Abstract:
A lamp driving apparatus of a liquid crystal display device and method of driving lamps in a liquid crystal display are described. The lamp driving apparatus includes lamps that irradiate a liquid crystal display panel with light. An inverter receives a DC voltage from an exterior voltage source, converts the DC voltage into an AC signal and supplies the converted AC signal to the lamps. A feedback circuit is arranged between the inverter and the lamps. The feedback circuit detects currents from the lamps. An inspecting part is disposed between the feedback circuit and the lamps. The inspecting part contains light emitting devices to determine if each of the lamps is operating normally or has an abnormality.

Description:
[0001]     This application claims the benefit of Korean Patent Application No. P2004-39137 filed in Korea on May 31, 2004, which is hereby incorporated by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to an apparatus and method for driving a lamp of liquid crystal display device, and more particularly, to an apparatus for driving a lamp of liquid crystal display device that is capable of protecting a lamp by intercepting a power supply flowing in a lamp when one lamp among a plurality of lamps is abnormal.  
       DESCRIPTION OF THE RELATED ART  
       [0003]     In general, the number of applications using liquid crystal displays (hereinafter, LCD) have been increasing due to the lightness, thinness, and low power consumption of the LCD. In accordance with such a trend, the LCD is used in an office automation device, an audio/video device and the like. The LCD adjusts transmittance of light in accordance with an image signal applied to a matrix of a plurality of control switches to thereby display desired pictures in a screen.  
         [0004]     Since the LCD is not a spontaneous light-emitting display device, the LCD device uses a back light unit as a light source. There are two types of back light units for the LCD, i.e., a direct-below-type and a light guide plate-type. In the direct-below-type, several lamps are arranged in the plane. A diffusion panel is installed between the lamp and the liquid crystal display panel to fixedly keep the distance between the liquid crystal display panel and the lamp. There are two types of direct-below-type units, i.e., a cold cathode fluorescent lamp (CCFL) and an external electrode fluorescent lamp (EEFL). In the CCFL type, an electrode is applied to both ends of glass tube of lamp to apply power supply. In the EEFL type, a power supply is applied to an electrode part in which a metal material is applied to both ends of glass tube of lamp.  
         [0005]     Referring to  FIGS. 1-3 , the LCD adopting a related art direct-below-type backlight includes a liquid crystal display panel  2  to display a picture, a direct-below-type backlight assembly to irradiate uniform light onto the liquid crystal display panel  2 , and a lamp driver  60  for driving the backlight assembly.  
         [0006]     In the liquid crystal display panel  2 , liquid crystal cells are arranged between an upper substrate and a lower substrate to form an active matrix type display. A common electrode and pixel electrodes that apply an electric field to each of the liquid crystal cells are also provided. Each of the pixel electrodes is connected to a thin film transistor that is used as a switch device. The pixel electrode drives the liquid crystal cell along with the common electrode in accordance with a data signal supplied through the thin film transistor, thereby displaying a picture corresponding to a video signal.  
         [0007]     The direct-below-type backlight assembly includes: a lamp housing  34 , a reflection sheet  14  stacked on a front surface of the lamp housing  34 , a plurality of lamps  36  located at an upper part of the reflection sheet  14 ; a diffusion plate  12 ; and optical sheets  10 .  
         [0008]     The lamp housing  34  prevents the light leakage of visible radiation emitted from each of the lamps  36  and reflects the visible radiation, progressing to the side surface and the rear surface of the lamps  36 , to the front surface, i.e., toward the diffusion plate  12 , thereby improving the efficiency of the light generated at the lamps  36 .  
         [0009]     The reflection sheet  14  is arranged between the lamps  36  and the upper surface of the lamp housing  34  to reflect the light generated from the lamps  36  so as to irradiate it to a liquid crystal display panel  2  direction, thereby improving the efficiency of light.  
         [0010]     Each of the lamps  36  includes a glass tube, an inert gas in the inside of the glass tube, and a cathode and an anode formed of metal metallic covering both ends of the glass tube. The lamps  36  are arranged in parallel on the lamp housing  34 .  
         [0011]     The diffusion plate  12  enables the light emitted from the lamps  36  to progress toward the liquid crystal display panel  2  and to be incident in a wide range of angles. The diffusion plate  12  contains a light diffusion member coated on both sides of a transparent resin film.  
         [0012]     The optical sheets  10  narrow the viewing angle of the light coming out of the diffusion plate  12 , thus improving the front brightness of the liquid crystal display device and reducing the power consumption.  
