Patent ID: 8243407

Claim:
A semiconductor switch control device that performs switching control of a semiconductor switch that switches power supply from a power source to a load, comprising: a current detecting unit that detects a current that flows in the semiconductor switch; a voltage detecting unit that detects a voltage applied to the semiconductor switch; a temperature detecting unit that detects a temperature of the semiconductor switch; a computing unit that calculates the temperature of the semiconductor switch based on a detected current value that is detected by the current detecting unit, a detected voltage value that is detected by the voltage detecting unit, and a detected temperature value that is detected by the temperature detecting unit; a driver that turns off the semiconductor switch when the temperature of the semiconductor switch calculated in the computing unit exceeds a set threshold value; a transient thermal resistance value providing unit that obtains transient thermal resistance characteristics of the semiconductor switch along with time elapse and outputs the transient thermal resistance characteristics, wherein the voltage detecting unit outputs an excess voltage signal when the detected voltage exceeds a set threshold value; the transient thermal resistance value providing unit provides a transient thermal resistance value Z th in accordance with an elapsed time from reception of the excess voltage signal to the computing unit; when the temperature detecting unit receives the excess voltage signal from the voltage detecting unit, the temperature detecting unit detects a temperature of the semiconductor switch at this time, and outputs the detected temperature to the computing unit as an initial temperature T J0 , and the computing unit calculates a temperature T J of the semiconductor switch by a following expression, where the detected current value is represented by I ds , and the detected voltage value is represented by V ds : (expression): temperature of the semiconductor switch T J =I ds ×V ds ×Z th ×T J0 .