JP2007128821A - Backlight and liquid crystal display device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight and a liquid crystal display device, which have a circuit board downsized with due consideration of safety, wherein a request for thinning and downsizing is strong with a portable personal computer or the like, and LEDs as light sources are being adopted from a viewpoint of the thinning, but even in this case, an occupied area of an LED-mounting circuit board tends to be larger. <P>SOLUTION: A diode circuit 41 with a plurality LEDs connected in series as light sources for the backlight 13 is divided into two systems, and input and output terminals of each diode circuit 41a, 41b are arranged in parallel on the same end face of the same circuit board. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight using a light emitting diode as a light source and a liquid crystal display device using the same, and a backlight and a liquid crystal display device which can be formed at low cost in consideration of safety in response to a reduction in thickness. About.

  A liquid crystal display device has low power consumption, is lightweight, suitable for thinning and downsizing, and is widely used as various monitors for personal computers, television receivers, portable terminals, navigation systems, and the like. In such a liquid crystal display device, there are a reflective liquid crystal display device and a transmissive liquid crystal display device, but a transmissive liquid crystal display device is often used in terms of brightness. In this transmissive liquid crystal display device, a backlight using a light emitting diode (LED) as a light source is used. This backlight is provided with a plurality of diode circuits in which a plurality of LEDs are connected in series, and the LEDs of each diode circuit are alternately arranged, and each diode circuit is individually pulse-driven (for example, , See Patent Document 1).

In the backlight having such a configuration, when the voltage input / output terminal of the diode circuit is positioned on one end side of the circuit board, the input / output terminal of each diode circuit is separated for each diode circuit, and withstand voltage In consideration of the characteristics, it is necessary to secure a sufficient space for preventing discharge such as disposing empty pins at the input / output terminals of each diode circuit.
JP 2001-76525 A

  As described above, when a diode circuit in which a plurality of LEDs are connected in series as a light source is divided into a plurality of systems and mounted on a circuit board, the voltage resistance between the anode side and the cathode side of each diode circuit is taken into consideration, and the space between them is eliminated. It is necessary to secure a sufficient space by arranging pins. For this reason, there has been a problem that the circuit board is enlarged and the price is increased.

  An object of the present invention is to provide a backlight and a liquid crystal display device that are small and inexpensive while ensuring safety while achieving a reduction in thickness.

  The backlight according to the present invention has at least a pair of diode circuits in which a plurality of light emitting diodes are connected in series, a circuit board in which the light emitting diodes of each diode circuit are alternately arranged in a line, and one side surface of the light emitting diode. In a backlight including a light guide plate arranged facing each other and a reflection sheet arranged on the back side of the light guide plate, a plurality of diode circuits are adjacent to each other at the same end of the circuit board. Arranged to be arranged.

  The liquid crystal display device according to the present invention includes an array substrate in which a plurality of pixel electrodes are disposed on a glass substrate, a counter substrate in which a common electrode is disposed to face the array substrate, and an enclosure between the substrates. A liquid crystal panel having a liquid crystal member formed thereon, a light guide plate disposed on the back side of the liquid crystal panel for irradiating the liquid crystal panel, and disposed on a circuit board facing at least one side surface of the light guide plate In a liquid crystal display device comprising a plurality of diode circuits in which a plurality of light emitting diodes arranged in parallel in series are connected in series, and a backlight having a reflective sheet disposed on the back side of the light guide plate, the plurality of diode circuits are The input / output ends are arranged adjacent to each other at the same end of the circuit board.

  According to the present invention, one end of each of the plurality of diode circuits is juxtaposed with the end of the circuit board, and the other end of each of the diode circuits is juxtaposed with the end of the circuit board. In other words, the voltage resistance on the input side and the output side can be achieved by arranging the LEDs on the input side and the output side in parallel by arranging the LEDs of a plurality of diode circuits alternately and paralleling each circuit. The only consideration is the one point between the input and output terminals, so that the space efficiency can be improved while ensuring safety, and the back can be made cheaper and more compact. Lights and liquid crystal display devices can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  As schematically shown in FIG. 1, the liquid crystal display device according to the present invention includes a liquid crystal panel 11 and a backlight 13 having a plurality of light emitting diodes (LEDs) 12 as light sources.

  The liquid crystal panel 11 has a rectangular array substrate 14 and a counter substrate 15, and is stretched through a sealing material 16 printed on the array substrate 14 so as to surround the outside of the display area of the array substrate 14. By being combined, they are arranged to face each other with a gap of about 5 μm or less, and the liquid crystal member 15 is sealed in this gap.

  The array substrate 14 has a rectangular glass substrate 17, and although not shown in the figure, a large number of signal lines and scanning lines are arranged orthogonally to each other. In addition, a plurality of auxiliary capacitance lines are arranged substantially parallel to the scanning lines. A protective film, an alignment film (not shown) and the like are further laminated on the inner surface of the glass substrate 17, and a polarizing plate (not shown) is attached to the outer surface side to constitute the array substrate 14.

  On the other hand, the counter substrate 15 facing the array substrate 14 includes a rectangular glass substrate 18 which is actually formed in a smaller size than the glass substrate 17 constituting the array substrate 14, and the inner surface of the glass substrate 18. Although not shown above, in the case of a color liquid crystal display device, a black matrix and a color filter are provided, and a counter electrode and an alignment film made of ITO are laminated to form a glass substrate 18. A polarizing plate (not shown) is attached to the outer surface side to constitute the counter substrate 15.

  TFTs (not shown) as switching elements are formed in the vicinity of the intersections between the signal lines and the scanning lines provided on the glass substrate 17 of the array substrate 14, and the gate electrodes of the TFTs are used as the scanning lines. In addition, the source electrode is connected to the signal line, the drain electrode of each TFT is connected to a pixel electrode (not shown) made of ITO, and between each auxiliary capacitance line and the pixel electrode facing it. An auxiliary capacity is formed.

  A driving circuit for supplying a video signal and a scanning signal to the signal line and the scanning line, and further supplying a reference voltage and the like to the auxiliary capacitance line is separated from the printed circuit board 19 along one long side of the array substrate 14. It is mounted on. The printed circuit board 19 and the liquid crystal panel 11 are connected by three flexible printed wiring boards 21 on which a source driver 20 is mounted with TAB (Tape Automated Bonding). This is to reduce the number of wires by driving the liquid crystal panel 11 to be multi-selective.

  On the surface of the printed board 19 where the flexible printed wiring board 21 does not exist, electrical components 22 such as a system LSI, various semiconductors, a chip resistor, a chip capacitor, and a connector are arranged.

  On one side of the liquid crystal panel 11 on which the three flexible printed wiring boards 21 are provided, on the remaining three side surfaces from the two side edge portions outside the flexible printed wiring board 21, synthetic resin or rubber material is provided. A frame body 23 made of a flexible elastic material such as the like is fitted to hold the side surface and protect the end surface of the liquid crystal panel 11.

  A backlight 13 is disposed on the back surface side of the liquid crystal panel 11 so as to face the liquid crystal panel 11 configured as described above. The backlight 13 includes a plurality of LEDs 12 and a light guide plate 24 in which the LEDs 12 are disposed on one side surface and set to a plate thickness of 1 mm or less. The light emitted from the LED 12 is reflected by the inner surface of the light guide plate 24 and propagates in the light guide plate 24, and the light is led out toward the liquid crystal panel 11 by the light guide plate 24. For this purpose, the light guide plate 24 is provided with a sawtooth reflection surface on the bottom surface or the lead-out surface of the light guide plate 24 or a prism-like reflection surface in order to efficiently guide light to the liquid crystal panel 11 side. Is used in combination to improve the light propagation efficiency.

  Further, the outer surface of the bottom surface of the light guide plate 24 is mirror-finished by depositing aluminum, silver, or the like on the surface of white paper or synthetic resin, or by sticking such a sheet so that there is relatively little deflection. For example, a reflective sheet 25 made of a slightly thick material of about 230 μm is disposed. If the amount of light is sufficiently secured, it is possible to use the reflection sheet 25 whose inner surface is white.

  On the other hand, an optical sheet 26 such as a diffusion sheet or a prism sheet is disposed on the light exit surface side of the light guide plate 24. The LED 12, the light guide plate 24, the optical sheet 26, and the reflection sheet 25 are made of metal such as stainless steel. Is housed in a frame-like back case 27. The LED 12 serving as the light source is mounted on a circuit board 28 made of a printed wiring board, preferably a flexible printed wiring board, and the backlight 13 is constituted by these.

