Inverter circuit, backlight assembly, and liquid crystal display with backlight assembly

In an inverter circuit, inverter transformers supply AC voltage to discharge tubes. The inverter transformers are arranged such that the AC voltage at a respective first terminal of each secondary coil has an opposite polarity with respect to a corresponding second terminal of each secondary coil. Balance transformers have primary coils inserted in series between a reference terminal of the secondary coils of the inverter transformers and ground. The secondary coils of the balance transformers are connected in series to form a loop. One node of the loop is grounded and a voltage detection node is located on the loop. At least one secondary coil of the secondary coils of the balance transformers is interposed between the grounded node of the loop and the voltage detection node. Thus, an abnormal state or condition, such as an open circuit or a short circuit may be detected.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Korean Patent Application No. 2005-115621 filed on Nov. 30, 2005 and all the benefits accruing therefrom under 35 USC § 119, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electronic display devices. More particularly, the present invention relates to an inverter circuit capable of driving a discharge tube, a backlight assembly including the inverter circuit, and a liquid crystal display (“LCD”) including the backlight assembly.

2. Description of the Related Art

Illustratively, discharge tubes may be implemented using cold cathode fluorescent lamps (“CCFLs”) as described hereinafter, but it is to be clearly understood that the present invention is not limited to CCFLs. For example, the present invention may be implemented in a system that turns on a plurality of discharge tubes in response to an applied alternating current (“AC”) voltage, wherein these discharge tubes are not construed as being limited to the CCFL.

A conventional LCD uses a CCFL as a backlight. In recent years, large LCD televisions have been developed which use correspondingly large LCD displays. Accordingly, plural CCFLs are used to provide a backlight for these large LCD displays.

FIG. 1is a schematic view illustrating light emitting properties for a prior art CCFL301. The CCFL301is a type of fluorescent lamp that operates in a normal glow discharge region. A phosphor322is coated inside a glass tube321of the CCFL301, and a slight amount of inert gas and mercury are sealed within the glass tube321. By applying an AC voltage between electrodes328disposed on both sides of the CCFL301, a glow discharge occurs in mercury vapor. Due to this discharge, mercury323is excited and an ultraviolet ray324is generated. The phosphor322coated in the glass tube321is excited by the ultraviolet ray324to a high energy level. Light is emitted at a wavelength corresponding to an energy difference occurring when the excited phosphor atoms return to a low energy level from the high energy level. The CCFL301emits light having a wavelength determined by the phosphor atom. Also, the CCFL301has a negative resistance characteristic in that impedance is reduced as a function of increasing current flowing therethrough. Also, because it is difficult to fabricate the CCFLs having the same (or uniform) impedance, the impedances of the CCFLs are dispersed throughout an arbitrary range.

The following approaches have been proposed to solve problems occurring when the number of CCFLs increases. For example, a structure may be employed in which a number of inverter transformers increases according to the number of CCFLs used. As illustrated in the prior art configuration ofFIG. 2, a plurality of inverter transformers900A to900N is provided to correspond to CCFLs301to310, respectively. As the number of inverter transformers increases, the inverter transformers occupy an undesirably large area on a printed substrate. Therefore, a size of the inverter circuit becomes large.

To reduce the size of the inverter circuit, driving a plurality of CCFLs301to310using a single inverter transformer may be considered as illustrated in the prior art configuration ofFIG. 3.

However, the structure ofFIG. 3causes interference with a driving circuit of the LCD because the CCFLs301to310are driven by a sinusoidal AC voltage94A of a same polarity. Consequently, noise such as fringe interference is observed on the display screen. This noise can be eliminated or reduced by providing a differential type inverter transformer901as illustrated in the prior art configuration ofFIG. 4. That is, the inverter transformer901is configured such that sinusoidal AC voltages95and96generated from two secondary coils have opposite polarities.

However, as described above, two secondary coils have to be constructed to provide opposite polarities with respect to each other in order to obtain voltages of reverse phase at the secondary sides of the inverter transformer901for a differential voltage implementation. It is difficult to obtain the AC voltages95and96for these reverse phases from the two secondary coils. When the AC voltages95and96of the reverse phases generated from the secondary coils of the inverter transformer901are not uniform, variations are observed in the currents flowing through the CCFLs301to310, thereby causing bright areas or dim areas or both.

