Brushless D. C. motor.

摘要

In a brushless DC motor having a magnet and multiphase coils, a current is distributed from a DC voltage source to the multiphase coils according to a set of output signals of a position detector detecting the relative position between the magnet and the multiphase coils. Two sets of output transistors, a first output transistors and a second output transistors, are used so as to distribute a current to corresponding some of the multiphase coils. A first distributor activates the first output transistors selectively corresponding to the output signals of said position detector so as to supply the multiphase coils with a current according to a command signal, and a second distributor activates the second output transistors selectively also corresponding to the output signals of the position detector. The second distributor has a voltage drop controller for detecting voltage drops across the first output transistors (or the second output transistors) in each activated period and for controlling output currents of the second output transistors so as to maintain the voltage drops across the first output transistors (or the second output transistors) in each activated period at a predetermined value regardless of the relative position between the magnet and the multiphase coils.