PURPOSE:To eliminate the application of a disturbing radio wave to a radio receiver or a television without a large spike noise by altering the amplitude of an AC waveform by increasing or decreasing a resistance value to eliminate the interruption of the AC waveform in the midway. CONSTITUTION:When the ports P1, P2, P3 of a microcomputer 24 are all high, LEDs 21-23 do not emit light. Thus, photocouplers 11, 13, 15 are all OFF, and transistors 7, 8, 9 all become ON. Accordingly, a resistance value applied to a fan motor 2 becomes 0OMEGA. When the only port P1 of the microcomputer becomes low, the LED21 emits a light, the photocoupler 11 becomes ON, and a transistor 7 becomes OFF. In this case, 75OMEGA of a resistor 4 is inserted in the current passage of the motor 2, a voltage applied to the fan motor decreases approx. 4V, and the rotating speeds decreases. Similarly, when the resistance is sequentially increased, the speed decreases.
展开▼
