KR100739115B1 - The the back light operating device of preventing the difference of the brightness between upper side and lower side of LCD and the method thereof - Google Patents

Abstract

Disclosed are a backlight driving apparatus and a method for preventing luminance variations in upper and lower parts of an LCD. In the backlight driving apparatus for preventing the luminance deviation of the upper and lower parts of the LCD according to the present invention, a backlight driving apparatus for irradiating a light source to the LCD by driving a plurality of lamps, the temperature for sensing the temperature of the lamp located above the LCD It is preferable to include a sensing unit and an inverter controller for controlling the temperature of the lamp to be smaller than the predetermined reference value when the temperature of the lamp located above the LCD is higher than the predetermined reference value and the brightness of the upper portion of the LCD is increased. According to the present invention, by using the output signal of the comparator can reduce the tube current of the lamp located above the LCD, it is possible to reduce the brightness of the upper LCD. Therefore, there is an advantage that can prevent the luminance non-uniformity occurring between the upper and lower LCD due to the movement of heat.

Brightness, thermistor, lamp, inverter, LCD

Description

The back light operating device of preventing the difference of the brightness between upper side and lower side of LCD and the method approximate

 1 is a block diagram showing the configuration of a backlight driving apparatus for preventing the luminance deviation of the upper and lower parts of the LCD according to the present invention;

2 is a detailed circuit diagram of the temperature sensing unit shown in FIG. 1, and

3 is a flowchart provided to explain the backlight driving method for preventing the luminance deviation of the upper and lower LCDs according to the present invention.

Brief description of the main parts of the drawing

10: AC input 20: rectifier

30: power factor improvement unit (PFC unit) 40: inverter unit

42: inverter controller 44: switching unit

46: transformer 50: lamp

60: current detection unit 70: temperature detection unit

72: thermistor 74: comparator

R1: Internal resistance of thermistor

R2 to R6: second to sixth resistors

C1 to C2: first capacitor to second capacitor

V1: power supply voltage applied to the temperature sensing unit

The present invention relates to a backlight driving apparatus and a method for preventing a luminance deviation between upper and lower liquid crystal displays (LCDs) due to thermal movement.

Recently, as the products are advanced and the information is expressed more, LCDs are widely used in portable video, cameras, TVs, computer monitors, mobile phones or car navigation systems.

The LCD is a light receiving display device that receives light from the outside and forms an image, and is irradiated with a light by a backlight unit provided on a rear surface of the liquid crystal display device. The backlight unit uses the lamp as a light source, and converts the light generated from the lamp into surface light having the same brightness to irradiate the liquid crystal display.

The general requirements of such a backlight unit are high brightness, high efficiency, uniformity of brightness, long life, thinness, low weight, and low cost, and particularly high brightness characteristics are required for an LCD monitor or a TV.

In order to obtain high luminance characteristics of the backlight unit, a backlight unit employing two or more lamps has been developed, and LCDs using such a backlight unit are increasing. That is, a plurality of lamps are used, and the inverter circuit drives the plurality of lamps.

In the case of using a plurality of lamps, a feedback means and a protection circuit are necessary to eliminate the deterioration of image quality or the risk of fire that may occur when a lamp has an abnormality, and to provide a higher quality and reliable driving circuit. Proceeded.

In a TV set provided with such a conventional LCD backlight driving apparatus, when the user turns on the power, since the heat moves from the lower side to the upper side of the TV set, the TV set generates a temperature difference between the lower side and the upper side. On the other hand, the luminance has a characteristic that varies with the change of temperature, the luminance increases as the temperature increases. Therefore, due to heat transfer, a phenomenon of luminance unevenness is caused between the upper side and the lower side of the LCD. In particular, such a luminance non-uniformity is recognized as a serious problem in large-sized TVs in mass production.

Accordingly, it is an object of the present invention to provide a backlight driving apparatus and a method for preventing luminance unevenness between upper and lower LCDs caused by temperature differences.

