| 摘要 |
PURPOSE: A speed control apparatus for fan motor is provided, in which the turn-off time of the solid state relay is changed when the sensed RPM of the fan motor is higher than the target RPM, to thereby control the fan motor at the desired RPM upon input of a low voltage. CONSTITUTION: A speed control apparatus comprises a power unit(10) for converting the AC voltage input through a power input terminal(1) into a DC voltage and outputting the converted voltage; a zero-crossing sensing unit(20) for sensing the zero-crossing where the AC voltage from the power input terminal is near the zero potential; an RPM set unit(60) for setting the target RPM of the fan motor; a solid state relay(40) which is turned on with a predetermined time delay from the zero-crossing point in accordance with the target RPM set by the RPM set unit, so as to drive the fan motor; an RPM sensing unit(50) for sensing the RPM of the fan motor; and a control unit(30) for controlling the fan motor to be maintained at the target RPM, by changing the turn-off time of the solid state relay in accordance with the result of comparison between the RPM sensed by the RPM sensing unit and the target RPM.
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