| 摘要 |
PURPOSE:To improve the control accuracy and the reliability of a device which is controlled via a power supply zero-volt cross point by securing the detection of the zero-volt cross point of a sine wave AC waveform despite the distortion, etc., of an AC power supply waveform. CONSTITUTION:A fact the a switching element is turned off is not recognized for an optional time T1 and an OFF state of the switching element is recognized after the time T1 after the switching element is turned off at a level near the zero-volt of a sine wave AC power supply. Then the OFF state of the switching element is decided before its ON state. Thus the switching element is judged to be kept under an ON state even though it is turned off during an optional time T2 smaller than the zero-volt period of the sine wave AC power supply. Then the ON and OFF states of the switching element are identified again after the time T2. As a result, the zero-volt cross point of a sine wave power supply waveform can be detected despite the distortion, the crack and the superposition of an impulse wavering of the AC power supply waveform. Thus the control accuracy and the reliability can be improved for a device which utilizes a power supply zero-volt cross point. |
