Abstract:
A ballast for electrical lighting fixtures with improved thermal protection features is disclosed. The ballast has ballast laminations, primary and secondary coils, and a thermal protector, the thermal protector being wired in series with the secondary coil. The ballast preferably is of the type having multiple input voltage taps on the primary coil; in such cases, the electrical positioning of the thermal protector in series with the secondary coil causes the wiring assembly of the thermal protector (as part of the ballast) to be independent of the primary coil input voltage tap used in a particular application. Also disclosed are improved electrical lighting circuits for high-intensity-discharge lamps, the circuits having the above-described thermally-protected ballasts.

Description:
RELATED APPLICATIONS  
       [0001]    This is a continuation-in-part of patent application Ser. No. 10/214,225, filed on Aug. 7, 2002 by the inventors named herein. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to ballasts with thermal protection, and more specifically to thermally-protected ballasts for lighting fixtures.  
         BACKGROUND OF THE INVENTION  
         [0003]    Electrical lighting fixtures often involve the use of ballasts, and it is known practice to provide protection from overheating by including thermal protectors in the circuitry in order to break the flow of current to the ballasts when the thermal protector reaches a predetermined temperature. The prior art includes ballasts with either internal or external thermal protectors (i.e., internal or external with respect to the coil) positioned to interrupt the input power flowing to the primary coil of the ballast. In many prior art ballasts, thermal protectors are positioned at or near what are believed to be the most likely locations for insulation degradation, i.e., potential insulation failure points.  
           [0004]    Ballasts for high-intensity-discharge (HID) lamps are often deemed to require thermal protection for various reasons:  
           [0005]    In the past, a predominant reason for thermal protection of ballasts has been the possibility of insulation failures occurring within a ballast due to the expansion and contraction of the core and coil caused by the on-and-off operation over an extended period of time. Ballast overheating is related to degradation of insulation on windings due to thermal stresses. Insulation degradation can frequently develop at or near points where input voltage taps are embedded within the layers of the primary coil. Ballast manufacturers have been particularly concerned, therefore, about protecting ballasts from such aging effects.  
           [0006]    Another known reason for providing thermal protection for a ballast is the overheating which can occur by virtue of the increased power requirements of lamps as they age, and it is this source of overheating which is the primary motivation for this invention. More specifically, as HID lamps age, two basic changes take place: One change involves the wearing (by sublimation) of the electrodes, causing the gap between the electrodes to increase slightly, raising the voltage and thereby the power required. Another change involves chemical variations and contaminations in the gaseous mixture within the lamp arc, which also tend to raise the power requirements of the lamp. Ballasts are designed to provide increasing power as demanded and, as the power rises, the steady-state temperature of the ballast also rises. In order to protect ballasts from failing catastrophically at the ends of the useful lives of certain HID lamps, it is desirable to break the flow of current at a point in time when the temperature has risen above a level deemed acceptable. These concerns are particularly important with respect to pulse-start HID lamps.  
           [0007]    In the prior art, thermal protection issues appear to have been dealt with primarily from the ballast manufacturer&#39;s viewpoint, as described above. Thermally-protected ballasts of the prior art most typically place thermal protectors in series with the primary coil, in the hot leg thereof or in the coil windings themselves, in order to interrupt the flow of power when the temperature rises above pre-set limits.  
           [0008]    The ballast industry has developed ballasts with multiple input voltage taps on the primary coils to address the requirements for multiple voltages in HID lighting applications, thereby providing ballasts which can be adapted to a variety of HID lighting situations. (HID lighting in, e.g., the United States operates at one of several voltages, including 120V, 208V, 240V, 277V and 480V.) However, providing such flexibility in a thermally-protected ballast translates into higher assembly or installation costs for the electrical lighting manufacturer or installer, and, in both cases, creates opportunities for assembly or installation errors. Among other things, in such situations the presence of multiple input taps can be a source of costly wiring errors caused by improper placement of a thermal protector (on the wrong input line) in particular lighting applications.  
           [0009]    There is a need for an improved thermally-protected ballast particularly suitable to protect against problems caused by end-of-life operation of HID lamps, particularly the increasingly common pulse-start HID lamps which are now frequently used in place of metal halide probe-start HID lamps of older design. While the old-style HID lamps typically reach a point where they can no longer operate and are replaced, the pulse-start HID lamps more typically will continue to operate longer and thus require higher power levels over time. Without appropriate protection, this entails greater risks of catastrophic failures.  
