Patent ID: 7199526

Claim:
An electronic ballast, comprising: a DC/AC converter, for receiving an input of direct current and transforming the input of direct current into an alternative current; a fluorescent lamp, including a first filament and a second filament; a transformer including: a primary-side winding for receiving the alternative current; a secondary-side winding which includes a first terminal and a second terminal, wherein the first terminal is connected to one terminal of the first filament; a preheating transformer including: a first winding which includes a third terminal connected to one terminal of the second filament and a fourth terminal connected to the second terminal; and a second winding which includes a fifth terminal connected to the other terminal of the first filament and a sixth terminal connected to the first terminal; and an AC switch whose one terminal is connected to the third terminal and the other terminal of the AC switch is connected to the fourth terminal; wherein the AC switch is turned off during a preheating period of time for the fluorescent lamp.