Patent ID: 8405401

Claim:
A device for diagnosing operation status of an external control unit, said device comprising: an insulation transformer having a primary side, a secondary side and an intermediate tap at a midpoint of the primary winding, a signal generating unit for generating a periodically vibrating voltage including a pulse voltage and alternating voltage, the signal generating unit connected to the primary side of the insulation transformer, a first switch circuit connected to the external control unit and to the secondary side of the insulation transformer, a second switch circuit which is connected to the intermediate tap of the primary winding of the insulation transformer, is configured to convert an output of the signal generating unit into a voltage for switching ON/OFF the first switch circuit, and comprises a switch and a resistance, the switch and the resistance being connected to the intermediate tap in parallel with each other, the switch configured to be switched by an ON/OFF signal, a detection circuit for detecting the operation status of the external control unit which is connected to the secondary side of the insulation transformer in series with the first switch circuit and to which a current flows when the first switch circuit is in an “ON” state while the current does not flow when the first switch circuit is in an “OFF” state, and a current measuring unit connected to the second switch circuit and configured to measure a current flowing through the switch or the resistance and to diagnose the operation status of the external control unit.