| 摘要 |
A drive circuit for a brushless DC motor assures that the stator coils of the motor do not generate unwanted electromagnetic noise, but does not sacrifice efficiency of the motor. The drive circuit can include an input circuit to which a rectangular switching signal is applied, a circuit including a drive transistor providing stator drive current in response to the input switching signal, and an RC smoothing circuit to impart sloping leading and trailing edges to the drive current so that the drive current assumes a somewhat sinusoidal shape and the electromagnetic noise is avoided. In order to prevent the motor efficiency from dropping under low-torque and high-speed conditions, the delay times for the leading and trailing edges are controlled to increase or decrease in dependence upon the load to the motor. In one embodiment, the collector-emitter voltage of the drive transistor is sensed and this voltage is furnished to a control transistor so that the latter adjusts the level of the input switching signal according to the sensed voltage level. Preferably, the base current applied to the drive transistor is kept near the saturation level. |