Also, as described above, the CCFLs have a negative resistance characteristic. When the CCFLs301to310are connected in parallel to the inverter transformer901, it is assumed that a current begins to flow through a specific CCFL having a relatively low impedance compared with the remaining CCFLs of CCFLs301to310. In this case, current is concentrated in the specific CCFL because the current flows more easily as the resistance of the specific CCFL decreases. As a result, the bright areas occur at one or more CCFLs, thereby shortening the lifespan of the CCFLs.

To avoid the aforementioned problem, a balance circuit may be connected in series with the CCFLs.FIG. 5is a prior art circuit diagram illustrating an example of a balance circuit400connected to CCFLs310to310. When a current flows through an arbitrary CCFL, a current flows through a primary coil of a balance transformer (for example, one of balance transformers401to410inFIG. 5) connected in series with the CCFL. This causes a current to flow through a secondary coil of the balance transformer. Since the secondary coil of the balance transformer is connected in series with the secondary coils of the remaining balance transformers, a current flowing through the secondary coils of the balance transformers forces a current to flow through the primary coils of the balance transformers401to410. Consequently, currents of the respective CCFLs301to310are controlled in the same manner. As illustrated inFIG. 5, a loop formed by the secondary coils of the balance transformers401to410is grounded. A detected voltage is detected at a contact node (detection node)501in a state wherein a secondary coil of at least one balance transformer is interposed between a grounded node and the contact node (detection node)501. The detected voltage is a voltage that is necessary for the balance transformers401to410to maintain balance of the CCFLs301to310. The magnitude of the detected voltage is different according to the dispersion of the resistances including the negative resistance characteristic of the CCFLs. Using this voltage observation, an open circuit or a short circuit caused by malfunction of the CCFLs can be detected. That is, when the open circuit or the short circuit occurs, a higher voltage compared to a voltage at a normal state is generated at the detection node501so as to maintain the balance of the balance transformers401to410.

When the impedance of a CCFL increases because the lifetime of the CCFL is nearly at an end, the Q of an inverter resonance circuit becomes high so that a relatively high voltage is generated. Therefore, a corona discharge is easily generated between a line disposed between the secondary coil of the inverter transformer and another line. The corona discharge gradually carbonizes an insulating coating of the lines, thereby causing short circuiting of the lines.

The balance transformer400used in the inverter circuit for turning on the CCFLs301to310for the backlight of the conventional LCD ofFIG. 5is connected to terminals of the CCFLs301to310which are opposite with respect to the inverter transformer901. When an abnormal state such as a current concentration on a specific CCFL occurs, the balance transformer400generates a higher voltage relative to a normal state at the voltage detection node501. Automatic operation of the control circuit is possible by detecting the voltage at the voltage detection contact point501. However, when a high voltage discharge such as a corona discharge occurs between a line disposed between the secondary coil of the inverter transformer901and the CCFLs301to310and another line, this high voltage discharge does not influence the balance between the CCFLs301to310. For this reason, it is virtually impossible to detect an abnormal state such as a high voltage discharge occurring in a voltage detection node of the balance transformers401to410connected to terminals of the CCFLs301to310.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention provide an inverter circuit capable of detecting an abnormal state such as a high voltage discharge in a circuit to drive a discharge tube.

Exemplary embodiments of the present invention also provide a backlight assembly including the foregoing inverter circuit.

Exemplary embodiments of the present invention also provide a liquid crystal display using the aforementioned backlight assembly.

Pursuant to one illustrative aspect of the present invention, an inverter circuit includes a plurality of inverter transformers that supply AC voltage to a plurality of discharge tubes, and a plurality of balance transformers having primary coils inserted in series between a reference terminal of the secondary coils of the inverter transformers and ground. The inverter transformers are arranged such that the AC voltage at a respective first terminal of each secondary coil has a substantially opposite polarity with respect to the AC voltage at a corresponding second terminal of each secondary coil. The secondary coils of the balance transformers are connected in series to form a loop. One node of the loop is grounded, and a voltage detection node is located on the loop. At least one secondary coil of the secondary coils of the balance transformers is interposed between the grounded node of the loop and the voltage detection node.

The voltage detection node is a circuit node on the loop where half of the secondary coils of the balance transformers are interposed between the voltage detection node and the grounded node.

