KR101414613B1 - System and method for cooling display - Google Patents

Abstract

The present invention relates to a cooling system and a cooling method for a display device, the method comprising: measuring an LED temperature; Changing a voltage of the cooling fan based on the measured LED temperature change; Analyzing a received image to determine a brightness level of the image signal; Changing an LED current according to the brightness level of the determined video signal; Comparing a rotation speed (RPM) of the cooling fan with a lookup table indicating a rotation speed value according to temperature and current based on the measured LED temperature and the changed LED current; And controlling the voltage of the cooling fan such that the fan rotation speed (Fan RPM) corresponding to the LED temperature and the LED current change amount coincides based on the lookup table value. The present invention can semi-permanently maintain the lifetime of the light source device, and can provide a color temperature that maintains a constant rate of brightness change with temperature, current, and time. In addition, a cooling system and a cooling method of a display device that responds to sudden temperature and current changes through Summer circuit using OP-AMP are provided.

LED, Cooling

Description

[0001] System and method for cooling display [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device, and more particularly, to a cooling system and a method according to an LED used as a light source in a display product.

2. Description of the Related Art Generally, a display device used for a monitor or a TV of a computer includes a light emitting diode (LED), an electroluminescence (EL) vacuum fluorescent display (VFD), a field emission display (FED), a plasma display panel (PDP), and a liquid crystal display (LCD) that does not emit light by itself and requires a light source.

A typical liquid crystal display device includes two display panels provided with field generating electrodes and a liquid crystal layer interposed therebetween and having a dielectric anisotropy. A voltage is applied to the electric field generating electrode to generate an electric field in the liquid crystal layer and the voltage is changed to adjust the intensity of the electric field so that the transmittance of light passing through the liquid crystal layer is adjusted to obtain a desired image. This light can be either an artificial light or a natural light. A light source for a liquid crystal display device, that is, a backlight device, uses a plurality of fluorescent lamps or light emitting diodes (LED) such as CCFL (Cold Cathode Fluorescent Lamp) or EEFL (External Electrode fluorescent Lamp) as a light source.

The advantage of LEDs used as light sources in display products is that they can be used semi-permanently. The existing lamps have a disadvantage that they must be replaced within one to two years. Cooling of the LED device is the most important factor for the semi-permanent use of the lifetime of the LED light source. There are many ways to cool, but the cheapest way is to use a heat sink and a cooling fan.

1 is a block diagram illustrating a conventional fan cooling method.

The current temperature measured by the temperature sensor from the external temperature measuring device (Temperator 1, Temperator 2) is input to the A / D conversion sections (A / D 1 and A / D 2). The A / D conversion unit converts the measured temperature into digital data that can be processed. When the temperature sensor is implemented by a digital temperature sensor, it is not necessary to provide an A / D converter. The CPU outputs a PWM (Pulse Width Modulation) signal corresponding to the digital temperature data applied from the A / D conversion unit and compares the measured value RPM and the target value RPM to control the increase or decrease of the PWM signal by an error.

FAN driving algorithm for cooling heat sink is also used in various ways. In order to maintain the temperature below the smallest critical temperature, the FAN RPM may be maintained constant regardless of the ambient temperature, or the FAN RPM may be varied depending on the ambient temperature. The way to vary the FAN RPM requires a controller that can sense the ambient temperature and adjust the FAN voltage accordingly. This approach is costly and causes a lot of errors in maintaining a constant temperature for the device.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a method of maintaining a constant Fan RPM so that a junction temperature of a display device is kept constant regardless of a current change and an external environment.

According to an aspect of the present invention, there is provided a cooling system for a display device, including: a temperature sensing unit for sensing a change amount of an LLED temperature; An LED current sensing unit for sensing a current change amount of the LED; A memory for storing the fan rotation speed (Fan RPM) according to the LED temperature change and the current change amount as a look-up table; Determines a cooling level based on the detected current change amount and the detected LED temperature change, and then determines a fan rotation speed (Fan RPM) according to the temperature and LED current variation based on the stored lookup table value And a control unit for changing the voltage of the cooling fan.

