| 摘要 |
PURPOSE:To detect service interruption at the side of a commercial AC power source, by detecting zero crossing of the waveform of an AC power source, operating a timer, and controlling the hold of the monitored result of the AC power source. CONSTITUTION:Zero crossing of the waveform of an AC power source is detected by a zero crossing detecting circuit 10, and through an edge detecting circuit 11, a timer 12 is reset at the time of rise of a zero crossing detecting pulse. Subsequently, the result of comparison of AC supply voltage and reference voltage from a reference power source 5, which is lower than a peak value of said voltage, by a comparator 6 is held by a sample holding circuit 13, between AC voltage half-waves, and at the side of a commercial AC power source, its service interruption is detected by a microcomputer 8. Accordingly, a capacitor having large capacity is unnecessary, and even in case when the variation, etc. of working voltage and reference voltage of the microcomputer are large, the service interruption is detected exactly, and a simple and small-sized service interruption detecting device is obtained. |
