Electricity: power supply or regulation systems – Output level responsive – Phase controlled switching using electronic tube or a three...
Reexamination Certificate
1999-09-28
2001-03-27
Nguyen, Matthew (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Phase controlled switching using electronic tube or a three...
C315SDIG004
Reexamination Certificate
active
06208122
ABSTRACT:
BACKGROUND—FIELD OF INVENTION
This invention relates to the control of power supplied to a lighting load to achieve variable intensity, and more particularly to the control of AC powered lighting loads.
BACKGROUND OF THE INVENTION
Dimmable lights are desirable in many contexts and applications including home, office, auto, theater, stadium, arena, and other contexts. Such contexts often require different lighting intensities at different times and different locations within the same structure.
Different methods of achieving dimmable systems in these contexts have evolved over the years. All methods are based on the principle that the illumination intensity of a lighting load will vary proportionally to the amount of power delivered to the load. The most common prior art systems revolve around phase angle control dimming, or variations thereof, which control the amount of power delivered to a load by determining what portion of each AC power cycle or half cycle is delivered to the load. In these instances, TRIACS and/or silicon controlled rectifiers (SCR) are fired at intervals that are a multiple of the power line frequency, typically 120 Hz, to achieve this control. See e.g. U.S. Pat. Nos. 4,080,548, 4,331,914, 4,423,478. The SCR's and TRIACS thereby limit the phase-angle conduction of AC voltage to a controlled AC load.
Hence, through phase control dimming, only a fraction of the power available during each power cycle is supplied to the load that needs to be dimmed resulting in the ability to vary the illumination level of the load from 0% to 100%. The illumination level varies proportionally to the amount of power delivered to the load based on what portion of the power cycle is delivered. This method is visually acceptable because the human eye is unable to discern the rapid flickering of the lighting loads in a dimmed state. While the foregoing capabilities are useful, there are three major deficiencies that remain unaddressed or unsolved by the prior art. While some methods have been employed to resolve one or more of these deficiencies, these methods often result in the addition and/or aggravation of all or some of the original deficiencies. Consequently, it is desirable for a dimming control system such as the one described herein, to minimize or virtually eliminate ALL of the following deficiencies simultaneously. The three deficiencies esoteric to current phase angle control dimming systems today are as follows:
First, phase angle control circuits produce relatively high amounts of acoustical output from the lighting load filaments during the dimming operation resulting in acoustical disturbances to those around the lighting load. This acoustical output results from the load current undergoing a dramatic rise over a relatively small time interval when the controller device is turned “on ” to conduction and the resultant instantaneous application of up to 172 volts across the load. In the case of incandescent lighting, this surge in current through the lighting filament will cause the filament and its supports to change their length—otherwise known as “magnetostriction”—and shake the light. The resultant noise, known as “singing” or “lamp-sing” is highly undesirable. Phase angle control systems currently in existence have dealt with lamp-sing by using series chokes or inductors to slow the rise of current in the load. Examples of dimming control systems that have attempted to deal with this “singing” through chokes, inductors, and more recently, inductorless systems are seen in U.S. Pat. Nos. 4,823,069, 5,004,969, 5,365,148, and 5,550,440.
The use of chokes or inductors, however, has not been a satisfactory resolution to deal with “singing” because their use introduces space restrictions that arise based on the generally voluminous and large sizes of chokes or inductors. The added inductors, which are made out of copper and/or iron are generally unwieldy and add significant weight to the control device. Further, inductors also have copper wire wrapped around them to absorb the heat generated by their slow-down of the rise of current in the load. Consequently, inductors have a great size requirement that reduces the density of dimming control devices that are available for any given amount of lighting loads and often leads to unwieldy and expensive setups depending on the application of the dimmer.
Another method intended to circumvent the deficiencies caused by the use of inductors is seen in inventions that have attempted to deal with the inductor problem by introducing MOSFET (MOS-field effect transistor) and/or IGBT (insulated gate bipolar transistor) devices to reverse-phase the switching process to minimize singing and/or the use of inductors as disclosed in U.S. Pat. No. 5,331,270. In these systems, the MOSFET and/or IGBT devices are utilized to detect the zero-cross of the power cycle and deliver power to the load beginning at the zero-cross point. The slow rise of the cycle is then delivered to the load at the slower gradient increase of the power cycle itself which is much more conducive to singing avoidance than the 90 degree “direct rise” conduction that occurs at the peak of the power cycle that results from typical phase control dimming systems. Problems still arise, however, because the sudden “shut-off” of power at the peak of the cycle and the sudden drop of potential presented to a lighting load results in massive heat generation. The substantial amounts of heat that are generated—up to 10 times the normal amount—require additional components to provide for adequate heat dissipation. These additional components, such as heat sinks and other hardware, require significant additional space and, consequently, reduce the density of space and therefore, the potential applications available for a dimming product as seen in U.S. Pat. Nos. 4,633,161, 5,268,631, 5,365,148, and 5,550,440.
The second deficiency with current dimming systems is their phase dependence and the requirement that they detect the zero-cross point of AC current cycles. This dependence requires the products to include additional devices to detect zero-cross (increasing the cost of the product) while also limiting the ability of the dimmer to certain cycles of power. That is, due to its analog nature, zero-crossing detection requires additional comparators, diodes, transistors, and various other analog components such as the pulse-shaping device disclosed in U.S. Pat. No. 4,528,494 which significantly adds to the cost and complexity of dimming systems such as in U.S. Pat. No. 5,004,969.
Finally, the third deficiency seen in many dimming systems is power factor distortion, which results from rapid changes in load voltage and current that are a part of the various phase control dimming schemes previously mentioned. This distortion is often troublesome to power monitoring devices which are unable to accurately monitor the amounts of power that are being sent to the lighting load. Additionally, an even greater issue is the variances in AC power line voltages delivered to the lighting load. As power intensities change, noticeable brightness variations to lighting loads can be seen which are highly undesirable in many dimming contexts such as television, movie, theater, and photography. This issue is noted in U.S. Pat. No. 5,268,631. As lighting designers require precise light levels for various effects, even relatively small distortions and variations can be destructive to their goals. Further, in long wire runs used in these applications between the dimmer and the load, unwanted voltage drops may occur which cause a high-wattage lighting to receive less voltage than it should exacerbating the distortion. Additionally, the sudden rise or drop in load potential introduces unwanted radio frequency interference. This interference is still present in systems that try to gradually “ramp” the applied potential of power to a load as in U.S. Pat. No. 5,365,148.
SUMMARY OF THE INVENTION
The system described herein minimizes and addresses the above-described problems and deficiencies by providing h
Nguyen Matthew
Triatek, Inc.
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