Each of the inverter transformers may include two primary coils and two secondary coils, wherein a first secondary coil of the two secondary coils is arranged to have an AC voltage of opposite polarity with respect to a second secondary coil of the two secondary coils.

Each of the inverter transformers may include a single primary coil and two secondary coils, wherein a first secondary coil of the two secondary coils is arranged to have an AC voltage of opposite polarity with respect to a second secondary coil of the two secondary coils.

The discharge tubes include a first discharge tube and a second discharge tube. The first discharge tube, the primary coils of the balance transformers, and the second discharge tube are connected in series across opposite polarity AC voltages outputted from the secondary coils of the inverter transformers. The secondary coils of the balance transformers are connected in series to form the loop.

Respective primary coils of the balance transformers are connected in series between ground and corresponding terminals of each of the discharge tubes that are not connected to the inverter transformers.

The inverter circuit further includes a comparator to compare the voltage at the voltage detection node with a predetermined reference voltage. The comparator generates a control voltage at either a low level or a high level when the voltage of the voltage detection node is higher than the reference voltage.

The inverter circuit compares the voltage of the voltage detection node with the reference voltage and adjusts a current supplied to the discharge tubes based on the comparison, wherein the adjustment includes cutting off a voltage supplied to the discharge tubes as a function of the comparison.

In another aspect of the present invention, a backlight assembly includes a plurality of discharge tubes, a plurality of inverter transformers supplying AC voltage to the plurality of discharge tubes, and a plurality of respective balance transformers having primary coils inserted in series between corresponding reference terminals of the secondary coils of the inverter transformers and ground. The inverter transformers are arranged such that the AC voltage at a first terminal of each secondary coil has an opposite polarity with respect to the AC voltage at a second terminal of each secondary coil. The secondary coils of the balance transformers are connected in series to form a loop. One circuit node of the loop is grounded and a voltage detection node is located on the loop. At least one secondary coil of the secondary coils of the balance transformers is interposed between the grounded node of the loop and the voltage detection node.

The discharge tubes may be cold cathode fluorescent lamps (CCFLs).

The voltage detection node is a circuit node on the loop where half of the secondary coils of the balance transformers are interposed between the voltage detection node and the grounded node.

Each of the inverter transformers may have two primary coils and two secondary coils, wherein a first secondary coil of the two secondary coils is arranged to have an AC voltage of opposite polarity with respect to a second secondary coil of the two secondary coils.

Each of the inverter transformers may have a single primary coil and two secondary coils, wherein a first secondary coil of the two secondary coils is arranged to have an AC voltage of opposite polarity with respect to a second secondary coil of the two secondary coils.

The discharge tubes include a first discharge tube and a second discharge tube. The first discharge tube, the primary coils of the balance transformers, and the second discharge tube are connected in series across opposite polarity AC voltages outputted from the secondary coils of the inverter transformers. The secondary coils of the balance transformers are connected in series to form the loop.

The primary coils of respective balance transformers are connected in series between ground and corresponding terminals of each discharge tube that are not connected to any inverter transformer.

The backlight assembly further includes a comparator to compare the voltage of the voltage detection node with a predetermined reference voltage. The comparator generates a control voltage at either a low level or a high level when the voltage of the voltage detection node is higher than the reference voltage.

The backlight assembly compares the voltage of the voltage detection node with the reference voltage, adjusts a current supplied to the discharge tubes based on the comparison, and may cut off a voltage supplied to the discharge tubes based on the comparison.

Pursuant to another illustrative embodiment of the present invention, a liquid crystal display includes a liquid crystal panel that displays an image and an inverter circuit. The liquid crystal panel includes a plurality of gate lines, a plurality of data lines approximately orthogonal to the gate lines, a plurality of switching elements connected to the gate lines and the data lines, and a liquid crystal element connected to the switching elements. The inverter circuit includes a plurality of inverter transformers that supplies AC voltages to a plurality of discharge tubes, and a plurality of balance transformers having primary coils inserted in series between a reference terminal of each secondary coil of the inverter transformers and a ground. The inverter transformers are arranged such that a first terminal of each secondary coil has an AC voltages of opposite polarity with respect to a second terminal of each secondary coil. The secondary coils of the balance transformers are connected in series to form a loop. One node of the loop is grounded and a voltage detection node is located on the loop. At least one secondary coil of the secondary coils of the balance transformers is interposed between the grounded node of the loop and the voltage detection node.

Liquid crystal displays as described herein may be used for liquid crystal monitors.

Liquid crystal displays as described herein may be used in liquid crystal television sets.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments illustrated hereinafter, and the embodiments herein are rather introduced to provide an easy and complete understanding of the scope and spirit of the present invention.

FIG. 6is a circuit diagram of an inverter circuit or backlight assembly (hereinafter, referred to as an inverter circuit) according to an embodiment of the present invention.FIG. 7is a circuit diagram of an inverter circuit1000that is one illustrative unit among a plurality of inverter circuits illustrated inFIG. 6.FIG. 11is a block diagram of an exemplary LCD including the inverter circuit.FIG. 12is a block diagram of an exemplary inverter90and backlight assembly30. In the inverter circuit1000ofFIG. 7, the number N2of turns in the secondary coil of the inverter transformer901is set to N1×V2/V1(N1indicates the number of turns in the primary coil of the inverter transformer901) so as to obtain a high AC voltage V2that drives a CCFL by applying AC voltages V194generated from the inverter90ofFIGS. 11 and 12to the primary coil of the inverter transformer901.

The secondary coil of the inverter transformer901is provided to output AC high voltages95and96having a phase differential therebetween of 180 degrees.

A first CCFL301, a primary coil of a balance transformer401, and a second CCFL302are connected in series across the AC high voltage95and the AC high voltage96. Next, operation of balance transformers400inserted between two CCFLs in series will be described. The balance transformers401to410are arranged such that their primary coils have opposite polarities with respect to their secondary coils. In each of respective balance transformers401to410, when a current flows through two CCFLs disposed at the primary coil of the balance transformer, a current flows through the primary coil of a corresponding balance transformer connected in series with the two CCFLs. This causes a current to flow through the secondary coils of the balance transformers401to410. Because the secondary coils of the balance transformers401to410are connected in series with each other to form a loop, a current flowing through the loop of the secondary coils forces a current to flow through the primary coils of the respective balance transformers401to410, so that the currents flowing through the respective CCFLs are controlled in the same manner.

In such a structure, one circuit node of the secondary coil loop of the balance transformers401to410is grounded, and the voltage detection node501is located on the loop. The secondary coil of at least one balance transformer is interposed between the voltage detection node501and the grounded node. A voltage sufficient for the balance transformers401to410to maintain balance of the CCFLs301to310is generated from the voltage detection node501. A suitable voltage detection node501may be a circuit node on the loop where the number of the secondary coils of the balance transformers401to410is half the number of coils from the grounded node.

Next, operation of a balance transformer group600inserted between the secondary coil of the inverter transformer901and the ground will be described. The primary coil of the balance transformer601is arranged to have an opposite polarity with respect to the secondary coil of the balance transformer601, and the primary coil of the balance transformer602is arranged to have substantially the same polarity with respect to the secondary coil of the balance transformer602. As in the case of the balance transformer group400, a current flowing through the secondary coils of two balance transformers601and602of the balance transformer group600forms a loop. In the balance transformers601and602, when a current flows through the inverter transformer901connected to the primary coils of the balance transformers601and602, a current also flows through the secondary coils of the balance transformers601and602. Since the secondary coils of the two balance transformers601and602are connected in series to form the loop, a current flowing through the secondary coil of one balance transformer forces a current to flow through the primary coil of the other balance transformer. Consequently, the currents flowing through the secondary coils of the two inverter transformers having opposite phases are controlled such that these currents are flowing in the same direction.

FIG. 6is a circuit diagram of an illustrative arrangement of a plurality of inverter circuits1000set forth inFIG. 7. Referring toFIG. 6, one node of the loop formed by the secondary coils of the balance transformers601to610is grounded, and a voltage detection node502is also located on the loop. The secondary coil of at least one balance transformer of the balance transformers610to610is interposed between the grounded node and the voltage detection node502. A voltage sufficient for the balance transformer group600to maintain the balance of the CCFLs is generated from the voltage detection node502. A suitable voltage detection node501is defined as a circuit node of the loop where the number of secondary coils of the balance transformers601to610from this circuit node to the grounded point is half the total number of secondary coils of the balance transformers601to610.

According to the present configuration in which the balance transformer group600is inserted between the secondary coil of the inverter transformer901and ground, it is possible to detect an abnormal high voltage discharge occurring between a line disposed between the inverter transformer901and the CCFL300and another line, while it is virtually impossible to detect such an abnormal high voltage discharge at the voltage detection node501of the balance transformer group400.

FIG. 8is a circuit diagram of an inverter circuit according to another illustrative embodiment of the present invention. Unlike the inverter circuit of FIG.7, an inverter transformer902has a single primary coil and two secondary coils. Such an inverter transformer902can be used to obtain almost the same effect as the inverter circuit ofFIG. 7.

FIG. 9is a circuit diagram of an inverter circuit according to another illustrative embodiment of the present invention. Unlike the inverter circuit ofFIG. 7, the terminals of the CCFLs301to310that are not connected to the inverter transformer901are grounded, with the primary coils of the balance transformers401to410being interposed. Also, when the AC voltage95has a reference phase, the other terminal of a plurality of parallel CCFLs driven by the AC voltage95of the reference phase and the other terminals of a plurality of parallel CCFLs driven by the AC voltage96of an opposite phase to the reference phase are grounded without being connected to one another. Further, a radiation noise caused by undesired emission of spurious radio frequency energy can be reduced by alternately arranging the CCFLs301,303,305to309turned on by the AC voltage95of the reference phase and the CCFLs302,304,306and310turned on by the AC voltage96having a phase opposite to the reference phase. Moreover, the structure of the balance transformer group400is different from that of the balance transformer group400illustrated inFIG. 7. The primary coils and the secondary coils of the balance transformers401,403,405and409are arranged to have opposite polarities, and the primary coils and the secondary coils of the balance transformers402,404,406and410are arranged to have the same polarities. As described above, the primary coils of the balance transformers401to410are inserted between a corresponding other terminal of a corresponding CCFL (this other terminal is the terminal which is not connected to the inverter transformer901) and ground. The secondary coils of the balance transformers401to410are connected in series with each other to form the loop. One node of the loop is grounded, and the voltage detection node501is located on the loop. The secondary coil of at least one balance transformer is interposed between the grounded node and the voltage detection node501. A voltage sufficient for the balance transformer group400to maintain the balance of the CCFLs301to310is generated from the voltage detection contact point501. A suitable voltage detection contact point501may be defined as a circuit node of the loop where the number of the secondary coils of the balance transformers401to410from this circuit node to the grounded point is half the total number of secondary coils of the balance transformers401to410.

Next, a device using the voltage detected at the voltage detection node501or502of the inverter circuit will be described.

FIG. 10is a circuit diagram of a voltage comparator comparing a reference voltage with a voltage detected at the voltage detection node501or502.

Referring toFIG. 10, the voltage comparator40is illustratively implemented using a conventional comparator circuit. The voltage detected at the voltage detection node501maintains a somewhat constant level in a normal state, but exhibits a higher level in an abnormal state, for example, when a high-voltage abnormal discharge, such as a corona discharge, an arc discharge, etc., occurs between lines. Using this characteristic, it is possible to configure a system that can immediately avoid the high-voltage abnormal discharge by controlling the inverter. In the comparator circuit ofFIG. 10, because a voltage detected at the voltage detection node501or502is an AC voltage, a rectifier42converts the detected voltage into a DC voltage, and a comparator41compares the DC voltage with a reference voltage and outputs a control voltage43. In the comparator circuit ofFIG. 10, when the detected voltage exceeds the reference voltage, the control voltage43output by the comparator41is, for example, a low level voltage. However, the control voltage43output by the comparator when the detected voltage exceeds the reference voltage may be either a low level voltage or a high level voltage according to the configuration of the comparator and according to the requirements of specific system applications. Also, comparing the detected voltage with the reference voltage is not limited to the specific embodiment shown inFIG. 10. For example, the detected voltage and the reference voltage may be compared by sampling a peak voltage without rectifying the detected voltage.

FIG. 11is a block diagram of a lamp driver of an LCD having an inverter circuit according to an illustrative embodiment of the present invention.

Referring toFIG. 11, the LCD includes an AC/DC power supply10and an LCD module20.

The AC/DC power supply10includes an AC/DC rectifier12and a DC/DC converter13. The AC/DC power supply10converts an external AC voltage in an approximate range of about 100 V to 240 V into a DC voltage, and outputs the DC voltage to the LCD module20.

The LCD module20includes a DC/DC converter21, a common electrode voltage (Vcom) generator22, a gamma voltage (y) generator23, an LCD panel24, an inverter circuit90, and a backlight assembly30. The LCD module20receives the DC voltage from the AC/DC power supply10and displays an image supplied from an external graphics controller (not shown).

The common electrode voltage generator22generates a common electrode voltage Vcom based on the DC voltage. The level of this DC voltage is shifted by the DC/DC converter21, and the DC/DC converter21supplies the common electrode voltage Vcom to the LCD panel24.

The gamma voltage generator23generates a gamma voltage Vdd based on the level-shifted DC voltage and supplies the gamma voltage to the LCD panel24. Although the common electrode voltage generator22and the gamma voltage generator23are shown as being separated from the LCD panel24inFIG. 11, this is for illustrative purposes as one or both of the common electrode voltage generator22and the gamma voltage generator23may be included in the LCD panel24.

As described above, the LCD includes the AC/DC power supply10and the LC module20. When an abnormal state or condition such as an abnormal discharge occurs, the output voltage level of the AC/DC power supply10is controlled using the control voltage43(either a low level or a high level voltage as discussed previously) from the voltage comparator ofFIG. 10detected at the voltage detection node501or502of the inverter circuit ofFIGS. 6 to 9. For example, the inverter circuit90is illustratively controlled by controlling a duty ratio of PWM oscillation, and the AC voltage supplied to the backlight assembly30is adjusted, thereby preventing a reduction in the lifetime of the CCFLs. Moreover, the balance transformer groups400and600may be embedded into the inverter circuit90or the backlight assembly30or both.

FIG. 12is a block diagram of an inverter circuit90and a backlight assembly30in an LCD according to an illustrative embodiment of the present invention.

Referring toFIG. 12, the inverter circuit90and the backlight assembly30include an oscillator91, a controller92connected to the oscillator91, a switch93connected to the controller92, an inverter transformer901A/B connected between the switch93and the CCFL unit300, a balance transformer400and a voltage comparator40connected in series between the CCFL unit300and the controller92, and a balance transformer600and a voltage comparator40connected in series between the inverter transformer901A/B and the controller92.

When an abnormal state or condition, such as a corona discharge, an arc discharge, etc., occurs in the line between the secondary coil of the inverter transformer901A/B and the CCFLs of the CCFL unit300, or when an abnormal state such as an open circuit or a short circuit occurs due to a malfunction of one or more of the CCFLs of the CCFL unit300, the controller92adjusts the driving frequency and driving voltage of the backlight assembly30according to the low level voltage or the high level voltage from the voltage comparator40that detects the voltage at the voltage detection nodes501and502. For example, when the PWM oscillation is used to control the inverter circuit90, the driving frequency and the driving voltage of the backlight assembly30are adjusted by controlling a pulse duty ratio. In this manner, when the abnormal state or condition such as a corona discharge occurs in the line disposed between the secondary coil of the inverter transformer901A/B and the CCFLs and another line, or when an abnormal state such as an open circuit or short circuit due to the damage of the CCFLs occurs, the foregoing abnormal states can be immediately avoided.

In addition, the present invention can improve the performance of the LCD by applying the inverter circuit to the LCD.

FIG. 13is an exploded perspective view of an LCD according to an illustrative embodiment of the present invention. Specifically,FIG. 13illustrates a mechanical structure of the LCD, and is not intended to show the electrical circuit configuration for the LCD.

Referring toFIG. 13, the LCD100includes a backlight assembly110, a display unit170, and a case180.

The display unit170includes a liquid crystal panel171that displays an image, and a data printed circuit172and a gate printed circuit173that both generate driving signals to drive the liquid crystal panel171. The data printed circuit172and the gate printed circuit173are electrically connected to the liquid crystal panel171, illustratively through a data tape carrier package (TCP) and a gate TCP175, respectively.

The liquid crystal panel171includes a thin film transistor (“TFT”) substrate176, a color filter substrate177disposed to face the TFT substrate176, and a liquid crystal layer178interposed between the TFT substrate176and the color filter substrate177.

