In some embodiments, a PLC system includes a memory unit configured to back up user data stored in a MCU thereto when the power supply from the power module is interrupted, a capacitor configured to be charged by the power module and supply accumulated power to the memory unit when the power from the power module to the MCU is interrupted, a variable resistor unit configured to be coupled between the power module and the capacitor, and a switching unit configured to alternatively couple either the power module or the capacitor to the memory unit depending on a state of power being supplied from the power module. Some embodiments may provide advantages that a PLC system can supply much more power while reducing a charging period of time of an auxiliary power supply for supplying power with urgency when an abnormality occurs in a power module of the PLC system.