Apparatus of driving lamp and liquid crystal display device using the same

An apparatus of driving a lamp includes a first inverter board having a first inverter for supplying a first high-voltage alternating-current waveform via a first high-voltage line to a first electrode of the lamp, and a second inverter board having a second inverter for supplying a second high-voltage alternating-current waveform via a second high-voltage line to a second electrode of the lamp, the second inverter being different from the first inverter.

The present application claims the benefit of Korean Patent Application No. P2003-79768 filed in Korea on Nov. 12, 2003, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device, and more particularly, to an apparatus of driving a lamp and a liquid crystal display device using the same that provide a uniform brightness in the device.

2. Discussion of the Related Art

LCD devices have been actively developed as flat display panels in laptop computers, desktop computers, and large-sized information displays because of their high quality image, lightness, thin thickness, compact size, and low power consumption. Most LCDs are passive devices in which images are displayed by controlling an amount of light input from an outside light source. Thus, a separate light source (back light unit) is generally employed for irradiating an LCD device.

In general, a halogen cathode fluorescent tube or a cold cathode fluorescent lamp (hereinafter, referred to as a “CCFL”) is used as the light source in the back light unit. The CCFL is a light source tube using a cold emission phenomenon (electrons are emitted due to a strong electric field applied to the surface of a cathode) and has a low heat generation, a high brightness, and a long life span. The CCFL is classified into a light guide system, a direct illumination system and a reflection plate system, and an appropriate light source tube system among them is adopted in accordance with the requirement of LCD device.

In addition, the light source is classified into an internal electrode fluorescent lamp in which electrodes are formed inside of a discharge tube and an external electrode fluorescent lamp in which the electrodes are formed inside of the discharge tube. The fluorescent lamps are driven by a high-voltage alternating-current waveform. For example, after a direct-current (DC) power source supplied from a direct-current power source part is converted into an alternating-current waveform by an inverter, the high-voltage alternating-current (AC) waveform for driving the fluorescent lamps is boosted by a transformer.

FIG. 1is a schematic view of an apparatus of driving a lamp according to the related art. InFIG. 1, an apparatus of driving a lamp includes lamps24for generating light and an inverter board12for driving the lamps24. Each of the lamps24includes a glass tube having inert gases filled therein, and a first electrode and a second electrode at the opposite ends of the glass tube. An inner wall of the glass tube is coated with phosphor. When an AC waveform from the inverter board12is applied to the first and the second electrodes, electrons are emitted. These emitted electrons collide with the inert gases contained in the glass tube, and the number of electrons exponentially grows. These increased electrons generate electric currents in the glass tube, and excite the inert gases to emit ultraviolet rays. These ultraviolet rays collide with the phosphor coated on the inner wall of the glass tube, and generate visible lights.

The inverter board12generates a high-voltage AC waveform and supply the high-voltage AC waveform via a high-voltage line to first and second electrodes of the lamps24. In particular, the inverter board12includes a plurality of inverters10. Each of the inverters10includes an inverter integrated circuit converting a DC power source supplied from an exterior into an AC power source, and a transformer converting the AC power source from the inverter integrated circuit into the high-voltage AC waveform. Then, the high-voltage AC waveforms are outputted via a plurality of output channels CH1to CH4to the lamps24.

For example, the first and the second channels CH1and CH2supply the high-voltage AC waveform to the first and the second electrodes of a first lamp24. The third and the fourth channels CH3and CH4also supply the high-voltage AC waveform to the first and the second electrodes of a second lamp24. A first high-voltage line22connected to the first electrode of the lamps24is connected to each of the first and the fourth output channels CH1and CH4, and a second high-voltage line20connected to the second electrode of the lamps24is connected to each of the second and the third output channels CH2and CH3.

Because a length of the first high-voltage line22is larger than a length of the second high-voltage line20, an impedance difference between the first high-voltage line22and the second high-voltage line20is generated. Thus, a deviation of currents and voltages outputted form the inverter board12occurs due to the impedance difference between the first and the second high-voltage lines22and20. As a result, a deviation in panel brightness is generated, to thereby induce an uneven brightness phenomenon in the panel.

FIG. 2is a graph showing a current deviation caused by a high-voltage line shown inFIG. 1, andFIG. 3is a graph showing a voltage deviation caused by the high-voltage line shown inFIG. 1.FIG. 2is a measurement of the currents flowing on the high-voltage lines22and20at a measurement location30apart by about 5 cm from the output channels CH1to CH4(shown inFIG. 1). As shown inFIG. 2, a current value of about 70 mA is measured on the first high-voltage line22connected to the first and the fourth output channels CH1and CH4having a relatively long length. A current value of about 60 mA is measured on the second high-voltage line20connected to the second and the third output channels CH2and CH3having a relatively short length. Although not shown, this current deviation increases between the high-voltage lines20and22increases as they locate further from the output channels CH1to CH4and closer to the lamps24.

Further, as shown inFIG. 3, the voltages flowing on the high-voltage lines22and20measured at a measurement location30apart by about 5 cm from the output channels CH1to CH4(shown inFIG. 1) has also a deviation due to a length difference between the first and the second high-voltage lines22and20.

Accordingly, a deviation of currents and voltages occurs in the AC waveforms supplied to drive the lamps24, the first and second electrodes of each the lamps24receive different waveforms. As a result, a deviation in panel brightness is generated, to thereby induce an uneven brightness phenomenon in the panel.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an apparatus of driving a lamp and a liquid crystal display device using the same that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide an apparatus of driving a lamp and a liquid crystal display device using the same capable of making an entire brightness uniform by making a length of a high-voltage line between inverters be the same to decrease a deviation of on output voltage and a current.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, the apparatus of driving a lamp includes a first inverter board having a first inverter for supplying a first high-voltage alternating-current waveform via a first high-voltage line to a first electrode of the lamp, and a second inverter board having a second inverter for supplying a second high-voltage alternating-current waveform via a second high-voltage line to a second electrode of the lamp, the second inverter being different from the first inverter.

In another aspect, the apparatus for driving at least first and second lamps includes a first inverter board having a first inverter and a second inverter, the first inverter for supplying a first high-voltage alternating-current waveform via a first high-voltage line to a first electrode of the first lamp, and the second inverter for supplying a second high-voltage alternating-current waveform via a second high-voltage line to a first electrode of the second lamp, and a second inverter board having a third inverter and a fourth inverter, the third inverter for supplying a third high-voltage alternating-current waveform via a third high-voltage line to a second electrode of the first lamp, and the fourth inverter for supplying a fourth high-voltage alternating-current waveform via a fourth high-voltage line to a second electrode of the second lamp.

In yet another aspect, the liquid crystal display device includes a liquid crystal display module including a liquid crystal panel and a lamp, a first inverter board arranged along an edge of a first side on a rear surface of the liquid crystal display module and having a first inverter for supplying a first high-voltage alternating-current waveform to a first electrode of the lamp via a first high-voltage line, and a second inverter board arranged along an edge of a second side on the rear side of the liquid crystal display module and having a second inverter for supplying a second high-voltage alternating-current waveform to a second electrode of the lamp via a second high-voltage line, the second side of the liquid crystal display module being different from the first side.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 4is a rear surface view of an apparatus of driving a lamp for a liquid crystal display device according to an embodiment of the present invention. InFIG. 4, a liquid crystal display device may include a liquid crystal display module100, a first inverter board116, a second inverter board112, and a cable130for connecting the second inverter board112to the first inverter board116. The first inverter board116may be along an edge of one side on a rear surface of the liquid crystal display module100, and the second inverter board112may be along an edge of another side of the liquid crystal display module100opposite from the first invert board116. The first and second inverter boards116and112may have inverters114and110and output channels CH1, CH2, CH3and CH4. A plurality of high-voltage lines120a,120b,122aand122bmay be connected to the first and second inverter boards116and112via the output channels CH1, CH2, CH3and CH4, respectively. These high-voltage lines120a,120b,122aand122bmay have the same length. Although not shown, the first and second inverter boards116and112may be placed other portions of the liquid crystal display module100, e.g., on a side surface or a front surface of the liquid crystal display module100.

