PURPOSE: To achieve self recovery property and reduce the number of parts by mounting a thermistor with positive characteristics whose resistance changes above a specified value to a signal line connecting a power supply and a load if temperature exceeds Curie temperature when a current above a specified value flows and changes from a temperature lower than the Curie temperature to one which is above it.
CONSTITUTION: When current flowing a signal line 4 is smaller than a specified value, temperature of a thermistor 1 with positive characteristics stays lower than a specified temperature. Also, resistance of the thermistor 1 at this time is low and the voltage drop is small, thus giving no influence to an original circuit. On the other hand, current equal to or larger than a specified value flows to the thermistor 1 due to short-circuiting, etc., an amount of generated Joule heat is increased, temperature of the thermistor 1 exceeds the Curie temperature, and then the resistance is increased extremely, thus enabling current to be broken. Then, when causes of generation of abnormal current are eliminated, the resistance of the thermistor 1 returns to the original low value and a current is supplied to the load side.
Kazuhiro Izumi
Hiroshi Sasaki
