Patent ID: 6809497
Filing Date: 2004-10-26
Classification: H02P

Abstract:
A drive unit for a brushless fan motor including a stator provided thereon with a plurality of excitation windings and a rotor including a plurality of rotor magnetic poles each constituted by a permanent magnet, comprising:a position detector for detecting a position of said rotor of the brushless fan motor; a rotational speed detecting means for detecting a rotational speed of said rotor; a plurality of excitation changing over semiconductor switches each connected in series to each of said excitation windings so as to permit an excitation current to flow therethrough to each of said excitation windings when they are turned on; a drive circuit for outputting an on/off change-over signal for said excitation changing over semiconductor switches depending on an output of said position detector; a power feed semiconductor switch arranged between said excitation windings and a power supply so as to permit power to be fed from said power supply therethrough to said excitation windings when it is turned on; and a power control circuit for outputting a control signal to control an on and off operation of said power feed semiconductor switch, thereby controlling the rotational speed of said rotor; said power control circuit controlling the on/off operation of said power feed semiconductor switch based on a value of the target rotational speed of said rotor given as a speed command and an actual rotational speed obtained by said rotational speed detecting means; said power control circuit being constructed so that after the rotational speed of said rotor is stabilized, said power feed semiconductor switch may have turn-off time set shorter when an actual rotational speed is slower, in comparison, than said target rotational speed, and set longer when the actual rotational speed is faster than said target rotational speed, and set as it is when an actual rotational speed is substantially equal to said target rotational speed.