  The backlight 13 and the liquid crystal panel 11 thus configured are positioned by superposing the liquid crystal panel 11 on the back case 27 of the backlight 13. Thereafter, the liquid crystal panel 11 and the backlight 13 are integrated to form a liquid crystal display device by adhering the three side surfaces of the overlapped liquid crystal panel 11 and the backlight 13 with an adhesive tape 29. .

  As shown in FIG. 2, the liquid crystal display device includes a multilayer printed circuit board 19 and a liquid crystal panel 11 connected by a flexible printed wiring board 21, and the width direction of the liquid crystal panel 11 or the backlight 13 is set on one side. Is held in parallel with the plane direction of the liquid crystal panel 11 and the backlight 13. Since this printed circuit board 19 is composed of the multilayer laminated printed circuit board 19, the thickness in the thickness direction is thicker than that of the single-layer wiring board, but the length in the width direction is shortened accordingly. Therefore, the size of the frame portion can be reduced.

  Moreover, even if the length of the printed board 19 in the width direction is shortened, the flexible printed wiring board 21 that connects the printed board 19 and the liquid crystal panel 11 can be constituted by three pieces. It is possible to dispose an electrical component 22 such as a system LSI, various semiconductors, resistors, and capacitors constituting a drive circuit in an intermediate space where no flexible printed wiring board 21 exists.

  Therefore, even if the width of the printed board 19 is reduced to 10 mm, the number of the flexible printed wiring boards 21 used is set to be 3 or less, and the surface of the printed board 19 is still In addition, it is possible to secure a sufficient component arrangement space, and it is possible to promote reduction in thickness and size.

  The relationship between the liquid crystal panel 11 and the backlight 13 using the LEDs 12 will be described in more detail with reference to FIG. Note that the same components as those described above are denoted by the same reference numerals, and detailed description thereof is omitted.

  That is, FIG. 3 is a partially cutaway sectional view of the portions of the liquid crystal panel 11 and the backlight 13, and the liquid crystal panel 11 provided with the polarizing plates 30 and 31 on both sides is engaged with one end of the light guide plate 24. The side surface of the back case 27 and the adhesive tape 34 are fixed. The back case 27 is formed in a U-shaped cross section on the inner side of the end surface on which the LED 12 is disposed, and one end of the light guide plate 24 is inserted into the U-shaped. An optical sheet 26 is disposed on the light guide plate 24 on the liquid crystal panel 11 side, and a reflective sheet 25 is disposed on the opposite surface side.

  A plurality of LEDs 12 connected and fixed by a wiring pattern are arranged in a line on the surface of the circuit board 28 made of a flexible printed wiring board in the space between one end of the light guide plate 24 and the side surface of the back case 27. The circuit board 28 and the bottom surface of the back case 27 are fixed by the adhesive tape 35 so that the optical axis as the light source of the LED 12 is in the end face thickness direction of the light guide plate 24.

  The back case 27 is formed in a wide U-shape including only the side on which the LEDs 12 are arranged, including the bottom plate side, but the portion corresponding to the other side is merely formed in an L-shape. Thus, the width is only enough to allow the reflection sheet 25 to be locked. For this reason, since the back case 27 has only an L-shaped frame as a member corresponding to the bottom plate, the weight of the metal back case 27 can be greatly reduced, This is suitable for mold products.

  A non-display portion on the front side of the liquid crystal panel 11 is covered with a front case 36, and the front case 36 is fitted and fixed to a back case 27. The entire liquid crystal display device is fixed to a housing 38 such as a personal computer by an adhesive tape 37.

  As shown in FIG. 4, the light source using the above-described LEDs 12 is arranged in parallel so that the emission surfaces 40 face the light guide plate 24 side by side in a row on one surface of the circuit board 28 on which the plurality of LEDs 12 are formed in a tape shape. It is installed.

  As shown in FIG. 5, the light source using this LED 12 is composed of, for example, a total of 40 LEDs 12, and a pair of circuit boards 28 each having a length of 20 are formed on each pair of circuit boards 28. It is installed. Further, the 20 LEDs 12 are connected in series in units of 10 to form two systems of diode circuits 41a and 41b, and the LEDs 12 constituting the diode circuits 41a and 41b are combined alternately and alternately. The LEDs 12 are arranged in a line on the circuit board 28.

