US Patent 7218060 Flyback ballast for fluorescent lamp

A flyback ballast for fluorescent lamps is provided. A transformer is utilized to control the power delivered to the lamp. A first switch is coupled to the first winding of the transformer. A first filter is coupled to a second filter through a first terminal pair of a lamp. The second switch is coupled to the third switch through a second terminal pair of the lamp. A switching signal is provided to the first switch to control the power of the transformer delivered to the filters. A second switching signal and a third switching signal are provided to the second switch and the third switch respectively to control the power delivered to the lamp. No glow discharge is occurred during the preheating interval.