As shown inFIG. 5, the liquid crystal display module100may include a back light unit having a plurality of lamps124, a liquid crystal display panel arranged on the back light unit (not shown), and a frame accommodating the back light unit and the liquid crystal display panel (not shown). Although not shown, more than two of the lamps124may be included in the liquid crystal display module100. In particular, these lamps124may be arranged parallel to each other in at least two groups. In particular, the back light unit may be classified into a direct-below-type back light unit and an edge-type back light unit depending on an arranged location of the lamps124. In the edge-type back light unit, the lamps124may be arranged at one side or both sides of in a light guide plate for converting light incident to the light guide plate into a surface light. In the direct-below-type back light unit, the lamps124may be arranged in parallel on a rear surface of the liquid crystal display panel.

Each of the lamps124may include a glass tube having inert gases filled therein, and a first electrode150and a second electrode152installed at opposite ends of the glass tube, respectively. In addition, an inner wall of the glass tube may be coated with phosphor. The lamps124may be classified into internal electrode fluorescent lamps in which electrodes are formed inside of discharge tubes and external electrode fluorescent lamp in which the electrodes are formed inside of the discharge tubes. An example of the external electrode fluorescent lamp among the internal electrode fluorescent lamp and the external electrode fluorescent lamp will be described as follows.

The first electrode150may be connected to the first inverter board116via the high-voltage lines120aand122a, and the second electrode152may be connected to the second inverter board112via the high-voltage lines120band122b. Each of the first and second inverter boards116and112may generate a high-voltage alternating-current (AC) waveform for driving the lamps124. In particular, the first and second inverter board116and112may supply the high-voltage AC waveforms to the first and second electrodes150and152of the lamps124via the high-voltage lines120a,120b,122aand122b. When an AC waveform from each of the first and the second inverter board116and112is applied to each of the first and the second electrodes150and152, electrons are emitted. These emitted electrons collide with the inert gases contained in the glass tube, and the number of electrons exponentially grows. These increased electrons generate electric currents in the glass tube, and excite the inert gases to emit ultraviolet rays. These ultraviolet rays collide with the phosphor coated on the inner wall of the glass tube to generate visible lights.

FIG. 6is a circuit diagram illustrating the apparatus of driving the lamp shown inFIG. 5. As shown inFIG. 6, the first inverter board116may include a plurality of first inverters114. Each of the first inverters114may include an inverter integrated circuit144for converting a DC power source supplied from an exterior power source device (not shown) into an AC power source and a transformer142for converting the AC power source from the inverter integrated circuit into a first high-voltage AC waveform160with a first phase. In addition, the second inverter board112may include a plurality of second inverters110. Each of the second inverters110may include an inverter integrated circuit for converting a DC power source supplied from an exterior into an AC power source and a transformer for converting the AC power source from the inverter integrated circuit into a second high-voltage AC waveform162with a second phase different from the first phase.

A synchronization controller140may be installed in one of the first and the second inverter boards116and112to synchronize driving timings of the first inverters114and the second inverters110. The synchronization controller140may generate a synchronization signal for synchronizing a driving timing of the first inverters114and a driving timing of the second inverters110, and then may supply the generated synchronization signal to the first inverters114and the second inverters110via the cable130. As a result, the driving timings of the first inverters114and the second inverters110may be synchronized with each other by the synchronization controller140.

