Power supply device and control method for stably operating a device when a frequency of an input power supply fluctuates

A power supply device comprising:

• a power input terminal connectable to an alternating current (AC) power supply whose power supply frequency fluctuates;
• a rectifier that rectifies an AC voltage applied to the power input terminal;
• a frequency detector that measures a frequency of the rectifier;
• a variable resistor that regulates current output from the rectifier, the variable resistor having a variable resistance;
• a charge accumulation unit that accumulates charge output from the variable resistor, the charge accumulation unit including a variable capacitor that has a variable capacitance;
• a current detector that measures current output from the charge accumulation unit;
• a load connection terminal connectable to a load that is operated by current output from the current detector;
• and
• a controller that controls the variable resistance of the variable resistor, in accordance with the frequency measured by the frequency detector and the current measured by the current detector, wherein
• the variable resistor is directly connected to the current detector, and
• the current detector is directly connected to the load connection terminal.