PROTECTIVE DEVICE FOR LOAD CIRCUIT

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PROBLEM TO BE SOLVED : To provide a protective device for a load circuit capable of detecting a temperature rise of a wire to reliably interrupt the load circuit when a rare short-circuit occurs. SOLUTION : When current flowing through a load 4 is increasing, the rising temperature of a wire 7 is calculated based on the heat characteristics (thermal resistance and heat capacity) of the wire 7 or a contact conductor. Furthermore, when the current flowing through the load 4 is zero or decreasing, the dropping temperature of the wire 7 is calculated based on the heat characteristics of the wire 7. Then, the determined rising temperature and dropping temperature are added to determine a total, thereby estimating the current temperature of the wire 7. When the estimated temperature exceeds a predetermined allowable temperature, the load circuit is interrupted. Therefore, highly accurate circuit protection based on the temperature rise of the wire 7 can be achieved. COPYRIGHT : (C)2010, JPO&INPIT