Deterioration checking apparatus and deterioration checking

A deterioration checking apparatus for a MOS transistor, the apparatus comprising:

• an inductor that is connected in series to a main current path of the MOS transistor to be checked, and forms a closed loop together with the MOS transistor when the MOS transistor is in an ON-state;
• a control circuit that controls ON/OFF of the MOS transistor;
• a current sensor that detects a current released from the inductor;
• and
• a processing circuit configured to:
• calculate an ON-resistance of the MOS transistor from an attenuation characteristic of the current released from the inductor when the MOS transistor is in an ON-state, and calculate a threshold voltage of the MOS transistor from an attenuation characteristic of the current released from the inductor when the MOS transistor is in an OFF-state;
• and
• determine a deterioration state of the MOS transistor by comparing an ON-resistance threshold and a threshold voltage threshold, which are set in advance, with the calculated ON-resistance and the calculated threshold voltage of the MOS transistor.