GB629886A - Improvements in and relating to control circuits for low pressure electric dischargelamps - Google Patents

Abstract

629,886. Control systems for space-discharge apparatus. BRITISH THOMSON-HOUSTON CO., Ltd. March 26, 1945, No. 7547. Convention date, March 29, 1944. [Class 38 (iv)] Means for operating an electric discharge lamp from A.C. or D.C. mains, the voltage of which is higher than that of the operating voltage of the lamp, comprises a series connected ballast resistance, a switch for opening the parallel starting circuit and a transformer in the switch circuit the secondary of which supplies a starting voltage to the lamp when the switch operates. In the embodiments described, an incandescent lamp functions as a ballast such that the voltage drop across the ballast does not exceed 50 per cent of the operating voltage of the lamp. In the arrangement in Fig. 2, lamp 5 is connected through switch 4, from supply mains 3, in series with the electrode preheating circuit 9, of the lamp 1, comprising the heater resistance 10 of thermal switch 8, filamentary electrodes 2 and the primary 7 of an auto transformer 11, the secondary of which is connected to an auxiliary external starting electrode 12. The opening of switch 8, due to heater current through the circuit 9 produces in combination with the heating of the electrodes 2 conditions permitting the lamp 1 to " strike ". In a modified arrangement, Fig. 4, the heating circuit includes a variable resistor 14 shunted by the primary of the auto-transformer and constituting a part of the ballast. In the arrangement shown in Fig. 3, the device is " struck " by the discharge of a condenser 13 connected in series with the secondary 6 of the autotransformer across the switch 8.