| 摘要 |
PURPOSE:To prevent malfunction of an image forming device or the like by providing a detection means or the like for detecting a zero cross of an AC power supply. CONSTITUTION:A zero cross detection circuit 2 detects an intersection point of AC power source input, and the output 3 is a zero cross signal which indicates an L (low) level in the case where input voltage is higher than zero potential and an H (high) level in the other case where the input voltage is lower than the zero potential. An oscillation circuit 4 produces an oscillation pulse 5 of 4MHz. A couter circuit 6 counts a detection cycle of the detection circuit 2 by the oscillation pulse 5, and the output 7 indicates a count value by a binary number by bus constitution of 16 bits giving importance from 0 to 15. A comparison circuit 8 discriminates whether the count output is within a specified range. For instance, in the case where the frequency of the power source 1 indicates 50Hz, the specified range is set at 50Hz+ or -10%. The output 9 of the comparison circuit 8 indicates the H level at the time when a comparison result is in the specified range, shows the L level at the time when the comparison result is out of the range, and is supplied to a control circuit as a reset signal. |
