GB1528033A - Ballast for an arc discharge lamp - Google Patents

Abstract

1528033 Discharge lamp ballast including a converter; converting GENERAL ELECTRIC CO 15 Oct 1975 [21 Oct 1974] 42137/75 Headings H2H and H2F A ballast arrangement 1 for an arc discharge lamp 36 comprises an inverter connected to a source of pulsating, unfiltered D.C. power 21, 22 across which is connected a capacitor 23 having a low impedance at the frequency of the inverter, the inverter including a transformer 24 having a centre-tapped primary winding 28, 29 to which are connected solid state switching devices capable of being turned ON and OFF, such as transistors 25, 26 and further having a secondary winding 32a, 33a to which the lamp 36 is connected by way of a rectifying device 32-36; means, such as a resistor 38 for providing a signal proportional to the instantaneous current through the lamp 36, the resistor 38 forming part of a control circuit which includes a device 41 for generating a reference signal, which signal together with the lamp current signal are fed to a comparator 39 so as to produce an output signal which controls the transistors 25, 26 by way of a JK flip-flop 43 and two logic gates 50, 51 in such a manner that the transistors 25, 26 are rendered conductive alternately, the conduction period off each transistor being followed by a period when neither transistor is conductive. A resistor 42 is provided across the output and input terminalsof the comparator 39 to provide a hysteresis effect. In other embodiments a resistor is placed in the common emitter connection to provide the lamp current signal and the control circuit may have a JK flip-flop and a one shot multivibrator with an optional ON TIME control. Capacitor and diode means are provided in the base circuit of one transistor to render the inverter self starting. Furthermore the transformer 24 may be replaced by an autotransformer, particularly when the lamp operating voltage is higher than the input supply voltage. If desired the transistors may be replaced by commutated thyristors or gate turn off thyristors. Ballast apparatus of the kind described is said to improve the power factor of the lamp operating system.