Patent ID: 8542510

Claim:
A power supply input device including an alternating current (AC) power supply unit, a bridge diode unit, and a direct current (DC) condenser unit, comprising: a discharge resistance unit connected to both ends of the DC condenser unit and for discharging the DC condenser unit; and a discharge resistance conversion circuit for changing a discharge resistance value when a normal operation mode in which a system that receives power supply from the power supply input device normally operates is converted to a standby mode in which power supply is saved or when the standby mode is converted into the normal operation mode, wherein the discharge resistance conversion unit comprises: a first resistance connected in parallel to the discharge resistance unit and having a resistance value smaller than a resistance value of the discharge resistance unit; and a switching unit connected in series to the first resistance and turned on or off in such a way that the resistance value is changed according to a control signal having a voltage level varying whenever an operation mode of the system is converted, wherein the control signal turns on the switching unit in such a way that the discharge resistance decreases if the normal operation mode of the system is converted into the standby mode, and turns off the switching unit in such a way that the discharge resistance increases if the standby mode of the system is converted into the normal operation mode, wherein the control signal functions as a ground signal in the normal operation mode and as a high impedance signal in the standby mode, wherein the switching unit comprises: a bipolar junction transistor that has a collector connected to the first resistance; a second resistance connected between a base of the bipolar junction transistor and the first resistance and having a value so as to operate the bipolar junction transistor; a first photo coupler connected to the second resistance and the base of the bipolar junction transistor; and a third resistance connected to the first photo coupler.