KR20070107540A - Liquid crystal display device having structure of light emitting diode back-light for temperature compensation - Google Patents

Abstract

An LCD having an LED backlight in a temperature compensation structure is provided to attach a temperature sensor per array on a PCB for sensing temperature per array and individually controlling an output current per array through a CPU of an LED driving part, thereby improving entire uniformity of the backlight. An LCD having an LED backlight in a temperature compensation structure includes an LCD panel for image display, a signal applying element for driving the LCD panel, an LED backlight for supplying light to the LCD panel, and an LED driver(132) for driving the backlight and compensating output current of LEDs per array by using a plurality of temperature sensors(144a-144h). The temperature sensors are controlled by a temperature compensating circuit(132) of the LED driver. The temperature compensating circuit has the temperature sensors for sensing ambient temperature per PCB(Printed Circuit Board) array, a memory part(152) for storing LED property data relating to the ambient temperature, a CPU(Central Processing Unit)(154) for operating and comparing output values of the temperature sensors and the LED property data, and an output part(156) for applying a current value to a corresponding one of the PCB arrays.

Description

LIQUID CRYSTAL DISPLAY DEVICE HAVING STRUCTURE OF LIGHT EMITTING DIODE BACK-LIGHT FOR TEMPERATURE COMPENSATION}

1 is a cross-sectional view of an entire assembly according to the present invention.

2 is a plan view showing a PCB array to which a temperature sensor is fixed

3 is a block diagram showing a temperature compensation circuit mechanism of the present invention.

※※ Explanation of symbols for main parts of drawing ※※

100: liquid crystal panel 102: diffusion plate

104, 106: Optical sheet 110: Main support

120: upper cover 130: lower cover

132: drive driver 140: printed circuit board (PCB)

142: LED 144: temperature sensor

The present invention relates to a liquid crystal display device having a temperature-compensated LED backlight structure, and more particularly, by attaching a temperature sensor to each array on a printed circuit board (PCB) in which the LEDs are formed in string units, sensing a temperature, and outputting each array. Individual control of the current is concerned with improving the overall uniformity of the backlight.

In general, most liquid crystal display devices are light-receiving devices that display an image by controlling the amount of light coming from the outside. Therefore, in order to irradiate light to the LCD panel, a separate light source, that is, a backlight (back light) is necessarily required. If a cold cathode lamp is used as a light source, the light emitted from the reflecting plate is reflected from the reflecting plate, and the light having a locally uniform illuminance through the milky white scattering plate disposed in the reflecting path of the light is emitted. It has been used to illuminate a liquid crystal panel.

However, this approach has a relatively fatal flaw that cannot make the backlight thin in the light of recent thinning trends. In other words, due to the drawback of making a liquid crystal display device complicated and large, in recent years, as a surface light source device, LEDs having characteristics such as fast response speed, low power consumption, and semi-permanent lifespan are racing. As a result, it was possible to form the backlight in a thin form and at the same time improve luminance. And, above all, the core of next-generation LCDs that can replace cold cathode backlight devices for natural cold colors and high-definition images, resolving after-image problems, and eco-friendly products that do not use mercury. It is attracting attention as a component.

In this regard, conventionally, as an example of an LED backlight, a plurality of LED chips are arranged in a predetermined pattern on a driving circuit board for uniform light emission. In this case, the total thickness of the surface light source itself was about 5 mm, which was relatively thinner than the conventional cold cathode surface light source device, but it was still insufficient to meet the thickness for the liquid crystal display device. Since it takes the form of light emission by a plurality of LED chips forming a), it was not easy to form a uniform illuminance on the whole surface.

On the other hand, the backlight system disclosed in US patent application 09 / 384,137 sometimes includes LEDs having any number of rows and columns. The system includes 10 × 12 matrix LEDs. However, it should be understood that any number of LEDs can be provided in forming the matrix. The LEDs are placed in a cavity that is suitably formed by walls connected to each other. The cavity here, of course, must be called a 'backlit cavity' to be precise. In particular, the wall is coated with a high light reflectance finish such as, for example, high gloss white paint or white reflector. It should also be understood that side-lit or edge-lit applications include LEDs on one or more walls.

Of course, the LEDs here are either current-mounted devices, whether surface mounted or through-holes. This allows each LED in the string to receive the same current. Among other reasons, it is also common to form electrical LED strings in series connection to conserve power. Multiple strings of LEDs not only increase the brightness, but also avoid higher voltage levels, increasing the safety margin of the LED's potential for failure and adjusting the various colors of the LED when color enhancement or color generation is required. It was expected to be used for.

