JP2007005007A - Inverter circuit, backlight unit, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inverter circuit that detects a fracture or breakage of each of a plurality of fluorescent tubes with reliability in a backlight that employs a parallel-connection driving system, without impairing merits of the backlight such as easiness of assembly and easiness of reduction in the number of components. <P>SOLUTION: The inverter circuit 28 comprises: a switching circuit 281 for converting inputted DC power to AC power; a booster circuit 282 for outputting an AC voltage signal for driving each of fluorescent tubes 21 by means of the AC power supplied from the switching circuit 281; a lamp error detection circuit 283 for detecting errors such as fractures or breakage of the fluorescent tubes 21; a lamp error signal receiving section 284 for receiving an error signal detected by the lamp error detection circuit 283; and a microprocessor 285 for controlling the inverter circuit 28. The lamp error detection circuit 283 is provided between the booster circuit 282 and each of the fluorescent tubes 21. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inverter circuit for driving a plurality of fluorescent tubes connected in parallel, a backlight unit including the inverter circuit and a plurality of fluorescent tubes, and a liquid crystal display device using the backlight unit.

  In a backlight unit used in a liquid crystal display device, for example, when an appropriate power is supplied to a plurality of fluorescent tubes connected in parallel with a single transformer, the transformer has a high frequency (several tens of kHz). And a high-voltage AC voltage of about several thousand kV is required, and the output current is required to flow a current value substantially proportional to the number of connected fluorescent tubes. In response to such a demand, for example, Patent Document 1 discloses a backlight assembly that drives a fluorescent tube unit in which a plurality of fluorescent tubes are connected in parallel with one transformer.

  FIG. 6 is a circuit diagram showing a configuration of a lamp driving device of a conventional backlight assembly disclosed in Patent Document 1. The lamp driving device includes a power transistor Q11, a diode D11, an inverter 120, a digital-analog converter ( DAC) 130, pulse width modulation control unit (PWM control unit) 140, and MOSFET drive unit 150, converting DC power provided from the outside into AC power and connecting the external electrode fluorescent lamps 110 connected in parallel. Is configured to provide.

  First, the DAC 130 converts a dimming signal (DIMM signal) provided from the outside into an analog signal, and outputs the DIMM signal 131 converted into the analog signal to the PWM control unit 140. The DIMM signal is a signal input by a user operation or the like to adjust the brightness of the lamp, and is a digital signal indicating a duty ratio. The PWM control unit 140 includes an on / off controller 141, is activated / stopped by an on / off signal (ON / OFF signal) provided from the outside, and supplies each fluorescent lamp in response to the DIMM signal 131. A switching signal 142 for adjusting the level of the AC power is provided to the MOSFET driving unit 150.

  The MOSFET drive unit 150 amplifies the switching signal 142 provided from the PWM control unit 140, and provides the amplified level adjustment signal 151 to the power transistor Q11. In general, since the switching signal 142 provided from the PWM control unit 140 is a low level signal, a MOSFET driving unit 150 is provided to amplify the low level signal and input it to the power transistor Q11. The power transistor Q11 controls the output of the input DC voltage (Vin) in response to the level adjustment signal 151.

  The inverter 120 includes an inductor L, a transformer (transformer) 122, a resonant capacitor C11, resistors R11 and R12, and transistors Q12 and Q13. One end of the inverter 120 is connected to the drain end of the power transistor Q11 and is output from the power transistor Q11. The pulsed power is converted into AC power, and the converted AC power is provided to each of the external electrode fluorescent lamps 110. The transformer 122 includes primary windings T11 and T12 that constitute the primary side and a secondary winding T13 that constitutes the secondary side. The AC power input to the primary winding T11 through the inductor L is transmitted to the secondary winding T13 by the electromagnetic induction action and converted to a high voltage, and the converted high voltage is applied to the external electrode fluorescent lamp 110. Is done.

  As described in Patent Document 1, a method of driving a fluorescent tube by supplying an appropriate electric power to a plurality of fluorescent tubes such as an external electrode fluorescent lamp (EEFL) connected in parallel with one transformer, for example (hereinafter referred to as a fluorescent tube) The parallel connection drive method) is a very effective method for driving a so-called direct type backlight in which fluorescent tubes are arranged and driven in parallel, considering the ease of assembly of the backlight. . In particular, a backlight using an external electrode type fluorescent tube is expected to have a merit that it tends to be freed from troublesomeness such as soldering of the electrode of the fluorescent tube.

