| 摘要 |
PROBLEM TO BE SOLVED: To sufficiently reduce cooling fan noise and to prevent the breakage of a switching element with a simple circuit structure by setting the inductance of a choke coil below a specific value, connecting a D.C power supply and the choke coil parallel with a switching element, a reverse blocking diode and a resonance circuit, and installing a self-short-circuiting means. SOLUTION: The inductance of a choke coil 12 connected to a D.C. power supply 11 in series is set roughly less than 1 mH. The other end of the choke coil 12 and the other end of the D.C. power supply 11 are connected in parallel with a resonance circuit composed of a switching element 13 and a reverse blocking diode 14 which are connected in series and a heating coil 15 and a resonance capacitor 16 which are also connected in series. The switching element 13 has a self-short-circuiting means 18 to short-circuit itself when the voltage across it is not less than a predetermined value. As a result, the current flowing through the switching element 13 is formed into a resonant wave and swathing element 13 is turned off when the current is zero, that its turn-off loss is not produced and the loss of the switching element 13 can be reduced. |