Wherein the temperature sensing unit measures the junction temperature of the LED and does not reflect the change in the external temperature.

And the temperature sensing unit supplies an output signal when the junction temperature of the LED junction is equal to or higher than a predetermined temperature.

The control unit controls the rotational speed (RPM) of the cooling fan by using a feedback method of an adder (Summer) circuit using OP-AMP when a temperature change is abruptly generated due to the LED current change.

And the current change amount is changed according to the brightness level of the image signal by analyzing the histogram of the input image.

The present invention also provides a method of cooling a display device, comprising: measuring an LED temperature; Changing a voltage of the cooling fan based on the measured LED temperature change; determining a brightness level of a video signal by analyzing a received image; Changing an LED current according to the brightness level of the determined video signal; Comparing a rotation speed (RPM) of the cooling fan with a lookup table indicating a rotation speed value according to temperature and current based on the measured LED temperature and the changed LED current; And controlling the voltage of the cooling fan such that the fan rotation speed (Fan RPM) corresponding to the LED temperature and the LED current change amount coincides based on the lookup table value.

The LED is a configuration of Red, Green and Blue LEDs and is characterized by measuring the temperature of an LED junction.

And the brightness level of the image signal is determined by analyzing the histogram of the received image.

And the fan rotation speed (Fan RPM) according to the LED temperature and the LED current variation amount is stored as a lookup table.

The present invention can semi-permanently maintain the lifetime of the light source device through the cooling system and the cooling method of the display device, and can provide a color temperature that keeps the rate of change of brightness according to temperature, current, and time constant. In addition, it is possible to respond to sudden temperature and current changes instantly through Summer circuit using OP-AMP.

The objects, features and advantages of the present invention will be more readily understood by reference to the accompanying drawings and the following detailed description. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

2 (a) to (c) are illustrations showing junction temperatures and amounts of light for respective R, G and B LEDs.

The present invention provides a circuit configuration capable of maintaining the most constant brightness and color temperature in a cooling system of a display device. To this end, the present invention uses an LED light source that is on / off (off) and brightness-controllable in addition to a semi-permanent advantage according to an embodiment. If the output image is a bright image, 100% of the current is flowed to express the brightness, and when displaying the dark image, about 60% of the current is flowed to express the brightness of the image. That is, when the 10A current is supplied and when the 6A current is supplied, the heating states of the R (a), G (b) and B (c) LEDs are different. Therefore, since the luminous efficiencies of R (a), G (b) and B (c) LEDs are different according to the current as shown in FIG. 2, The brightness ratio is different, and the constant color temperature can not be maintained. In order to solve this problem, the present invention maintains the junction temperature constant for the luminous efficiency of R (a), G (b) and B (c) LEDs depending on the current. The junction temperature is the temperature at which the integrated circuit (IC) can withstand. In other words, when the temperature is higher than the junction temperature, a heat sink or fan is installed outside to lower the temperature. The present invention controls the fan revolution per minute (Fan RPM) of the cooling fan to maintain a constant junction temperature.

3 is a block diagram illustrating a cooling system of a display device that maintains a constant Fan RPM according to the present invention.

In the case of LED, efficiency of luminous flux (brightness) varies depending on the amount of heat generated by the LED device. As the temperature increases, the luminous flux decreases and the color temperature of White changes as the ratio of R, G, B changes. If the luminous flux efficiency according to the temperature of each of the R, G and B LEDs is the same, only the brightness changes and the color temperature does not change. However, since the luminous flux efficiency according to the temperature of the R, G, and B LEDs is not the same, a color temperature difference occurs depending on the temperature change. Thus, to maintain a constant color temperature, the temperature of the LED device must be kept constant.

The temperature sensing unit 101 detects the amount of change in the junction temperature of the LED without reflecting the change in the external temperature according to the present invention.