  By the way, also in this parallel connection drive system, a lamp error detection circuit for confirming the right or wrong state of each fluorescent tube is indispensable in terms of reliability, as in the case of a backlight using a fluorescent tube so far. For example, a mounting method such as that disclosed in Patent Document 2 can be employed.

That is, in the configuration example described in Patent Document 2, a voltage dividing circuit such as a resistor is provided in series with the electrode terminal on the ground side (GND) of each fluorescent tube, and the divided AC signal is DC-converted by a rectifier circuit or the like. By converting this voltage signal into a voltage signal and reading this DC voltage signal, it is detected whether the fluorescent tube is damaged or broken.
JP 2004-31338 A JP 2004-281361 A

  However, in the conventional configuration including Patent Document 2, it is possible to surely check the breakage or disconnection of each fluorescent tube. (1) A dedicated substrate for the lamp protection circuit on the GND side of the fluorescent tube As well as (2) lead wires corresponding to the number of fluorescent tubes arranged are required.

  Regarding the above (1), in particular, in a direct backlight, it is common that one electrode is arranged as a GND side where the other electrode is connected to the high voltage side and the other is grounded. In order to detect the state, an error detection circuit is arranged on the GND side of the lamp and a rectified DC voltage signal is transmitted to the inverter circuit arranged on the high voltage side via a lead wire. However, in such a configuration, at least one lamp error circuit board is required separately from the inverter circuit board. For this reason, in view of the circuit configuration, the number of parts increases, and there is a problem that efficiency in the production process may be reduced.

  In order to avoid the configuration (1), the lamp protection circuit may be designed to be mounted on the same substrate as the inverter circuit. When such a design is performed, it is necessary to route the lead wires by the number of the fluorescent tubes as connection means from the ground-side electrode terminal of each fluorescent tube to the inverter circuit on which the lamp protection circuit is mounted. For example, if 20 fluorescent tubes are arranged, it is necessary to prepare 20 lead wires in different lengths. However, with this configuration, even in the parallel connection method in which the assembly of the folded fluorescent tube is simplified, a plurality of lead wires are eventually required, so that the merit of the backlight as a whole is not enjoyed so much. The problem remains.

  Therefore, with respect to the fluorescent tube of the parallel connection driving method, which is originally a technique for simplifying the mounting of the fluorescent tube, each fluorescent tube is surely damaged or disconnected without impairing its ease of assembly. In order to be able to detect this, another means of mounting this lamp error circuit is required.

  The present invention has been made in view of the above circumstances, and in a backlight such as a direct type that employs a parallel connection drive method, the advantages of ease of assembly and ease of reducing the number of parts are impaired. Inverter circuit, backlight unit including the inverter circuit and the plurality of fluorescent tubes, and liquid crystal using the backlight unit An object is to provide a display device.

  In order to solve the above problems, a first technical means of the present invention is an inverter circuit for driving a plurality of fluorescent tubes connected in parallel to one booster circuit, each of the plurality of fluorescent tubes On the other hand, a lamp error detecting means for detecting an error is provided, and each lamp error detecting means is disposed between each fluorescent tube and a winding that constitutes the booster circuit and outputs an AC signal. It is what.

  According to a second technical means, in the first technical means, the lamp error detecting means emits a lamp error signal when detecting an error in the fluorescent tube, and the inverter circuit receives the lamp error signal. A signal receiving means is further provided.

  According to a third technical means, in the second technical means, the lamp error signal receiving means is arranged on a low pressure side of the booster circuit.

  According to a fourth technical means, in the second or third technical means, the lamp error signal emitted from the lamp error detecting means is transmitted as optical information to the lamp error signal receiving means. circuit.

  A fifth technical means is a direct type backlight unit including the inverter circuit according to any one of the first to fourth technical means and a plurality of fluorescent tubes connected to the inverter circuit.

  A sixth technical means is a liquid crystal display device comprising the backlight unit in the fifth technical means and a liquid crystal panel illuminated by the backlight unit.

