JP2007005006A - Inverter circuit, backlight unit, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent, with reliability, wiring for a high-voltage signal outputted from an inverter transformer to a plurality of fluorescent tubes from being in contact with another high-voltage wiring, and thereby to suppress quality degradation caused by a discharge phenomenon or the like unpredictable by a designer. <P>SOLUTION: An inverter circuit 28 is formed of at least two substrates, i.e., a first substrate 28a and a second substrate 28b. The first substrate 28a is provided with: a booster circuit 282 for driving a plurality of fluorescent tubes; and wiring patterns 288 as many as the plurality of fluorescent tubes, which are provided and arranged for branching a high-voltage signal outputted from the booster circuit 282. The second substrate 28b is provided with at least a part of an extension wiring patterns 290 for connecting two located at both ends out of the wiring patterns 288 disposed on the first substrate 28a, and is disposed nearly perpendicular to a mounting surface 289 of the first substrate 28a. The extension wiring patterns 290 on the second substrate 28b are disposed at a distance L, which is greater than a specific distance, from a side of the second substrate 28b. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inverter circuit for driving a plurality of fluorescent tubes, a backlight unit having 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. 7 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 pulse 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 has primary windings T11 and T12 constituting the primary side and a secondary winding T13 constituting the secondary side. The AC power input to the primary winding T11 via 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.
JP 2004-31338 A

  In the method of driving a plurality of parallel-connected fluorescent tube units by a single transformer as in the invention described in Patent Document 1, the high-voltage AC signal generated by the inverter circuit is connected to the electrodes of the fluorescent tube. In addition, a mounting method using a lead wire is generally performed. At this time, depending on the specifications, for example, in order to average or stabilize the tube currents flowing in the fluorescent tubes, a high voltage wiring may be used to connect the inverter circuit and the fluorescent tube electrode via the lead wire. Must be done on the pattern.

  As described above, in the system in which a plurality of fluorescent tube units connected in parallel with one transformer is used, there arises a problem that the area of the high-voltage wiring pattern is desired to be reduced as much as possible from the safety management of the inverter circuit. In addition, when measures are taken such that various circuits are arranged on the high-voltage wiring pattern and the phase of the fluorescent tube is adjusted, it is necessary to extend the high-voltage wiring pattern depending on the arrangement condition of the backlight including the fluorescent tube. Contact between these configurations and the above-described inverter circuit and the lead wire connecting the fluorescent tube must be prevented as much as possible. However, the designer predicts that the wiring that contacts each other is composed only of flexible lead wires. Contact between the lead wires that cannot be done can occur.

The present invention has been made in view of the above circumstances, and by reliably preventing the high-voltage signal wiring output from the inverter transformer to the plurality of fluorescent tubes from coming into contact with other high-voltage wirings, the designer Providing an inverter circuit capable of suppressing deterioration in quality due to an unpredictable discharge phenomenon, a backlight unit including the inverter circuit, and a liquid crystal display device,
Another object of the present invention is to allow high-voltage signal wiring to be installed without increasing the area of the inverter circuit board that occupies the back surface of the backlight unit including the liquid crystal panel.

  In order to solve the above-mentioned problem, a first technical means of the present invention is an inverter circuit for driving a plurality of fluorescent tubes arranged side by side, wherein the inverter circuit includes at least two of the first substrate and the second substrate. The first substrate has a booster circuit for driving the plurality of fluorescent tubes, and a wiring pattern arranged side by side by the number of the plurality of fluorescent tubes to branch the high-voltage signal output from the booster circuit The second substrate is provided with at least a part of an extended wiring pattern extended from one wiring pattern toward another wiring pattern among the wiring patterns arranged side by side on the first substrate. It is characterized by.

  According to a second technical means, in the first technical means, the extended wiring pattern on the second substrate connects between the wiring patterns at both ends among the wiring patterns arranged side by side on the first substrate. It is a feature.

  A third technical means is the first or second technical means, wherein the first substrate includes a mounting surface including a first region where the wiring pattern is disposed and a second region adjacent to the first region, The second substrate is arranged in the second region and is characterized in that the extended wiring pattern is provided with a certain distance from one side of the second substrate.

  According to a fourth technical means, in the third technical means, the second substrate is arranged substantially perpendicular to the mounting surface of the first substrate.

  According to a fifth technical means, in any one of the first to fourth technical means, the second substrate is disposed so as to be within an area of the entire mounting surface of the first substrate. It is.

  A sixth technical means is a backlight unit having an inverter circuit according to any one of the first to fifth technical means and a plurality of fluorescent tubes connected to the inverter circuit, wherein the plurality of fluorescent tubes are arranged in parallel. It is characterized by being connected.

  A seventh technical means is a liquid crystal display device having the backlight unit in the sixth technical means and a liquid crystal panel illuminated by the backlight unit, wherein the inverter circuit is disposed on the back side of the liquid crystal panel, and The mounting surface is disposed so as to be substantially parallel to the back surface of the liquid crystal panel.

According to the present invention, it is possible to reliably prevent the high-voltage signal wiring output from the inverter transformer to the plurality of fluorescent tubes from coming into contact with other high-voltage wiring. Can be suppressed.
Further, the high voltage signal wiring can be installed without increasing the area of the inverter circuit board that occupies the back surface of the backlight unit including the liquid crystal panel.

  FIG. 1 is a sectional view 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. 5 and 6 described later. Lamp) or the like is used. The backlight unit 2 of the present invention is configured such that a fluorescent tube unit in which a plurality of fluorescent tubes are connected in parallel is driven by a single transformer.

  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. On the back surface of the housing 23 (that is, the surface opposite to the installation surface of the fluorescent tube 21), a first substrate 28a for mounting the inverter circuit 28 and a second high voltage wiring for the first substrate 28a are provided. A substrate 28b is disposed. At this time, the mounting surface of the first substrate 28 a is disposed so as to be substantially parallel to the back surface of the liquid crystal panel 1.

  Each component such as an inverter transformer is provided in the inverter circuit 28 as a booster circuit that supplies 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.

  FIG. 2 is a block diagram illustrating a configuration example of the inverter circuit 28 according to the present invention. The inverter circuit 28 includes a switching circuit 281 for converting DC power input to the inverter circuit 28 into AC power, and a switching circuit 281. The booster circuit 282 that outputs an AC voltage signal for driving each of the fluorescent tubes 21 with the AC power supplied from the, and the phases of the AC voltage signals that are output from the booster circuit 282 and supplied to the fluorescent tubes 21. A phase adjustment circuit 283 for adjusting, a lamp protection circuit 284 for detecting breakage or disconnection of the fluorescent tube 21, a microcomputer 285 for controlling the inverter circuit 28, and a pair for performing power conversion by the switching circuit 281 A pulse oscillation circuit 286 that oscillates a first control signal (hereinafter, DRV1, DRV2) and a pair of DRV1, Corresponding to each of the RV2 second control signal power amplified by a predetermined amplification factor (hereinafter, AMP1, AMP2) includes a pulse amplifier circuit 287 for generating a.

  The plurality of fluorescent tubes 21 are connected in parallel, one end of each fluorescent tube 21 is connected via a booster circuit 282 and a phase adjustment circuit 283, and the other end is grounded. The switching circuit 281 controls the AC power supplied to the booster circuit 282 according to the AMP1 and AMP2 that are amplified by the pulse amplifier circuit 287. 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.

  The phase adjustment circuit 283 is configured to adjust the phase of each AC voltage signal output from the booster circuit 282 and supplied to each fluorescent tube 21 so as to be substantially in phase as a whole. Regarding the effective value of power, if 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 the effective power is instantaneously zero when the phase difference is 90 °. It becomes. 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 the present embodiment, the phase adjustment circuit 283 reduces the phase difference that causes the effective power to decrease with respect to the AC voltage signal of each fluorescent tube 21, that is, the AC voltage signals have substantially the same phase. ing.

  FIG. 3 is a diagram showing a configuration example of a main part of the inverter circuit 28 shown in FIG. The inverter circuit 28 is composed of at least two substrates of a first substrate 28a and a second substrate 28b provided for high-voltage wiring of the first substrate 28a. Each phase adjustment circuit 283 provided on the first substrate 28 a includes a phase adjustment transformer 283 a and a ballast capacitor 283 b and is connected to each fluorescent tube 21 via a high-voltage lead wire 29. Further, the phases of the respective fluorescent tubes 21 are adjusted between the adjacent phase adjusting circuits 283, and the AC voltage signals of the fluorescent tubes 21 are adjusted so as to have substantially the same phase as a whole.

