Fluorescent dimming circuit with D-C flicker elimination

Claim 1

A controlled energizing circuit for a gas discharge lamp; said energizing circuit including an a-c power source, an inductive ballast, a bidirectional controllably conductive device, and a phase control circuit for controlling the points in the positive and negative half waves of said a-c power source at which said bidirectional controllably conductive device begins to conduct; said ballast coupling said a-c power source to said gas discharge lamp; said bidirectional controllably conductive device being connected in series with said lamp and permitting current flow to said lamp only after said bidirectional controllably conductive device is fired; said phase control circuit including trigger circuit means for applying a firing signal to said bidirecTional controllably conductive device; a charging circuit coupled to said trigger circuit means for operating said trigger circuit means when said charging circuit is charged to a given voltage, and an input reference voltage circuit for driving said charging circuit; said input reference voltage circuit including an adjustable resistor means having a wiper arm and first and second oppositely poled diodes having first terminals connected to the opposite ends of said adjustable resistor means; second terminals of said oppositely poled diodes and said wiper arm, respectively, being connected to said a-c power source; said input reference voltage circuit defining separate reference voltages to said charging circuit for positive and negative half waves, respectively, of said a-c power source, whereby adjustment of said wiper arm of said adjustable resistor means is adjustable to compensate against the asymmetric firing of said bidirectional controllably conductive device.