| 摘要 |
PURPOSE:To set a heater temperature to an optional value without generating a high frequency noise by comparing a detected voltage with a set voltage so as to control a comparison voltage synchronously with zero crossing of a power supply voltage. CONSTITUTION:A voltage detection circuit 5 detects the application of an AC voltage to a heater 2 and gives a detected voltage to a voltage averaging circuit 9. The detected voltage averaged by the circuit 9 is compared with an output of a power setting circuit 10 at a comparator circuit 11, and its output is given to a control circuit 12. On the other hand, a clock generating circuit 8 generates a clock pulse synchronously with zero cross points of the primary AC voltage of a power transformer 6 and gives it to the circuit 12, and when the output of the circuit 11 is smaller than the output of the circuit 10, a triac 3 is turned on. Then a current is given to the heater 2 and the circuit 10 sets the heater temperature to an optional value without generating a high frequency noise. |
