| 摘要 |
PURPOSE:To reduce abnormal sound and regulate the speed of ventilating fan by a method whereby the motor of the ventilating fan, which is connected to the A.C. side of a commutating bridge circuit, is conducted in synchronizing with zero crossing detection. CONSTITUTION:In a system consisting of a switching element, connected to the D.C side of the commutating bridge circuit 2, a zero crossing detecting circuit 10 and the driving circuit 8 of the switching element, when the zero crossing detecting circuit 10 for an electric source has detected zero crossing, the potential of a point A becomes zero, the potential of the point B is increased for a given period of time by a timer element and a base current is supplied to a transistor 1 to conduct it. The terminal of the motor 9 for the ventilating fan is conducted by a phase angle theta from a zero crossing point by the conduction of the transistor 1 while the same terminal is not conducted from the phase angle theta to pi. The current of the motor is controlled by the conducting time of the motor 9 to regulate the speed of the ventilating fan, therefore, uncomfortable noise may be reduced.
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