Patent ID: 7505240

Claim:
An overcurrent protecting device for protecting a semiconductor element from an overcurrent, comprising: the semiconductor element for outputting a signal to a communication line in order to communicate with an electronic device mounted on an automotive vehicle; a shunt resistor for directly detecting an electric current flowing through the semiconductor element, wherein the shunt resistor detects the overcurrent when the electric current in the semiconductor element exceeds a threshold value; a reference resistor for setting the threshold value for starting a protecting operation with respect to the overcurrent; a constant electric current circuit for supplying a constant electric current to the reference resistor; a comparator for comparing a terminal voltage of the shunt resistor and a terminal voltage of the reference resistor; a holding circuit for holding a change of output of the comparator; a reset circuit for periodically resetting the change of output of the holding circuit; and a filter disposed between the comparator and the holding circuit, wherein the shunt resistor is made of a same kind of material as the reference resistors, the filter has a signal delay time, the reset circuit has a reset period, and a time ratio between the signal delay time of the filter and the reset period of the reset circuit is equal to or smaller than a ratio between an input resistance of the semiconductor element and a load resistance of the electronic device.