| 摘要 |
PURPOSE:To obtain a low-cost AC load control system of less noise by defining the unit of conduction and nonconduction as a half cycle and changing a ratio of the half cycle of non-conduction to the conduction cycle. CONSTITUTION:A computer 20 discriminates the set stage of a fan speed; and if speed 0 (stop) is set, a turning-off signal is outputted after input to a terminal C, and a switch element 3 is made non-conductive during a half cycle. If a switch 23 is made to set speed 6 (full speed of 100% conduction rate), a turning-on signal is outputted after input to a terminal CLK, and the element 3 is made conductive during this half cycle. If setting is not changed, speed 0 or 6 is kept. If speed 1 is set, the number of times of turning-on/off is counted up by +1 and the turning-on signal is outputted in case of the first time, but it is counted down by -1 and an adder and a subtractor are cleared together and the turning-on signal is outputted if turning-on is already set once, and the conduction rate is kept at set 50% to keep speed 1. In the other cases, the number of times of turning-on/off is counted similarly to hold the set operating state. The noise is reduced because a waveform has not a quick rise, and the cost is reduced because the number of circuit parts is small.
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