         [0013]     The lamp driver  60 , as shown in  FIG. 3 , includes an inverter  46  to receive DC voltage from an external voltage source and to convert it into an AC signal; a transformer  48  boosting the AC signal generated from the inverter  46  to apply the boosted AC signal to the lamp  36 ; a feedback circuit  42  to detect a current supplied from the inverter  46  to the lamp  36 ; and a controller  44  to control the inverter  46  in accordance with a feedback signal generated from the feedback circuit  42 .  
         [0014]     Each of the lamps  36  includes a glass tube, an inert gas in the inside of the glass tube, and a cathode and an anode installed at both ends of the glass tube. The inside of the glass tube is charged with the inert gas, and the phosphorus is spread over the inner wall of the glass tube. Further, the cathode and the anode of each lamp  36  are integrated in the same polarity.  
         [0015]     The inverters  46  receive a DC voltage from an external voltage source and use a switch device included in the inverter circuit  46  to thereby convert the DC source into an AC signal.  
         [0016]     Each of the transformers  48  is induced to an AC voltage generated to a primary winding  51  by switching of the switch device included in the inverter  46 , to include a secondary winding  53  generating an AC high voltage and an auxiliary winding  52  arranged between the primary winding  51  and the secondary winding  53 . These transformers  48  boost the AC signal generated from the inverter  46  to supply it to the lamps  36 .  
         [0017]     The feedback circuit  42  detects the AC high voltage, generated from the inverter  46  to be supplied to the lamps  36 , to generate a feedback voltage. If the feedback circuit  42  is instead located at the output terminal of the lamp  36 , the feedback circuit  42  detects the output value outputted from the lamp  36 .  
         [0018]     The controller  44  receives the feedback voltage F/B generated from the feedback circuit  46  to control the switch device included in the inverter circuit  46 . More specifically, if the feedback voltage F/B is higher than a predetermined reference voltage, then the controller  44  makes the switch device transmit a voltage lower than the reference voltage. In other words, a voltage amount is lowered, so that a current flowing in the lamp  36  is lowered. On the other hand, if the feedback voltage F/B is lower than the predetermined reference, then the controller  44  makes the switch device transmit a voltage higher than the reference voltage. In other words, a voltage amount becomes higher, so that a current flowing in the lamp  36  becomes higher.  
         [0019]     The liquid crystal display device having the above compositions has a problem in that it is difficult to control the lamps  36  because the lamps  36  are integrated to apply power thereto. In other words, if one or more of the lamps  36  are turned-off due to a bad lamp or a breakage of more than one of the lamps  36 , then the lamps that are not turned-off become brighter in order to maintain a regular brightness. Accordingly, since a load on each of the lamps becomes larger, there is a problem that a life span of these lamps becomes reduced. Thus, a system for inspecting bad lamps and the breakage of a lamp is desirable.  
       SUMMARY OF THE INVENTION  
       [0020]     By way of introduction only, in one aspect, a lamp driving apparatus of a display device comprises a plurality of lamps to irradiate light to a display panel. An inverter receives a DC voltage from an exterior voltage source to convert the DC voltage into an AC signal and to supply the converted AC signal to the lamps. A feedback circuit is arranged between the inverter and the lamps to detect a current outputted from the lamps. An inspecting part is disposed between the feedback circuit and the lamps. The inspecting part comprises a light emitting device to determine if one of the lamps has an abnormality.  
         [0021]     In another aspect, the lamp driving apparatus comprises a plurality of lamps that irradiates a display panel with light. A feedback circuit adjusts a voltage supplied to the lamps dependent on a feedback signal from the lamps. A determination circuit comprises an optical transmitter-receiver pair for each of the lamps. Each optical transmitter-receiver pair reacts differently when the associated lamp has an abnormality than when the associated lamp is operating normally and adjusts the feedback signal dependent on output signals from the optical transmitter-receiver pairs.  
