| 摘要 |
A brushless DC motor of the type including a rotor having a magnet for generating magnetic flux of alternating magnetic field polarities in a rotary path about its axis of rotation and a stator coaxial with the rotor and having a plurality of coils of respective phases in linking relation to the magnetic flux and adapted to be energized for the flow of current therethrough so as to produce a rotational torque, is provided with a control circuit in which switching transistors are connected with the coils of respective phases and are selectively turned ON in response to respective switching signals for energizing the respective coils, a switching signal generating circuit is normally responsive to the rotational position of the rotor for periodically changing its condition and thereby providing the switching signals to the switching transistors, and an additional switch device is connected to the switching signal generating circuit and is actuable to fix the condition of the latter so that only one of the switching transistors is continuously turned ON for energizing only the respective coil and thereby locking the rotor against rotation. Such locking of the rotor against rotation is particularly desirable in the case where the brushless DC motor is provided to directly drive a reel mount in a video tape recorder (VTR) or similar apparatus in which it is desired to prevent rotation of the reel mount during tape loading and unloading operations.
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