| 摘要 |
The invention relates to a timing and fixed-frequency preheating ballast circuit for a fluorescent lamp. The timing and fixed-frequency preheating ballast circuit comprises an excited power driving circuit, a resonant circuit and a preheating circuit, wherein the preheating circuit is used for preheating lamp filaments at two ends of the fluorescent lamp in a timing and fixed-frequency mode before the fluorescent lamp is lightened by the ballast circuit; during the preheating of the lamp filaments, the power driving circuit generates an output signal of which the frequency is greater than the resonant frequency of the resonant circuit to prevent high voltage for lightening the lamp sufficiently from being formed on the fluorescent lamp, and the power driving circuit can control the preheating circuit, so that the preheating circuit ripples the voltage of the output signal to the lamp filaments by utilizing a lamp filament transformer and a high-frequency rippling capacitor in the preheating circuit during the preheating to preheat the lamp filaments; and when the preheating period is finished, the power driving circuit stops the preheating action of the preheating circuit, and replaces the frequency of the output signal with frequency which is close to the resonant frequency of the resonant circuit, so that the resonant circuit can lighten the lamp due to the high voltage formed by oscillation. |
