| 摘要 |
PURPOSE:To decrease the rating of a switching element and reduce its cost by detecting the phase of the power voltage and shorten the on-time of the switching element near the peak value of the power voltage. CONSTITUTION:A control circuit 7 controlling the on or off of a switching element 5 by the voltage or current of a heating coil 4 and the signal of a phase compensating circuit shortens the on-time of the switching element 5 near the peak of the power voltage and controls the switching element current. The phase of the power voltage is detected and the on-time of the switching element 5 near the peak value of the power voltage is shortened, thereby the peak value of the current of the switching element 5 has a flat wave-form near the peek of the power voltage. The increased quantity of the peak value from the average value of the current of the switching element 5 is made small, the rating of the switching element is decreased, its cost can be reduced. |