           [0010]    Such need is particularly applicable to ballasts with multiple input voltage taps. There is also a need for low-cost, reliably assembled, and easily usable thermally-protected ballasts, and for devices to hold thermal protectors in place to ensure good thermal contact.  
         OBJECTS OF THE INVENTION  
         [0011]    Accordingly, a principal object of this invention is to provide an improved thermally-protected ballast overcoming the problems and shortcomings described above.  
           [0012]    Another object of this invention is to provide a thermally-protected ballast that is particularly suitable to the needs of lighting manufacturers in connection with the aging of HID lamps, particularly pulse-start HID lamps.  
           [0013]    Another object of this invention is to provide a thermally-protected ballast with multiple input voltage taps that is assembled with its thermal protector in a manufacturing plant, independent of which primary leads of the ballast are required by the input voltage of the particular lighting application—rather than being wired during installation into a particular lighting fixture.  
           [0014]    Yet other objects of this invention are to minimize the cost of assembly and installation of thermal protectors into ballasts for HID lighting fixtures, and to increase the reliability of assembly operations.  
           [0015]    These and other objects of the invention will be apparent from the following descriptions and from the drawings.  
         SUMMARY OF THE INVENTION  
         [0016]    The present invention is an improved thermally-protected ballast for use with HID lamps. Such improved ballast overcomes the above-noted problems and shortcomings and satisfies the objects of the invention. The ballast of this invention is of the type having ballast laminations, primary and secondary coils, and a thermal protector. In an improved thermally-protected ballast in accordance with this invention, the thermal protector is wired in series with the secondary coil.  
           [0017]    A highly preferred thermally-protected ballast of this invention which has a thermal protector in series with the secondary coil has multiple input voltage taps on the primary coil; since the electrical positioning of the thermal protector is in series with the secondary coil, wiring assembly of the thermal protector with the ballast is independent of which input voltage tap on the primary coil is used in a particular application.  
           [0018]    In certain preferred embodiments, the thermal protector is mounted externally (i.e., not in the coils), most preferably on the ballast laminations. Most preferably, the improved ballast includes a mounting device secured to the laminations which sandwiches the thermal protector against the laminations.  
           [0019]    This invention also involves an electrical lighting circuit for a HID lamp, such circuit using the above-described thermally-protected ballast. That is, the circuit, which includes the lamp and a ballast with ballast laminations, primary and secondary coils, and a thermal protector, has the thermal protector wired in series with the secondary coil. As noted, the ballast is preferably of the type having multiple input voltage taps on the primary coil. The lamp is preferably a pulse-start lamp.  
           [0020]    Another aspect of this invention is an improved ballast of the type having ballast laminations, primary and secondary coils, the primary coil having multiple input voltage taps and a common tap thereon, and a thermal protector, in which the thermal protector is wired in series with one of the common tap and the secondary coil. As described above, the electrical positioning of the thermal protector causes wiring assembly of the thermal protector with the ballast to be independent of which input voltage tap on the primary coil is required in a particular application.  
           [0021]    A preferred mounting device for a thermal protector is preferably used. Such preferred mounting device is a unitary bracket which is the subject of a concurrently-filed patent application. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 is a exploded perspective view of the ballast with thermal protection in accordance with this invention.  
         [0023]    [0023]FIG. 2 is a rear inverted perspective view of the bracket of FIG. 1.  
         [0024]    [0024]FIG. 3 is a partially broken-away top plan view of the bracket.  
         [0025]    [0025]FIG. 4 is a front elevation of the bracket.  
         [0026]    [0026]FIG. 5 is a left side elevation of the bracket.  
         [0027]    [0027]FIG. 6 is a right side elevation of the bracket.  
         [0028]    [0028]FIG. 7 is a fragmentary front elevation of the ballast with the bracket and thermal protector assembled, partially broken away to show the thermal protector.  
         [0029]    [0029]FIG. 8 is a sectional view along section  8 - 8  as indicated in FIG. 7.  
         [0030]    [0030]FIG. 9 is an electrical schematic of an improved thermally-protected ballast in accordance with this invention, shown as a component in a lighting circuit.  
         [0031]    FIGS.  10 - 12  are electrical schematics showing other embodiments of the improved thermally-protected ballast of this invention, each as a component of a lighting circuit.  
