| 摘要 |
PROBLEM TO BE SOLVED: To surely cut off a circuit without relying on the performance or reliability of an overvoltage protection element if an input overvoltage is generated in a power supply line. SOLUTION: An inrush current prevention circuit 25 is interposed in at least one of AC line L1 and L2, and a detection circuit 24 detects voltages of the AC lines L1 and L2. If a detected voltage exceeds a prescribed value, a switch circuit 26 is turned on to transmit the excess to the inrush current prevention circuit 25 by a phototriac coupler 41 of a transmission circuit 27. In the inrush current prevention circuit 25, a resistor 43 with a temperature fuse and a triac 42 which is a semiconductor switch element are connected in parallel. The triac 42 is normally conductive, and when information that the switch circuit 26 is turned on is transmitted by the transmission circuit 27, it is opened. It makes a current to flow the resistor 43 with temperature fuse, and a power feeding circuit is disconnected when the temperature fuse is blown off. COPYRIGHT: (C)2004,JPO
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