  According to the present invention, in a backlight such as a direct type that employs a parallel connection drive system, it is ensured that each of the plurality of fluorescent tubes can be reliably manufactured without losing the advantages such as ease of assembly and reduction in the number of parts. It becomes possible to detect breakage and disconnection.

  FIG. 1 is a cross-sectional view showing a configuration example of a liquid crystal display module using a backlight unit according to the present invention. The liquid crystal display module includes a liquid crystal panel 1 and a backlight unit 2 as main components.

  The liquid crystal panel 1 supplies the video information processed by the video signal as a predetermined gradation voltage for each pixel in accordance with the clock signal of the liquid crystal panel 1, and performs image display processing by sequential scanning on the screen to obtain a predetermined video. Display information. Further, the backlight unit 2 emits light from the opposite side of the display surface of the liquid crystal panel 1. Examples of the light source of the backlight unit 2 include a cold cathode fluorescent lamp (CCFL) and an external (extra-tube) electrode fluorescent lamp (EEFL: External Electrode Fluorescent) shown in FIGS. 4 and 5 described later. Lamp) or the like is used. The backlight unit 2 of the present invention is configured to drive a fluorescent tube unit in which a plurality of fluorescent tubes are connected in parallel with a single transformer, and is preferably a direct type.

  The backlight unit 2 includes a plurality of fluorescent tubes 21 for supplying light to the liquid crystal panel 1 and a reflection sheet or a reflection plate (hereinafter referred to as “effectively irradiating light emitted from each fluorescent tube 21 to the liquid crystal panel 1 side”). , Which is represented by a reflection sheet) 22 and a housing 23 for storing them. An inverter circuit board 28 (hereinafter simply referred to as an inverter circuit 28) for mounting the inverter circuit according to the present invention is disposed on the back surface of the housing 23 (that is, the surface opposite to the installation surface of the fluorescent tube 21). The The inverter circuit 28 is provided with various components such as an inverter transformer as a booster circuit for supplying power to each fluorescent tube 21. As this inverter transformer, for example, there is a winding type that transforms based on the ratio of the number of turns of each coil by the electromagnetic induction effect of two coils.

  As the inverter circuit 28, for example, a separately excited inverter can be applied. In general, a separately excited inverter is provided with an oscillation circuit on the primary side and converts it into an alternating current having the same frequency as the drive frequency of the oscillation circuit. This separately excited inverter is used for driving a winding type inverter transformer as described above. As a result, it is possible to realize a small-sized and highly efficient inverter that exceeds the piezoelectric type inverter while being of the winding type.

  The liquid crystal panel 1 is composed of two glass substrates with polarizing plates having a crossed Nicols relationship with a liquid crystal layer interposed therebetween, and the liquid crystal panel 1 is fixedly held by two frames 3 and 4 in the thickness direction. These frames 3 and 4 have a structure bent in a substantially L shape so as to cover the entire backlight unit 2.

  The fluorescent tube 21 constituting the backlight unit 2 may have, for example, a U-shape or a U-shape in addition to the linear shape, and the linear portions of all the fluorescent tubes 21 are arranged substantially parallel to each other. . Moreover, the shape of the reflection sheet 22 may be, for example, a shape having a concave-convex section as shown in FIG.

  Furthermore, various optical members may be provided according to the optical performance required for the liquid crystal display device. For example, as shown in FIG. 1, a diffusion plate 24 for reducing the luminance difference between the arrangement position of the fluorescent tube 21 and other positions is required for a light source composed of a plurality of fluorescent tubes 21. A diffusion sheet 25 for supplying optimal light distribution characteristics to a usage pattern, a prism sheet 26 for collecting light in a specific direction, and selectively transmitting / reflecting the polarization of light in a specific direction. The reflective polarizing plate 27 is used to improve the degree of polarization of light incident on the liquid crystal panel 1. These various optical members (diffusion plate 24, diffusion sheet 25, prism sheet 26, reflection polarizing plate 27, etc.) are formed in a plate shape or a sheet shape, and are arranged between the fluorescent tube 21 and the liquid crystal panel 1. Yes.

