| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a control circuit for a rotating speed by which power-saving of an IC is attained and the noise of a motor is made quiet, according to a drop in supply voltage. <P>SOLUTION: The control circuit includes a triangular wave generating circuit and a comparator, wherein the triangular wave generating circuit generates a triangular wave in which at least one of the upper limit voltage or the lower limit voltage of an amplitude changes according to the level of a supply voltage, and the comparator compares a level between a reference voltage not depending on the supply voltage with the triangular wave, then outputs one logical value when the triangular wave is higher than the reference voltage, and outputs the other logical value when the triangular wave is lower than the reference voltage. A driving current supply circuit which supplies a driving current to the drive coil of the motor according to the level of the supply voltage supplies the driving current to the drive coil when the output of the comparator equals to one logical value, and suspends supply of the driving current to the drive coil when the output of the comparator equals to the other logical value, then decreases duty of one logical value in the output of the comparator according to the drop in the supply voltage, by which the driving current supplied to the drive coil is reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI |
