GB1190690A - Regulating Circuit for Discharge Devices. - Google Patents

Abstract

1,190,690. Supply circuits for discharge lamps. SYLVANIA ELECTRIC PRODUCTS Inc. 30 Dec., 1968 [29 Dec., 1967], No. 61738/68. Heading H2H. An operating circuit applies a voltage pulse to a discharge lamp once each half-cycle of the supply just sufficient to maintain conduction through the half-cycle. Means is also provided for compensating variations in supply voltage and lamp current. In the circuit shown, two lamps x are connected to an A.C. source by way of an autotransformer L1, L2 and a resistor R. Also connected across the supply terminals there is a timing circuit comprising a photo-conductor Rt and two capacitors C2, C3. In operation, voltage builds up at the junction j between the capacitors until a diac D1 breaks down and triggers a triac V1, allowing a capacitor C1 to discharge and supply a pulse through the autotransformer to the lanps. The lamp filaments are supplied from a transformer secondary T3, and a further secondary winding T2 serves to energize a lamp E, the light from which falls on the photo-conductor Rt. Thus, changes in the supply voltage alter the characteristics of the timing circuit and cause, for example, earlier pulsing of the lamp if the supply voltage rises. This maintains the average lamp current constant, since the line voltage will be lower earlier in the cycle, leading to less ionization in the lamp and compensating for the increased voltage amplitude. In a similar way, the circuit also compenates for variation in the lamp impedance, e.g. during warming up, since the auxiliary lamp E is connected in series with the main lamps x.