  The fluorescent tube 21 excites mercury in the fluorescent tube 21 by a high-voltage AC voltage supplied to an electrode from an inverter circuit 28 disposed substantially parallel to the back surface of the backlight unit 2, and near the ultraviolet light by its energy level. The ultraviolet light emits light, and phosphors of three colors of red, blue, and green in the fluorescent tube 21 emit light, and white light is supplied by mixing these emitted colors. The white light thus emitted has its light distribution characteristics controlled by the various optical members described above, and can effectively supply light to the liquid crystal panel 1. By supplying light from the backlight unit 2, the brightness of each pixel is controlled by the light transmittance according to a predetermined gradation voltage in each pixel of the liquid crystal panel 1, so that video information can be displayed on the screen. It becomes.

  Hereinafter, when a fluorescent tube unit in which a plurality of fluorescent tubes are connected in parallel is driven by a single transformer, which is a main feature of the present invention, an error such as disconnection or breakage of each fluorescent tube is detected, and at least the fluorescent tubes are A configuration example of an inverter circuit for enabling the power supply to the high voltage side of the transformer to be stopped when one is not normal will be described.

  FIG. 2 is a block diagram showing a configuration example of an inverter circuit according to the present invention, and shows a configuration example of an inverter circuit to be incorporated in the liquid crystal display module of FIG.

  The inverter circuit 28 includes a switching circuit 281 for converting the DC power input to the inverter circuit 28 into AC power, and an AC voltage signal for driving each fluorescent tube 21 by the AC power supplied from the switching circuit 281. , A phase adjustment circuit 288 for adjusting the phase between the AC voltage signal output from the voltage boosting circuit 282 and the AC voltage signal applied to the fluorescent tube 21, and the fluorescent tube 21 Error detection circuit 283 for detecting an error such as breakage or disconnection of the lamp, a lamp error signal receiving unit 284 for receiving an error signal detected by the lamp error detection circuit 283, a microcomputer 285 for controlling the inverter circuit 28, and a switching circuit In order to perform power conversion at 281, a pair of first control signals (hereinafter referred to as DRV) , DRV2) and a pulse amplifying circuit 287 for generating a second control signal (hereinafter, AMP1, AMP2) amplified by a predetermined amplification factor corresponding to each of the pair of DRV1, DRV2. And.

  Here, the booster circuit 282 generates a high-voltage AC signal of about several kV boosted by the movement of the current flowing through the primary winding of the transformer and the turn ratio of the primary and secondary windings, thereby generating a fluorescent tube. Gives a discharging effect. The switching circuit 281 supplies the voltage to the booster circuit 282 by controlling the movement of the current flowing through the primary winding of the transformer in accordance with the pair of amplification control signals (AMP1, AMP2) subjected to the current amplification action by the pulse amplification circuit 287. To control AC power. As the switching circuit 281, even if it is a half-bridge type switching circuit or a so-called full-bridge type switching circuit composed of four switching elements and four control signals, the same effect can be obtained.

  The phase adjustment circuit 288 is configured to perform so-called feedback control for adjusting the phase of each AC voltage signal output from the booster circuit 282 and supplied to each fluorescent tube 21. Thereby, it adjusts so that the phase difference of each AC voltage signal supplied to each fluorescent tube 21 may become small.

  Here, regarding the effective value of power, when the phase difference is zero and the power is 1 in the direction of the real part, the effective power decreases when the phase difference occurs, and instantaneously effective when the phase difference is 90 °. The power is zero. The reason why this phase difference occurs is that the transmission form of the power wave has a characteristic that it varies depending on the component (element). For example, when a peak of a waveform generated at the same time is input to the coil and the resistor at the same time, the phase of the coil is delayed at the output. On the other hand, when it is input to the capacitor and the resistor, the phase of the capacitor advances. In an actual circuit, both the coil and the capacitor are affected, and the output waveform is obtained by superimposing all the phase advance and delay. In this example, the phase adjustment circuit 288 performs feedback control on the AC voltage signal of each fluorescent tube 21 so as to reduce the phase difference that causes the effective power to decrease.

  The plurality of fluorescent tubes 21 are connected in parallel, one end of each fluorescent tube 21 is connected via a booster circuit 282, a lamp error detection circuit 283, and a phase adjustment circuit 288, and the other end is grounded. Note that the number of the fluorescent tubes 21 is not limited to four, and may be appropriately determined according to the screen size of the liquid crystal display device.

