Method and apparatus for dimming high-intensity fluorescent lamps
AssigneeNorthrop Grumman Corporation
InventorKevan O'Meara
Life of this patent
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Abstract
A fluorescent ballast control process for a fixed and variable frame rate method of driving a fluorescent ballast to control the brightness of a fluorescent lamp load over a brightness range. The fixed frame rate process uses a fixed number of pulses in each frame. The variable frame rate process uses a variable number of pulses in each frame. When the two processes are combined, the control is gradual in response to a user control signal (BRIGHT). The transition from the fixed to the variable frame rate control process occurs seamlessly as the variable BRIGHT×BRIGHT×OVER where BRIGHT×OVER is calculated.
Claims21
A fixed frame rate method of providing drive signals to a ballast to control the brightness of a fluorescent lamp load, the method comprising the steps of:
- A. providing a high frequency clock signal,
- B. monotonically incrementing the value of a digital variable COUNT-F with the high frequency clock signals, the digital value of the variable COUNT-F COUNT-Fing from an initial value to a final value in a frame interval of fixed duration, the value of the digital number being reset to the initial value at the end of each frame interval,
- C. sampling an input signal and scaling the sample to form a digital input variable BRIGHT, the digital value of BRIGHT being scaled to represent a portion of the value of the range of variable COUNT-F,
- D. while the value of COUNT-F is incrementing monotonically from its initial value to a value equivalent to the value of the BRIGHT variable, outputing a ballast pulse of power to the lamp load with each increment of the value of the COUNT-F variable, and
- E. repeating steps C and D.
A variable frame rate method of providing fixed frame rate drive signals to a ballast to control the brightness of a fluorescent lamp load, the method comprising the steps of:
- A. providing a high frequency clock signal and establishing the value of a digital constant GROUP characterizing a number of ballast pulses of power to be delivered to a lamp load during a continuing series of frame intervals of variable duration,
- B. monotonically incrementing the value of a digital number COUNT-V with the high frequency clock signals, the value of COUNT-V counting from an initial value to a variable final value in each frame interval of variable duration,
- C. sampling an input signal and scaling the sample to form a digital input variable BRIGHT, the digital value of BRIGHT being scaled and used to calculate the value of a variable OFFTIME, a measure of the time that the process will wait after a predetermined GROUP of pulses have been delivered to the lamp load before starting another frame,
- D. determining if the value of COUNT-V exceeds the digital value of a variable OFFTIME and if true, setting the value of COUNT-V to its initial value,
- E. determining if the value of COUNT-V is less than the value of GROUP and if true, advancing to step F. and if false returning to step C. to complete steps C, D and E,
- F. outputing a ballast pulse of power to the lamp load and returning to step C to complete steps C, D and E.
A method of providing drive signals to a ballast to control the brightness of a fluorescent lamp load the method comprising the steps of:
- a. incrementing a counter with a high-frequency clock, the value of the counter representing a first variable, COUNT-F,
- b. resetting the counter with a low-frequency clock having a low frequency clock period if the low frequency clock period has expired;
- c. determining if the first variable COUNT-F is less than a second variable BRIGHT, where BRIGHT is a signal value supplied to command the average brightness of the lamp load, and if the variable COUNT-F is less than the second variable BRIGHT, supplying a pulse to the array of lamps for illumination thereof,
- d. repeating steps “a” through “c”.
A fluorescent ballast control process comprising:
- a low brightness control process to control the brightness of a fluorescent lamp load over a brightness range extending from a lowest brightness level through a lowest brightness range up to a predetermined intermediate brightness level using a variable frame rate, and
- a high brightness control process to control the brightness of the fluorescent lamp load over a brightness range extending from a the intermediate brightness level through a high brightness range using a fixed frame rate up to a predetermined maximum brightness level, and
- means for transitioning from the low brightness control process to the high brightness control process seamlessly in response to a variable control signal input, BRIGHT.
Dependencies are inferred from the claim text.