GB1342026A - Ballast for gas discharge lamp - Google Patents

Abstract

1342026 Starting and operating discharge lamps W ZUMTOBEL 19 April 1971 [9 April 1970] 26636/71 Heading H2H A circuit for starting and operating a preheated electrode discharge lamp is adapted to cause the electrodes to heat to a suitable temperature and then to apply a series of high voltage pulses to start the lamp, and also, in the event of non-ignition, to cease the application of the pulses for a short period and then to continue therewith. As shown, a lamp 6 having electrodes 4, 5 is connected at1, 2 across an A.C. source, the electrodes being in series with inductors 7a, 7b and shunted by a series circuit comprising a third inductor adapted as an auto-transformer 8, 9, and a capacitor and resistor 23, 24. Also in shunt with the lamp is a control circuit adapted to selectively operate a triac 3 connected between the windings of the transformer 8, 9. In operation, upon the A.C. supply first being connected, the trigger voltage of a diac 37 is reached near the start of each ¢ cycle by the action of a capacitor, resistor branch 28, 33, and a resistor 38, which causes the triac 3 to conduct for most of each ¢ cycle to provide a low impedance path via the coil 8 so that a high current is drawn through the lamp electrodes to heat them rapidly. Simultaneously, a capacitor 30 is charged during each half cycle under the action of a bridge formed by diodes 29, 32, 34, 35 and the rising potential across this capacitor causes the switching instant of diac 37 to be progressively displaced towards the peak voltage of each ¢ cycle. At the instant of switching, capacitor 23 charged during the preceding part of the ¢ cycle discharges rapidly through the primary winding 9 causing a high voltage pulse to be produced in the secondary 8. As the instant approaches the peak voltage point, these pulses are sufficient to ignite the lamp 6. In the event of ignition failure, the potential across capacitor 30 exceeds the threshold voltage of the diac 37 so that no triggering of the triac 3 takes place. Capacitor 30 during this period discharges slowly via a resistor 31 so that a second series of igniting pulses may be produced a short while later. The time constants of the control circuit are adapted such that the rate of charging at 30 is proportional to the rate of increase of temperature of the electrodes 4, 5, and the discharge rate is proportional to the rate of cooling.