CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of Korean Patent Application No. 2006-119049 filed on Nov. 29, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a backlight unit having a protection circuit using induced voltage detection, and more particularly, to a backlight unit having a protection circuit using induced voltage detection that determines whether a lamp performs an abnormal operation by detecting a voltage induced in a power conversion transformer. 
         [0004]    2. Description of the Related Art 
         [0005]    In recent years, liquid crystal displays (LCDs) have received a lot of attention in that they can be reduced in size and weight as compared with the existing displays. Among the LCDs, especially LCD TVs have attracted attention. The LCD includes a backlight unit that emits light. 
         [0006]      FIG. 1  is a configuration view illustrating a backlight unit according to the related art. 
         [0007]    Referring to  FIG. 1 , a backlight unit according to the related art includes an inverter  10 , a lamp group  20 , adetection circuit  30 , and a determination circuit  40 . The inverter  10  includes a switching part  11  that switches DC power and a power conversion transformer  12  that converts the switched power into AC power that is required for driving lamps. The lamp group  20  includes a plurality of lamps each of which receives the AC power from the inverter  10  to emit light. The detection circuit  30  detects voltages that are supplied to the individual lamps from output terminals of the power conversion transformer  12 . The determination circuit  40  compares each of the voltages that are detected by the detection circuit  30  with a reference voltage that is set beforehand so as to determine an abnormal operation of each of the lamps. 
         [0008]    The detection circuit  30  that is used in the backlight unit according to the related art includes a plurality of detection elements C 1 , C 2 , C 3 , and C 4  and a plurality of stabilizing elements C 5 , C 6 , C 7 , and C 8 . 
         [0009]    Pairs of the detection elements C 1 , C 2 , C 3 , and C 4  and the stabilizing elements C 5 , C 6 , C 7 , and C 8  are connected in series with each other. The pairs are individually connected in parallel with the output terminals of the power conversion transformer  12 . 
         [0010]    The detection circuit  30  that is connected to the output terminals of the power conversion transformer  12  detects a voltage that is transmitted to each of the lamps, and transmits the detected voltage to the determination circuit  40 . The detection circuit  40  compares the voltage detected by the detection circuit  30  with the reference voltage set beforehand so as to determine whether the corresponding lamp performs an abnormal operation. When the lamp performs the abnormal operation, the power conversion transformer  12  controls a switching operation of the switching part  11  of the inverter  10  to thereby cut off power supply of the inverter  10 . 
         [0011]    Each of the plurality of detection elements C 1 , C 2 , C 3 , and C 4  of the detection circuit  30  may use a high-voltage discrete capacitor or a pattern capacitor to detect the voltage that is transmitted from the power conversion transformer  12  to each of the lamps. 
         [0012]    When the voltage transmitted to each of the lamps is detected by using the high-voltage discrete capacitor, a circuit area is reduced as required to mount the high-voltage discrete capacitor. Further, since the high-voltage discrete capacitor is expensive, and a process of mounting the high-voltage discrete capacitor is required, manufacturing costs are increased. 
         [0013]    When the pattern capacitor is used to detect the voltage transmitted to each of the lamps, a double sided printed circuit board is required in order to use the pattern capacitor. Further, the pattern capacitor needs to be formed of CTI 600 so that the double sided PCB has a desired dielectric constant, which results in an increase in manufacturing costs. 
       SUMMARY OF THE INVENTION 
       [0014]    An aspect of the present invention provides a backlight unit having a protection circuit using induced voltage detection that determines whether a lamp performs an abnormal operation by detecting a voltage that is induced in a power conversion transformer without using a complicated and expensive detection circuit. 
         [0015]    According to an aspect of the present invention, there is provided a backlight unit having a protection circuit using induced voltage detection, the backlight unit including: an inverter part including a primary coil receiving power and at least one secondary coil converting the power from the primary coil to AC power set beforehand; a lamp part including at least one lamp receiving the AC power from the inverter part to emit light; a detection part including conductors detecting voltages electromagnetically induced in the secondary coil; and an abnormality determining part comparing detection voltages from the detection part with a reference voltage set beforehand. 
         [0016]    The primary coil and the secondary coil of the inverter part may form one transformer, the primary coil and the secondary coil may be wound around a bobbin of the transformer and separated from each other, and the conductors of the detecting part may be inserted into the bobbin of the transformer. Further, the conductors may be separated from output terminals of the secondary coil transmitting the AC power to the lamp by an insulating distance set beforehand. 
