Dimming controller for a fluorescent lamp

• US 5,504,398 A
• Filed: 03/16/1995
• Issued: 04/02/1996
• Est. Priority Date: 06/10/1994
• Status: Expired due to Fees

• Current Assignee: Beacon Light Products, Inc.
• Original Assignee: Beacon Light Products, Inc.
• Inventors: Rothenbuhler, Dan E.
• Primary Examiner(s): Gonzalez, Frank
• Assistant Examiner(s): Ratliff, Reginald A.
• Application Number:
  US08/404,880
• Time in Patent Office: 383 Days
• Field of Search: 315/209 R, 315/360, 315/DIG. 4, 315/291, 315/293, 315/307, 315/283, 315/242, 315/362, 315/DIG. 7
• US Class Current: 315/209.00R
• CPC Class Codes: H05B 41/046 using controlled semiconductor devices
• CPC Class Codes: H05B 41/3924 by phase control, e.g. using a triac H05B41/3922 takes precedence
• CPC Class Codes: H05B 41/3927 by pulse width modulation H05B41/3922 takes precedence

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.

Claims

1. 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.

2. A control module as defined in claim 1 wherein the ignition point occurs near the end of the half-cycle in which the extinguishing point occurs.

3. A control module as defined in claim 2 wherein the ignition pulse occurs during each half-cycle of applied AC voltage.

4. A control module as defined in claim 2 wherein lamp includes an ionizable medium between the cathodes which has a characteristic operating voltage when ignited into a plasma, and the ignition pulse occurs when the voltage during a half-cycle of applied AC voltage is greater than a characteristic operating voltage of the lamp.

5. A control module as defined in claim 1 wherein:

the control module operatively responds to control signals to vary the extinguishing point within and prior to the end of each half-cycle of applied AC current.

6. A control module as defined in claim 5 wherein:

the control module responds to control signals communicated through the connection of the control module to the AC power source.

7. A control module as defined in claim 5 wherein:

the control signals to which the control module responds are momentary interruptions in power from the AC power source.

8. A control module as defined in claim 7 wherein:

the controller senses the momentary power interruptions as power interruption detections (PIDs);

the controller includes programmed information which establishes the predetermined extinguishing point; and

the controller correlates the PIDs with the preprogrammed information to vary the extinguishing point.

9. A control module as defined in claim 5 wherein:

the controller varies the extinguishing point to achieve illumination intensities between approximately ten percent of maximum intensity and full intensity.

10. A control module as defined in claim 1 wherein lamp includes an ionized medium between the cathodes which has a characteristic operating voltage when ignited into a plasma, and wherein:

the switch device commutates to the non-conductive condition and creates the ignition pulse at a fixed predetermined point within the half-cycle of applied AC voltage when the voltage across the cathodes is at least equal to the operating voltage of the medium.

11. A control module as defined in claim 10 wherein:

the switch device comprises a thyristor having a predetermined holding current equal to the predetermined level near the zero crossing point of each half-cycle of applied AC current at which the switch device is commutated into the non-conductive condition; and

the controller selectively triggers the thyristor into conduction at the extinguishing point.

12. A control module as defined in claim 11 wherein:

the thyristor is connected to conduct AC current between the cathodes and short circuit the ionized medium and extinguish the plasma during each half-cycle of applied AC current from the time the thyristor is conductive until the time the thyristor is commutated into non-conduction when the current flowing through the thyristor drops below the holding current of the thyristor.

13. A control module as defined in claim 12 wherein:

the holding current is at least 100 milliamperes.

14. A control module as defined in claim 12 wherein the thyristor has a characteristic holding current which is substantially non-variable.

15. A control module as defined in claim 14 wherein:

the thyristor includes a gate terminal which to which a trigger signal is applied to trigger the thyristor into the conductive condition;

the controller delivers a trigger signal for triggering the thyristor into the conductive condition; and

further comprising;

at least one pilot device connected between the controller and the gate terminal, each pilot device amplifying the trigger signal from the controller to a greater value before applying the trigger signal to the gate terminal of the thyristor.

16. A control module as defined in claim 11 wherein:

the thyristor includes a gate terminal which to which a trigger signal is applied to trigger the thyristor into the conductive condition; and

the thyristor has a characteristic holding current which varies according to an impedance connected to the gate terminal.

17. A control module as defined in claim 16 wherein:

the holding current increases when the impedance connected to the gate terminal is relatively low, and the holding current decreases when the impedance connected to the gate terminal is relatively high; and

the controller is connected the gate terminal of the thyristor and delivers a relatively high impedance to the gate terminal after triggering the thyristor at the extinguishing point and delivers a relatively low impedance to the gate terminal before the thyristor is commutated into non-conduction prior to the ignition point.

18. A control module as defined in claim 1 wherein lamp includes an ionized medium between the cathodes which has a characteristic operating voltage when ignited into a plasma, and wherein:

the switch device when triggered into the conductive condition at the extinguishing point reduces the voltage between the cathodes to a value less than the characteristic operating voltage to extinguish the plasma.

19. 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.

20. A control module as defined in claim 19 wherein:

the controller further comprises a sensing circuit operative to detect momentary interruptions in AC power of varying durations; and

the controller is further operative to vary the extinguishing point in response to predetermined ones of the momentary power interruptions sensed.