Abstract:
A fluorescent lamp includes three transformers, a power supply, a converter, and four lamp tubes. The converter converts a direct current (DC) provided by the power supply into an alternating current (AC) generated in a first transformer and a second transformer for driving the four lamp tubes to emit light. The third transformer is connected to the four lamp tubes to balance working electric potentials of the four lamp tubes.

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to fluorescent lamps, and particularly to a fluorescent lamp capable of providing balanced driving electric potentials to a plurality of lamp tubes thereof. 
     2. Description of Related Art 
     Cold cathode fluorescent lamps (CCFL) are widely used in electronic displays as backlights. Referring to  FIG. 3 , one such CCFL driving circuit  1  generally includes a first transformer  10 , a second transformer  12 , a power supply  14 , a converter  16 , and four lamp tubes  18 ,  20 ,  22 ,  24 . The first transformer  10  includes a first primary side  100  and a first secondary side  102 . The second transformer  12  includes a second primary side  120  and a second secondary side  122 . The power supply  14  is connected to the first primary side  100  and the second primary side  120 . The converter  16  includes two transistors  161 ,  162  both connected to the first primary side  100  and the second primary side  120 . The lamp tubes  18 ,  20  are respectively connected to two ends of the first secondary side  102 . The lamp tubes  22 ,  24  are respectively connected to two ends of the second secondary side  122 . 
     In use, the two transistors  160 ,  162  of the converter  16  are alternately turned on, such that a direct current (DC) provided by the power supply  14  periodically passes through the first primary side  100  and the second primary side  120 . Thus, the DC is converted into a square wave alternating current (AC) passing through the first primary side  100  and the second primary side  120 . The square wave AC generates a corresponding sine wave AC in the first secondary side  102  and the second secondary side  122 , and the sine wave AC drives the lamp tubes  18 ,  20 ,  22 ,  24  to emit light. 
     For maximum light quality, in the CCFL  1 , every pair of lamp tubes connected to the same transformer, such as the pair of lamp tubes  18 ,  20  both connected to the first transformer  10  or the pair of lamp tubes  22 ,  24  both connected to the second transformer  12 , must be configured to exhibit identical parasitic parameters, such as capacitances, inductances, and other parameters. If any pair of lamp tubes connected to the same transformer exhibits different parameters, the light quality of the CCFL  1  may be adversely affected. For example, referring to  FIG. 4 , if the parasitic parameters of the lamp tubes  18 ,  20  are different from each other, when they are driven by the same sine wave AC provided by the first transformer  10 , the sine wave AC may generate different electric potentials in the lamp tubes  18 ,  20 . Thus, luminance among the lamp tubes  18 ,  20  may vary, adversely affecting light quality of the CCFL  1 . 
     Therefore, there is room for improvement within the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present fluorescent lamp can be better understood with reference to the following drawings. The components in the various drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present fluorescent lamp. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the figures. 
         FIG. 1  is a circuit diagram of a fluorescent lamp, according to an exemplary embodiment. 
         FIG. 2  is an electric potential diagram of lamp tubes of the fluorescent lamp shown in  FIG. 1 . 
         FIG. 3  is a circuit diagram of a commonly used fluorescent lamp. 
         FIG. 4  is an electric potential diagram of lamp tubes of the fluorescent lamp shown in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a fluorescent lamp  3 , according to an exemplary embodiment, is shown. The fluorescent lamp  3  can be a CCFL, which includes a first transformer  30 , a second transformer  32 , a third transformer  46 , a power supply  34 , a converter  36 , a first lamp tube  38 , a second lamp tube  40 , a third lamp tube  42 , and a fourth lamp tube  44 . 
     The first transformer  30  includes a first primary side  300  and a first secondary side  302 . The second transformer  32  includes a second primary side  320  and a second secondary side  322 . The power supply  34  is connected to the first primary side  300  and the second primary side  320 . The converter  36  is a half-bridge converter, including two transistors  361 ,  362 , both connected to the first primary side  300  and the second primary side  320 . The first lamp tube  38  is connected to one end  3020  of the first secondary side  302 , and the second lamp tube  40  is connected to another end  3022  of the first secondary side  302 . The third lamp tube  42  is connected to one end  3220  of the second secondary side  322 , and the fourth lamp tube  44  is connected to another end  3222  of the second secondary side  322 . 
     The third transformer  46  includes a third primary side  460  and a third secondary side  462 . The number of turns in the third primary side  460  and the third secondary side  462  are equal. The third primary side  460  has one end  4600  connected between the end  3020  of the first transformer  30  and the first lamp tube  38 , and another end  4602  connected between the end  3222  of the second transformer  32  and the fourth lamp tube  44 . The third secondary side  462  has one end  4620  connected between the end  3022  of the first transformer  30  and the second lamp tube  40 , and another end  4622  connected between the end  3220  of the second transformer  32  and the third lamp tube  42 . Thus, the third primary side  4660  is connected between the first lamp tube  38  and the fourth lamp tube  44 , and the third secondary side  462  is connected between the second lamp tube  40  and the third lamp tube  42 . 