         [0017]    The conductors may be floating terminals, which are not connected to the primary coil and the secondary coil, among terminals of the transformer. 
         [0018]    The detection part may further include level control elements controlling levels of the detection voltages from the conductors, and capacitors stabilizing the detection voltages from the conductors. The level control elements may be composed of capacitors or resistors. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0020]      FIG. 1  is a configuration view illustrating a backlight unit according to the related art. 
           [0021]      FIG. 2  is a configuration view illustrating a backlight unit according to an exemplary embodiment of the present invention; 
           [0022]      FIG. 3  is a configuration view illustrating one example of a power conversion transformer that is used in the backlight unit according to the exemplary embodiment of the present invention. 
           [0023]      FIG. 4  is a configuration view illustrating a backlight unit according to another exemplary embodiment of the present invention. 
           [0024]      FIG. 5  is a graph illustrating detection voltages of the backlight unit according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]    Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. However, in description of operation principles associated with the embodiments of the present invention, detailed description of a known art or construction is omitted because it may obscure the spirit of the present invention unnecessarily. 
         [0026]      FIG. 2  is a configuration view illustrating a backlight unit according to an exemplary embodiment of the present invention. 
         [0027]    Referring to  FIG. 2 , a backlight unit  100  according to an exemplary embodiment of the present invention includes an inverter part  110 , a lamp part  120 , a detection part  130 , and an abnormality determining part  140 . 
         [0028]    The inverter part  110  may include a switch  111  and a transformer  112 . The switch  111  switches DC power and transmits the switched DC power to the transformer  112 . 
         [0029]    The transformer  112  includes a primary coil  112   a  and one or more secondary coils  112   b   1  and  112   b   2 . Preferably, the number of secondary coils  112   b   1  and  112   b   2  is in proportion to the number of lamps. Here, the two secondary coils  112   b   1  and  112   b   2  are shown in  FIG. 2 , but the present invention is not limited thereto. 
         [0030]    The lamp part  120  includes one or more lamps  121  and  122 . As described above, the number of lamps is preferably in proportion to the number of secondary coils. Here, the two lamps  121  and  122  are shown in  FIG. 2 , but the present invention is not limited thereto. The lamps  121  and  122  are connected to ends of the secondary coils  112   b   1  and  112   b   2 , respectively, and receive AC power to emit light. 
         [0031]    The detection part  130  includes one or more conductors  131  and  132 . Preferably, the number of conductors is in proportion to the number of secondary coils. Here, the two conductors  131  and  132  that correspond to the secondary coils  112   b   1  and  112   b   2 , respectively, are shown in  FIG. 2 . Preferably, the above-described conductors  131  and  132  are formed at positions corresponding to lamp output terminals of the secondary coils  112   b   1  and  112   b   2 , respectively. Further, the conductors  131  and  132  may be included in the transformer  112 , which will be described in detail with reference to  FIG. 3 . 
         [0032]    The detection part  130  may further include level control elements C 1  and C 2  and capacitors C 5  and C 6  that are connected in series with the conductors  131  and  132 , respectively. The level control elements C 1  and C 2  may be composed of capacitors or resistors. 
         [0033]    The abnormality determining part  140  receives a detection voltage Ver from each of the conductors  131  and  132 , and a reference voltage Vref that is set beforehand, and transmits a determination voltage vju to the inverter part  110 . Preferably, the abnormality determining part  140  transmits the determination voltage vju to the switch  111  of the inverter part  110 . 
         [0034]      FIG. 3  is a configuration view illustrating one example of a power conversion transformer that is used in the backlight unit according to the exemplary embodiment of the present invention. 
         [0035]    Referring to  FIG. 3 , the inverter part  110  of the backlight unit  100  according to the exemplary embodiment of the present invention includes a power conversion transformer  112 . 
         [0036]    The power conversion transformer  112  includes a bobbin Bo and a core Co. The bobbin Bo is a stationary part where each of the primary coil  112   a  and the secondary coils  112   b   1  and  112   b   2  is wound according to a winding ratio that is set beforehand. The core Co is coupled to the bobbin Bo and forms magnetic paths by electromagnetic induction between the primary coil  112   a  and the secondary coils  112   b   1  and  112   b   2 . 