Another object of the present invention is to provide a backlight driving apparatus and a method capable of reducing the luminance of a lamp located above an LCD by reducing the tube current of the lamp by using the output signal of the comparator.

In order to achieve the above object, a backlight driving apparatus for preventing brightness deviation of upper and lower parts of an LCD according to the present invention includes a backlight driving apparatus for irradiating a light source to an LCD by driving a plurality of lamps, the LCD among the plurality of lamps. It is installed in the vicinity of the lamp to feed back the temperature of the lamp located at the top, the temperature sensing unit for detecting the temperature of the lamp, and the temperature of the lamp located at the top of the LCD is higher than a predetermined reference value, the brightness of the top of the LCD When raised, it is preferable to include an inverter controller which controls the current of the lamp so that the temperature of the lamp becomes smaller than a predetermined reference value.

Here, when the temperature of the lamp located at the top of the LCD is lowered, it is preferable that the brightness of the top of the LCD is lowered.

Here, the temperature sensing unit converts the temperature detected by the lamp located at the top of the LCD into a predetermined voltage value, compares the converted voltage value with a predetermined reference voltage, and if the converted voltage value is greater than the predetermined reference voltage, It is preferable to determine that the temperature of the lamp located is higher than a predetermined reference value.

Here, the temperature sensing unit may include a thermistor for detecting a temperature change of a lamp positioned at the top of the LCD based on the change in the internal resistance value, and a non-inverting input voltage applied to the non-inverting input terminal through the thermistor with a predetermined reference voltage. For example, when the non-inverting input voltage is greater than a predetermined reference voltage, the comparator may generate a control signal having a first logic level and output the comparator to the inverter controller.

Here, it is preferable that the thermistor decreases as the internal resistance value increases as the temperature of the lamp located at the top of the LCD increases.

Here, when the control signal of the first logic level is input to the inverter controller, the inverter controller preferably reduces the tube current of the lamp located at the top of the LCD so that the temperature of the lamp located at the top of the LCD is lower than a predetermined reference value. .

Here, it is preferable that the magnitude | size of a predetermined reference voltage is about 2.5 [V].

The backlight driving method for preventing the luminance deviation between the upper and lower LCD according to the present invention is a backlight driving method for irradiating a light source to the LCD by driving a plurality of lamps, the temperature of the lamp located at the top of the LCD among the plurality of lamps And detecting the current of the lamp so that the temperature of the lamp at the top of the LCD is lower than the predetermined reference value when the temperature of the lamp at the top of the LCD is higher than the predetermined reference value and the brightness of the top of the LCD is increased. It is preferable to include.

Here, the step of sensing the temperature of the lamp located at the top of the LCD, the internal resistance value of the thermistor changes according to the temperature change of the lamp located at the top of the LCD, through the internal resistance of the thermistor to the non-inverting input terminal of the comparator Comparing the applied voltage with a predetermined reference voltage, and as a result of the comparison, when the voltage applied to the non-inverting input terminal is greater than the predetermined reference voltage, it is determined that the temperature of the lamp located at the top of the LCD is higher than the predetermined reference value. It is preferable to generate and output a control signal of a logic level.

Here, in response to the control signal of the first logic level, the tube current of the lamp located at the top of the LCD is controlled to be reduced, so that the brightness of the lamp located at the top of the LCD is preferably lowered.

Hereinafter, with reference to the accompanying drawings illustrating the present invention.

1 is a block diagram showing the configuration of a backlight driving apparatus for preventing the luminance deviation of the upper and lower parts of the LCD according to the present invention. Referring to FIG. 1, the backlight driving apparatus 100 for preventing the luminance deviation of the upper and lower parts of the LCD may include an AC input unit 10, a rectifying unit 20, and a power factor correction unit (PFC unit) 30. , An inverter unit 40, a lamp 50, a current detection unit 6, and a temperature sensing unit 70.

