US 5,504,398 AGranted

Dimming controller for a fluorescent lamp

AssigneeBeacon Light Products, Inc.

InventorDan E. Rothenbuhler

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Abstract

A control module controls the illumination intensity of a fluorescent lamp. A controller controls a switch to conduct current through cathodes of the lamp, and the switch ceases conducting current when commutated into non-conduction. The switch is triggered into conduction at a predetermined extinguishing point within and prior to the end of each half-cycle of applied AC current. The switch is thereafter commutated into non-conduction at a predetermined ignition point when the applied AC current reaches a predetermined level near the zero crossing point of each half-cycle of applied AC current. The current level at commutation creates a sufficiently high di/dt effect to cause an ignition pulse of voltage from the ballast across the lamp cathodes sufficient to ignite the ionized medium into an illumination plasma. The switch extinguishes the plasma. The illumination intensity of the lamp is related to the time between the ignition point and the extinguishing point. The extinguishing point is variable and selected by control signals, such as momentary power interruptions.

Claims20

Dependent claims

A control module for controlling the illumination intensity of a fluorescent lamp having cathodes, the control module adapted to be connected in series with the lamp cathodes and in series with a ballast and a source of AC power which is applied in alternating half-cycles of AC voltage and AC current, the control module comprising:

a current switch device which selectively conducts current through the cathodes when triggered into a conductive condition and which ceases conducting current when commutated into an non-conductive condition;
a controller connected to trigger the switch device into the conductive condition and to commutate the switch device into the non-conductive condition, the controller triggering the switch device into the conductive condition at a predetermined extinguishing point within and prior to the end of each half-cycle of applied AC current, and the controller commutating the switch device into the non-conductive condition at a predetermined ignition point when the applied AC current reaches a predetermined level near the zero crossing point of each half-cycle of applied AC current;
the predetermined level of the current at the ignition point and the commutation of the switch device to the non-conductive condition creating an ignition pulse of voltage from the ballast of a magnitude sufficient to ignite an illumination plasma between the cathodes;
the conductive condition of the switch device at the extinguishing point extinguishes the illumination plasma;
and
the illumination intensity of the lamp is related to the time between the ignition point and the extinguishing point.

3 more elements

A control module for controlling the illumination intensity of a fluorescent lamp having cathodes and an ionizable medium between the cathodes, the ionizable medium having a characteristic operating voltage when ionized into the plasma, the control module adapted to be connected in series with cathodes and in series with a ballast and a source of AC power applied in alternating half-cycles of voltage and current, the control module comprising:

a thyristor having a gate terminal to which a trigger signal is applied for triggering the thyristor into conduction, the thyristor also having a predetermined relatively high holding current level above which conduction through the thyristor is maintained and below which conduction through the thyristor is terminated, the thyristor adapted to be connected in series between the cathodes to conduct current through the cathodes and to reduce the voltage between the cathodes to a value less than the characteristic operating voltage when triggered into conduction;
a controller connected to the gate terminal of the thyristor, the controller supplying the trigger signal to the thyristor to selectively trigger the thyristor into conduction at a predetermined extinguishing point during each half-cycle of applied AC current near the zero crossing point before the end of each half-cycle of applied AC current;
the controller further ceasing delivery of the trigger signal to the thyristor prior to the applied AC current flowing through the thyristor reaching the holding current level near a zero crossing point before the end of each half-cycle of applied AC current, the thyristor commutating into non-conduction to cease conducting current through the cathodes when the applied AC current flowing through thyristor reaches the holding current level at an ignition point;
the resulting change in current from the holding current level to non-conduction in the time of commutation at the ignition point generating an ignition pulse from the ballast of a magnitude greater than the operating voltage to ignite the ionizable medium into the plasma during a point in each half-cycle of applied AC voltage when the instantaneous voltage from the applied AC voltage is also greater than the operating voltage.

1 more element

Dependencies are inferred from the claim text.