Patent ID: 8362784

Claim:
A capacitor capacitance diagnosis device comprising: a power supply which charges a capacitor; a discharge circuit which is composed of a discharge resistor and a discharge switch connected in series, and is connected to the capacitor in parallel; a resistance dividing circuit which is composed of a first resistor and a second resistor connected in series, and is connected to the capacitor in parallel; a measurement circuit which measures by amplifying a voltage at a dividing point between the first resistor and the second resistor; and a diagnosis circuit which stops charging of the capacitor, discharges energy charged in the capacitor for a predetermined time by electrically conducting the discharge switch of the discharge circuit, and determines adequacy of capacitor capacitance from a voltage drop value due to the discharge, the voltage drop value being measured by the measurement circuit, wherein the voltage drop value during diagnosis due to the discharge of the charged capacitor is limited to within a predetermined value.