| 摘要 |
PURPOSE:To reduce switching losses and noises and to increase the conduction angle of an input rectifier by driving a switching element in synchronization with the loweset potential of the resonance output waveform of an LC resonance circuit, and separating a rectifying smoothing capacitor from the circuit when necessary. CONSTITUTION:A resonance circuit of a coil 12 and a capacitor 13 is connected in series with the secondary winding 10 of a voltage transformer 8 or with a fluorescent lamp 16, and when a switching element 9 is turned off, a resonance voltage waveform is generated in the drain of the element 9. The element 9 is driven in synchronization with the lowest potential of the resonance voltage waveform, so that switching losses and noises are reduced. When a voltage input to a rectifying smoothing capacitor 4 is at or greater than a predetermined value, a transistor 33 is turned off, the rectifying smoothing capacitor 4 is separated from the circuit, and therefore the conduction angle of an input rectifier is increased, whereby a power factor is prevented from dropping. |
