Automatic state tranition controller for a fluorescent lamp

• US 5,652,481 A
• Filed: 03/15/1996
• Issued: 07/29/1997
• Est. Priority Date: 06/10/1994
• Status: Expired due to Fees

• Current Assignee: Beacon Light Products, Inc.
• Original Assignee: Beacon Light Products, Inc.
• Inventors: Miller, Gerald G., Johnson, Samuel A., Rothenbuhler, Dan E.
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Philogene, Haissa
• Application Number:
  US08/616,739
• Time in Patent Office: 501 Days
• Field of Search: 315/307, 315/308, 315/289, 315/291, 315/290, 315/246, 315/247, 315/283, 315/243, 315/209 SC, 315/209 R, 315/200 R, 315/103, 315/105, 315/106, 315/159
• US Class Current: 315/308
• 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
• CPC Class Codes: H05B 47/185 via power line carrier transmission

Abstract

A control module and method controls the operation of a fluorescent lamp in a circuit in which the lamp is connected to a ballast and energized by alternating half-cycles of power supplied from an AC power source. The fluorescent lamp has cathodes and a medium which emits light energy when energized into a plasma. A controllable switch conducts half-cycles of AC current through the cathodes and commutates into a non-conductive condition. A sensor supplies sensing signals related to an electrical condition at the cathodes. A state transition controller controls the switch. The state transition controller establishes a power-up, warm-up, ignition and fire operational states and transitions between the states in response to the electrical condition sensed and the time duration of those conditions. The lamp lights more reliably, premature failure of the ballast and cathodes is prevented due to overheating, and the lamp is controlled effectively by input signals in the form of short power interruptions.

Claims

1. A control module for use with a fluorescent lamp to control operation of the lamp in a circuit in which the lamp is connected to a ballast and energized by alternating half-cycles of power supplied from an AC power source, the fluorescent lamp having cathodes and a medium which emits light energy when energized into a plasma, said control module comprising:

a controllable switch adapted to be connected to the cathodes and triggerable into a conductive condition to conduct half-cycles of AC current from the source through the cathodes and commutatable into a non-conductive condition to cease conducting the AC current through the cathodes;

a sensor adapted to be connected to the cathodes and to deliver at least one sensing signal related to at least one predetermined electrical condition at the cathodes; and

a state transition controller receptive of the sensing signal and connected to the controllable switch for controlling the controllable switch to assume the conductive and non-conductive conditions, the state transition controller establishing a plurality of predetermined operational states and transitioning between the states in response to conditions including the sensing signal and time conditions, the operational states and the transitions including;

a power-up state during which the controllable switch is commutated into the non-conductive condition to prevent energization of the medium;

a warm-up state during which the controllable switch is triggered into the conductive condition for a warm-up time period during which the current conducted by the controllable switch heats the cathodes;

a transition from the power-up state to the warm-up state occurring at the conclusion of a stabilizing time period after the power-up state is first entered, the stabilizing time period allowing operation of the state transition controller to stabilize before transitions occur and other states are established;

an ignition state during which the controllable switch is commutated into the non-conductive condition at a predetermined ignition point during at least one of a plurality of half-cycles of AC power conducted from the source by the controllable switch through the cathodes during an ignition time period, the commutation of the controllable switch into the non-conductive condition creating a di/dt effect which causes the ballast to generate an ignition pulse to ionize the medium into a plasma;

a transition from the warm-up state to the ignition state occurring at the conclusion of the warm-up time period;

a fire state in which the controllable switch is commutated into the non-conductive condition to allow power from the source to sustain the plasma between the cathodes; and

a transition into the fire state from the ignition state occurring after the conclusion of the ignition time period.

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

the state transition controller counts half-cycles of power applied to the cathodes; and

the predetermined stabilizing time period, the warm-up time period and the predetermined ignition time period are each defined by a predetermined plurality of half-cycles counted by the state transition controller.

3. A control module as defined in claim 2 wherein:

the number of half-cycles counted to define the stabilizing time period, the warm-up time period and the ignition time period is different for each time period.

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

the state transition controller utilizes the sensing signal to determine the occurrence and time duration of any momentary interruptions in power applied to the cathodes; and

the transitions from the power-up state to the warm-up state and from the warm-up state to the ignition state each can occur in the presence of a momentary power interruption occurring during the state from which the transition occurs only if the momentary power interruption has a time duration less than a first predetermined time.

5. A control module as defined in claim 4 wherein:

the transition from the ignition state to the fire state does not occur if a momentary power interruption occurs during the ignition state.

6. A control module as defined in claim 4 wherein:

a transition from the ignition state to the warm-up state occurs after sensing a momentary power interruption while in the ignition state.

7. A control module as defined in claim 4 wherein:

a transition from the fire state to the warm-up state occurs if a momentary power interruption occurs during the fire state and the time duration of the momentary power interruption indicates that the cathodes have cooled sufficiently during the power interruption to significantly increase erosion of the cathodes upon application of the ignition pulse.

