GB1451186A - Arrangement for supplying a gas and/or vapour discharge lamp - Google Patents

Abstract

1451186 Operating discharge lamps PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 7 March 1975 [11 March 1974] 9576/75 Heading H2H A discharge lamp circuit comprises a first pair of input terminals 2, 5 connected by a series arrangement of a triac 6, or a pair of backto-back thyristors, and a lamp 1, and a third input terminal 3 also connected through a triac 7 to the lamp and terminal 5, an A.C. supply of mains frequency being connected across the terminals 2, 5 and a further similar supply across the terminals 3, 5 the latter supply differing in phase from the former, each triac 6, 7 being gated into conduction at a late stage in each ¢ cycle of the respective supplies. As shown a 3-phase input R, S, T is connected to inputs 2-4 and terminal 5 is common. Triacs 6, 9, 10 are used in each phase and each are controlled by means adapted to fire their respective device at a late stage in the input ¢ cycles. That controlling triac 6 is illustrated and comprises a fall-wave bridge 11-14 with RC circuit 17, 18 across its diagonal. In parallel with the RC circuit is a potentiometer 15 having its slide connected to the trigger of an auxiliary thyristor 16. In operation, the capacitor 18 charges during a ¢ cycle to a point when thyristor 16 is rendered conductive and then discharges through the thyristor and transformer coil 19 to pvode a pulse in coil 21 which, via diode 22, gates triac 6 into conduction. A lamp starting circuit comprising transformer coil 25, capacitor 26, resistor 27 and triac 28 is connected across the lamp 1, the triac being rendered conductive for the first few ¢ cycles of the 3-phase input after switching the circuit on. On starting, current flows in the circuit 2, 6, 25, 26, 27, 28, 5 which induces a voltage in winding 7 to ignite the lamp 1.