         [0032]    [0032]FIG. 13 is an electrical schematic of another embodiment of the ballast of this invention shown in a lighting circuit, such ballast having its thermal protector in series with the common tap of the primary coil. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0033]    The figures illustrate preferred embodiments of this invention. Of primary importance to this invention are FIGS.  9 - 12 , which illustrate preferred thermally-protected ballasts, each identified by the numeral  100 , as components of lighting circuits. Each lighting circuit includes an HID lamp  40 , such as a pulse-start metal halide lamp. FIGS.  1 - 8  illustrate a preferred mounting bracket  10  and a preferred external mounting of thermal protector  12  as part of improved ballast  100 .  
         [0034]    Each preferred ballast  100  of FIGS.  9 - 12  has multiple voltage input taps (labeled in each case V 1  through V 5 ) and includes ballast laminations  16 , primary and secondary coils  18  and  20 , and a thermal protector  12 . In each case, thermal protector  12  is wired in series with secondary coil  20 .  
         [0035]    [0035]FIG. 9 shows a constant-wattage autotransformer ballast used with a pulse-start lamp; this lighting circuit includes a capacitor  42  and a starter  44 . FIG. 10 illustrates a high-reactance ballast also applied in a pulse-start lamp circuit, which also includes a capacitor and starter, but in positions differing from those shown in FIG. 9. FIG. 11 shows a circuit using a regulated lag ballast, again with a pulse-start lamp, capacitor and starter in still other positions. FIG. 12 shows another circuit using a constant-wattage autotransformer ballast, and such circuit includes a capacitor.  
         [0036]    As hereafter described, ballast  100  is in each case a modification of a non-protected ballast  14 . As indicated above, wiring assembly of thermal protector  12  in series with secondary coil  20  of the ballast is independent of the input voltage to the primary coil required by the particular lamp in connection with which improved ballast  100  is used. Mechanical assembly is carried out reliably, quickly and easily at the time of manufacture.  
         [0037]    The preferred mounting device (bracket  10 ) by which thermal protector  12  is integrated with ballast  14  will now be described in detail:  
         [0038]    Bracket  10  serves the purpose of improved external mounting of thermal protector  12  to ballast  14 . As already noted, ballast  14  is of the type having ballast laminations  16  and primary and secondary coils  18  and  20 , respectively. Ballast bolts  22  extend through laminations  16  and assist in holding them together. One of such ballast bolts and its associated nut and lock washer serve to secure bracket  10  to ballast  14 . Ballast  14  has a contact surface  14   a  (for contact with thermal protector  12 ) and an adjacent surface  14   b,  as shown best in FIGS. 1 and 8. FIGS. 7 and 8 illustrate bracket  10  and thermal protector  12  mechanically assembled with ballast  14 , but with thermal protector wires  24  unconnected.  
         [0039]    FIGS.  1 - 8  illustrate details of unitary bracket  10  and its relationship with respect to ballast  14 . Unitary bracket  10  is formed of spring steel cut and bent into the desired shape, creating its various portions which will now be described. Bracket  10  includes: a holding-face portion  26 , which is an unbroken planar wall that has opposite edges 26 a  and 26 b , a mounting end 26 c  and an entry end 26 d  (see FIG. 4); first and second edge portions  28  and  30  on opposite edges 26 a  and 26 b , respectively, of holding-face portion  26  and angled with respect to holding-face portion  26  toward ballast  14 ; a mounting-end portion  32  on mounting end 26 c  of holding-face portion  26  and extending toward ballast  14 ; and a finger-tab portion  34  on entry end 26 d  of holding-face portion  26 .  
         [0040]    Mounting-end portion  32  includes a spacing portion  32   s  which is contiguous with holding-face portion  26  and a mounting tab  32   t  which is contiguous with spacing portion  32   s  and is positioned for engagement with contact surface  14   a  of ballast  14 . Bracket  10  is attached to ballast  14  by one ballast bolt  22 , which firmly secures mounting tab  32   t  against contact surface  14   a.  Both mounting tab  32   t  and spacer portion  32   s  have free opposite edges, and this allows the remainder of bracket  10  to pivot slightly about mounting tab  32   t , taking advantage of the spring qualities of the spring steel material of which bracket  10  is made. Finger-tab portion  34  extends part way toward contact surface  14   a  of ballast  14 , and presents a smooth grip surface  34   a  for finger displacement of bracket  10  and for contact with wires  24  of thermal protector  12 .  
