| 摘要 |
PROBLEM TO BE SOLVED: To provide a device preventing the break of a switching element by connecting a parallel body of a DC power supply, a heating coil and a resonance capacitor and a parallel body of a choke coil, a self-arc-extinguishing switching element and a reverse blocking diode in series, and self-short-circuiting the switching element when the voltage between both ends of the switching element receiving on/off-signals from a control circuit becomes a prescribed value or above. SOLUTION: A control circuit 17 including an oscillating circuit controls a switching element 13. A self-short-circuiting means 18 self-short-circuits the switching element 13 when the voltage between both ends of the switching element 13 becomes a prescribed value or above. If the switching element 13 is turned off while a current flows in it, an extremely high surge voltage is generated between both ends of the switching element 13, however the switching element 13 is self-short-circuited at the voltage of the prescribed value, and the voltage does not exceed the breakdown voltage of the switching element 13. A device reducing the loss in the switching element 13 with a simple structure and preventing the withstand voltage breakdown of the switching element 13 even at an abnormality is obtained. |
