JPH1049067A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate excess power consumption for temperature compensation and to obtain a structure for a liquid crystal device useful for such purpose by obtaining the structure where heat generated by a limit resistance is transmitted to liquid crystal. SOLUTION: A light emitting element substrate 4 is made of comparatively thin circuit board material having flexibility. Then, an LED chip 41 functioning as the light source of a backlight and the limit resistance 49 restraining the lighting current of the chip 41 are mounted on the substrate 4. A temperature sensor circuit detects the ambient temperature of a liquid crystal panel 1 or the device and controls a switching circuit so as to select the resistance 49 positioned away from the panel 1 when the detected temperature is higher than a predetermined one and a resistance pattern brought into contact with the panel 1 when it is lower than the predetermined one. Thus, the panel 1 is heated by using the resistance 49 of the chip 41, whereby the excess power for the temperature compensation for the panel 1 is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device provided with backlight illumination.

[0002]

2. Description of the Related Art Liquid crystal displays are generally used in a great number of electronic information devices. Further, the liquid crystal display is often configured to be illuminated from the back side by a so-called backlight light source. The liquid crystal display panel and the backlight light source are often mechanically integrated (unitized).

[0003] In some cases, the backlight light source simply serves as bright background light of the liquid crystal display to increase the brightness of the display. However, a plurality of light sources having different peak wavelengths are simultaneously used to illuminate the display with a mixed color. Actively, for example,
As disclosed in Japanese Patent Application Laid-Open No. 3-41078 and Japanese Patent Publication No. Hei 8-27453, light sources of three primary colors emit light in a time-division manner, and a liquid crystal panel is opened and closed in accordance with the light emission timing of a light source of a specific color. It can also be used as an optical shutter to perform color display without expensive color dot filters. In this last example, a single color light emitting element such as an LED or a colored lamp is used as a backlight light source in combination with different colors.

[0004] Examples of the structure of a backlight light source using a light emitting element such as an LED combined with a liquid crystal panel are disclosed in JP-A-3-111886 and JP-A-4-55086. According to these, a large number of light emitting elements are arranged and mounted on a flat printed circuit board, and a resin frame which also serves as a spacer for a liquid crystal panel and a light source while forming an inclined reflecting wall on the upper surface (light emitting element side) is formed. Provided,
Further, a structure in which a light diffusion plate is provided on the upper surface to reduce illumination unevenness is disposed as a light shutter on the back side of a liquid crystal panel for displaying information.

[0005]

The response of a liquid crystal panel rapidly deteriorates as the temperature of the liquid crystal decreases. In particular,
In the technology of performing color display by switching the color of the backlight in a time-division manner, since the operation time assigned to each color is limited due to the use of the afterimage phenomenon of the naked eye, the optical shutter operation of the liquid crystal display device is also sufficient. If it is not early, the operation time given to each color cannot be fully utilized. Depending on the natural temperature characteristics of the liquid crystal itself, the display at low temperatures is dark or mixed colors appear. Therefore, it becomes necessary to perform temperature compensation of the response of the liquid crystal.

A method of temperature compensation is, for example, to warm the liquid crystal. That is, in the related art, a resistor for a heater is brought into contact with a peripheral portion of a liquid crystal panel substrate, and energized and heated as needed to heat the liquid crystal through the liquid crystal panel substrate. Therefore, power consumption for heating is required, and there are problems in energy saving of electronic devices and portability (small and lightweight power supply batteries).

In the present invention, it is an object of the present invention to eliminate the disadvantages of the prior art and to eliminate the need for extra power consumption due to temperature compensation, and to provide a structure of a liquid crystal display device useful for that purpose. Aim.

