GB652500A - Improvements in or relating to circuits for electric discharge lamps - Google Patents

Abstract

652,500. Control systems for space discharge lamps. GENERAL ELECTRIC CO., Ltd., and CATES, J. Sept. 27, 1948, No. 25138. [Class 38 (iv)] To avoid re-operation of the usual starting switch 12 included in a discharge lamp circuit, upon diminution of the supply voltage as might occur in a vehicle lighting system or with a battery source, a relay 14, 15 responsive to the lamp discharge current is included to actuate contacts 16 which duplicate the function normally performed by the starting switch, thereby holding a circuit open or closed whilst the lamp operates. The starting switch may be of the thermal type, e.g. glow discharge or resistance heated. The relay contacts are included in series with the starting switch in the preheating circuit between the lamp electrodes, the resistance heater 13 of the starting switch also being included in this part of the circuit or in series with the ballast impedance 10. The relay is preferably magnetically operated and comprises a pair of balanced coils 14, 15 which render the relay operative upon a predetermined difference of current in the coils, i.e. when the discharge starts. For series-connected lamps either a single starting switch associated with one lamp and a set of relay contacts for each lamp may be provided, or a starting switch and relay associated with each lamp. To control the magnitude of the preheating current a resistance 18 may be included in series with the starting switch to limit the preheating current, or an additional normallyclosed relay contact 19 may short-circuit all or part of the ballast impedance 10 to increase the preheating current. To obtain a high ratio of lamp voltage to supply voltage a tungsten filament lamp may be used as the ballast impedance. A condenser 17 may be included to suppress interference and improve starting. The circuit operates on A.C. or D.C. Specification 625,558 which discloses a similar arrangement is referred to.