| 摘要 |
PROBLEM TO BE SOLVED: To obtain an open-phase detection circuit by which not only the on-off operation of an AC input voltage but also an open phase in only one phase out of three phases can be detected by a method, wherein output signals of a plurality of AC-voltage detection circuits are combined. SOLUTION: Photocouplers 1, 2 are AC-voltage detection circuits which output a logic signal which is turned on at a time when the absolute value of an AC input voltage as viewed from a pseudoneutral point becomes a fixed value or higher. A CPU 4 is a discrmination means which discriminates the on-operation or the off- operation of the AC input voltage on the basis of the logic level of output signals (a), (b). Then, when three phases are normal, both the output signals (a), (b) are square- wave outputs at H→L and L→H. When an R-phase is an open phase, the signal (a) is at solid H, and the signal (b) is a square-wave output at H→L and L→H. In addition, when an S-phase is an open phase, the signal (b) is at solid H, and the signal (a) is a square-wave output at H→L and L→H. When a T-phase is an open phase, the signal (b) is at solid H, and the signal (a) is a square-wave output at H→L and L→H. When a power supply is cut off, the signals (a), (b) are both at solid H. That is to say, when one out of the signals (a), (b) is at solid H, it can be judged that an open-phase state exists in the three phases.
|