The TFT substrate176is a transparent glass substrate in which switching TFTs (not shown) are arranged in a matrix. Source terminals and gate terminals of the TFTs are connected to data lines and gate lines, respectively. Also, a common electrode (not shown) formed of a transparent conductive material is connected to drain terminals of the TFTs.

For example, the color filter substrate177may include red, green, and blue (“RGB”) pixels (not shown) that are formed using a thin film process. The color filter substrate177includes the common electrode.

The case180has a bottom plate181and sidewalls182extending from edges of the bottom plate181to provide a receiving space. The case180receives the backlight assembly110and the liquid crystal panel171.

The bottom plate181has a size sufficient to receive the backlight assembly110. It is acceptable if similar or identical shapes are used for the bottom plate181and the backlight assembly110. In this embodiment, the bottom plate181and the backlight assembly110have a rectangular plate-like shape. The sidewalls182are extended from the edges of the bottom plate181in a substantially vertical direction so that the backlight assembly110cannot be readily released from the case180.

In this embodiment, the LCD100further includes an inverter circuit160and a top chassis190.

The inverter circuit160is disposed outside the case180to generate a discharge voltage to drive the backlight assembly110. The discharge voltage generated from the inverter circuit160is applied to the backlight assembly110through a first voltage line163and a second voltage line164. The first voltage line163and the second voltage line164are electrically connected to a first electrode140aand a second electrode140bformed on either or both sides of the backlight assembly110. The first voltage line163and the second voltage line164may be directly connected to the first electrode140aand the second electrode line140b. Also, the first voltage line163and the second voltage line164may be connected to the first electrode140aand the second electrode line140bthrough an additional connecting member (not shown). Moreover, the balance transformer groups400and600may be built in the inverter circuit160or the backlight assembly110.

The top chassis190is coupled to the case180while surrounding the edges of the liquid crystal panel171. The top chassis190can prevent the liquid crystal panel171from being damaged due to externally applied mechanical impacts. Also, the top chassis190can prevent the liquid crystal panel from being released from the case180.

The liquid crystal panel100may further include at least one optical sheet195so as to improve characteristics of light emitted from the backlight assembly110. The optical sheet195may optionally include at least one of a diffusion sheet to diffuse the light, or a prism sheet to condense the light.

According to the present invention, when an abnormal state or condition such as a corona discharge occurs in the line between the secondary coil of the inverter transformer and the discharge tube, the current flows through the primary coil of the balance transformer serially connected to the inverter transformer. The current then flows through the secondary coil of the balance transformer, thereby changing an electrical load applied to the reference phase or the reverse phase attributable to the serial insertion of the balance circuit between the secondary coil of the inverter transformer and ground. Since the secondary coil is connected in series to the secondary coil of another balance transformer, the current flowing through the secondary coil forces the current to flow through the primary coil of each balance transformer. Consequently, the currents of the respective inverter transformers are controlled to flow in the same direction. A voltage necessary to maintain the balance of the balance transformer is generated by detecting the voltage at the contact node (detection node) located on the loop of the secondary coils of the balance transformers in a state wherein one node of the secondary coil is grounded. Using this characteristic, it is possible to detect an abnormal state of high voltage discharge such as a corona discharge between the lines disposed between the secondary coil of the inverter transformer and the CCFL and another line.

Also, it is possible to detect an abnormal state or condition such as an open circuit or a short circuit caused by current concentration on a specific CCFL and the resulting malfunction of the CCFLs.

In addition, abnormal discharges, such as a corona discharge caused when a failure occurs between the line disposed between the secondary coil of the inverter transformer and the CCFL and another line, and abnormal states such as an open circuit or a short circuit caused by current concentration on a specific CCFL and consequent damage to the CCFLs may be detected in the form of voltages using the inverter circuits and comparing these detected voltages with the reference voltage. When the detected voltage exceeds the reference voltage, the comparator outputs the control signal (the control signal may be in the form of either a high level voltage or low level voltage). Therefore, an abnormal state or condition can be immediately or promptly avoided by stopping the driving of the inverter or controlling the driving voltage.

It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention. Thus, it is intended that the present invention cover such modifications and variations, the invention being characterized with reference to the scope of the appended claims and equivalents thereof.