GB793582A - Improvements in or relating to discharge lighting installations - Google Patents

Abstract

793,582. Supply systems for space discharge lamp; converting. SIEMENS-SCHUCKERTWERKE AKT.-GES. Dec. 22, 1955 [Jan. 8, 1955; Sept. 15, 1955], No. 36852/55. Classes 38 (2) and 38 (4). In a discharge lighting installation a modulator 2 comprising at least one controllable semi-conductor resistance 8 is connected to at least one electric discharge lamp 1 and is connectable to either an A.C. or a D.C. supply to modulate respectively the former to produce an output having a pulsation frequency greater than that of the supply or the latter to produce a pulsating current output, and a control circuit 3 is provided to produce an A.C. control voltage which is fed to and controls the semi-conductor resistance so that the output pulsation frequency is dependent on the control voltage frequency; by thus increasing the output frequency the lamp ballast is reduced or eliminated and it is stated that the light yield of the lamp is increased. The semi-conductor resistance 8 may be a transistor, preferably symmetrical, or a material whose resistance varies with the magnitude of an applied magnetic field, and the control circuit 3 may be an oscillator which also may comprise a transistor. In another arrangement, not shown, the modulator comprises four symmetrical transistors connected as a bridge circuit to form an inverter, and to give an output of constant amplitude a rectifier and a smoothing condenser are connected between the A.C. supply and the modulator. The waveform of the output voltage may be varied by variation of the control voltage waveform or appropriate choice of the characteristics of the semi-conductor resistances. The control voltage is fed to the modulator directly, as shown, or, not shown, through a transformer or through coupling condensers. In another embodiment, not shown, a photodiode transistor which is responsive to the luminous flux of the lamp 1 controls the conduction of the modulator.