Electronic ballast for a fluorescent lamp

摘要

An operating tuned circuit (20, 21) which is driven periodically by a push-pull switch arrangement (15, 16) is used for generating a high AC voltage for a fluorescent lamp (22). The fluorescent lamp (22) is connected in parallel with the capacitor (21). The electrodes of said fluorescent lamp (22) consist of heating wires (26, 27), each of which is connected to the secondary winding (28 or 29, respectively) of a transformer (30). The primary winding (31) of the transformer (30) is connected in series with the operating tuned circuit (20, 21). A switching element (32) having a threshold-value behaviour is connected between each secondary winding and to the associated heating wire. In consequence, heating currents flow in the heating wires (26, 27) only before the fluorescent lamp (22) has been started, and not after starting has been completed. <IMAGE>