| 摘要 |
PURPOSE:To reduce the generation of noise, by applying proper bias to a full- wave rectification circuit, to generate a zero-cross trigger at the time of full ignition. CONSTITUTION:The output of a commercial power full-wave rectification circuit 3 is connected to the non-inverting terminal (+) of a comparator 4. A variable reference voltage 5 is applied to the inverting terminal (-) of the comparator 4, and the output of the comparator 4 is connected to the base of a transistor 6. The transistor 6 is connected to the DC terminal of a diode bridge 2. Then, in case that the reference voltage 5 is of a low value, the transistor 6 is turned ON and the input of a motor fan 1 is increased. On the contrary, when the value of the reference voltage 5 is set to be a high value, then the period of turning the transistor 6 ON is shortened, and the input of the motor fan 1 is lowered. By varying the reference voltage in this manner, the power of the motor fan 1 can be controlled. |
