| 摘要 |
PROBLEM TO BE SOLVED: To prevent the deterioration of a metal body and a bobbin, which supports the metal body and which is wound with a coil, for protection by fitting a temperature sensing element to a diode so as to accurately detect a change of an electrical characteristic at the time when temperature of a metal body rises, and controlling a driving circuit of a transistor on the basis of the information. SOLUTION: A capacitor 5 and a coil 4 form a resonance circuit so as to generate the voltage having since-waveform, and a loss at the time of turning on/off a transistor 6 is reduced. A driving circuit 8 gives the ON signal to the transistor 6 when the voltage of the transistor 6 becomes 0. An electric characteristic of the coil 4 is changed by a foaming metal body 9. As an electric characteristic of the metal body 9, magnetic permeability is lowered with a temperature rise, and change thereof gives influence to voltage, current waveform, and current waveform of a diode 7. Consequently, since temperature of the diode 7 rises earlier than the temperature rise of the transistor 6, a temperature sensing element 10 is fitted to the diode 7 so as to detects the temperature condition of the metal body 9 without delay. When a temperature of the diode 7 achieves a high temperature, the temperature sensing element 10 stops the operation of the driving circuit 8. |