In practice, however, most backlights, including LED backlights, are placed in a vertical orientation to allow us to see the image when used in computer monitors and LCD TVs. In this case, the LEDs of the monitor and the LEDs of the backlight react with each other due to the heat emitted by the internal LEDs of the monitor and the backlight. Especially, in the vertical state, the temperature of the upper side is higher than the lower side due to the convection of air present in the backlight. Implemented differently, the overall uniformity is reduced. Above all, the solution is urgently needed in large models such as PC monitors and LCD TVs of 30 inches or more, which are beginning to increase in demand.

Therefore, in the present invention, in order to solve this problem, the LED is attached to each array on a printed circuit board (PCB) consisting of a string unit temperature sensor for sensing the temperature and output current for each array through the CPU of the LED driver The purpose is to improve the overall uniformity of the backlight by individual control.

According to an aspect of the present invention, there is provided a liquid crystal display device having a temperature-compensated LED backlight structure comprising: a liquid crystal panel for implementing data information in an image; Signal applying means for driving the liquid crystal panel; An LED backlight device providing light to the liquid crystal panel; And an LED driver for driving the backlight device and compensating the output current of the LEDs for each array by using a plurality of temperature sensors in the device.

In addition, the temperature compensation circuit for controlling the temperature sensor includes a temperature sensing unit for sensing the ambient temperature for each PCB array; A memory unit for storing LED characteristic data according to ambient temperature in advance; A CPU for calculating and comparing the output value of the temperature sensor and the LED characteristic data read out from the memory; And an output unit providing the current value to the PCB array.

First, before discussing the above configuration, we will briefly look at the temperature sensor (temperature sensor) applied to the present invention. The temperature sensor is a sensing element that senses temperature, which is one of the basic physical quantities, and converts it into an electrical signal. As a result, it has been widely used in industrial system control, environmental control, and biomedical medical devices.In recent years, high-speed measurement capable of remote measurement for the prevention of fires in communication networks due to the development of information and communication technology and the increasing demand of high-speed information and communication networks has emerged. Research is being actively conducted in the field of application, such as the need for high-sensitivity temperature sensors.

The types are classified into contact type and non-contact type. The contact type is a method of measuring temperature through contact with a measuring object, and most sensors such as (platinum) resistance temperature sensors, thermistors, thermocouples, and bimetals correspond to them. Non-contact types include radiation thermometers and advertisement thermometers.

Thermistors are the most used among them, but linearity, sensitivity, and reference temperature are becoming a problem. In addition, thermocouples are used to change the electromotive force generated at the junctions of two types of metal wires, and are widely used for industrial purposes such as steel, power plants, and heavy chemicals. Complementing the shortcomings of the two devices, linearity, sensitivity, and reference temperature, is an IC (Integrated Circuit) temperature sensor, which uses the current-voltage characteristics of the PN junction according to the temperature. There are two kinds.

In particular, the present invention employs a current output type of the IC temperature sensor, and will now be described in detail the configuration of the present invention in consideration of this point. As shown in FIG. 1, red (R), green (G), and blue (B) are formed on a printed circuit board (PCB) arranged at least eight lines in the lower cover 130. LEDs are fixed and the temperature sensor 144, which is the core of the present invention, is fixed at each one of the PCB boards 140. Of course, the drawing shows that the ideal case is fixed at the center. However, the present invention is not limited thereto, and the driving unit for driving the upper LED 142 outside or below the lower cover 130 and sensing the output current value of the temperature sensor 144 is provided on the printed circuit board. It is configured to be wrapped in a protective cover such as aluminum as the LED drive driver 132.

Meanwhile, a diffuser plate 102 is first placed on the front surface of the substrate on which the LED 142 and the temperature sensor 144 are arranged to form a plurality of lines. This is usually for uniformly dispersing the light from the LED light source to the front surface where the liquid crystal panel 100 is located. Next, two optical sheets 104 and 106 are additionally attached to complement the function.

