TEMPERATURE CONTROL METHOD OF HEATER

摘要

PURPOSE:To attain a long lifetime of a planar heating element by comparing the sawtooth wave voltage with the voltage of a temperature detecting element and controlling the energization of the heating element by the signal obtained from said comparison. CONSTITUTION:A comparator 13 compares a level VTH which is divided by a thermistor 10 and a resistance R1 and a sawtooth wave level corresponding to the VREF produced by a sawtooth wave generating circuit 15. Then a signal HEATER ON-N which energizes a heater is extracted while VTH>VREF is satisfied. The width of the energizing signal is reduced as the temperature rises after energization and the VTH is gradually reduced. Then the temperature rise of a heating element is gradually saturated. The generation of the energizing signal is discontinued in the case of VTHVREF is satisfied. In such a way, the peak value of the planar heating element is suppressed. Thus the lifetime of the heating element is greatly increased.