GB761688A - Improvements in or relating to circuit arrangements for operating low pressure electric discharge lamps - Google Patents

Abstract

761,688. Supply systems for space discharge tubes; protective arrangements. GENERAL ELECTRIC CO., Ltd., ANDERSON, S., and CATES, J. April 21, 1955 [April 23, 1954], No. 11814/54. Class 38 (4). In a circuit arrangement for starting and operating on a D.C. supply at least one L.P. electric discharge lamp 1 connected in series with a stabilizing resistance R and a choke L to the circuit input terminals T1, T2 and having shunted across the lamp a starting switch S so that after connection of the circuit to the supply the opening of the switch contacts results in the production of a H.V. pulse which is applied between the lamp electrodes 3, 6 for starting the lamp discharge, a capacitor C is shunted across the choke C but not across the lamp(s) to reduce relatively high audio-frequency oscillations which may emanate from the choke L arising from ionic oscillations generated in the lamp discharge; the capacitance of the capacitor C is sufficiently great to force a relatively low impedance path across the choke for oscillations of frequency exceeding 1000 c.p.s. but is not so great that the voltage pulses produced between the lamp electrodes on openings of the starting switch contacts are insufficient to start the lamp discharge. The capacitor C may be connected, as shown, directly across the choke C, or where the resistance R is directly in series with the choke L it may be connected across both the choke and the resistance. Suitable values and construction of the choke and capacitor are described in the Specification. Also as shown, the lamp has heatable electrodes and the starting switch is of the type having a resistance heater H and normally closed contacts opened by a bimetallic strip, but the lamp may be of the cold cathode type. A radio interference suppression capacitor 8 is connected between the lamp electrodes, and where a plurality of lamps are connected in series each may have its own starting switch or there may be one switch connected across all the lamps.