In addition, the main support 110 is positioned between the upper cover 120 and the lower cover 130 to maintain the balance of the overall force of the liquid crystal display, and the information from the outside is displayed on the support 110. The liquid crystal panel 100 for implementation is loaded. Of course, the liquid crystal panel 100 is formed by the bonding of a TFT (Thin Film Transistor) array substrate and a color filter substrate, and liquid crystal is injected therebetween, and is applied between the color filter substrate, which is the upper plate, and the array substrate, which is the lower plate. The liquid crystal is distorted by the voltage difference, which causes the light emitted from the light source LED to irritate our eyes.

The operation principle for controlling the temperature sensor of the present invention will now be described in more detail with reference to the accompanying drawings. As shown in FIG. 2, the core of the present invention detects the ambient temperature by mounting a temperature sensor 144 for each array on a printed circuit board 140 in which the LEDs 142 are formed in strings, and is proportional thereto. The output current of each array is generated. At this time, the CPU in the LED driver reduces or increases the current value to the LED output current value of each PCB array to provide a current value compensated for each PCB array.

In the present invention, a voltage of 1.4 V to 2.6 V is applied to both R, G, and B LEDs formed on eight PCB array stages according to desired brightness or forward current, and based on an absolute temperature of 25 ° C. The current suitable for the applied voltage is set. Here it is normal for most LEDs to be combined with resistors or transistors in series to provide a stable voltage.

For example, if a voltage between 1.4V and 2.6V is applied to both ends of all the LEDs formed on the eight PCB array stages, approximately 10mA of current flows on the LEDs until the temperature of the PCB array stage reaches 25 ℃. Suppose there is. In this case, the temperature of the junction of the LED itself gradually increases over time, resulting in a heat generation of the device as power consumption increases. This eventually leads to a phenomenon in which the temperature is different as the temperature rises to the top of the backlight due to air convection.

More precisely, the junction temperature of the LED itself can vary substantially with ambient temperature. For example, as shown in FIG. 3, assuming that the inner temperature of the LED backlight 160 has a difference of 25 ° C. at the lower end 144a and the next step at 26 ° C., the eight PCB arrays are basically as in the present invention. In the case of forming a stage, the difference between the lowermost 144a and the uppermost 144h will be approximately 7 ° C. due to the convection of air. In this case, the junction temperature difference of the LED itself is imaginable.

In this case, the temperature sensor fixed to each PCB array stage detects the temperature change through the detector and compensates the current proportional to this. Of course, the IC temperature sensor here may be more suitable, for example, from National Semeconductor's LM35 series. Briefly, the LM35 series includes a plurality of PN junction transistors so that no correction circuit is required, and a reference voltage generator and an amplifier are mounted on one chip. In particular, the LM35DZ not only obtains a linear output voltage with respect to degrees Celsius (℃) but also has a relatively wide range of measurement temperatures from 0 to 100 ℃, and is inexpensive due to wafer level trimming. In addition, the nonlinearity range is ± 1/4 ℃, the power supply range is wide from 4V to 30V, and the leakage current is small, less than 60mA. In addition, there are many advantages, such as low self-generated temperature in the air, low impedance output.

Meanwhile, as shown in FIG. 3, the central processing unit (CPU) 154 in the microprocessor 150 controls the information of the current value according to the temperature from the temperature sensors 144a to 144h. In other words, the role of the CPU 154 is to receive the current value according to the temperature from the temperature sensor, and instructs the operation and comparison with data already stored in the separate memory unit 152 in advance.

In particular, the memory unit 152 includes a ROM and a RAM. The ROM is intended to store in advance the reference current value corresponding to the set temperature (for example, 25 ° C) at which the LED's current characteristics change, while the RAM is used for each PCB array as the ambient temperature in the LED backlight changes. This is to temporarily store different current values flowing in the stage. Of course, it is more preferable to store the current values from each array stage in the RAM sequentially.

For example, in the LED backlight of FIG. 3, if it is ideal to have a current of 10 mA applied to each of the LEDs at 25 ° C., the reference value is stored first in the ROM in the memory unit 152. When the ambient temperature of the bottom 144a rises to 26 ° C. as time elapses, 12 mA of current flows through the LEDs of the PCB array stage as the temperature changes.

In this case, the CPU 154 in FIG. 3 stores a current of 12 mA flowing in the PCB array stage in the RAM, and receives a current value from the corresponding temperature sensor 144a in response to 26 ° C. ), We are working with 12ms temporarily stored in RAM. In this case, subtraction is preferable because the current characteristic increases as the temperature of the LED increases. However, if the current characteristic decreases as the LED temperature increases, it is preferable to perform the addition. Ideal.