         [0041]    Thermal protector  12  has a main body  12   b  which includes a contact side  12   c  (see FIG. 8) for engagement with contact surface  14   a  of ballast  14  and a thickness dimension T (see FIG. 8) extending from contact side  12   c  to the side in contact with ballast  14 . Mounting-end portion  32 , particularly its spacing portion  32   s , is configured and dimensioned such that, with thermal protector  12  removed, holding-face portion  26  is positioned no farther from contact surface  14   a  of ballast  14  than thickness T of thermal protector  12 .  
         [0042]    Indeed, with thermal protector  12  removed from bracket  10 , holding-face portion  26  is in fact positioned slightly closer to contact surface  14   a  of ballast  14  than thickness T. When thermal protector  12  is in place, it is sandwiched against ballast  14  by bracket  10 , acting through its holding-face portion  26 . The various portions of bracket  10  are configured and dimensioned to provide such sandwiching of thermal protector  12  against ballast  14 .  
         [0043]    First and second edge portions  28  and  30  of unitary bracket  10  are parallel to one another; they are in substantially parallel planes. First edge portion  28  is wider than second edge portion  30 ; i.e., first edge portion  28  extends from holding-face portion  26  to a distal edge 28 e  which is spaced farther from holding-face portion  26  than thickness dimension T of thermal protector  12 . As shown best in FIG. 8, first edge portion  28  extends far enough that it is in position to engage adjacent surface  14   b  of ballast  14 , and in this way to serve an alignment function to properly position thermal protector  12  on contact surface  14   a  of ballast  14 . Indeed, bracket  10  is configured such that the tightening of ballast bolt  22  on mounting tab  32   t  during assembly tends to rotate bracket  10  until first edge portion  28  engages adjacent surface  14   b , where it stays as tightening of ballast bolt  22  is completed.  
         [0044]    First and second edge portions  28  and  30  and holding-face portion  26  of unitary bracket  10  form an opening  36  (see arrow in FIG. 1) for insertion of thermal protector  12  and from which its wires  24  extend. Insertion of thermal protector  12  during assembly and any later replacement thereof are carried out easily and accurately by simply flexing the non-attached end of bracket  10 , i.e., the end where finger-tab portion  34  is located, slightly away from ballast  14 —enough to allow insertion. Bracket  10  also includes a retention spur  38  (see FIGS.  2 - 4 ), which is bent inwardly from holding-face portion  26  in a position near opening  36  which is beyond the end of main body  12   b  (of thermal protector  12 ) from which wires  24  project. Retention spur  38  projects from holding-face portion  26  in position to engage main body  12   b  of thermal protector  12  in order to prevent unintended withdrawal of thermal protector  12 .  
         [0045]    In the circuit illustrated in FIG. 9, lamp  40  is an M132 ANSI Code 320W metal halide lamp, and capacitor  42 , starter  44 , and ballast  14  from which improved ballast  100  is made all are specified in accordance with the M132 ANSI Code 320 rating of the lamp. Thermal protector  12  of improved ballast  100  is a Texas Instruments Series 7AM thermal protector designed to open at a temperature of 150° C. with a current rating in accordance with the lamp specified above, such thermal protector being placed in series with the secondary coil of the ballast. Thermal protector  12  as used in the preferred embodiment includes, on its outside, an electrically-insulating Mylar sleeve.  
         [0046]    [0046]FIG. 13 illustrates another constant-wattage autotransformer ballast that is used with a pulse-start lamp  40  and has multiple input voltage taps V 1  through V 5  as in FIG. 9; however, thermal protector  12  of the ballast of FIG. 13 is wired in series with the common tap  46  of primary coil  18 . Wiring the thermal protector in series with the secondary coil as described above is highly preferred because of risks associated with some types of failures in the circuit of FIG. 13 (e.g., a short to ground bypassing the thermal protector, thus removing its protection function from the circuit). However, aside from such risks, the thermally-protected ballast in the circuit of FIG. 13 provides a key advantage of this invention—i.e., causing wiring assembly of the thermal protector with the ballast to be independent of which input voltage tap on the primary coil is required in a particular application.  
         [0047]    Appropriate materials and parts for the devices of this invention will be apparent to those who are skilled in the art and are made aware of this invention. Also, a great many substantial variations are possible in the configurations of unitary brackets designed to include the characteristics and requirements of this invention; variations in size, shapes and materials for the inventive bracket are possible. Likewise, substantial variations are possible in ballasts with thermal protection which include the inventive characteristics described and claimed herein.  
         [0048]    While the principles of the invention have been shown and described in connection with specific embodiments, it is to be understood that such embodiments are by way of example and are not limiting.