         [0022]     In another aspect, a method of driving a plurality of lamps of a display device comprises supplying a current from each of the lamps to a different optical transmitter; altering transmission from the optical transmitters dependent on the current from the lamps; and adjusting a voltage supplied to the lamps dependent on a signal from each of the optical transmitters. The current from each of the lamps is dependent on whether the lamp has an abnormality or whether the lamp is operating normally. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]     The invention will be apparent from the following detailed description of the embodiments of the present invention with reference to the accompanying drawings, in which:  
         [0024]      FIG. 1  is a perspective view illustrating a related art direct-below-type liquid crystal display device;  
         [0025]      FIG. 2  is a sectional view illustrating the liquid crystal display device taken along the line II-II′ in  FIG. 1 ;  
         [0026]      FIG. 3  is a block diagram illustrating a lamp driver of the related art liquid crystal display device;  
         [0027]      FIG. 4  is a block diagram illustrating a lamp driver of a liquid crystal display device according to an embodiment of the present invention;  
         [0028]      FIG. 5  is a block diagram illustrating an inspecting part in  FIG. 4 ;  
         [0029]      FIG. 6  is a block diagram illustrating a lamp measuring part in  FIG. 5 ;  
         [0030]      FIG. 7  is a block diagram illustrating a voltage maintaining part in  FIG. 5 ; and  
         [0031]      FIG. 8  is a circuit diagram showing a switching part in  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0032]     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0033]     Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to FIGS.  4  to  8 .  
         [0034]     Referring to  FIG. 4 , an apparatus for driving a lamp of a liquid crystal display device according to an embodiment of the present invention includes: a plurality of lamps  136  to generate light; an inverter  146  to receive a DC voltage from an external voltage source (not shown) and to convert it into an AC signal and to supply the AC signal to the lamps  136 ; a transformer  148  to boost the AC signal generated from the inverter  146 ; a feedback circuit  142  to detect a tube current flowing in the lamps  136 ; a controller  144  to control the inverter  146  in accordance with the feedback signal F/B generated from the feedback circuit  142 ; and an inspecting part  170  arranged between the lamps  136  and the feedback circuit  142  to inspect each lamp  136 .  
         [0035]     Each of the lamps  136  includes a glass tube, an inert gas in the inside of the glass tube, and a cathode and an anode installed at both ends of the glass tube. The inside of the glass tube is charged with the inert gas, and the phosphorus is spread over the inner wall of the glass tube. Further, the cathode and the anode of each lamp  36  are integrated in the same polarity. In each of the lamps  136 , if the AC voltage of high voltage supplied from the inverter circuit  146  and the transformer  148  is applied to a high voltage electrode and a low voltage electrode, then an electron is emitted from the low voltage electrode to collide with the inert gas inside the glass tube, thereby increasing the amount of electrons by geometric progression. The increased electrons cause electric current to flow in the inside of the glass tube, thereby exciting the inert gas by the electron to emit ultraviolet radiation. At this time, the AC waveform of the high voltage is continually supplied to the lamps  136 , so that the lamps  136  are continually turned-on.  
         [0036]     The inverters  146  receive a DC voltage from an external voltage source and use a switch device included in the inverter circuit  146 , to thereby convert the DC voltage into an AC signal  
         [0037]     Each of the transformers  148  is induced to an Ac voltage generated to a primary winding  151 ,  161  by switching of the switch device included in the primary windings  151 ,  161 , an auxiliary winding  152 ,  162 , and the inverter circuit  146 , to include a secondary winding  153 ,  163  generating an AC high voltage and the auxiliary windings  152 ,  162  arranged between the primary windings  151 ,  161  and the secondary windings  153 ,  163 . These transformers  148  boost the AC signal generated from the inverter  146  to supply it to the lamps  136 .  
         [0038]     The feedback circuit  142  detects the AC high voltage, generated from the inverter  146  to be supplied to the lamps  136 , to generate a feedback signal F/B. If the feedback circuit  142  is located at the output terminal of the lamp  136 , the feedback circuit  142  detects the output value outputted from the lamp  136 .  
         [0039]     The controller  144  receives the feedback signal F/B generated from the feedback circuit  146  to control the switch device included in the inverter circuit  146 . More specifically, if the feedback signal F/B is higher than a predetermined reference voltage, then the controller  144  makes the switch device transmit a voltage lower than the reference voltage. In other words, a voltage amount is lowered, so that a current flowing in the lamp  136  is lowered. On the other hand, if the feedback signal F/B is lower than the predetermined reference, then the controller  144  makes the switch device transmit a voltage higher than the reference voltage. In other words, a voltage amount becomes higher, so that a current flowing in the lamp  136  becomes higher.  
         [0040]     The inspecting part  170 , as shown in  FIG. 5 , includes: a lamp measuring part  180  connected to each lamp  136 ; a voltage maintaining part  190  connected to the lamp measuring part  180 ; and a switching part  175  connected to the voltage maintaining part  190 .  
