| 摘要 |
PURPOSE:To decide whether line is ON or OFF, by judging whether or not the 2nd voltage based on the line voltage is over the predetermined rate against the 1st voltage based on the maximum voltage of the line. CONSTITUTION:When the voltage V1 of a voltage dividing circuit 10 exceeds the voltage V2 of a voltage holding circuit 12, an output is generated to a comparator Q3. In case three-phase AC voltage is applied normally to a line 1, the output V3 of the comparator Q3 becomes a pulse train of a specified cycle. Let the output voltage of a rectification circuit 10, i.e. the voltage at a point A be V0 and the forward voltage drop of a diode D8 be VD. The voltage V1 is a voltage value across a resistance R3 where the voltage V0 is divided by resistances R2 and R3. The voltage V2 is a value which the voltage across a resistance R5, where the voltage (V0-VD) is divided by resistances R4 and R5, is exponentially decreased with a time constant C2R5. A voltage attenuation detection circuit 14 therefore generates the output of a H level when V1>V2 regardless of the output voltage V0 of the rectification circuit. The ON or OFF state of the line 1 can thereby be discriminated, even if any load such as a motor, etc., to generate residual voltage is connected to the line 1. |