In addition, the integrated circuit144may convert the DC power source from the exterior into the AC waveform in response to the synchronization signal from the synchronization controller140, to supply the converted AC waveform to the transformer142. The transformer142then may convert the received AC waveform into the high-voltage AC waveform and supply the converted high-voltage AC waveform to the lamp124. The converted high-voltage AC waveform may be outputted via the output channels CH1, CH2, CH3and CH4. In particular, each of the first inverters114installed in the first inverter board116may supply the high-voltage AC waveform160having a positive phase to the first electrode150of the lamp124. In addition, each of the second inverters110installed in the second inverter board112may supply the high-voltage AC waveform162having a reversed phase to the second electrode152of the lamp124. Thus, the phase of the AC waveform160supplied to the first electrode150and the phase of the AC waveform162supplied to the second electrode152may have a phase difference of 180° with respect to each other.

Further, the output channels CH1to CH4provided in each of the first and the second inverter boards116and112may be connected, via the high-voltage lines120a,120b,122aand122bhaving the same length, to the electrodes150and152of each lamp124. More specifically, the first inverter board116for supplying the high-voltage AC waveform160to the first electrode150of the lamp124may be arranged along the edge of one side of the rear surface of the liquid crystal display module100adjacent to the first electrode150of the lamp124, and the second inverter board112for supplying the high-voltage AC waveform162to the second electrode152of the lamp124may be arranged along the edge of the other side on the rear surface of the liquid crystal display module100adjacent to the second electrode152of the lamp124.

Since the lengths of the high-voltage lines120a,120b,122aand122bare the same, it is possible to decrease the deviation of an output electrical voltage and current due to the impedance difference of the high-voltage line as shown in the related art. Thus, in the apparatus of driving the lamp and the liquid crystal display device using the same according to an embodiment of the present invention, all of the impedances in the high-voltage lines120a,120b,122aand122bmay be the same, to thereby decrease the deviation of the output electrical voltage and current. Therefore, a brightness deviation in the back light unit is uniform. Although the high-voltage lines120a,120b,122aand122bare shown to have the same length, the high-voltage line120amay be different from the high-voltage line122a, and the high-voltage line120bmay be different from the high-voltage line122b. As long as the high-voltage lines120aand120bhave the same length and the high-voltage lines122aand122bhave the same length, the deviation of the output electrical voltage and current may still be decreased.

In addition, since the AC waveforms having the phase difference of about 180° are supplied to each of the first and the second electrode150and152of the respective lamps, a power consumption is reduced and a driving efficiency is improved.

FIG. 7is a waveform diagram illustrating an alternating-current waveform of an analog mode supplied to the lamp shown inFIG. 5, andFIG. 8is a waveform diagram illustrating an alternating-current waveform of a burst mode supplied to the lamp shown inFIG. 5. As shown inFIG. 7, the high-voltage AC waveforms160and162may be in an analog mode having an oscillating amplitude P for continually turning on the lamp124. The high-voltage AC waveforms160and162may adjust the amplitude P, to thereby adjust a brightness of the lamp124(shown inFIG. 6). Alternatively, as shown inFIG. 8, the high-voltage AC waveforms160and162may be in a burst mode having a turning-on period Ton and a turning-off period Toff during each designated period T. The high-voltage AC waveforms160and162may have an oscillating amplitude only during the period of Ton and may adjust the brightness of the lamp124(shown inFIG. 6) by adjusting a time ratio of the turning-on period Ton and the turning-off period Toff to selectively turn on or off the lamp124.

As described above, according to the apparatus of driving the lamp and the liquid crystal display device according to an embodiment of the present invention, the first and the second inverter boards may be arranged on the rear surface of the liquid crystal display device corresponding to each of the first and the second electrodes of the respective lamps and the lengths of the high-voltage lines are the same. Accordingly, the deviation of the impedance caused by the length difference in the high-voltage lines is minimized, and the deviation in the output voltage and the current of the AC waveform are minimized. As a result, the panel has uniform brightness. Further, the AC waveforms being respectively supplied to the first and the second electrodes of a lamp have a phase difference of about 180° with respect to each other. Thus, the power consumption is reduced and the driving efficiency is improved.