Patent ID: 8476860

Claim:
An electric power converter for supplying power to a motor, comprising: a control unit outputting PWM signals; a bridge circuit producing AC electric power supplied to the motor, by turning semiconductor switching devices in the bridge circuit ON and OFF with the PWM signals; a cut off unit, provided between the control unit and the bridge circuit, for cutting the PWM signals supplied from the control unit off from the bridge circuit in response to a gate signal; and a monitoring unit generating a test signal for checking the cut off unit, wherein the cut off unit comprises: a switching circuit that switches between the test signal and an external cut off signal to output one of the test signal and the cut off signal as a switching circuit output signal; a delay circuit that receives the switching circuit output signal and allows the switching circuit output signal to pass through the delay circuit as a delayed signal after a predetermined time has elapsed from the time at which the switching circuit switches; and means for inputting the switching circuit output signal to the monitoring unit as a feedback signal, wherein the test signal generated by the monitoring unit has a duration shorter than the predetermined time of the delay circuit, and the monitoring unit makes a decision as to whether the feedback signal from the cut off unit is in agreement with the test signal and, if the feedback signal and the test signal are in disagreement with each other, makes a decision that the cut off unit is in an abnormal state.