[0007]

According to the present invention, the LE
Focusing on the fact that a limiting resistor is always used in a lighting circuit of a light emitting element such as D, temperature compensation is performed by adopting a structure that transmits heat generated by the limiting resistor to a liquid crystal.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an exploded perspective view of a liquid crystal display device according to a first embodiment of the present invention. Reference numeral 1 denotes a liquid crystal display panel having a supertwisted nematic liquid crystal layer or a layer of ferroelectric or antiferroelectric liquid crystal, and having a pixel pattern such as a dot shape or a sun-shaped segment shape. A polarizing plate is also integrated as needed to act as a shutter. Of course, the liquid crystal driver circuit may be mounted on a glass substrate. Reference numeral 2 denotes a light diffusion sheet, and reference numeral 3 denotes a reflection frame, which is a molded product made of synthetic resin. The light reflection surface 31 and the hook portion 32 for fixing the liquid crystal display panel 1 and the light diffusion sheet 2 for improving the efficiency of use of emitted light. have.

The light emitting element substrate 4 is made of a relatively thin flexible circuit board material. The wiring pattern and the resistance pattern printed thereon are not shown. Reference numeral 41 denotes an LED chip, which is mounted in large numbers as a backlight light source. Reference numeral 49 denotes a limiting resistor for suppressing the lighting current of the LED chip 41. In addition, the LED driver IC 100 and the like may be mounted together as long as board space permits. Reference numeral 43 denotes a first branch portion, which carries liquid crystal wiring (not shown) as a plurality of conductive lines formed by printing. The distal end portion 45 of the first branch portion 43 is connected to a drive electrode pattern (not shown, formed on the glass substrate surface) of the liquid crystal display panel 1 by a conductive adhesive or the like.
The liquid crystal wiring passes through the main surface of the light emitting element substrate 4, and its end is gathered together with the end of the lighting circuit pattern (not shown) in the connector terminal portion 46 at the end of the light emitting element substrate 4. And a drive circuit (both not shown) of the liquid crystal display panel 1 connected to a power supply on a base substrate (not shown). The light emitting element substrate 4 is adhered to the lower surface of the reflection frame 3 to be integrated as a display device, or is sandwiched and fixed between the upper surface of the base substrate (not shown) and the lower surface of the reflection frame 3.

The light emitting element substrate 4 has a frame-shaped heater section 48 connected to the second branch section 47. This heater part 4
When the liquid crystal display device 8 is assembled, it is brought into close contact with the peripheral portion of the liquid crystal panel 1 from the back and transfers heat to the liquid crystal panel 1. On the surface of the heater section 48, a pattern of a resistor serving as a heater is formed by printing as indicated by hatching. (The resistance pattern is shown in the case where the resistance pattern substantially goes around the frame portion, but the pattern can be made to reciprocate almost all around or along the long side of the liquid crystal panel. If not, the shape of the frame-like portion itself does not necessarily have to be a closed hollow shape), and the lead wires at both ends of the resistor are connected to the connector terminal portion 46 via the second branch portion 47 by another pattern ( (A wiring group for lighting and a wiring group for liquid crystal). 49 is a limiting resistor, LED
Connected in series with the power supply.

FIG. 2 is a diagram showing a main part of the temperature compensation circuit according to the present embodiment. The LED chip 41 has three colors of red (R), green (G), and blue (B), and there are a plurality of sets of the same color, and each set has a limiting resistor 49 (light emitting element substrate). Are connected in parallel with each other (chip resistors mounted on the main surface of FIG. 1) and a resistance pattern 50 (printed on the heater section 48 in FIG. 1). A switching circuit 60 includes a plurality of switches for selecting one of two types of limiting resistors. Reference numeral 70 denotes a temperature sensor circuit which detects the environmental temperature of the liquid crystal panel 1 or the apparatus, and if the temperature is higher than a predetermined temperature, the liquid crystal panel 1
The switching circuit 60 is controlled so that the limiting resistor 49 located at a position distant from the liquid crystal panel 1 is selected, and if the temperature is lower than a predetermined temperature, the resistance pattern 50 closely contacting the liquid crystal panel 1 is selected. This 2
The types of limiting resistors may be switched at the same time. Alternatively, a step may be provided for the switching temperature to finely adjust the number of selected resistor patterns 50 according to the detected temperature. It is not always necessary to prepare two types for all limiting resistors. Although not shown, the terminal 80 is connected to an external control circuit (a time-division lighting control circuit for each color of the LED) or a power supply.

