second primary winding are connected, and a secondary winding; a primary-side smoothing capacitor whose positive electrode-side terminal is connected to a terminal at a side opposite to the tap of the first primary winding and whose negative electrode-side terminal is connected to a negative electrode-side output terminal of the rectifier; a first switching element whose drain and source terminals are connected between the negative electrode-side output terminal of the rectifier and a terminal at a side opposite to the tap of the second primary winding; a reactor and backflow preventing diode that are connected in series between a positive electrode-side output terminal of the rectifier and the tap of the transformer; a direct-current smoothing circuit that includes a rectifying diode, which is connected to the secondary winding of the transformer, and a secondary-side smoothing capacitor; and discharging means for detecting a light-load state of an output and discharging electric charge of the primary-side smoothing capacitor in a way that suppresses an increase in voltage of the primary-side smoothing capacitor.