| 摘要 |
PURPOSE:To reduce evil influrnce of variation in an electric power source voltage due to the on-off control over a heater upon peripheral equipment by dividing the heater into plural parts and then driving them individually, and driving the driving circuits individually on detecting the temperature of one heater. CONSTITUTION:When a heater 12a is below set temperature, a driving circuit 18a is driven by the output of a comparing circuit 16 to turn on a triac 13a and when the heater 12a is above the set temperature, on the other hand, the triac 13a is turned off to hold the heater 12a at the set temperature. A driving circuit 18b, on the other hand, is driven by the output obtained by delaying the output of the comparing circuit 16 by very short time through a section 19 to delay the switching operation of the triac 13b, and a heater 12b is brought under on-off control with delay behind the heater 12a. Consequently, electric power supplied to the whole heater varies stepwise in the starting and ending periods of the voltage variation to reduce a variation level per stage. |
