a main power supply configured to receive external power and output a charge voltage and main power; and

an auxiliary power supply including a capacitor array configured to charge auxiliary power using the charge voltage and output the auxiliary power and a charge controller connected to the capacitor array through a charge line,

wherein the charge controller is configured to perform a main charge check operation for checking whether the charge of the capacitor array is completed, and repeatedly perform a monitoring operation independently of the main charge check operation, until a detected voltage charged in the capacitor array reaches a target level,

wherein the monitoring operation includes:

a discharge operation to decrease a level of the charge voltage;

a sub charge operation to increase the level of the charge voltage; and

a detect operation to detect the detected voltage, and

wherein the charge controller determines the monitoring operation as a failure when the charge voltage is less than the target level at a predetermined point in time.