This invention relates to an anti-arcing protection device for ballasts driving fluorescent lamps. More particularly, it relates to a passive anti-arcing protection device for instant-start type electronic ballasts.
Fluorescent lamp is a very popular way of lighting. It has the advantages of high efficacy, long service life and does not emit much heat through radiation. The lamp, however, has to be started by introducing a high ignition voltage across it. There are many starting scheme for fluorescent lamps by using an electronic ballast. One popular type of electronic ballast is the instant-start ballasts.
The instant-start type ballast features almost immediate start of the lamps when the AC power is applied to the ballast. It does not require a starter device or circuit. It consumes less energy during operation and thus it is more efficient. However, as the lamp is started with a brute force by building a very high ignition voltage to the lamp, frequent on-and-off switching of the lamp will decrease the useful service life.
Therefore instant-start type ballasts are the most useful in applications where very long time of continuous lighting is anticipated. With many other advantages such as simple installation and the capability of independent lamp operation, i.e., when one of the lamps is worn out or removed, the remaining lamps can still operate normally, the instant-start type ballast enhances safety and the ease of maintenance.
For an instant-start type ballast, it is not uncommon to see an ignition voltage going as high as 600V-1000V peak and more. In cases such as individual lamp removal during maintenance while the AC power is still applied to the ballast, or the lampholder being aged, sporadic open circuit in the lampholder may occur. As a result, a high voltage will be induced and cause arcing. Arcing is a very high energy path of plasma discharge when electrical breakdown of air occurs under a very high potential difference. Arcing inside the lampholders is not favorable, as the resultant high temperature can melt the plastic housing and cause the exposure of metallic contacts and even cause a fire. Moreover it will degrade the contacts and over-stress the components inside the ballasts.
Therefore, recently global product safety certification agencies such as the Underwriters Laboratories (UL) have introduced a class of “Type CC” (short for Commercial Cabinets) ballasts that are designed to minimize arcing within the lampholder. Since then many lighting ballast manufacturers start to design “Type CC” ballasts with anti-arcing protection, or non-arcing fluorescent lamp holders. The usual approach is to sense abnormal voltage and/or current inside the ballast circuit to detect the occurrence of arcing, and cease the ballast operation once the condition is confirmed. They usually involve active devices and even micro-controllers. Thus, a more cost-effective and miniature solution is needed so that the additional components can fit into the existing casings.
Accordingly, one object of the present invention is to provide a cost-effective and less bulky anti-arcing component for fluorescent lamp electronic ballasts. This anti-arcing protection component is a low-resistance redirection path for any sudden changes in energy and is connected to the load of a fluorescent lamp as a potential bypass which springs into action when an arcing condition is about to occur by absorbing the spark energy and thereby ceasing the arcing condition. A preferred implementation of the protection component of the present invention is by using a bridge-rectifier-resistor-capacitor network, containing at least a bridge-rectifier, a resistor, and a capacitor. However, other equivalent implementations known to people of ordinary skill in the art are also workable as long as a low resistance bypassing is provided parallel to the load. The choice of capacitance and resistance can be predetermined by a person of ordinary skill in the art, which represents a tradeoff between the steady-state power loss of the resistors and the anti-arcing effect. As a guideline, larger capacitance and lower resistance values will result in higher loss, but will give better anti-arcing performance. Thus, the specific choices of resistors and capacitors are not part of the present invention. Rather, they are within ordinary skill of the art in light of the principles of the present invention.
Another object of the present invention is to provide an anti-arcing protection device which can fit into casings of existing electronic ballasts. The protection components according to the present invention can afford a miniature design for an internal addition for making existing ballasts safe, thus eliminating the need to change the existing fixtures.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be made to the drawings and the following description in which there are illustrated and described preferred embodiments of the invention.
The present invention is now described below in detail with reference to the figures.
Turning to
Similar problems exist in the general structure of an instant-start type electronic ballast shown in
Similar arcing condition may also be present in the general structure of an instant-start type electronic ballast that drives four lamps as shown in
To prevent or minimize the dangerous arcing conditions as discussed above, the present invention develops a novel structure of an electronic ballasts.
Similarly, the present invention can be applied to a configuration used for driving four lamps as shown in
Satisfactory results were obtained in an experiment set up to demonstrate the functioning behavior of the additional circuit. The experiment used the electronic ballast according to
The results of the experiment is shown in
On the other hand,
While there have been described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes, in the form and details of the embodiments illustrated, may be made by those skilled in the art without departing from the spirit of the invention. The invention is not limited by the embodiments described above which are presented as examples only but can be modified in various ways within the scope of protection defined by the appended patent claims.
This application claims benefit from U.S. provisional application No. 61/425,770, filed Dec. 22, 2010, the content of which is incorporated herein by reference.
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Number | Date | Country | |
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20120161657 A1 | Jun 2012 | US |
Number | Date | Country | |
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61425770 | Dec 2010 | US |