| 摘要 |
PURPOSE:To eliminate spike voltage generated at the both ends of a switching element when shutting down, and thereby prevent the switching element from being damaged by providing a chopper control section assuming an on/off control for the control and the actuation/suspension of input electric power. CONSTITUTION:In normal operation, DC voltage supplied is applied to the mid-point terminal of a heating coil 5, No.2 switching element 7 and No.3 switching element 8 are interchangeably controlled to be turned on and/or off by an oscillation control section 9 so as to let both the heating coil 5 and a resonance capacitor 6 be actuated as a resonance circuit. On the other hand, when shutting down, No.1 switching element 2 is controlled by a chopper control section 10 in such a way that the period of 'on' time is gradually shortened so that DC voltage supplied from the both ends of a smoothing capacitor 4 is gradually attenuated as to be zero. This permits the voltage of No.2 switching element 7 and No.3 switching element 8 to be gradually attenuated, thereby eliminating the occurrence of spike voltage. |
