Patent ID: 8054015

Claim:
A motor drive apparatus equipped with a dynamic braking circuit fault detection capability having a dynamic braking circuit for producing a deceleration torque utilizing a braking force caused by a synchronous motor acting as a generator when said synchronous motor is deenergized, comprising: a DC power supply which is obtained by rectifying input AC power; voltage application means for applying a voltage to a winding of said synchronous motor and to said dynamic braking circuit for a predetermined length of time by switching a power transistor connected to said DC power supply; current detection means for detecting the value of a current flowing from said power transistor; fault checking means for checking said dynamic braking circuit for the presence or absence of a fault, based on the current value detected by said current detection means and on a predefined threshold value; and wherein an overcurrent detection circuit incorporated in a motor drive control circuit is used as said current detection means, and said threshold value is changed from a normal first level threshold value to a second level threshold value for checking said dynamic braking circuit for a fault so as to serve as an overcurrent detection level when checking said dynamic braking circuit for a fault, and said predetermined length of time during which said voltage is applied from said DC power supply is chosen so that a transient current that flows through said motor winding after said power transistor is turned on does not exceed a current that flows through a dynamic braking resistor.