         [0037]    The primary coil  112   a  receives the power switched by the switch  111  through input terminals I 1  and I 2  of a terminal Cn that is formed on the bobbin Bo. The power that is induced by the electromagnetic induction between the primary coil  112   a  and the secondary coils  112   b   1  and  112   b   2  is transmitted to the lamp part  120  through respective output terminals O 1  and O 2  of the secondary coils  112   b   1  and  112   b   2 . 
         [0038]    The conductors  131  and  132  of the above-described detection part  130  may be formed on the terminal Cn while each of the conductors  131  and  132  is separated from each of the input terminals I 1  and I 2  of the primary coil  112   a  or each of the output terminals O 1  and I 2  of the secondary coils  112   b   1  and  112   b   2  by an insulating distance that is set beforehand. Preferably, the conductors  131  and  132  may be floating terminals, which are not used to input and output power, among terminals that are formed on the terminal Cn. 
         [0039]      FIG. 4  is a configuration view illustrating a backlight unit according to another exemplary embodiment of the present invention. 
         [0040]    Referring to  FIG. 4 , a transformer  212  according to another exemplary embodiment of the present invention includes secondary coils  212   b   1  and  212   b   2 . One end and the other end of each of the secondary coils  212   b   1  and  212   b   2  can transmit AC power to lamps. Here, there may be four lamps in proportion to the secondary coils  212   b   1  and  212   b   2 . That is, a lamp part  220  includes lamps  221 ,  222 ,  223 , and  224 . Further, a detection part  230  may include four conductors  231 ,  232 ,  233 , and  234  according to the number of lamps such that each of the conductors detects a voltage transmitted to each of the lamps. 
         [0041]    Since a switch  211  of an inverter part  210 , level control elements C 1 , C 2 , C 3 , and C 4 , capacitors C 5 , C 6 , C 7 , and C 8 , and an abnormality determining part  240  shown in  FIG. 4  are the same as those described in  FIG. 2 , the description thereof will be omitted. 
         [0042]      FIG. 5  is a graph illustrating detection voltages of a backlight unit according to the present invention. 
         [0043]    The conductors  231 ,  232 ,  233 , and  234  of the detection part  230  detect voltages according to the voltages of the secondary coils  212   b   1  and  212   b   2  when the lamps perform normal operations or abnormal operations. Here, the detected voltages are shown in  FIG. 5 . 
         [0044]    Hereinafter, the operation and effect of the present invention will be described in detail with reference to the accompanying drawings. 
         [0045]    Referring to  FIGS. 2 and 3 , DC power is switched by the switch  111  of the inverter part  110  and transmitted to the transformer  112 . The DC power that is switched by the switch  111  is input to the primary coil  112   a  of the transformer  112 . The switched DC power is converted into AC power by electromagnetic induction between the primary coil  112   a  and the secondary coils  112   b   1  and  112   b   2  each of which has the winding ratio set beforehand. Then, the AC power is transmitted to each of the lamps  121  and  122  of the lamp part  120  through each of the output terminals of the secondary coils  112   b   1  and  112   b   2 . 
         [0046]    Each of the conductors  131  and  132  of the detection part  130  is separated from each of the input terminals I 1  and I 2  of the primary coil  112   a  or each of the output terminals O 1  and I 2  of the secondary coils  112   b   1  and  112   b   2  by the insulating distance that is set beforehand so as to detect voltages that are induced in the secondary coils  112   b   1  and  112   b   2  by the electromagnetic induction. The insulating distance set beforehand may vary according to electrical conditions of the transformer. For example, when a withstanding voltage of the transformer is 5 KV, the insulating distance is preferably 5 mm or more. 
         [0047]    The lamps  121  and  122  receive the AC power that is transmitted through the output terminals of the secondary coils  112   b   1  and  112   b   2 , respectively, and emit light. In this way, each of the lamps  121  and  122  performs a normal operation. When the lamps  121  and  122  may be open circuit due to aging of the lamps  121  and  122  or a short circuit of power input terminals, the lamps  212  and  122  cannot emit light. At this time, impedance of one lamp that performs an abnormal operation is different from that of the other lamp that performs the normal operation. This difference results in a change of the power that is induced in the secondary coils. Further, the change in the induced power results in a change in the power that is input to the primary coil. 
