| 摘要 |
<p>PURPOSE:To prevent breakage of an electric heater[s line and deterioration of characteristics at the time when gas flow becomes zero in the condition that a power source is switched on, by limiting output voltage of a voltage control circuit and providing a heat generation liminting circuit which limits heat generation of a heat- generating heater. CONSTITUTION:If the condition that suction air flow is zero lasted for a long period of time, heat generation of a heat-generating heater 10 increases and surface temperature rises. At this time, resistance value of the heat-generating heater 10 itself increases and potential of a connecting point e between a base resistance 23 of No.2 bridge and the heat-generating heater 10 rises. And when the potential became larger than the prescribed potential of connecting point f between base resistances 24 and 25, an output of a comparator 47 becomes 1 level and a transistor 50 is switched on and a power transistor 43 is turned off. In this manner, a resistance value of a resistance 42 is selected to an appropriate value in advance, a voltage to be impressed on No.2 bridge becomes small, and heat generation of the heat- generating heater 10 decreases. It is possible in this way to prevent breakage of line of the electric heater 10 and deterioration of characteristics.</p> |
