GB1437764A - Discharge lamp arrangement - Google Patents

Abstract

1437764 Control systems for gas discharge lamps PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 17 May 1974 [21 May 1973] 22053/74 Heading H2H An arrangement for igniting and operating a gas discharge tube comprises means for generating high voltage pulses during the lamp operation so as to ensure re-ignition of the lamp in the event of the tube being extinguished. A low pressure sodium or mercury vapour lamp 5 is supplied from an A.C. source 1, 2 by way of a series connected choke ballast 3. Connected in parallel with the lamp 5 is a diode bridge 9-12 across the D.C. terminals of which is connected a transistor 13. The control circuit for the transistor 13 includes a capacitor 15, chargeable from the bridge output by way of a resistor 14, and a diac 16. When the capacitor is charged sufficiently the diac 16 breaks down and the transistor 13 becomes conductive. The capacitor 15 discharges by means of a resistor 17 until the diac 16 recovers and the transistor 13 goes non-conductive. Thus, the choke 3 causes a high voltage pulse to appear across the lamp 5 which would cause re-ignition thereof if necessary. The time constant of the components 14, 15 is such that a plurality of high voltage pulses are produced during each cycle of the A.C. supply. If the control circuit does not include a diode bridge, two transistors may be used in reverse-parallel, each being provided with its own control circuit. In a further embodiment a control circuit which includes a thyristor is also connected in parallel with the lamp to provide the pulses for the initial ignition of the lamp, and this circuit may include a negative temperature coefficient resistor.