The AC input unit 10 receives AC power from the outside and transfers the AC power to the rectifier 20, and the rectifier 20 performs a rectification process for the received AC power. The PFC unit 30 performs a power factor improvement process for the received power to increase the use efficiency of the power.

Power output from the PFC unit 30 is transferred to the inverter unit 40. The inverter unit 40 includes an inverter controller 42, a switching unit 44, and a transformer 46. The inverter unit 40 converts DC power received from the PFC unit 30 into AC power.

The switching unit 44 repeatedly performs an on / off operation in order to transfer the first stage power received from the PFC unit 30 to the second stage. In general, up to the primary side coil of the transformer 46 is referred to as the primary stage, and after the secondary side coil of the transformer 46 is referred to as the secondary stage.

The transformer 46 transfers the first-stage power supply to the second-stage according to the on / off operation of the switching unit 44. By the on / off operation of the switching unit 44, the transformer 46 generates induction power, and transfers the generated induction power to the lamp 50.

Two or more lamps 50 are provided and connected to the secondary side of the transformer 46. The lamp 50 is turned on or off depending on the power supplied by the transformer 50. In addition, in one embodiment of the present invention, the lamp 50 is an EFFL type lamp having an external electrode on both sides of the lamp tube, or an EIFL having an external electrode on one side of the lamp tube and an internal electrode on the other side of the lamp tube. Type lamps, or cold cathode light lamps, CCFL type, all of which are not intended to limit the spirit of the present invention to a particular type of lamp.

The current detector 60 detects the amount of current flowing through the lamp 50 and outputs the amount of current to the interlock controller 42 of the inverter unit 40. That is, when the amount of current sensed by the current detector 60 is smaller than the predetermined reference current amount, the inverter controller 42 increases the amount of current flowing through the total lamp 50 by controlling the on / off of the switching unit 44. On the contrary, when the amount of current sensed by the current detector 60 is greater than the predetermined reference current amount, the inverter controller 42 controls the on / off of the switching unit 44, thereby controlling the amount of current flowing through the total lamp 50. Decrease.

The temperature detecting unit 70 detects a temperature of a lamp (hereinafter, referred to as an “upper lamp”) located above the LCD in real time, compares the detected upper lamp temperature with a predetermined reference temperature, and compares the result with an inverter controller ( To 42). At this time, the comparison between the temperature of the upper lamp and the reference temperature is made by comparing a predetermined voltage value corresponding to the temperature of the upper lamp with a predetermined reference voltage corresponding to the reference temperature.

FIG. 2 is a detailed circuit diagram of the temperature sensing unit shown in FIG. 1. Referring to FIG. 2, the temperature sensing unit 70 includes at least one operational amplifier (OP-AMP) 74, at least one thermistor 72, a plurality of resistors R2 to R6, and a plurality of capacitors C1 to C2. )

Thermistor 72 is an abbreviation of Thermally Sensitive Resistor, which means a temperature sensitive resistor. Thermistor 72 is a temperature-sensitive semiconductor whose resistance value changes extremely greatly with temperature change. In a preferred embodiment of the present invention, thermistor 72 is a negative thermistor coefficient thermistor, and has a characteristic that the jinging value decreases as the temperature increases.

The operational amplifier OP-AMP 74 serves as a comparator 74. A comparator is a type of operational amplifier that is used to compare one voltage to see if it is greater than another. The comparator has a plurality of input voltages (non-inverting input and inverting input) and one output voltage. If the non-inverting input voltage (+) is greater than the inverting input voltage (-), the comparator generates a large output voltage. If the voltage (+) is less than the inverting input voltage (-), the output voltage is lowered. At this time, if the comparator is operated from a single power supply, the output voltage has only one polarity, whether it is low or high.

