GB644547A - Improvements in operating circuits for electric discharge lamps - Google Patents

Abstract

644,547. Control systems for space discharge lamps. BRITISH THOMSON-HOUSTON CO., Ltd., and CLARKE, M. G. Aug. 25,1948, No. 22419. [Class 38 (iv)] [Also in Group XL (a)] Dimming of an electric discharge lamp 1 is effected by supplying the lamp through a variable ratio transformer 10 having a fixed number of secondary turns adapted to be connected directly or indirectly to the lamp electrodes and a variable number of primary turns connected to the supply 2 through the usual choke 9 whereby as the effective number of primary turns is reduced a progressively higher voltage and lower current is supplied to the lamp. Preheating of the lamp electrodes 3, 4 may be effected by providing additional windings on the transformer so that upon reduction of the discharge current the heating current is increased. Should it be inconvenient to provide the heating windings on the transformer, e.g. in the case of an auto-transformer, in additional transformer 5 may be interposed between transformer 10 and the lamp 1 and which may be provided with the heating windings 6, 7. To improve starting capacity electrodes 8 may be arranged external to the lamp and earthed. A pluraluty of lamps may be operated in series from a single variable ratio transformer by, in the case of lamps having preheating electrodes, supplying each lamp from its own transformer 5 the primaries of which are connected in series with the secondary winding of the variable ratio transformer 10 (Fig. 3, not shown). In the case of high voltage lamps with non-preheated electrodes the lamps are in series with the secondary of a transformer having its mid-point earthed and its separate primary winding supplied from the variable ratio transformer.