| 摘要 |
PURPOSE:To omit temperature detecting parts such as a thermistor, etc., by detecting a variation of a resistance value of a heater due to a variation of a temperature, and controlling the temperature. CONSTITUTION:A heater 2 whose resistance value is increased due to a temperature variation, a semiconductor switching element SCR 3 and a resistance 4 for detecting a load current are connected in series. Also, a means (consisting of a zero crossing pulse generator 13, an AND circuit 14, a synchronizing signal generating circuit 11, an OR circuit 12, etc.) for turning on the SCR 3 at least for a half-cycle or more by a period set in advance is provided. Also, a means (consisting of a rectifying circuit 6, a comparator 7, etc.) for detecting a load current after the SCR 3 is turned on, and driving the SCR until it is made smaller than a reference value set in advance is provided. On-off control of the SCR is executed by an igniting circuit consisting of both these means. By such a circuit, temperature detecting parts such as a thermistor, a thermocouple, etc. can be made unnecessary. |