3 is a flowchart provided to explain the backlight driving method for preventing the luminance deviation of the upper and lower LCDs according to the present invention. 1 to 3, first, when heat is moved from the bottom of the LCD to the top in the power-on state of the TV set, the temperature of the lamp (hereinafter referred to as the “top lamp”) located at the top of the LCD becomes high. The brightness of the upper lamp rises. That is, the luminance difference occurs between the upper and lower parts of the LCD due to the movement of heat (S310).

The temperature detector 70 detects a temperature of a lamp (hereinafter, referred to as an “upper lamp”) located above the LCD in real time (S320).

At this time, the internal resistance (R1) value of the thermistor 72 changes according to whether the temperature of the upper lamp rises (S330). That is, since the type of thermistor 72 is a negative temperature coefficient (NTC) thermistor in this embodiment, as the temperature of the upper lamp rises, the internal resistance (R1) value of the thermistor 72 becomes smaller, and the temperature of the upper lamp is increased. When the value falls, the value of the internal resistance R1 of the thermistor 72 increases.

On the other hand, the power supply voltage V1 is divided by a predetermined voltage according to the ratio of the internal resistance R1 of the thermistor to the magnitude of the second resistor R2. At this time, the magnitude of the voltage applied to the voltage distribution point a is as follows.

In Equation 1, Va denotes a voltage applied to the node a, V1 denotes a power supply voltage applied to the temperature sensing unit, R2 denotes a second resistor, and R1 denotes an internal resistance of the thermistor. In addition, in this embodiment, the power supply voltage V1 applied to the temperature sensing unit 70 is preferably 5 [V].

The divided voltage Va is reduced by a predetermined magnitude through the fifth resistor R5, and the reduced voltage is finally applied to the non-inverting input terminal (+) of the comparator 74. That is, the voltage V ₊ applied to the non-inverting input terminal + of the comparator 74 is inversely proportional to the magnitude of the internal resistance R1 of the thermistor 72.

Therefore, when the temperature of the upper lamp decreases, the value of the internal resistance R1 of the thermistor 72 increases, thereby decreasing the voltage V ₊ applied to the non-inverting input terminal +. On the contrary, when the temperature of the upper lamp rises, the value of the internal resistance R1 of the thermistor 72 decreases, thereby increasing the voltage applied to the non-inverting input terminal (-) of the comparator 74.

In addition, the power supply voltage is divided by a predetermined ratio according to the magnitudes of the third resistor R3 and the fourth resistor R4 and applied to the inverting input terminal (-) of the comparator 74. The voltage V ₋ applied to the inverting input terminal (−) becomes a reference voltage Vref for comparing the magnitude of the voltage applied to the non-inverting input terminal (+). The reference voltage Vref applied to the inverting input terminal (-) is expressed as a formula as follows.

In Equation 2, Vref denotes a reference voltage applied to the inverting input terminal (-), R3 denotes a third resistor, R4 denotes a fourth resistor, and V1 denotes a power supply voltage applied to the temperature sensing unit. In this embodiment, the reference voltage Vref applied to the inverting input terminal (-) is preferably about 2.5 [V].

The comparator 74 measures the magnitude of the non-inverting input voltage (V ₊ ) applied to the non-inverting input terminal ( ₊ ) and the reference voltage applied to the inverting input terminal (-) through the internal resistance (R1) of the thermistor (72). Compare (S340). As a result of the comparison, when the non-inverting input voltage (V ₊ ) applied to the non-inverting input terminal (+) is greater than the reference voltage (S350), the comparator 74 generates and outputs a high level control signal (S360).

In this way, the high level control signal output from the comparator 74 is applied to the inverter controller 42 of the inverter unit 40. In response to the high level control signal, the inverter controller 42 controls the on / off of the switching unit 44 to reduce the tube current of the upper lamp (S370). When the tube current of the upper lamp is reduced in this way, the brightness of the upper lamp is lowered (S380). Therefore, the luminance non-uniformity phenomenon between the upper and lower LCD parts due to the movement of heat is prevented.

