Electric lamp and discharge devices: systems – Current and/or voltage regulation
Reexamination Certificate
2000-02-24
2001-05-08
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
C315S194000, C315S225000, C315SDIG004
Reexamination Certificate
active
06229271
ABSTRACT:
TECHNICAL FIELD
The present invention relates to dimmable ballast systems.
BACKGROUND OF THE INVENTION
In today's dimmable fluorescent lighting market, a number of different methods are used for dimming control. One popular method for dimming control employs a dimmer control interposed between a power line and an input of a dimming ballast. The dimming control comprises a phase-control device, such as a triac, to modify a firing phase angle of an alternating current (AC) powering signal. A dimming ballast circuit, in turn, controllably dims a fluorescent lamp based on the firing phase angle.
In some applications, the aforementioned dimming control approach yields an undesirably-high total harmonic distortion (THD) and an undesirably-low power factor. The high THD is caused by the chopping action of the triac. As a result, applications of the aforementioned dimming control approach have been limited.
U.S. Pat. No. 5,872,429 discloses use of coded perturbations in the line signal to obtain a lower THD. An encoder encodes a command over a command period of several cycles in the line signal. The encoder encodes the command by selectively injecting perturbations near zero-crossings of specific cycles in the command period. A controller within a ballast detects the perturbations over the command period, and decodes the command. The perturbations may be injected only when a change of light level is needed.
SUMMARY OF THE INVENTION
The present invention provides a dimming ballast apparatus including a firing-angle-to-pulse-width-modulation converter to generate a pulse width modulated signal based on a firing angle of a powering signal. The firing angle is less than or equal to 30 degrees. A filter generates a dimming command signal based on the pulse width modulated signal. A method is also disclosed which includes generating a pulse width modulated signal based on a firing angle of a powering signal wherein the firing angle is less than or equal to 30 degrees, generating a dimming command signal based on the pulse width modulated signal, and dimming a lamp based on the dimming command signal.
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Bessone Carlo S.
Osram Sylvania Inc.
Philogene Haissa
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