         [0048]    That is, the impedance of the lamp performing the abnormal operation becomes larger than that of the lamp performing the normal operation. Further, the voltages that are induced in the secondary coils are increased by LC resonance of the transformer  112 . 
         [0049]    Referring to  FIG. 3 , the conductors  131  and  132  of the detection part  130  are located adjacent to the input terminals I 1  and I 2  of the primary coil  112   a , respectively. However, a voltage that is input to the primary coil  112   a  is DC 24 V, and voltages that are induced in the secondary coils  112   b   1  and  112   b   2  are approximately AC 700 V. Therefore, even though the conductors  131  and  132  are located adjacent to the input terminals I 1  and I 2  of the primary coil  112   a , the conductors  131  and  132  can detect the voltages that are induced in the secondary coils. 
         [0050]    The conductors  131  and  132  of the detection part  130  detect the voltages that are induced in the secondary coils when the lamps perform abnormal operations, and transmit detection voltages Ver to the abnormality determining part  140 . Before the detection voltages Ver are transmitted to the abnormality determining part  140 , the level control elements C 1  and C 2  control levels of the detection voltages Ver so that the detection voltages Ver can be applied to the abnormality determining part  140 . Further, the detection voltages Ver, whose levels are controlled, are stabilized by the capacitors C 5  and C 6 , and then transmitted to the abnormality determining part  140 . 
         [0051]    The abnormality determining part  140  compares each of the detection voltages Ver with the reference voltage Vref that is set beforehand. When any one of the detection voltages Ver is larger than the reference voltage Vref, the abnormality determining part  140  determines that the corresponding lamp performs the abnormal operation, and transmits a corresponding determination voltage vju to the inverter part  110 . 
         [0052]    The switch  111  of the inverter part  110  is turned off according to the determination voltage vju so as to cut off power supply of the inverter part  110 . 
         [0053]    The operation of the backlight unit according to the exemplary embodiment of the present invention is the same as the operation as described above with reference to  FIG. 2 . However, referring to  FIG. 4 , one end and the other end of the secondary coil  212   b   1  supply the AC power to the lamps  221  and  222 , respectively, and one end and the other end of the secondary coil  212   b   2  supply the AC power to the lamps  223  and  224 . In order to detect abnormal operations of the lamps, the detection part  230  includes the four conductors  231 ,  232 ,  233 , and  234  that detect voltages from one end and the other end of each of the secondary coils  212   b   1  and  212   b   2 . 
         [0054]    Referring to  FIG. 5 , the voltages that are detected by the conductors  231 ,  232 ,  233 , and  234  are shown. 
         [0055]    A voltage C of when each of the lamps  221 ,  222 ,  223 , and  224  performs a normal operation, and a voltage D of when each of the lamps  221 ,  222 ,  223 , and  224  performs an abnormal operation are shown in  FIG. 5 . A voltage that is obtained by detecting the voltage C when each of the lamps  221 ,  222 ,  223 , and  224  performs the normal operation is a detection voltage A. A voltage that is obtained by detecting the voltage D when each of the lamps  221 ,  222 ,  223 , and  224  performs the abnormal operation is a detection voltage B. 
         [0056]    As shown in  FIG. 5 , conductors that are included in a transformer detect voltages that are induced in the secondary coils without using an expensive detection device so as to determine whether lamps perform abnormal operations, such that it is possible to protect the lamps or the transformer. 
         [0057]    As set forth above, according to exemplary embodiments of the invention, voltages induced in secondary coils that transmit power to lamps are detected by conductors included in a transformer without using an expensive detection device, thereby increasing an available circuit area and reducing the unit cost. 
         [0058]    While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.
There is provided a backlight unit that determines whether a lamp performs an abnormal operation by detecting a voltage that is induced in a power conversion transformer without using a complicated and expensive detection circuit. A backlight unit having a protection circuit using induced voltage detection according to an aspect of the invention includes an inverter part including a primary coil receiving power and at least one secondary coil converting the power from the primary coil to AC power set beforehand, a lamp part including at least one lamp receiving the AC power from the inverter part to emit light, a detection part including conductors detecting voltages electromagnetically induced in the secondary coil, and an abnormality determining part comparing detection voltages from the detection part with a reference voltage set beforehand.