| 摘要 |
PURPOSE:To prevent fusing of an evaporating heater through releasing of it from self-holding before the evaporating heater is extraordinarily increased in temperature and fused even if circuit-forming parts are failed in operation, by a method wherein, when an evaporating heater is, under energizing condition, extraordinarily increased in temperature to higher than a specified temperature, failure in operation of the circuit-forming parts is determined to release it from self-holding. CONSTITUTION:If the output terminal of a comparator IC 25 is failed, an evaporating heater 15 is increased in temperature. If the temperature exceeds about 300 deg.C, the inversion input terminal voltage of a comparator IC 42 is lower than a non-inversion input terminal voltage, whereby the output of the comparator IC 42 is inverted and is forced into an open state, and a current flows to the base of a transistor 45 through resistors 39, 41 and 43 to bring the transistor 45 into an ON-state. Thus, the anode side of a diode 32 is attracted to an L-level, whereby a transistor 30 is turned OFF, and the flow of an exciting current to a relay coil 14b is stopped, resulting in causing a relay contact 14a to be turned OFF to release the heater from self-holding. |
