Patent ID: 7638925

Claim:
A power supply device, comprising: an electrical element including a driving unit that converts a direct current power supply voltage into a sinusoidal alternating current voltage of a predetermined frequency; and a voltage resonating unit that receives the sinusoidal alternating current voltage output from the driving unit through an input electrode, boosts the sinusoidal alternating current voltage to a predetermined level, and outputs boosted voltage to a load based on an inductance component and a capacitance component; an input voltage monitoring circuit including a comparing unit configured to also receive the sinusoidal alternating current inputted to the input electrode of the voltage resonating unit from the driving unit, and to compare a signal directly representing the sinusoidal alternating current voltage inputted to the input electrode of the voltage resonating unit with a reference voltage signal generated by a standard voltage setting unit, to output an optimal control signal that drives a switch in a step-down chopper circuit; and the step-down chopper circuit that controls switching on and off of the direct current power supply voltage at a duty ratio based on the optimal control signal, the step-down chopper including the switch that receives the optimal control signal from the input voltage monitoring circuit and turns on or off based on a voltage level of the optimal control signal.