Patent Publication Number: US-7592750-B2

Title: Fluorescent lamp with external electrodes

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a tube-type fluorescent lamp and, more particularly, to a back-lighting panel having a plurality of such fluorescent lamps. 
     BACKGROUND OF THE INVENTION 
     In a transmissive or transflective liquid-crystal display panel, a back-lighting source is used behind the display panel to provide illumination. The back-lighting source can be a panel having an array of tube-type fluorescent lamps arranged in parallel, as shown in  FIG. 1 . As shown in  FIG. 1 , the back-lighting panel  1  has a plurality of external-electrode fluorescent lamps (EEFLs)  10  mounted between a pair of upper supports  30  and a pair of lower supports  20  mounted on a base plate  18 . As can be seen from  FIG. 2 , each of the EEFLs  10  is a tube-type fluorescent lamp  12  having two external electrodes  14  at its ends. As shown in  FIG. 2 , the fluorescent tube  12  and the external electrodes  14  are cylindrical. 
     In order to supply electrical power to the lamps, each of the lower supports  20  has an electrically conductive strip  26  to be made contact with the external electrode  14 . For example, the lower support  20  can have a supporting base  22  with a row of seats  23  to accommodate a plurality of cushions  24  so as to allow a strip  26  of electrically conductive material to be mounted on the supporting base  22 . The conductive strip  26  has a plurality of curved sections  28  for placing the EEFLs. Each of the curved sections  28  has a curvature to accommodate the cylindrical external electrodes  14 . The upper support  30  can be similar to the lower support  20  with or without the conductive strip  26 . Two upper supports  30  and two lower supports  20  can be used to clamp down on a row of EEFLs as illustrated in  FIG. 1 . 
     Alternatively, a simpler mounting base can be used for mounting the EEFLs. As illustrated in  FIG. 4   a , a mounting base  40  has a supporting base  42  with a row of seats  44  so as to allow a conductive strip  46  to be mounted thereon. The conductive strip  46  has a plurality of curved sections  48  for placing the EEFLs  10 . The curved section  48  is a V-shaped trough to allow an external electrode  14  to make electrical contact at two points on opposite sides of the trough as shown in  FIG. 4   b . A straight strip of material  50  can be used to hold down the EEFLs  10  seated in the curved sections  48 . 
     Due to the shapes of the curved sections  28 ,  48  of the conductive strips  26 ,  46  and the cylindrical shape of the external electrode  14 , the electrical contact between the EEFLs  10  and the supporting base  42  may not be satisfactory. 
     It is thus desirable and advantageous to provide an external-electrode fluorescent lamp and a matching mounting base with improved electrical contacts. 
     SUMMARY OF THE INVENTION 
     The external-electrode fluorescent lamp, according to the present invention, has two external electrodes disposed on its ends. The external electrode has an extended portion which is flattened to form two substantially flat circumferential areas. With such flat circumferential areas, the electric contact made to the conductive strip can be improved. For mounting a row of external-electrode fluorescent lamps, a mounting base with two electrically conductive strips are used. Each electrically conductive strip has a plurality of curved sections to fit the extended portion of the external electrode. The curved section has two substantially sidewalls to make contact with the flat circumferential areas of the extended portion of the external electrode. It is possible that the width of the curved section is slightly smaller than the width of the extended portion of the external electrode so that the curved section is slightly expanded when the external electrode is inserted into it. As such a tight fit between an external electrode and the mounting base can be achieved. 
     The present invention will become apparent upon reading the description taken in conjunction with  FIGS. 5   a  to  10 . 
    
    
     
