GB1411575A - Two-terminal electronic starters for fluorescent lamps - Google Patents

Abstract

1411575 Control circuits for gas discharge tubes COMPAGNIE DES LAMPES SA 20 Dec 1972 58955/72 Heading H2H A starting device for use with fluorescent lamps comprises a pair of terminals across which are connected at least one semi-conductor bidirectional switching element and a trigger circuit for rendering the switching element conductive during successive half cycles of an A.C. supply connected to the device, means being provided for rendering the trigger circuit unable to render the switching element conductive after a period sufficient to allow the filamentary electrodes of the lamps to be heated adequately to allow the lamps to strike. A fluorescent lamp L having filamentary type electrodes 2, 3 is connected to an A.C. supply by way of a ballast inductor S and a starting device 1 having two terminals 1a, 1b. Across the terminals 1a, 1b are connected in series a triac 4 and a heater resistor R 5 for a negative temperature coefficient resistor R 3 , such that the inductor S, the electrodes 2, 3, the triac 4 and the resistor R 5 form a series circuit across the A.C. supply. Across the terminals 1a 1b is connected a further series circuit forming a potential divider and comprising resistors R 1 , R 2 , R 3 and R 4 in parallel, and R 5 , the point 6 on the potential divider being connected to the gate of the triac 4 by way of a diac 5. A capacitor C 2 is connected across the resistor R 4 and a capacitor C 1 between a main electrode of the triac 4 and a point between resistors R 1 , R 2 . Upon switching on, the voltage developed across the capacitor C 2 in each half wave of the A.C. supply reaches a value which breaks down the diac 5 thereby triggering the triac 4. Current then flows in the electrodes 2, 3 of the lamp L and the heating resistor R 5 . The electrodes 2, 3 and the N.T.C. resistor R 3 continue to be heated until the resistance of the resistor R 3 decreases to such an extent that the potential at the point 6 of the potential divider falls to a value such that the charge on the capacitor C 2 is insufficient to break down the diac 5 and thus the triac 4 is not triggered. At this point the filamentary electrodes 2, 3 will have been heated sufficiently, and the non-triggering of the triac will result in the ballast S and the capacitor C 1 will go into oscillation to produce a high voltage pulse to strike the lamp L. Thereafter the capacitor C 2 charges insufficiently to cause conduction of the triac 4. Modifications of the trigger circuitry are described in which capacitors are added thereto and/or resistors dispensed with and modifications of the complete circuitry disclosed in which two triacs in series are used and a pair of fluorescent lamps utilized.