| 摘要 |
PURPOSE:To adjust brightness by making capacitance of a capacitor variable in a system to obtain a frequency to light a discharge lamp from a resonance circuit composed of a transistor and the capacitor. CONSTITUTION:A variable capacitance circuit is formed being connected in parallel to a capacitor C1 and by connecting a resonance capacitor C3 and a switch 51 in series to each other. When an electric current is supplied from an input terminal when the switch is opened, self-oscillation is continued on the primary side of a transformer T1, and high frequency electric power generated on the secondary side thereby is supplied to a cold cathode tube CFL through a ballast capacitor C2, and a discharge lamp is lighted. When the switch is closed, the capacitors C1 and C3 are connected in parallel to each other, and since a frequency of secondary side high frequency electric power is reduced, an effective tube electric current value is reduced, and brightness of the cold cathode tube is also reduced. Even a system to switch these to/from each other by a three contact point switch by adding a capacitor in parallel to the capacitor C3 can work well, and a resonance frequency and brightness may be changed linearly by replacing these capacitors with variable capacity-capacitors. |
