Dimming control system for electronic ballasts

Details Dimming control system for electronic ballasts Dimming control system for electronic ballasts

2001-09-28

2003-03-18

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Current and/or voltage regulation

C315S294000, C315S207000

Reexamination Certificate

active

06534931

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the general subject of circuits for powering discharge lamps. More particularly, the present invention relates to a dimming control system for electronic ballasts.
BACKGROUND OF THE INVENTION
Conventional dimming ballasts for gas discharge lamps include low voltage dimming circuitry that is intended to work in conjunction with an external dimming controller. The external dimming controller is connected to special inputs on the ballast via dedicated low voltage control wiring that, for safety reasons, cannot be routed in the same conduit as the AC power wiring. The external dimming controller is usually very expensive. Moreover, installation of low voltage control wiring is quite labor-intensive (and thus costly), especially in “retrofit” applications. Because of these disadvantages, considerable efforts have been directed to developing control circuits that can be inserted in series with the AC line, between the AC source and the ballast(s), thereby avoiding the need for additional dimming control wires. The resulting approaches are sometimes broadly referred to as “line control” dimming.
A number of line control dimming approaches exist in the prior art. One known type of line control dimming approach involves introducing a notch (i.e., dead-time) into the AC voltage waveform at or near its zero crossings. This approach requires a switching device, such as a triac, in order to create the notch. Inside of the ballast(s), a control circuit measures the time duration of the notch and generates a corresponding dimming control signal for varying the light level produced by the ballast. In practice, these approaches have a number of drawbacks in cost and performance. A significant amount of power is dissipated in the switching device, particularly when multiple ballasts are to be controlled. Further, the method itself distorts the line current, resulting in poor power factor and high harmonic distortion, and sometimes produces excessive electromagnetic interference. Additionally, the control circuitry tends to be quite complex and expensive.
What is needed, therefore, is a dimming control system that avoids any need for additional dimming control wires, but that does so without introducing undesirable levels of steady-state power dissipation, line current distortion, or electromagnetic interference. A need also exists for a dimming control system that is structurally efficient and cost-effective. A dimming control system with these features would represent a significant advance over the prior art.


REFERENCES:
patent: 6300727 (2001-10-01), Bryde et al.
patent: 6346778 (2002-02-01), Mason et al.
patent: 6380696 (2002-04-01), Sembhi et al.

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