The LED current detection unit 102 detects a current change amount of the LED serving as a current sweep element. When the LED is supplied with a lot of current, the brightness increases. Conversely, the brightness decreases. The increase in brightness means that the amount of heat generated also increases. Therefore, when a large amount of current flows, the amount of heat generated increases, and the color temperature is changed due to the difference in the heat generation efficiency of the respective R, G, and B LEDs.

The control unit 103 determines the cooling level based on the change in the junction temperature detected by the temperature sensing unit 101 with respect to the amount of current change detected from the LED current sensing unit 102. [ The cooling level is determined on the basis of a junction temperature stored in the memory 104 and a look up table indicating the fan RPM value according to the LED current change. The control unit 103 controls the cooling fan 105 voltage to match the fan RPM according to the junction temperature and the LED current variation based on the determined cooling level.

FIG. 4 is a circuit diagram for maintaining a constant junction temperature for a current change and an external environment in a display device according to an embodiment of the present invention.

The CUP 11 measures the LED junction temperature (Junction temperature) change. Also, the CUP 11 analyzes the histogram of the image, determines the brightness level of the input video signal, and changes the current of the LED connection portion 12 in proportion to the brightness level. Therefore, the CUP 11 always checks the junction temperature of the LED to check whether the temperature is constant. If there is a change, the CUP 11 uses the PWM port of the CPU that has been used, ). At this time, when the temperature change suddenly occurs due to the current change of the LED connection part 12 according to the brightness level of the video signal, the RPM of the cooling fan 14 is changed to the feedback mode of the summer circuit using the OP- So as to maintain a constant temperature.

In the cooling system according to the present invention, the voltage value V_o of the cooling fan 14 output from the circuit that maintains a constant junction temperature with respect to the current change and the external environment is expressed by Equation (1).

V_o = Vref - (V_pwm / R1 + V_current / R2) * Rf

5 (a) to 5 (c) are graphs showing current changes according to the brightness levels of the R, G and B LEDs in the display device according to the embodiment of the present invention.

According to the embodiment of the present invention, R (red), G (green), and B (blue) LEDs are used for color implementation in a display device using an LED as a light source. Since the inherent wavelength characteristics of the LED are different depending on the ambient temperature, the power driving state, and the operating time, the brightness level of the image signal should be determined so as to maintain the proper color temperature by continuously measuring the current change of the LED. G, and B LEDs are added in accordance with the brightness ratios of R, G, and B so that the R, G, and B LEDs obtain the respective light emission efficiency characteristics, Adjust the brightness of the display accordingly. The forward driving current suitable for the R, G, and B LEDs is generated, and each forward driving current sequentially emits light to realize the luminance-adjusted color. It also optimizes the white balance of colors implemented by adjusting different PWM (Pulse Width Modulation) values for the R, G, and B LEDs. At this time, the PWM value has a different value for each R, G, B LED. The brightness level of the image signal is determined based on histogram analysis results of the input image based on R (FIG. 5A), G (FIG. 5B) and B (FIG.

FIG. 6 is an exemplary view illustrating numerical values of Fan RPM for each LED junction temperature according to an exemplary embodiment of the present invention. Referring to FIG.

The LED backlight consists of R, G, and B LEDs, which are repeatedly arranged on the substrate and emit light by current. LEDs are characterized in that the temperature and wavelength of emitted light are changed when the internal temperature is increased. In particular, when white light is mixed by mixing R, G, and B LED lights, problems occur. This is because the R, G, and B LEDs are current-driven devices, so if a large amount of current is supplied to the LEDs, the brightness increases and the amount of heat generated increases. As a result, the color temperature of White is changed due to the difference in the heat efficiency of R, G, B LED, so that it is impossible to realize accurate white color.

The cooling system of the display device of the present invention keeps the junction temperature constant regardless of the current change and the external environment so that the LED backlight maintains a constant color temperature and an accurate white color is realized. The RPM of the cooling fan is determined based on the amount of change of the junction temperature without reflecting the change amount of the external temperature as shown in FIG.

7 is a flowchart illustrating a cooling method in which a change in LED current is detected in a display device according to the present invention.

The display device is powered up to boot the system (S700).