FIG. 3 is an assembled sectional view of a liquid crystal display device according to a second embodiment of the present invention. The cross section is perpendicular to the long side of the liquid crystal panel. Descriptions of the liquid crystal display panel 1, the light diffusion sheet 2, the reflection frame 3, the LED chip 41, and the limiting resistor 49, which are not essentially different from the first embodiment, are omitted. The light emitting element substrate 4 has a substantially gutter shape,
The upwardly protruding portions 90 that are warped upward on both sides have only two resistance patterns serving as limiting resistances of other types on each side, and are provided one by one on the surface of a portion in contact with both long sides of the liquid crystal panel. The printing pattern of the resistor can be appropriately selected whether it is one-way or reciprocating.

As a simplified embodiment of the present invention,
A configuration is conceivable in which the limiting resistance of the LED is always used only as a printed resistance pattern and no switching circuit is provided by a temperature sensor. This can be adopted if it is determined that even if the heat generated by the resistance pattern further heats the liquid crystal when the ambient temperature is high, the characteristics are not adversely affected. Further, it is needless to say that the chip-shaped or solid-state limiting resistor does not necessarily have to be mounted on the light emitting circuit board.

A liquid crystal panel, a heater section, a light diffusion sheet,
It is preferable that the reflection frame, the light emitting element substrate, and the like have an integrated structure. The reason is that if this part is collectively manufactured by the manufacturer as a part, the user can easily assemble it into the final product by purchasing it and preparing only the liquid crystal drive signal generation circuit, the LED driver and the power supply. Further, if the LED driver IC 100 is mounted on the light emitting element substrate, the liquid crystal driver IC is mounted on the liquid crystal panel, and the temperature sensor is mounted on the reflection frame, the burden on the user can be further reduced.
A liquid crystal display device is further unitized to promote industrial use.

[0015]

Since the liquid crystal is heated by using the limiting resistor of the LED, no extra power is required for temperature compensation of the liquid crystal display panel. Thereby, power saving can be achieved while improving the characteristics of the electronic display device. Also, a configuration has been shown in which temperature compensation control in a plurality of stages is also possible. The structure of the present invention is also effective for unitizing a liquid crystal display device.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a main part of a temperature compensation circuit according to the embodiment of the present invention.

FIG. 3 is an assembled sectional view of a liquid crystal display device according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal panel 2 Light diffusion sheet 3 Reflection frame 31 Light reflection surface 32 Hook part 4 Light emitting element board 41 LED chip 43 First branch part 45 Tip part 46 Connector terminal part 47 Second branch part 48 Heater part 49 Limiting resistance 50 Resistance pattern 60 Switching circuit 70 Temperature sensor circuit 80 Terminal 90 Upper part 100 Driver IC

Claims (4)

[Claims] 1. A liquid crystal display device configured to illuminate the liquid crystal panel using a plurality of LED elements arranged on the rear side of the liquid crystal panel as a light source, the liquid crystal panel being provided on the rear side of the liquid crystal panel via a frame member. LE on the light emitting element substrate
A liquid crystal display device, wherein a lighting circuit for a D element is formed, the LED element is mounted, and a limiting resistor of the LED element is provided on a circuit board close to the liquid crystal panel. 2. The light-emitting element substrate is a flexible circuit board, the circuit board adjacent to the liquid crystal panel is an extension of the flexible circuit board, and the limiting resistor is a printed resistor provided on the extension. 2. The liquid crystal display device according to claim 1, wherein an extended portion is held close to said liquid crystal panel surface. 3. A limiting resistor provided on a circuit board close to the liquid crystal panel is defined as a first limiting resistor, and a solid resistance element mounted on a portion of the light emitting element substrate not close to the liquid crystal panel is a first limiting resistor. 2. A selecting means for selecting one of the first and second limiting resistors according to the necessity of temperature compensation for a display operation of the liquid crystal panel. Liquid crystal display device. 4. A control circuit having a temperature sensor for detecting whether the temperature of the liquid crystal panel or its vicinity is lower than a predetermined value is selected between the first limiting resistor and the second limiting resistor. The liquid crystal display device according to claim 3, wherein: