Patent GB-692702-A (GB)
Title: Improvements in and relating to starting circuits for electric discharge devices
IPC: H05B41/22
Filed: 1949-10-18
Abstract: 692,702. Supply systems for space discharge lamps. BRITISH THOMSON-HOUSTON CO., Ltd. Oct. 18, 1949 [Oct. 26, 1948], No. 26739/49. Class 38 (iv). [Also in Group XL (a)] In a combination of a supply circuit and a plurality of discharge devices, as shown two fluorescent lamps, each device has a filling of mercury and a gas including Kr and/or Xe, the gas pressure being 2-3.5 mms., starting means, 7, 7<SP>1</SP>, Fig. 1, extend between the pairs of electrodes 3, 4, 5, 6, and transformer means are connected to the supply circuit and comprise primary and associated secondary winding sections for supplying circuits, associated with each device, with starting and operating voltages, and the circuit has means for impressing on each starting means a potential of 150-300 volts with respect to'earth and differing by not less than 150 volts from that applied to either of the electrodes of the device with which the starting means is associated. In one arrangement, Fig. 1, two lamps 2, 21 are employed; they have fluorescent coatings and employ preheated coiled coil thermionic electrodes as shown, but may alternatively have cold activated or unactivated electrodes. The starting gas may comprise 50 per cent Argon and 50 per cent Krypton, Xenon or mixtures thereof, or as little as 10-15 per cent of the latter constituent and the mercury vapour is at a pressure of several microns to twenty or thirty microns, preferably 10 microns, in operation. The metallic starting strips 7, 7<SP>1</SP> are coatings on the outside of the envelope wall. An autotransformer 12 having primary winding 15 and secondary windings 13 and 14 supplies the preheating, starting strip and the operating current and voltage, and the secondary windings 13, 14 also serve as ballasts, and a capacitor 17 introduces a phase displacement between circuits 9, 10 and 10<SP>1</SP>, 11 supplying lamps 2, 2<SP>1</SP> respectively. The preheating circuits are connected to terminals a, b, c, d and are as described in Specification 646,515. Tertiary windings 18-21, 22-25 and 26-29 are coupled to the primary and secondary windings 15, 13, 14 respectively, and each preheating circuit includes three tertiary windings, one from each group. The secondary winding 13 is wound in the reverse direction with respect to windings 14, 15. Considering the tertiary windings serving electrodes 3, 5, windings 22, 24, 26, 28 are wound in the opposite direction to 13, 14, respectively, and windings 18, 20 are wound in the same direction as 15. The starting strips 7, 71 have cross-over connections 36, 35, which include current limiting resistances 8<SP>1</SP>, 8. By proper proportioning and phasing of the three induced voltages in the preheating circuits, the changes in magnitudes and phases of these voltages when the discharges start have the effect of reducing the heating current almost to zero, while due to the leakage reactance of transformer 12 the starting voltage is reduced to a lower arc-maintaining voltage. In a modification, Fig. 6 (not shown), the phase displacing capacitor is placed in series with the primary winding of the transformer. In another modification, Fig. 7 (not shown) the starting devices may be metallic housings or reflectors non-integral with the lamps, and additional inductances may be provided in the lamp circuits, for example as ballasts. In another modification, Fig. 8 (not shown), the starting means are connected to tertiary windings of the supply transformer. In another modification, Fig. 9, the transformer has primary winding 84, secondary windings 85, 86, and tertiary windings 90-95 connected in two groups of three 90, 92, 94 and 91, 93, 95 to energize electrodes 77, 80, respectively. Similar sets of windings may also be provided for electrodes 78, 79. Separate step-up transformers 96, 97 are provided for supplying the starting means 81, 82. A phase-displacing capacitor 90 is provided. In another modification, Fig. 10 (not shown), the starting means are external metal coatings or conductive members of a separate fixture. The supply transformer has a primary and two secondary windings, and a tertiary winding is connected to the primary winding for energizing the starting means. The secondary windings also serve as ballasts.