DIRECT CURRENT BALLASTING AND STARTING CIRCUITRY FOR GASEOUS DISCHARGE LAMPS

摘要

DIRECT CURRENT BALLASTING AND STARTING CIRCUITRY FOR GASEOUS DISCHARGE LAMPS Direct current ballasting and starting circuitry for efficiently operating a gaseous discharge lamp on direct current. Series-pass switching means in one of a pair of input lines alternatively switches between on and off states to periodically supply pulses of energy from a source of direct current voltage. During steady-state operation, current sensing means limits the maximum current conductable by said switching means such that the output of the circuitry is current regulated. Filter means, in series with the switching means, smoothes the pulses of energy delivered by the switching means into direct current with a comparatively small alternating current component. Starting means, in series connection between the filter means and an output terminal, senses the nonionized state of the lamp and provides a voltage pulse of sufficient magnitude and duration to initiate ionization in the lamp. The starting means permits uninterferred passage of current from the filter means to the output terminal. Various forms of control means or drive means for controlling the conductive state of the switching means are disclosed, including a phase-corrected oscillator which is momentarily excited by a starting pulse delivered at the output terminal and oscillation is thereafter sustained by interaction with the switching means; a resonant transformer capacitor circuit with a secondary winding of the transformer controlling the conductive state of the switch ing means; and a pulse width modulation drive means. Operation of the circuitry in a current-limited output mode is accomplished by either sensing current delivered by the switching means or by sensing the current level through a commutating diode. various starting means are disclosed, including one embodiment in which a single starting means senses the nonionized state of one of a plurality of lamps, with each lamp operating from a separate ballasting circuit, and provides a starting pulse for the nonionized lamp. An A.C. to D.C. power conversion circuit, for operating a plurality of ballasting and starting circuits therefrom, utilizes a portion of a primary winding of a transformer for connection to the A.C. voltage source. A stepped up A.C. voltage across the entire primary winding is applied to a rectification means, which rectifies the A.C. voltage and supplies the same to a filter means. The filter means provides a D.C. voltage for input to the ballasting and starting circuits. A center-tap on a secondary winding of the transformer is referenced to the second of a pair of input lines of the ballasting and starting circuit, and the ends of the secondary winding provide a small A.C. voltage to the cathodic heater element of the lamp.