Here, if the temperature sensor 144a is designed to flow a current of 2 ㎃ each time it increases by 1 ° C, and can be equal to the decrease or increase width of the current according to the temperature increase of the LED, the LED driving driver (described later) The additional circuitry in 132, i.e. the comparator, becomes unnecessary. In other words, the calculation unit (not shown) that performs the addition and subtraction can compensate the current to the backlight 160 as much as possible. However, in the case of the LM35 series, the increase in current due to the temperature increase of the temperature sensor is generally increased. It is quite small, about 4㎂.

Therefore, in this case, the CPU 154 in FIG. 3 performs the same operation as the above subtraction or addition, as well as the size of the reference current value stored in the ROM, that is, 10 ㎃ and the comparison unit (not shown). If the operation value is larger than the reference value, the operation is repeated until the reference value is reached. However, as mentioned earlier, as mentioned above, if the current value of 4 위 is appropriately amplified to match the current increase according to the temperature increase of the LED, a comparison unit (not shown) may not be necessary. have.

In addition, the output unit 156 here represents the previous step for the compensated current value to simultaneously enter the corresponding PCB array in accordance with the control signal. Therefore, it may be configured as a kind of buffer. For example, as the corresponding information in the data driver is applied to the liquid crystal panel via the output unit, the compensation current value is also introduced from the CPU 154 to each PCB array stage of the LED backlight according to the corresponding bit information.

So far, the structure of the present invention has been described, and the device of a specific company has been introduced. Anyone with ordinary skill in the art, however, may think that the approach may be as varied as the components present in the construction of the circuit, and therefore, the introduction of such elements here is not intended to provide a more detailed description of the present invention. I hope this will help you understand without difficulty.

As a result of the above configuration, the liquid crystal display device having the temperature-compensated LED backlight according to the present invention compensates for the characteristic change according to the temperature, which is a disadvantage of the LED, and particularly, in the large model such as a PC monitor or LCD TV, Uniformity may be improved.

Claims (13)

A temperature sensing unit sensing an ambient temperature for each PCB array; A memory unit in which LED characteristic data according to ambient temperature is stored in advance; A CPU for comparing and calculating the output value of the temperature sensor and the LED characteristic data read out from the memory; And A temperature compensation circuit comprising an output unit for providing a compensation current value of the CPU to the PCB array. The temperature compensation circuit according to claim 1, wherein the temperature sensing unit comprises an IC temperature sensor. The temperature compensation circuit of claim 1, wherein the memory unit comprises a kind of registers such as a ROM and a RAM. The temperature compensation circuit according to claim 1, wherein the CPU comprises a computing unit or a comparing unit. A liquid crystal panel for implementing data information in an image; Signal applying means for driving the liquid crystal panel; An LED backlight device providing light to the liquid crystal panel; And And a LED driver for driving the backlight device and compensating the output current of the LEDs for each array by using a plurality of temperature sensors in the device. 6. The apparatus of claim 5, wherein the signal applying means comprises: a data driver for supplying data to data lines of the liquid crystal panel; A gate driver for supplying a gate pulse to the gate line of the liquid crystal panel; And a timing controller controlling the data driver and the gate driver. 6. The liquid crystal display device according to claim 5, wherein the LED backlight device is formed by mixing R, G, and B light emitting diodes on at least eight PCBs forming a predetermined interval array. 6. The liquid crystal display device according to claim 5, wherein the temperature sensor is fixed to a center or any one on each array substrate. The liquid crystal display of claim 5, wherein the LED driver comprises a microprocessor IC configured to sense an output current value of a temperature sensor.  The LED driving apparatus of claim 5, wherein the LED driver comprises: a temperature sensing unit sensing an ambient temperature of each PCB array; Memory unit for storing the LED characteristic data according to the ambient temperature in advance; A CPU for comparing and calculating the output value of the temperature sensor and the LED characteristic data read out from the memory; And a temperature compensating circuit comprising an output unit configured to provide a compensation current value of the CPU to a corresponding PCB array. The liquid crystal display of claim 10, wherein the temperature sensing unit comprises an IC temperature sensor. The liquid crystal display device according to claim 10, wherein the memory unit comprises a kind of register such as a ROM and a RAM. 12. The liquid crystal display device according to claim 10, wherein the CPU comprises a calculation unit or a comparison unit.

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