8. A control module as defined in claim 4 wherein:

a transition from the fire state to the ignition state occurs if a momentary power interruption occurs during the fire state and the time duration of the momentary power interruption indicates that the cathodes have maintained a temperature during the momentary power interruption which will not require heating during the warm-up state to avoid significant erosion upon application of an ignition pulse.

9. A control module as defined in claim 4 wherein:

the state transition controller responds to input control signals in the form of momentary power interruptions of a second determined time duration which is greater than the first predetermined time.

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

a transition from the ignition state to the warm-up state occurs after sensing a momentary power interruption of the first or second predetermined time while in the ignition state.

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

the state transition controller further responds to input control signals in the form of momentary power interruptions of a third determined time duration which is greater than the second predetermined time;

a transition from the fire state to the ignition state occurs after sensing a momentary power interruption of the first or second predetermined time while in the fire state; and

a transition from the fire state to the warm-up state occurs when the time duration of a momentary power interruption is of a third predetermined time duration indicative of sufficient cooling of the cathodes to significantly increase erosion of the cathodes upon application of the ignition pulse.

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

the state transition controller determines the magnitude of voltage between the cathodes at a predetermined point during at least one half-cycle of AC voltage while in the fire state and compares determined voltage to a predetermined characteristic operating voltage of the plasma to determine if the lamp is lighted.

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

a transition from the fire state to the power-up state occurs when it is determined that the lamp is not lighted while in the fire state.

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

the state transition controller counts the number of transitions from the fire state to the power-up state and determines an overheating condition after the occurrence of a predetermined number of transitions from the fire state to the power-up state within a predetermined time period.

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

the power-up state is maintained without transitions from the power-up state for at least a predetermined time duration after determining an overheating condition.

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

the power-up state is maintained without transitions from the power-up state until the state transition controller is reset after the determination of an overheating condition.

17. A method of establishing a plurality of predetermined operational states and transitioning between the states to control lighting conditions of a fluorescent lamp connected in a circuit with a ballast and energized by half-cycles of AC current and AC voltage from an AC power source, the fluorescent lamp having cathodes and a medium which is energized into a plasma which emits light energy, said method comprising the steps of:

establishing a power-up state in which the conduction of AC current from the power source through the cathodes is prevented for a stabilizing time period;

establishing a warm-up state in which the conduction of AC current from the power source through the cathodes occurs for a warm-up time period sufficient to heat the cathodes for reliable ignition of the lamp;

transitioning from the warm-up state to the power-up state at the conclusion of the stabilizing time period beginning after the power-up state is first entered;

establishing an ignition state in which the conduction of AC current from the power source through the cathodes is terminated at a predetermined ignition point during at least one of a plurality of half-cycles of current conducted from the source through the cathodes during an ignition time period;

transitioning from the warm-up state to the ignition state at the conclusion of the warm-up time period;

generating an ignition pulse of voltage to ionize the medium into a plasma from a di/dt effect of the ballast caused by the termination of current flow through the cathodes during the ignition state;

establishing a fire state during which AC voltage from the AC power source is applied to the cathodes to maintain the plasma between the cathodes; and

transitioning into the fire state from the ignition state after the conclusion of the ignition time period.

18. A method as defined in claim 17 further comprising the steps of:

predetermining the time length of the stabilizing time period, the warm-up time period and the ignition time period;

counting half-cycles of power applied from the source to the cathodes; and

establishing the time length of the stabilizing time period, the warm-up time period and the ignition time period from the number of half-cycles counted while in each state.

19. A method as defined in claim 17 further comprising the steps of:

sensing any momentary interruption in the AC power supplied to the cathodes;

determining the time duration of the sensed momentary power interruption;

transitioning from the power-up state to the warm-up state and from the warm-up state to the ignition state only if a momentary power interruption of a time duration less than a first predetermined time occurs while in the state from which the transition occurs; and

transitioning from the ignition state to the fire state only in the absence of any momentary power interruptions.

20. A method as defined in claim 19 further comprising the steps of:

determining the magnitude of the voltage between the cathodes at a predetermined point during at least one half-cycle of AC voltage applied to the cathodes during the fire state;

comparing the determined voltage to a predetermined operating voltage of the plasma to determine if the lamp is lighted, a lighted lamp being indicated by a determined voltage approximately equal to the characteristic operating voltage and an extinguished lamp being indicated by a determined voltage greater than the characteristic operating voltage;

controlling the lighting conditions of the lamp by creating input control signals in the form of momentary power interruptions of a second determined time duration which is greater than the first predetermined time;

transitioning from the fire state to the power-up state when the lamp is determined to be extinguished during the fire state;

transitioning from the fire state to the warm-up state when the lamp is determined to be lighted and upon the occurrence of a momentary power interruption of a third predetermined time duration which is greater than the second time duration; and

transitioning from the fire state to the ignition state when the lamp is determined to be lighted and upon the occurrence of a momentary power interruption of the first or second time durations.

21. The method as defined in claim 20 further comprising the steps of:

counting transitions between the fire state and the power-up state;

determining the existence of an overheating condition when the counted transitions from the fire state to the power state exceed a predetermined number; and

maintaining the power-up state without transitioning therefrom for at least a predetermined period of time in response to determining an overheating condition.