To surely prevent an accident by means of a thermal fuse when an overcurrent protection element is anomalously overheated.
This safety device is equipped with a PTC element (overcurrent protection element) or a first protection means for protecting an electric circuit from an overcurrent, and a thermal fuse 30 or a second protection means provided near the PTC element and made up of a first electrode 31a of a conductor pattern 31 connected to the PTC element, a second electrode 32a of a conductor pattern 32 insulated by a gap 33, and solder 34 bridging the two electrodes and separated into two on both the electrode sides by being melted by the heat of the PTC element. Or, a through hole in a circuit board is filled with solder, the solder is adapted to form a recessed part on one opening side of the through hole and a projecting part on the other opening side, and the projecting part can bridge the two electrodes. The inner diameter of the through hole is larger than the plate thickness of the circuit board. The outer diameter of an exposed conductor part on the recessed part side of the circuit board can be made larger than the outer diameter of the second electrode. The circuit board is disposed vertically or with the projecting part up.
SODA OSAMU
MARUO HISAFUMI
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