Method of protecting semiconductor device and protection apparatus for semiconductor device using the same

A protection apparatus for a semiconductor device comprising:

• a DC power source;
• a load;
• a semiconductor device, arranged between the DC power source and the load, and changes the load between a driving state and a stopping state;
• a circuit element, connected to the semiconductor device;
• a comparator, comparing a voltage drop across the semiconductor device with a predetermined reference voltage;
• and
• a cut off section, cutting a conduction of the semiconductor device between the DC power source and the load when the voltage drop is greater than the predetermined reference voltage,
• wherein a constant of the circuit element is set so that the reference voltage is not greater than a critical voltage;
• and
• wherein the critical voltage is a product of the on-resistance of the semiconductor device when its channel temperature is at an upper limit of a permissible temperature, and a minimum current value which causes the channel temperature to reach the upper limit of the permissible temperature by the self-heating due to Joule heat.