| 摘要 |
PURPOSE:To lower switching loss at the time of turning on of a switching device by operating a resonance circuit constant alternating circuit so as to make load voltage applied to the switching device lower than a predetermined value by a voltage detecting apparatus. CONSTITUTION:In the case voltage applied to a switching device 3 is not minus, a switch 11 is turned off by a resonance circuit constant alternating circuit 10 and the capacity of a resonance capacitor 2 of a resonance circuit is lowered and as a result, a minus voltage is not applied to the switch device. In order not to turn on a switch 11 even if a voltage detecting circuit 9 detects minus voltage applied to the device 3 after the switch 11 is turned off, resistors 32 and 33 are set in the voltage detecting circuit and when output voltage V5 of a comparator 24 becomes 'H' by a transistor TR34, the TR34 is turned on and reverse input terminal voltage V4 of the comparator is set to be lower than a voltage VA applied to a resistor 28. By this method, in the case an object 8 to be heated is a material to which negative voltage is applied at the time of switch device off, the negative voltage is not loaded at the time of off of the switch 11. |