       BRIEF DESCRIPTION OF THE INVENTION 
         FIG. 1  shows a prior art back-lighting panel. 
         FIG. 2  shows a prior art external-electrode fluorescent lamp. 
         FIG. 3  is an exploded view of a prior art mounting support. 
         FIG. 4   a  is an exploded view of a different prior art mounting support, including a plurality of prior art external-electrode fluorescent lamps. 
         FIG. 4   b  shows a cross sectional view of a prior art back-lighting panel having a mounting support as shown in  FIG. 4   a.    
         FIG. 5   a  is a front view of the external electrode fluorescent lamp, according to the present invention. 
         FIG. 5   b  shows a side view of the external-electrode fluorescent lamp, according to present invention. 
         FIG. 5   c  shows a different side view of the external-electrode fluorescent lamp, according to present invention. 
         FIG. 6   a  is a schematic representation of the mounting support with a plurality of external electrodes, according to the present invention. 
         FIG. 6   b  is a schematic representation of the mounting support with a plurality of external electrodes, according to another embodiment of the present invention. 
         FIG. 7   a  is an exploded view showing the relationship between the extended portion of the external electrode and the curved section of the conductive strip as shown in  FIG. 6   a.    
         FIG. 7   b  shows how a tight fit between the curved section and the external electrode according to  FIG. 7   a.    
         FIG. 7   c  is an exploded view showing the relationship between the extended portion of the external electrode and the curved section of the conductive strip as shown in  FIG. 6   b.    
         FIG. 7   d  shows how a tight fit between the curved section and the external electrode according to  FIG. 7   c.    
         FIG. 8  shows the cross sectional view of the external electrode, according to another embodiment of the present invention. 
         FIG. 9   a  shows a side view of an external-electrode fluorescent lamp having a different external electrode, according to present invention. 
         FIG. 9   b  shows a different side view of the external-electrode fluorescent lamp as shown in  FIG. 9   a.    
         FIG. 10  shows a typical mounting panel for mounting a plurality of external-electrode fluorescent lamps, according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the prior art external-electrode fluorescent lamp (EEFL)  10  as shown in  FIG. 2 , the external electrode  14  is essentially conformal to the end of the fluorescent tube  12 . Thus, the cross section of the external electrode  14  has the same shape as the cross section of the fluorescent tube  10 . 
     In the EEFL, according to the present invention, the cross section of the external electrode of the EEFL is different from that of the fluorescent tube. As shown in FIGS.  5   a  to  5   c , the EEFL  70  has a cylindrical fluorescent tube  72  and an external electrode  74  on each of the tube&#39;s ends. While the cross section of the fluorescent tube  72  is substantially round, the cross section of the external electrode  74  is different. The external electrode  74  has an electrically conductive sleeve  82  formed on the fluorescent tube  72 , and extended portion  80  connected to the sleeve  82 . While the sleeve  82  is substantially conformal to the tube&#39;s end, the extended portion  80  is not. As shown in  FIGS. 5   a  to  5   c , the extended portion  80  is flattened on two sides so that the circumferential surface of the extended portion  80  has two substantially flat areas  180 . As such, the cross section of the extended portion is elongated such that the width, W, of the cross section is smaller than the height, H. The electrically conductive portions of the extended portion  80  and the sleeve  82  may be formed simultaneously in the same fabrication process. For example, the electrically conductive portions of the extended portion  80  and the sleeve  82  may be made of a metal or other electrically conductive materials formed by coating, sputtering, dipping or plating processes. 
     In order to provide electrical power to the EEFLs  70 , a mounting base has an electrically conductive strip to make electrical contact to the extended portion  80  of the external electrodes. The mounting base  90  has two base supports  92  and two electrically conductive strips  96  for mounting a plurality of EEFLs  70 . A schematic representation of the mounting base  90  is shown in  FIG. 6   a . As shown, each conductive strip  96  has a row of curved sections  98  shaped to fit the extended portion  80  of the external electrode  74 . A straight strip  100  of a suitable material is used to secure the extended portion  80  of each EEFL  70  in a curved section  98  on each side of the mounting base  90 . The strip  100  can be electrically conductive or non-conductive. An exploded view of a section of the strip-electrode assembly is shown in  FIG. 7   a . As shown, the curved section  98  of the conductive strip  96  has two sidewalls  198  to make electrical contact to the flat circumferential areas  180  of the extended portion  80 . Because the inner side-walls are flat and the shape of the curved section  98  is made conformal to the extended portion  80 , the electrical contact is improved over the prior art. Furthermore, it is possible that the width, w, of the curved section  98  is slightly smaller than the width, W, of the extended portion  80 . As such, when the extended portion is inserted into the curved section  98  of the conductive strip  96 , the curved section  98  is slightly expanded. As a result, an inward urging force acting on the side-walls further improves the electrical contact between the side walls of the curved section and the flat areas of the extended portion  80 , as illustrated in  FIG. 7   b.    
     It should be noted that the base support  92  and its conductive strips  96  can be shaped differently to mount the EEFLs  70  with the same external electrode  74 . As shown in  FIGS. 6   b ,  7   c  and  7   d , the width w of the curved section  98  is made to fit the larger dimension of the extended portion  80 . 
     The cross section of the extended portion  80  of the external electrode  74  can be different from that depicted in  FIGS. 5   a  to  7   d . For example, the flat areas of the extended portion  80  are not necessarily parallel to each other. In other words, the width of the extended portion  80  is not necessarily uniform throughout the height. For example, the extended portion  80  can have a constant width section  182  and a tapered section  184 , as shown in  FIG. 8 . Nevertheless, the extended portion has flat circumferential areas to achieve good electric contact with a curved section of a matched shape. 
     Moreover, the sleeve portion of the external electrode can be short or long. For example, the external electrode  74  can have an extensive sleeve  84  covering a sufficient portion of the fluorescent tube, as shown in  FIGS. 9   a  and  9   b.    
     A typical mounting panel for mounting a plurality of external-electrode fluorescent lamps, according to the present invention, is shown in  FIG. 10 . 
     Although the invention has been described with respect to one or more embodiments thereof, it will be understood by those skilled in the art that the foregoing and various other changes, omissions and deviations in the form and detail thereof may be made without departing from the scope of this invention.