| 摘要 |
PURPOSE:To improve the responsiveness to a target value, to obtain an exact time average power value and to make possible the accurate control of an electric power supply quantity by detecting the integrated value of one cycle of the supply power waveform in a power detecting part. CONSTITUTION:A zero cross signal ZC which resets the integrated value is supplied to an integrator 36A outputs a saw tooth wave signal SW. The respective values of a supply voltage signal V, supply current signal I, instantaneous supply power signal W, integrated supply power signal F, max. integrated supply power signal Fm and phase control signal PC are made smaller (larger) than standard values when the supply current to an electrical heating element 14 is smaller (larger) than the target value. The pulse width of a gate trigger pulse GP is then made longer (shorter) than the standard and the firing angle thetaincreases (decreases). The values are therefore so controlled as to follow up the target values, by which the supply of the desired power to the element 14 is made possible regardless of the variance in the resistance value Rx of the element 14 and the quality of the heating is improved.
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