Patent ID: 8373424

Claim:
An apparatus for detecting a fault of a flying capacitor of an insulated condition detecting unit that detects an insulated condition of a DC power source being insulated from a ground potential portion according to (i) a charge voltage of the flying capacitor charged with a charge amount corresponding to a voltage of the DC power source and (ii) a charge voltage of the flying capacitor charged through an insulation resistance measuring circuit including an insulation resistance of the DC power source, the apparatus comprising: a charge voltage measuring unit configured to measure a peak charge voltage of the flying capacitor; a discharge voltage measuring unit configured to measure a discharge voltage of the flying capacitor a predetermined time after the start of discharge of the flying capacitor, the flying capacitor being charged at the peak charge voltage measured with the charge voltage measuring unit; and a diagnosing unit configured to diagnose a fault of the flying capacitor according to a discharge amount of the flying capacitor in a period from the start of discharge of the flying capacitor, the discharge amount being obtained from a difference between the peak charge voltage measured with the charge voltage measuring unit and the discharge voltage measured with the discharge voltage measuring unit.