  In the present invention, each lamp error detection circuit 283 is provided between the booster circuit 282 and each fluorescent tube 21. As illustrated in FIG. 2, the lamp error detection circuit 283 is preferably provided between the booster circuit 282 and each phase adjustment circuit 288. The lamp error detection circuit 283 and the lamp error signal receiving unit 284 function as a lamp protection circuit.

  As described above, the inverter circuit 28 according to the present invention is a circuit for driving a plurality of fluorescent tubes 21 connected in parallel to one booster circuit 282. A lamp error detection circuit 283 is provided. Each lamp error detection circuit 283 is disposed between each fluorescent tube 21 and the winding that constitutes the booster circuit 282 and outputs an AC signal. That is, in the present invention, a single lamp error detection circuit 283 is preferably provided in combination with the booster circuit 282 so as to arrange the lamp error detection circuit 283 between each fluorescent tube 21 and the winding that constitutes the booster circuit 282 and outputs an AC signal. It consists of a substrate.

  With the configuration as described above, the ground line can be fed back with a single lead wire for mounting. Therefore, in a backlight such as a direct type that employs a parallel connection drive system, its ease of assembly and the number of parts There is no loss of benefits such as ease of reduction. In addition, the present invention detects an error such as disconnection or breakage of each fluorescent tube 21 and receives an error signal detected by the lamp error detection circuit 283 when at least one of the fluorescent tubes is not normal. By receiving the signal at the unit 284 and controlling the inverter circuit 28 with the microcomputer 285, the power supply to the high voltage side of the transformer can be stopped.

  FIG. 3 is a circuit diagram showing a configuration example of a main part of the inverter circuit according to the present invention, and shows a configuration example of the lamp error detection circuit 283 and the lamp error signal receiving unit 284 of FIG.

  The lamp error detection circuit 283 and the lamp error signal receiving unit 284 in FIG. 2 preferably convert an electrical signal from the fluorescent tube 21 (from the phase adjustment circuit 288 in the example of FIG. 2) via an optical signal (optical information). It is good to comprise by the photocoupler which transmits by transmitting, ie, transmitting as optical information. A photocoupler is a light-emitting element such as a compound semiconductor light-emitting diode and a light-receiving element such as a silicon photodiode, phototransistor, optical thyristor, or OEIC (optoelectronic integrated circuit) sealed in the same package with a transparent insulating layer in between. It is.

  For example, the lamp error detection circuit 283 connected to the first fluorescent tube 21 via the phase adjustment circuit 288 includes a diode D1 that rectifies an electrical signal indicating an error in the first fluorescent tube 21; A light-emitting element of the photocoupler PC1 is provided. The lamp error signal receiver 284 outputs an error detection signal to the microcomputer 285 when the resistor R2, the capacitor C, the transistor Q, and the resistor R1 together with the light receiving element of the photocoupler PC1 exceed a predetermined voltage value. It is configured. The lamp error signal receiving unit 284 forms an AND circuit by connecting the light receiving elements of the photocouplers PC1 to PC4 in series. Therefore, if damage is detected in any one of the fluorescent tubes 21, the microcomputer An error signal can be transmitted to H.285. A configuration in which the detection result is transmitted to the microcomputer 285 for each light receiving element of each of the photocouplers PC1 to PC4 may be employed.

  By using the photocouplers PC1 to PC4, a lamp error signal receiving unit that receives a lamp error signal generated when a lamp error detection circuit disposed on the high voltage side (secondary circuit side) detects breakage of a fluorescent tube, It can be arranged on the low pressure side (primary circuit side) of the booster circuit. In the example of FIG. 3, a photocoupler is used, and the light emitting element and the light receiving element are one to one. However, for example, a configuration in which a plurality of ones are used even when an optical fiber or the like is used can be employed.

  As described above, in the circuit configuration illustrated in FIG. 3, since the lamp error detection circuit is provided on the high voltage side, it is not preferable in terms of product reliability to configure the signal transmission from the high voltage side to the low voltage side. In view of this, the lamp error signal is transmitted by the photocoupler light transmission means. As a result, it is possible to reliably transmit error information of each lamp between the secondary side and the primary side (that is, the high voltage side and the low voltage side) of the inverter transformer without impairing the reliability of the components.