The CPU measures the junction temperature of the LED and checks whether the temperature is constant (S701). If there is a change in the junction temperature of the LED, the voltage of the cooling fan is changed using the PWM port of the CPU (S703). When power is applied to the display device, the received image is received and the histogram is analyzed (S702).

The brightness level of the image signal is determined so as to show the luminous efficiency characteristics of the R, G, and B LEDs (S704). The current of the LED is changed to the added voltage level according to the brightness ratio of the R, G, and B LEDs (S705).

The current cooling fan rotation speed is compared with the fan RPM lookup table value based on the measured LED junction temperature and the changed LED current value (S706). The junction temperature of the LED is measured to match the fan RPM based on the temperature and the current state, and the voltage of the cooling fan is changed (S707).

The terminology used in the present invention is defined in consideration of the functions of the present invention, and it may vary depending on the intention or custom of a technician working in the field. Therefore, .

The present invention is not limited to the above-described embodiments and various changes and modifications may be made by those skilled in the art.

1 is a block diagram showing a conventional fan cooling method.

2 (a) to (c) are views showing respective junction temperatures and amounts of light for R, G, B LEDs in a display device.

3 is a block diagram illustrating a cooling system of a display device that maintains a constant Fan RPM in accordance with the present invention.

FIG. 4 is a circuit diagram showing a current variation and a constant junction temperature for an external environment in a display device according to an embodiment of the present invention; FIG.

5 (a) to 5 (c) are graphs showing current changes according to brightness levels of R, G and B LEDs in a display device according to an embodiment of the present invention.

FIG. 6 is an exemplary view showing numerical values of a fan RPM according to an LED junction temperature of a display device according to an embodiment of the present invention; FIG.

7 is a flowchart illustrating a cooling method in which a change in LED current is detected in a display device according to the present invention.

Description of the Related Art [0002]

101. Temperature sensing unit 102. LED current sensing unit

103. Control unit 104. Memory

105. Cooling fan

Claims (9)

A method of cooling a display device, Measuring an LED junction temperature; Changing the voltage of the cooling fan based on the measured change in the junction temperature of the LED; Analyzing a histogram of an image received on a display device; Determining a brightness level of a video signal based on a histogram of the analyzed image and a luminous efficiency characteristic of each of Red LED, Green LED, and Blue LED constituting the LED; Changing an LED current according to the brightness level of the determined video signal; Comparing a rotation speed (RPM) of the cooling fan with a lookup table indicating a rotation speed value according to temperature and current based on the measured LED temperature and the changed LED current; And And changing the voltage of the cooling fan such that the fan rotation speed (Fan RPM) according to the LED temperature and the LED current change amount coincides with the lookup table value. delete delete The method according to claim 1, And the fan rotation speed (Fan RPM) according to the LED temperature and the LED current variation amount is stored as a lookup table. In a cooling system of a display device, A temperature sensing unit for sensing a change in LED temperature; An LED current sensing unit for sensing a current change amount of the LED; A memory for storing the fan rotation speed (Fan RPM) according to the LED temperature change and the current change amount as a look-up table; And Measuring a temperature of the LED junction, changing a voltage of the cooling fan based on the measured temperature change of the LED junction, analyzing a histogram of an image received by the display device, Determining a brightness level of the video signal based on the histogram and the luminous efficiency characteristics of the red LED, the green LED and the blue LED constituting the LED, changing the LED current according to the determined brightness level of the video signal, (RPM) of the cooling fan based on the changed LED temperature and the changed LED current with a lookup table indicating a rotation speed value according to temperature and current, and based on the lookup table value, And changes the voltage of the cooling fan so that the fan rotation speed (Fan RPM) corresponding to the change amount coincides. delete 6. The method of claim 5, Wherein the temperature sensing unit supplies an output signal when the temperature of the LED junction is equal to or higher than a predetermined temperature. 6. The method of claim 5, Wherein the control unit controls the rotational speed (RPM) of the cooling fan by using a feedback method of an adder (Summer) circuit using OP-AMP when a temperature change rapidly occurs due to the LED current change. Cooling system. delete

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