GB639295A - Improvements in supply circuits for electric discharge tubes - Google Patents

Abstract

639,295. Supply systems for space discharge lamps. THORN ELECTRICAL INDUSTRIES, Ltd., and WAIGH, D. T. Feb. 18, 1948, No. 4834. [Class 38 (iv)] [Also in Group XL (a)] In a circuit arrangement for a discharge lamp having a pair of filamentary electrodes El, E2 adapted to be preheated from a transformer comprising a primary winding T connected in series with a ballast impedance B across the supply and in shunt with the lamp discharge path, and two secondary windings W1, W2, connected with the respective lamp filaments, a normally-closed switch M is included in the primary circuit and adapted to be opened automatically with a predetermined delay in response to the establishment of a discharge so as to open-circuit the transformer primary and obviate loss of power in the transformer whilst the lamp is running. The switch may be electromagnetically operated, as shown, the operating coil M1 being connected across the ballast impedance. Alternatively the switch may be thermally operated (Fig. 2, not shown) the heater being connected in series with the lamp discharge path. To assist starting an auxiliary electrode may be provided inside or outside the envelope and preferably consists of a metallic shield A extending the greater part of the length of the lamp envelope, and connected either directly to earth, or to the neutral supply lead through a small condenser and/or a high resistor.