Patent ID: 8693156

Claim:
A protection apparatus for a load circuit in which current flowing into an electric wire is detected to thereby turn a semiconductor switch off based on the detected current in the load circuit wherein a power supply, the semiconductor switch and a load are connected via the electric wire, comprising: a switch unit which is provided between the power supply and the load; a current detection unit which detects current flowing into the electric wire; a temperature calculation unit which is provided with a pseudo heat generation temperature calculation expression and a pseudo heat dissipation temperature calculation expression, in which a conductor resistance (r) used in a calculation expression for calculating heat generation amount and heat dissipation amount of the electric wire is changed into a non-actual pseudo conductor resistance (r*) which has a value simulating current interruption time characteristics of a fuse instead of the conductor resistance (r)and which is capable of being used to protect the electric wire used in the load circuit, and in which a heat resistance (R) used in the calculation expression is changed into a non-actual pseudo heat resistance (R*) which has a value simulating the current interruption time characteristics of the fuse instead of the heat resistance (R) is set, the temperature calculation unit estimating temperature of the electric wire by using the pseudo heat generation temperature calculation expression, the pseudo heat dissipation temperature calculation expression and the current detected by the current detection unit; an over-current determination unit which determines to be over-current when the estimation temperature calculated by the temperature calculation unit reaches allowable temperature; and an interruption control unit which interrupts the switch unit when the over-current determination unit determines to be over-current.