GB937576A - Pulsed operation of a discharge lamp - Google Patents

Abstract

937,576. Supply systems for cinematograph projector lamps. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. June 15, 1962 [June 27, 1961], No. 23227/61. Class 38 (4). The high pressure, xenon-filled, cold cathode lamp 3 of a cinematograph projector is supplied with pulses of energy from the terminals 1, 2 of a D.C. source by applying alternate signals of opposite polarity to the control electrode 6 of a semi-conductor rectifier 5, which is thereby made conductive or non-conductive at the frequency of the pulses to be supplied. The rectifier 5 may have two control electrodes to which switching-on and switching-off signals are applied respectively. A resistor 4 maintains a small discharge through the lamp between pulses of current. The signals applied to the rectifier 5 may be obtained by arranging for the flicker shutter of the projector (or a member associated with this shutter) to periodically interrupt a beam of light impinging on a phototransistor, whose output is converted into pulses of alternating polarity by a conventional amplifier, phase-splitter and differentiator circuit, Figs. 2 and 3 (not shown) Alternatively the signals may be produced by associating with the shutter a magnetically-cored inductance so that the leading and trailing shutter edges produce a signal through the winding associated with the core. If the flicker shutter is omitted the signals may be supplied by means moving synchronously with the movement of the film through the gate.