  Conventionally, in order to adjust the phase of the AC high-voltage signal between the fluorescent tubes arranged at both ends, it is necessary to extend the wiring from the phase adjustment circuit at both ends to straddle the high-voltage wiring on the substrate. Therefore, contact between the lead wires is likely to occur, which is not preferable. Therefore, in the present invention, a part of the extended wiring pattern 290 is secondly arranged so that the extended wiring pattern 290 obtained by extending the wiring patterns 288 at both ends does not discharge due to contact with other high-voltage wiring (such as the high-voltage lead wire 29). It is provided on the substrate 28b.

  In FIG. 3, the first substrate 28 a is arranged side by side by the number of the plurality of fluorescent tubes 21 in order to branch the high-voltage signal output from the booster circuit 282 and the booster circuit 282 for driving the plurality of fluorescent tubes 21. And the second substrate 28b includes at least one of the extended wiring patterns 290 extended from one wiring pattern toward another wiring pattern among the wiring patterns 288 arranged on the first substrate 28a. Some are provided. The extended wiring pattern 290 is provided on the second substrate 28b with a certain distance L (a sufficient distance to prevent discharge of a high-voltage signal) from one side of the second substrate 28b. It is arranged on one substrate 28a. The interval L is a safety distance necessary for preventing discharge of a high-voltage signal, and is preferably set to, for example, about 1 mm per kW as a design standard.

  The material of the first substrate 28a and the second substrate 28b is preferably composed of an epoxy resin having a certain degree of hardness so that the wiring patterns do not come into contact with each other.

  FIG. 4 is a perspective view showing an example of a substrate configuration on which the inverter circuit 28 shown in FIG. 3 is provided. The inverter circuit 28 includes a first substrate 28a and a second substrate 28b. In one region (left region in the figure) of the mounting surface 289 on the first substrate 28a, a booster circuit 282 that is an inverter transformer, each phase adjustment transformer 283a included in each phase adjustment circuit 283, and the booster circuit 282. And a wiring pattern 288 arranged side by side to connect the phase adjusting transformers 283a. In addition, in the other region (the region on the right side in the drawing) of the mounting surface 289, the second substrate 28b is disposed substantially perpendicular to the mounting surface 289. Here, an example is shown in which the second substrate is arranged substantially vertically. However, in order to arrange the high-voltage wiring without increasing the area of the inverter circuit substrate, the second substrate is accommodated within the entire mounting surface of the first substrate. The arrangement is not limited to the above arrangement example.

  Further, as described with reference to FIG. 3, the extended wiring pattern 290 is provided on the second substrate 28b with a certain distance L from one side of the second substrate 28b. By this extended wiring pattern 290, the phase adjusting transformers 283a arranged at both ends are connected to each other. As a result, when the wiring pattern 288 is extended from the phase adjustment circuits at both ends, the wiring pattern 288 can be connected to high voltage without contacting other high voltage wiring, and fluorescent tubes (not shown) arranged at both ends can be connected. It is possible to adjust the phase of the AC high voltage signal. Note that sockets for connecting to the fluorescent tubes are provided for the number of fluorescent tubes on the right side (opposite to the side where the booster circuit 282 is installed) as viewed from the second substrate 28b in the figure. To do.

  In addition, as shown in FIG. 4, the second substrate 28b is disposed substantially perpendicular to the mounting surface 289 of the first substrate 28a, so that the inverter circuit substrate that occupies the back surface of the backlight unit including the liquid crystal panel can be used. High voltage signal wiring can be installed without increasing the area.

  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. 5 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, reference numeral 31 denotes a belt-type external electrode fluorescent lamp, and the belt-type external electrode fluorescent lamp 31. Are provided with electrodes 312 and 312 ′ at both ends of the glass tube 311, and electrodes 313 and 313 ′ at intermediate portions. The electrodes 312 and 312 ′ at both ends are driven at a high frequency of several MHz or more. The intermediate electrodes 313 and 313 ′ can be provided particularly when the glass tube 311 is long by high-frequency driving.

