TEMPERATURE CONTROL CIRCUIT FOR HEATER

PURPOSE:To obtain an on/off temperature difference of nearly the same quantity regardless of the setting temperature by providing a means varying the amplification factor of a temperature conversion input signal in response to the setting temperature. CONSTITUTION:The temperature conversion input signal is inputted to a noninverting input terminal of an amplifier A1, an inverting input terminal of the amplifier A1 is connected to ground via a resistor R1 and connected to an output terminal of the amplifier A1 via a resistor R2 and a variable resistor VR. Further, the output of the amplifier A1 is rectified and smoothed by a diode D and a capacitor C and inputted to an inverting input terminal of a comparator CP1, where said output is compared with a prescribed value. Through the constitution above, the gain control is applied in response to the setting temperature, then the change of rate of the voltage per 1 deg.C after the output of the amplifier A1 is kept nearly equal independently of the setting temperature. Thus, the on/off temperature difference of nearly the same quantity is obtained even when the on-off control is performed by applying a feedback of a prescribed voltage in a switching circuit comprising the comparator.