| 摘要 |
PROBLEM TO BE SOLVED: To make suppressible the cost of an apparatus for controlling a brushless motor, by increasing its driving voltages when all its driving current values which are sensed by all-current-value sensing means after its starting becomes not larger than a fixed threshold. SOLUTION: A control portion 121 of this apparatus is connected with the output sides of comparators 120u, 120v, 120w, and when the rotational speed of a predetermined magnet rotor 103 exceeds a fixed value, its state is switched to a feedback synchronous control for generating and outputting respective six-phase control signals based on zero-cross-point sensing signals VU0, VV0, VW0 inputted from a zero-cross-point sensing portion 120. Just after the start of a brushless motor, all its large driving currents flow, and as increasing the rotational speed of the permanent magnet rotor 103, all its driving currents are reduced to become a fixed value when it begins to rotate stably and synchronously with a forced synchronous signal. Therefore, by setting as a threshold a slightly larger current value than the fixed value, its driving voltages are so increased when its driving currents become not larger than the threshold as to make avoidable the increases of its starting currents. As a result, the use of any element having a high withstanding voltage is made unnecessary to make suppressible the cost of this apparatus. |