     In use, the two transistors  360 ,  362  of the converter  36  are alternately turned on, such that a DC provided by the power supply  34  periodically passes through the first primary side  300  and the second primary side  320 . Thus, the DC is converted to a square wave AC passing through the first primary side  300  and the second primary side  320 . The square wave AC generates a corresponding sine wave AC in the first secondary side  302  and the second secondary side  322 , where the sine wave AC drives the lamp tubes  38 ,  40 ,  42 ,  44  to emit light. 
     When any pair of lamp tubes both connected to either of the first transformer  30  or the second transformer  32 , such as the pair of lamp tubes  38 ,  40  both connected to the first transformer  30  or the pair of lamp tubes  42 ,  44  both connected to the second transformer  32 , exhibit different parasitic parameters, such as capacitances, inductances, and others, the third transformer  46  can cooperate with the other pair of lamp tubes, both of which are connected to the first transformer  30  or the second transformer  32  and exhibit similar parameters, to regulate the electric potentials of the two lamp tubes exhibiting different parameters, such that the working electric potentials of the lamp tubes  38 ,  40 ,  42 ,  44  are balanced and the fluorescent lamp  3  continues to emit even light. 
     For example, referring to  FIG. 2 , the first lamp tube  38  and the second lamp tube  40  both connected to the first transformer  30  can exhibit different parasitic parameters, and the third lamp tube  42  and the fourth lamp tube  44  both connected to the second transformer  32  exhibit similar parasitic parameters. In use, the electric potentials of the third lamp tube  42  and the fourth lamp tube  44  are both provided by the second transformer  32 , and the third lamp tube  42  and the fourth lamp tube  44  have similar parasitic parameters, therefore, the electric potentials of the third lamp tube  42  and the fourth lamp tube  44  are similar. Furthermore, since the number of turns in the third primary side  460  and the third secondary side  462  are equal, the electric potential difference between the two ends  4620 ,  4622  of the third secondary side  462 , that is the electric potential difference between the second lamp tube  40  and the third lamp tube  42 , is regulated to equal the electric potential difference between the two ends  4600 ,  4602  of the third primary side  460 , that is the electric potential difference between the first lamp tube  38  and the fourth lamp tube  44 . Thus, it can be inferred that the electric potentials of the first lamp tube  38  and the second lamp tube  40  are regulated to be similar to each other, and thus the working electric potentials of the lamp tubes  38 ,  40 ,  42 ,  44  are balanced. Despite the first lamp tube  38  and the second lamp tube  40  exhibiting different parasitic parameters, they still receive similar working electric potentials and emit light in similar luminance. In this way, the fluorescent lamp  3  emits uniform light, thereby maximizing light quality. 
     Alternatively, the third primary side  460  and the third secondary side  462  of the third transformer  46  can be interchanged with each other. Particularly, the end  4600  is connected between the end  3022  of the first transformer  30  and the second lamp tube  40 , the end  4620  is connected between the end  3020  of the first transformer  30  and the first lamp tube  38 , the end  4602  is connected between the end  3220  and the third lamp tube  42 , and the end  4622  is connected between the end  3222  and the fourth lamp tube  44 . Thus, the third primary side  4660  is connected between the second lamp tube  40  and the third lamp tube  42 , and the third secondary side  462  is connected between the first lamp tube  38  and the fourth lamp tube  44 . However, the changed fluorescent lamp  3  can also be used according to the method described. In either case, the two lamp tubes connected to the same side of the third transformer  46 , that is the third primary side  460  or the third secondary side  462 , are respectively connected to the first transformer  30  and the second transformer  32 . In this way, despite one pair of lamp tubes both connected to either of the first transformer  30  or the second transformer  32  exhibiting different parasitic parameters, if only the other pair of lamp tubes both connected to another of the first transformer  30  or the second transformer  32  have similar parameters, the third transformer  46  can cooperate with the pair of lamp tubes exhibiting similar parameters to regulate the electric potentials of the two lamp tubes exhibiting different parameters, such that the fluorescent lamp  3  continues to emit uniform light. 
     The converter  36  can also be a full-bridge converter, a push-pull converter, or other. Additionally, for conserving power consumption of the fluorescent lamp  3 , the third transformer  46  can further include a current-limiting resistor  463 / 464  connected to either of the third primary side  460  and the third secondary side  462 , or include two current-limiting resistors  463 ,  464  respectively connected to the third primary side  460  and the third secondary side  462 , as shown in  FIG. 1 . Two ends of the current-limiting resistor  463  can be respectively connected to the third primary side  460  and either of the two lamp tubes connected to the third primary side  460 , i.e., respectively connected to one end of the third primary side  460  and the first lamp tube  38 , or respectively connected to another end of the third primary side  460  and the fourth lamp tube  44 . Two ends of the current-limiting resistor  464  can be respectively connected to the third secondary side  462  and either of the two lamp tubes connected to the third secondary side  462 , i.e., respectively connected to one end of the third secondary side  462  and the second lamp tube  40 , or respectively connected to another end of the third secondary side  462  and the third lamp tube  42 . 
     It is to be further understood that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of structures and functions of various embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.