Patent ID: 8432155

Claim:
A signal status diagnosing device 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 a primary winding on the primary side, the secondary side connected to said external control unit, a signal generating unit for generating a periodically vibrating voltage including a rectangular pulse voltage and an alternating voltage, the signal generating unit connected to the primary side of the insulation transformer, a switch circuit which is connected to the intermediate tap of the primary winding of the insulation transformer and is configured to convert an output of the signal generating unit into a voltage for switching ON/OFF the external control unit and to send a driving electric power to the external control unit to drive the external control unit, the switch circuit having a switch and a resistance, the switch and the resistance being connected to the intermediate tap in parallel with each other, and a current measuring unit connected to the switch circuit and configured to measure a first current which flows in the switch or the resistance corresponding to a second current which flows in the secondary side of the insulation transformer, wherein the first current is used to diagnose signal status of the external control unit.