         [0041]     The lamp measuring part  180  is a control device that receives a signal outputted from the lamp  136  and uses an opto-coupler, that is, a device for generating light, as a first switch device, to thereby control a power supply. Herein, since the voltage and the current generated from the lamp  136  are high, the high voltage and the high current generated from the lamp  136  are not directly applied to the inspecting part  180 . Accordingly, the opto-coupler is used generate signals in the inspecting part  180 . With reference to  FIG. 6 , when a power supply is supplied to the lamp  136 , the opto-coupler  182  connected to the lamp  136  generates light and the generated light permits switch terminals  183  and  184  of the opto-coupler  182  to be connected to each other. A first reference voltage source Vref. 1 , e.g. 5 v, is connected to a collector terminal  183  of the opto-coupler  182 , so that the first reference voltage Vref. 1  is connected to the voltage maintaining part  190  via an emitter terminal  184  if the opto-coupler  182  is activated.  
         [0042]     The voltage maintaining part  190  is reciprocally connected to a voltage transmitted from the lamp measuring part  180  by use of a PNP type transistor as a second switch device  192 , to thereby control a second reference voltage Vref. 2 . With reference to  FIG. 7 , the emitter terminal  193  of the second switch device  192  is connected to the second reference voltage source Vref. 2 , e.g. 5 v. A base terminal  195  is connected to the emitter terminal  184  of the opto-coupler  182  to receive the first reference voltage Vref. 1  connected to the opto-coupler  182  in accordance with a condition of the lamp  136 . The collector terminal  194  of the second switch device  192  is grounded.  
         [0043]     Referring to  FIG. 8 , the switching part  175  supplies a voltage, generated from a third reference voltage source Vref. 3  connected to the switching part  175 , to the feedback circuit  142  in accordance with the voltage applied from the voltage maintaining part  190 . The switching part  175  includes a diode  177  arranged between the voltage maintaining part  190  and the feedback circuit  142  and a third switch device  179 , that is a NPN type transistor, arranged between the diode  177  and the third reference voltage source Vref. 3 . An input terminal of the third reference voltage source Vref. 3  and the feedback circuit  142  is connected to a collector terminal  174  of the third switch device  179 , and an emitter terminal  176  of the third switch device  179  is grounded. An output terminal of the voltage maintaining part  190  is connected to a base terminal  178  of the third switch device  179 . Herein, a signal ground SG is connected in parallel between the diode  177  and the switch device  179 , to remove signal noise.  
         [0044]     A performing process of the inspecting part having the above structure will be described as follows.  
         [0045]     First of all, if light of the lamp is not generated due to a bad connection or a breakdown of a specific lamp among the lamps  136 , then the opto-coupler  182  is not activated because the opto-coupler  182  of the lamp measuring part  180  is a NPN type transistor. Accordingly, the first reference voltage Vref. 1  is not supplied to the voltage maintaining part  190 .  
         [0046]     Next, if the first reference voltage Vref. 1  is not supplied to the base terminal  195  of the second switch device  192 , then the second switch device  192  is turned on and the second reference voltage Vref. 2  is grounded to a ground terminal via the collector terminal  194  because the second device  192  of the voltage maintaining part  190  is a PNP type.  
         [0047]     Finally, the third switch device of the switching part  175  does not receive the second reference voltage Vref. 2  from the voltage maintaining part  190 , as the second reference voltage Vref. 2  is grounded, thereby interrupting a path between the emitter  176  and collector  174 . Accordingly, no current flows in the third switch device  179  and thus the third reference voltage Vref. 3  is supplied to the feedback circuit  142 . The feedback circuit  142  supplied with the third reference voltage Vref. 3  passes through the controller  144  to shut down the inverter  146 .  
         [0048]     Each switch device in the inspecting part  170  can be an NPN type or the PNP type transistor. When the opto-coupler  182  is replaced by a PNP transistor, the second switch device  192  in the voltage maintaining part  190  is replaced by a NPN type transistor, to thereby have the same effect. By the same technique, when the switch device type of the voltage maintaining part  190  is changed, the switch device type included in the switching part  175  is changed, to thereby have the same effect.  
         [0049]     As described above, the apparatus for driving the lamp of the liquid crystal display device according to the embodiment of the present invention uses the current generated from the lamps and the opto-coupler to thereby decrease the power supply applied to the lamps when an abnormity exists in one of the lamps. Accordingly, a load amount generated in the lamps that are turned on remains the same even through one of the lamps is turned off. Thus, it is possible to protect the lamps.  
         [0050]     Although the present invention has been explained by the embodiments shown in the drawings described above, it should be understood to the ordinary skilled person in the art that the invention is not limited to the embodiments, but rather that various changes or modifications thereof are possible without departing from the spirit of the invention. Accordingly, the scope of the invention shall be determined only by the appended claims and their equivalents.