Patent ID: 8884559

Claim:
A motor drive device comprising: an inverter circuit, in which at least three sets of a pair of upper and lower arms including a semiconductor switching element on an upper arm and a lower arm is arranged, for supplying voltage to a motor based on ON/OFF operation of each semiconductor switching element by a PWM (Pulse Width Modulation) signal; an inverter drive unit for outputting the PWM signal to each semiconductor switching element of the inverter circuit; a fail safe circuit, arranged between the inverter circuit and the motor, including a semiconductor switching element for shielding the voltage supply from the inverter circuit to the motor for each phase; a fail safe drive unit for outputting a signal for turning ON/OFF the semiconductor switching element of the fail safe circuit; a control unit for outputting a command signal for commanding the drive of each semiconductor switching element of the inverter circuit to the inverter drive unit, and outputting a command signal for commanding the drive of each semiconductor switching element of the fail safe circuit to the fail safe drive unit; and an abnormality detecting section for detecting an abnormality; wherein when the abnormality detecting section detects an abnormality, the inverter drive unit carries out a control to turn OFF all the semiconductor switching elements of the inverter circuit based on the command signal from the control unit, and thereafter, the fail safe drive unit carries out a control to maintain each semiconductor switching element of the fail safe circuit in an ON state until elapse of a predetermined time, and to turn OFF all the semiconductor switching elements of the fail safe circuit based on the command signal from the control unit at a time point the predetermined time has elapsed, a back electromotive force generated by the motor is absorbed to an inverter circuit side through each semiconductor switching element in the ON state of the fail safe circuit until elapse of the predetermined time.