Electric lamp and discharge devices: systems – Regulation of the control current and/or potential applied...
Reexamination Certificate
1998-04-20
2001-04-17
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Regulation of the control current and/or potential applied...
C315S291000, C315SDIG004
Reexamination Certificate
active
06218787
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electronic system for dimming fluorescent lamps and, more particularly, to a control system which utilizes existing building wiring to transmit dimming control signals to an electronic ballast for use in a fluorescent lighting system.
BACKGROUND OF THE INVENTION
Lighting applications account for about 30% of the electrical energy consumption in the United States. With increasing interest in energy conservation, lighting systems that use less energy and are easy and cost-effective to install are becoming more important. One effective way to reduce energy consumption of lighting is to use dimmable fluorescent lighting systems. Newer lighting systems can control light output and energy consumption by adjustment of lighting levels throughout the day, reducing energy usage when light is not needed. Existing dimmable fluorescent lighting systems require extra, low-voltage control wiring to provide control signals to the ballasts contained within lighting luminaires. The present invention allows the lighting control signals to be sent over the same wiring that is used to provide AC power to the ballasts. By using the existing wiring, the changeover from conventional lighting is greatly simplified and installation costs are significantly reduced.
Presently there are two types of dimmable ballasts for fluorescent lighting. The first type utilizes a phase-controlled thyristor dimming control to reduce the AC current provided to a special lighting ballast. These ballasts respond by creating suitable internal dimming signals that are then used to vary light intensity. This type of ballast can use conventional, two-wire AC power wiring, allowing them to be installed easily. However, the abrupt modulation of the AC line current causes severe distortion, greatly reducing the power factor, and increasing the harmonic content of the line current. This type of ballast, therefore, can introduce significant problems into the power distribution when a significant number of the ballasts are installed within a large building.
The second type of dimming ballast uses separate low-voltage control wiring to provide dimming signals to the ballast. The control voltages are typically DC signals that may vary from 0 volts (fully dimmed) to 10 volts (full brightness). The AC power is handled on separate conventional AC power wiring. Because the control function is separated from the power line, no distortion is introduced by the control system to the AC power, making this type of ballast suitable for use in large installations. The drawback to their use is the added complexity of installation, since the additional low-voltage control wiring is needed.
DISCUSSION OF THE RELATED ART
U.S. Pat. Nos. 4,876,498 and 4,954,768 for TWO-WIRE LOW VOLTAGE DIMMER, issued Oct. 24, 1989 and Sep. 4, 1990, respectively, to David G. Luchaco, et al. describe a dimming control system of the first type described above. Luchaco, et al. teach a low-voltage, two-wire dimming circuit comprising a voltage compensating circuit for regulating the RMS value of an AC voltage applied to a load and a correcting circuit for eliminating DC current that may flow through the load. The desired dimming level is accomplished by varying the phase angle of the applied AC voltage. In contradistinction, the dimming control system of the present invention does not utilize phase control of the AC power line supplying the ballast, but rather encodes dimming control information as a slight asymmetry in the AC waveform without any of the waveform distortion problems described hereinabove. The power factor of the AC supply to even a great number of ballasts is unaffected by the control system of the present invention.
Another prior art ballast control system is described in U.S. Pat. No. 5,107,184 for REMOTE CONTROL OF FLUORESCENT LAMP BALLAST USING POWER FLOW INTERRUPTION CODING WITH MEANS TO MAINTAIN FILAMENT VOLTAGE SUBSTANTIALLY CONSTANT AS THE LAMP VOLTAGE DECREASES, issued Apr. 21, 1992 to Feng-Kang Hu, et al. A dimming ballast system allows the light output of the lamp to be controlled by a remote source. The system encodes the remote control signal by interrupting the current flow to the ballast. On the other hand, the control system of the present invention does not interrupt the current flow to the ballast and, consequently, does not introduce power line distortion and power factor alteration. The control system of the instant invention encodes a DC control signal onto the AC power lines by means of a slight asymmetry of the AC waveform.
U.S. Pat. No. 5,675,221 for APPARATUS AND METHOD FOR TRANSMITTING FORWARD/RECEIVING DIMMING CONTROL SIGNAL AND UP/DOWN ENCODING MANNER USING A COMMON USER POWER LINE; issued Oct. 7, 1997 to Hong K. Yoo et al. describes an apparatus and a method for transmitting a dimming control signal in an up/down encoding manner. The encoded binary data is set as transmission data on the AC power line. The Yoo, et al. system transmits a series of bits at zero-crossing time in the AC waveform. Unlike the Yoo system, the inventive system requires no microcomputer, zero-crossing detector or pulse train generator.
U.S. Pat. No. 5,691,605 for ELECTRONIC BALLAST WITH INTERFACE CIRCUITRY FOR MULTIPLE DIMMING INPUTS, issued Nov. 25, 1997 to Yongping Xia, et al. describes a lamp controller (including a receiver) which receives an input signal and decodes control signals supplied from a transmitting device such as a power line wall controller. The system operates in accordance with at least two of the following communication techniques: phase angle control, step control, and coded control. Each of these control types is subject to the problems described hereinabove. The inventive system, on the other hand, relies on none of these techniques with their attendant problems, but rather utilizes a control signal encoded onto the AC power line by a slight asymmetry in the AC waveshape.
Accordingly, it is an object of the invention to provide a fluorescent lighting system that can simply control the lighting level through signals sent over the conventional two wire AC power wiring of a building.
It is another object of the invention to provide a dimming control that uses minimal power and has a low cost.
It is yet another object of this invention to provide a dimming control system that also allows for the use of standard 0-10 volt dimming electronic ballasts.
It is a still further object of the invention to provide a dimming control system that produces minimal disturbances of the AC power quality by maintaining high power factor and low harmonic distortion of the AC power line current.
It is an additional object of the invention to provide a dimming control system that can offer remote control of a device from more than one location.
It is a still further object of the invention to provide a dimming control system that may be readily integrated into overall building energy management systems.
SUMMARY OF THE INVENTION
The present invention features a new type of control system for a dimmable fluorescent ballast that inserts a slight voltage asymmetry or DC offset into an AC power supply line to an electronic ballast. The asymmetry or offset is inserted only during one half cycle of the power voltage alternation. This asymmetry or DC offset is “transmitted” over the power wiring to the device(s) being controlled where it is decoded by a small circuit module preferably located in the lighting luminaire adjacent to the dimming ballast. A low voltage control signal in the range of approximately the 0-10 volts is derived by the circuit module and is fed to the low voltage control lines of the ballast. According to standard industry practice, at maximum light output the low voltage ballast control signal is set to 10 volts. To minimize power dissipation in the dimmer, the DC offset is required to be zero at maximum lighting levels, so that the full offset is transmitted.
In the embodiment chosen for purposes of disclosure, the DC offset is introduced by a variable voltage reference circuit
Dranchak David W.
Katyl Robert H.
Murcko Robert M.
JRS Technology Inc.
Salzman & Levy
Vu David
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