GB1398383A - Starting circuits for electric discharge lamps - Google Patents

Abstract

1398383 Starting fluorescent lamps GENERAL ELECTRIC CO Ltd 28 June 1972 [28 June 1971] 30227/71 Heading H2H A circuit arrangement for starting a discharge lamp comprises resonant circuit means connected between the supply and lamp terminals. When an A.C, source is connected to terminals 2, 3 a voltage is applied to the gate of a triac TR1 by way of a resistor R2 causing conduction thereof. A capacitor C2 then resonates with the primary winding of a transformer T1 at a frequency of the order of 10-15 KHz. The Q-factors of the capacitor and transformer are chosen high so that the circuit will ring freely for a sustained period-say 15 cycles, the amplitude of the second pulse being at least 70% of that of the first and of five to seven of the pulses at least 40% of that of the first, in other words, a highly damped oscillation. The pulses so produced are stepped up by the transformer T1 and applied to the mercury discharge lamp. If desired a small capacitor C x may be connected across a portion of the primary winding of the transformer T1 thereby producing a series of secondary oscillations. Numerous modifications of the circuit are described, using a back-to-back thyristor and diode instead of a triac; using a firing circuit including a second triac to fire the triac TR1; omitting the resistor R2; using Zener or Shockley diodes instead of the second triac or using a cut-off circuit to permit the starter circuit to operate for a limited period only. Two lower voltage triacs in series may also be used and the firing circuit may include a unijunction transistor. In other embodiments the starting pulses may be produced in a resonant circuit in parallel with the discharge lamp.