  FIG. 6 is an external view showing a metal capsule external electrode fluorescent lamp as another example of a general external electrode fluorescent lamp (EEFL). In FIG. 6, 32 is a metal capsule external electrode fluorescent lamp, and the metal The capsule-type external electrode fluorescent lamp 32 is provided with metal capsules 322 and 322 ′ at both ends of a glass tube 321. Such a metal capsule external electrode fluorescent lamp 32 is used particularly when the diameter of the glass tube 321 is large.

  Thus, according to the present invention, it is possible to reliably prevent the high voltage signal wiring output from the inverter transformer to the plurality of fluorescent tubes from coming into contact with other high voltage wirings. It is possible to suppress deterioration in quality due to the like. Further, the high voltage signal wiring can be installed without increasing the area of the inverter circuit board that occupies the back surface of the backlight unit including the liquid crystal panel.

It is sectional drawing 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. FIG. 3 is a diagram illustrating a configuration example of a main part of the inverter circuit illustrated in FIG. 2. It is a perspective view which shows an example of the board | substrate structure in which the inverter circuit shown in FIG. 3 was provided. 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, 28a ... first substrate, 28b ... second substrate, 29 ... high-voltage lead wire, 31 ... belt-type external electrode fluorescent lamp, 32 ... metal capsule-type external electrode fluorescent lamp, 110 ... extra-tube electrode Fluorescent lamp, 120 ... inverter, 130 ... digital-analog converter (DAC), 140 ... pulse width modulation controller (PWM controller), 141 ... on / off controller, 150 ... MOSFET driver, 281 ... switching circuit, 282 ... Booster circuit, 283 ... Phase adjustment circuit, 283a ... Transformer for phase adjustment, 283b ... Ballast capacitor, 284 ... Lamp maintenance Circuit, 285 ... Microcomputer, 286 ... Pulse oscillation circuit, 287 ... Pulse amplification circuit, 288 ... Wiring pattern, 289 ... Mounting surface, 290 ... Extension wiring pattern, 311, 321 ... Glass tube, 312, 312 ', 313, 313' ... electrodes, 322, 322 '... metal capsules.

Claims (7)

  In an inverter circuit for driving a plurality of fluorescent tubes arranged side by side, the inverter circuit is composed of at least two substrates, a first substrate and a second substrate, and the first substrate is the plurality of fluorescent tubes. And a wiring pattern arranged side by side by the number of the plurality of fluorescent tubes for branching a high-voltage signal output from the booster circuit, and the second substrate includes the first substrate An inverter circuit comprising: at least a part of an extended wiring pattern extended from one wiring pattern toward another wiring pattern among wiring patterns arranged side by side on a substrate.   The inverter circuit according to claim 1, wherein the extended wiring pattern on the second substrate connects between the wiring patterns at both ends among the wiring patterns arranged side by side on the first substrate. Inverter circuit.   3. The inverter circuit according to claim 1, wherein the first substrate includes a mounting surface including a first region in which the wiring pattern is disposed and a second region adjacent to the first region. An inverter circuit, wherein two substrates are arranged in the second region, and the extended wiring pattern is provided with a certain distance from one side of the second substrate.   4. The inverter circuit according to claim 3, wherein the second substrate is disposed substantially perpendicular to the mounting surface of the first substrate.   5. The inverter circuit according to claim 1, wherein the second substrate is disposed so as to be within a region of the entire mounting surface of the first substrate. 6.   A backlight unit comprising the inverter circuit according to any one of claims 1 to 5 and a plurality of fluorescent tubes connected to the inverter circuit, wherein the plurality of fluorescent tubes are connected in parallel. Characteristic backlight unit.   The liquid crystal display device comprising the backlight unit according to claim 6 and a liquid crystal panel illuminated by the backlight unit, wherein the inverter circuit is disposed on a back side of the liquid crystal panel, and the mounting surface is A liquid crystal display device, wherein the liquid crystal display device is disposed so as to be substantially parallel to a back surface of the liquid crystal panel.

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