  Here, in order to realize a backlight unit capable of ensuring the high brightness and high efficiency of the liquid crystal display device as well as increasing the size of the liquid crystal panel in recent years, and achieving a long life and light weight, An external electrode fluorescent lamp (EEFL) in which an external electrode is formed on a glass tube has been proposed. This EEFL may be applied to the fluorescent tube 21 of the present invention.

  FIG. 4 is an external view showing a belt-type external electrode fluorescent lamp which is an example of a general external electrode fluorescent lamp (EEFL). In the figure, 29 is a belt-type external electrode fluorescent lamp, and the belt-type external electrode fluorescent lamp 29 is shown in FIG. Are provided with electrodes 292 and 292 'at both ends of the glass tube 291 and electrodes 293 and 293' at the middle. The electrodes 292 and 292 ′ at both ends are driven at a high frequency of several MHz or more. Further, the intermediate electrodes 293 and 293 ′ can be provided particularly when the glass tube 291 is long by high frequency driving.

  FIG. 5 is an external view showing a metal capsule type external electrode fluorescent lamp which is another example of a general external electrode fluorescent lamp (EEFL). In FIG. 5, 30 is a metal capsule type external electrode fluorescent lamp. The capsule-type external electrode fluorescent lamp 30 is provided with metal capsules 302 and 302 ′ at both ends of a glass tube 301. Such a metal capsule external electrode fluorescent lamp 30 is used particularly when the diameter of the glass tube 301 is large.

It is sectional drawing which shows the structural example of the liquid crystal display module using the backlight unit by this invention. It is a block diagram which shows the structural example of the inverter circuit by this invention. It is a circuit diagram which shows the example of a principal part structure of the inverter circuit by this invention. It is an external view which shows the belt-type external electrode fluorescent lamp which is an example of a general external electrode fluorescent lamp (EEFL). It is an external view which shows the metal capsule type | mold external electrode fluorescent lamp which is another example of a general external electrode fluorescent lamp (EEFL). It is a circuit diagram which shows the structure of the lamp drive device of the conventional backlight assembly currently disclosed by patent document 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal panel, 2 ... Backlight unit, 3, 4 ... Frame, 21 ... Fluorescent tube, 22 ... Reflection sheet, 23 ... Housing, 24 ... Diffusing plate, 25 ... Diffusing sheet, 26 ... Prism sheet, 27 ... Reflection Polarizer, 28 ... Inverter circuit, 29 ... Belt-type external electrode fluorescent lamp, 30 ... Metal capsule-type external electrode fluorescent lamp, 110 ... External electrode fluorescent lamp, 120 ... Inverter, 130 ... Digital-analog converter (DAC), DESCRIPTION OF SYMBOLS 140 ... Pulse width modulation control part (PWM control part) 141 ... On / off controller, 150 ... MOSFET drive part, 281 ... Switching circuit, 282 ... Booster circuit, 283 ... Lamp error detection circuit, 284 ... Lamp error signal receiving part 285, microcomputer, 286, pulse oscillation circuit, 287, pulse amplification circuit, 288, phase adjustment circuit, 29 , 301 ... glass tube, 292, 292 ', 293, 293' ... electrode, 302, 302 '... metal capsule.

Claims (6)

  An inverter circuit for driving a plurality of fluorescent tubes connected in parallel to one booster circuit, comprising lamp error detection means for detecting an error for each of the plurality of fluorescent tubes, and detecting each lamp error An inverter circuit characterized in that the means is disposed between each of the fluorescent tubes and a winding that constitutes the booster circuit and outputs an AC signal.   2. The inverter circuit according to claim 1, wherein the lamp error detecting means generates a lamp error signal when detecting an error in the fluorescent tube, and the inverter circuit includes a lamp error signal receiving means for receiving the lamp error signal. An inverter circuit further comprising the inverter circuit.   3. The inverter circuit according to claim 2, wherein the lamp error signal receiving means is disposed on a low voltage side of the booster circuit.   4. The inverter circuit according to claim 2, wherein the lamp error signal emitted from the lamp error detecting means is transmitted to the lamp error signal receiving means as optical information.   A direct type backlight unit comprising the inverter circuit according to any one of claims 1 to 4 and a plurality of fluorescent tubes connected to the inverter circuit.   A liquid crystal display device comprising the backlight unit according to claim 5 and a liquid crystal panel illuminated by the backlight unit.

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