  The anode side of the diode circuits 41a and 41b is connected to first and second anode connection terminals 42a and 42b provided on the circuit board 28, and the final cathode side wiring portion is connected to each diode circuit 41a and 41b. The circuit board 28 is connected to cathode connection terminals 43a and 43b formed at the end of the same circuit board 28 provided with the anode connection terminals 42a and 42b by bending in the same direction and further folding back. In this circuit board 28, in order to ensure the voltage resistance of the anode connection terminals 42a and 42b and the cathode connection terminals 43a and 43b, an empty terminal 44 is provided at the end of the circuit board 28 between the terminals 42 and 43. By forming this, a sufficient distance is secured so that no discharge or the like occurs between the terminals 42 and 43.

  The anode connection terminals 42 a and 42 b and the cathode side connection terminals 43 a and 43 b are connected to the lighting control drive circuit 45. The lighting control drive circuit 45 can employ a drive method such as direct current drive or pulse voltage drive, and each LED 12 is driven by being connected to a circuit pattern formed on the circuit board 28. At this time, in order to improve luminance and reduce variations in luminance, the uneven luminance is improved by alternately connecting adjacent LEDs 12 so that the LEDs 12 of other diode circuits 41 are alternately arranged. In addition, if a pulse voltage driving method is employed, it is possible to drive with low power consumption.

  The present invention is not limited to the above-described embodiment, and can be applied to a color or monochrome type liquid crystal display device, and the back case has been described as having a frame shape. It is possible to use a cross-shaped or cross-shaped reinforcing bar that passes through the center of the frame to improve mechanical strength, or to use a box with a bottom. Depending on the case, the LEDs may be arranged on a plurality of sides of the light guide plate.

The disassembled perspective view which shows the outline | summary of the backlight and liquid crystal display device which concern on this invention. The front view of a liquid crystal display device similarly. FIG. 3 is a partially cutaway cross-sectional view showing main parts of the backlight and the liquid crystal display device. The perspective view which similarly shows an LED light source. The circuit diagram which shows a diode circuit similarly.

Explanation of symbols

11 ... Liquid crystal panel 12 ... Light emitting diode (LED)
DESCRIPTION OF SYMBOLS 13 ... Backlight 14 ... Array substrate 15 ... Opposite substrate 24 ... Light guide plate 25 ... Reflection sheet 28 ... Circuit board 41a, 41b ... Diode circuit 42a, 42b ... Anode side connection terminal 43a, 43b ... Cathode side connection terminal 45 ... Lighting control Driving circuit

Claims (4)

A circuit board having at least a pair of diode circuits in which a plurality of light emitting diodes are connected in series, the light emitting diodes of each of the diode circuits being alternately arranged in a line, and a conductor disposed on one side facing the light emitting diodes. In a backlight including a light plate and a reflective sheet disposed on the back side of the light guide plate,
The backlight is characterized in that the plurality of diode circuits have their input / output ends arranged adjacent to each other at the same end of the circuit board.   The plurality of diode circuits are composed of two systems, the anode side connection terminals of the respective diode circuits are arranged in parallel with one end of the circuit board, the light emitting diodes are arranged along the circuit board, and the cathode side of the diode circuit is respectively provided. 2. The backlight according to claim 1, wherein a cathode side connection terminal is disposed at the same end of the circuit board by being folded in the same direction. A liquid crystal panel having an array substrate in which a plurality of pixel electrodes are disposed on a glass substrate, a counter substrate in which a common electrode is disposed to face the array substrate, and a liquid crystal member sealed between the substrates;
A light guide plate disposed on the back side of the liquid crystal panel for irradiating the liquid crystal panel, and a plurality of light emitting elements disposed in parallel with each other on at least one side surface of the light guide plate. In a liquid crystal display device comprising a plurality of diode circuits in which diodes are connected in series, and a backlight having a reflective sheet disposed on the back side of the light guide plate,
The liquid crystal display device according to claim 1, wherein input / output ends of the plurality of diode circuits are arranged adjacent to each other at the same end of the circuit board. The plurality of diode circuits are composed of two systems, the anode side connection terminals of the respective diode circuits are arranged in parallel with one end of the circuit board, the light emitting diodes are arranged along the circuit board, and the cathode side of the diode circuit is respectively provided. 4. The liquid crystal display device according to claim 3, wherein a cathode side connection terminal is disposed at the same end of the circuit board by being folded back in the same direction.

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