Fluorescent lamp brightness control

A rapid start type fluorescent lamp system comprising:

• an elongated fluorescent lamp with low voltage filaments at opposite ends thereof;
• a step-up autotransformer having a primary circuit and a plurality of secondary circuits, the primary circuit adapted to be energized by line voltage, one secondary circuit for providing a high voltage between lamp ends to initiate lamp operation and thereafter providing an inductive impedance limiting lamp current, a second secondary circuit for energizing one of the low voltage filaments, and a third secondary circuit for energizing the other low voltage filament;
• a thermal protection device responsive to autotransformer temperature for opening the primary circuit when the autotransformer temperature exceeds a predetermined value;
• a phase control circuit
• comprises a bilateral solid state gate controlled switching device
• connecting the lamp to said one secondary circuit for selectively controlling lamp current and, therefore, also controlling lamp intensity
• and a relaxation oscillator connected in controlling relation to the gate of the switching device;
• isolating means
• comprises a transformer having a Primary winding and a secondary winding with a 1:1 winding turns ratio
• for coupling the second secondary circuit and the one low voltage filament without shunting the phase control circuit;
• a printed circuit board having a plurality of leads extending therefrom to be crimp connected to other leads in the lamp system including at least leads to the lamp and leads to the autotransformer;
• and
• an on-off switch to be connected in series with the primary circuit, the phase control circuit, on-off switch, and isolating means being permanently connected to the printed circuit board.