| 摘要 |
PURPOSE:To decrease the rating of a switching element and reduce its cost by detecting the current of a heating coil to limit its peak value and providing a frequency limiting circuit so that the frequency is not lowered to the fixed value or below. CONSTITUTION:A heating coil current detecting circuit 8 detecting the current of a heating coil 4, a voltage and input current detecting circuit 7 at both ends of the heating coil, an oscillation timing circuit 9 controlling the timing of the on or off of a switching element 5 by the signal from the heating coil current detecting circuit 8, and a frequency limiting circuit 10 limiting the frequency of the output signal of the oscillation timing circuit 9 are provided. The current of the heating coil 4 is detected, the peak value of the current of the heating coil 4 is limited regardless of the phase of the power voltage. The frequency limiting circuit 10 to suppress the frequency to the fixed value or below is also provided. The peak value of the switching element current has a flat wave-form, the increased quantity of the peak value from the average value of the switching element current is small, the rating of the switching element can be decreased, and its cost can be reduced. |