As described above, according to the present invention, the tube current of the lamp located at the top of the LCD can be reduced by using the output signal of the comparator, so that the brightness of the top of the LCD can be reduced. There is an advantage that can prevent the uneven phenomenon.

Although the preferred embodiments of the present invention have been illustrated and described above, the present invention is not limited to the specific embodiments described above, and the present invention is not limited to the specific embodiments of the present invention without departing from the spirit of the present invention as claimed in the claims. Anyone skilled in the art can make various modifications, as well as such modifications are within the scope of the claims.

Claims (10)

In the backlight driving device for irradiating a light source to the LCD by driving a plurality of lamps, A temperature sensing unit installed at a periphery of the lamp to feed back a temperature of the lamp located at the top of the LCD among the plurality of lamps, and detecting a temperature of the lamp; And And an inverter controller configured to control a current of the lamp so that the temperature of the lamp is lower than a predetermined reference value when the temperature of the lamp positioned at the top of the LCD is higher than a predetermined reference value and the brightness of the uppermost level of the LCD is increased. Backlight driving device for preventing the luminance deviation between the upper and lower parts of the LCD. The method of claim 1, When the temperature of the lamp located at the top of the LCD is lowered, the brightness of the top of the LCD is lowered, the backlight driving device for preventing the deviation between the upper and lower LCD. The method of claim 1, wherein the temperature sensing unit, The temperature sensed by the lamp positioned at the top of the LCD is converted into a predetermined voltage value, and the converted voltage value is compared with the predetermined reference voltage, and when the converted voltage value is greater than the predetermined reference voltage, Backlight driving device for preventing the luminance deviation between the upper and lower LCD, characterized in that the temperature of the lamp is determined to be higher than the predetermined reference value. The method of claim 3, wherein the temperature sensing unit, A thermistor for detecting a temperature change of a lamp positioned at the top of the LCD based on a change in an internal resistance value; And When the non-inverting input voltage is greater than the predetermined reference voltage by comparing the non-inverting input voltage applied to the non-inverting input terminal through the thermistor, a control signal having a first logic level is generated to generate the control signal. Backlight driving device for preventing the luminance deviation between the upper and lower LCD, characterized in that it comprises a comparator for outputting. The method of claim 4, wherein the thermistor, And a backlight resistance device for preventing luminance deviation between upper and lower LCDs as the temperature of a lamp positioned at the top of the LCD increases. The method of claim 4, wherein When the control signal of the first logic level is input to the inverter controller, And the inverter controller controls the tube current of the lamp positioned at the top of the LCD to be reduced, so that the luminance of the lamp positioned at the top of the LCD is lowered. The method of claim 4, wherein the predetermined reference voltage has a magnitude of: Backlight drive device for preventing the luminance deviation between the upper and lower LCD, characterized in that approximately 2.5 [V]. In the backlight driving method for irradiating a light source to the LCD by driving a plurality of lamps, Sensing a temperature of a lamp positioned at the top of the LCD among the plurality of lamps; And Controlling the current of the lamp so that the temperature of the lamp located at the top of the LCD is lower than a predetermined reference value when the temperature of the lamp at the top of the LCD is higher than a predetermined reference value and the brightness of the top of the LCD is increased. Backlight driving method for preventing the luminance deviation between the upper and lower LCD, characterized in that. The method of claim 8, Detecting the temperature of the lamp located at the top of the LCD, Changing an internal resistance value of a thermistor according to a temperature change of a lamp positioned at the top of the LCD; Comparing a voltage applied to a non-inverting input terminal of a comparator with a predetermined reference voltage through an internal resistance of the thermistor; And As a result of comparison, when the voltage applied to the non-inverting input terminal is greater than the predetermined reference voltage, it is determined that the temperature of the lamp located at the top of the LCD is higher than the predetermined reference value, and generates and outputs a control signal having a first logic level. Back light driving method for preventing the luminance deviation between the upper and lower LCD, characterized in that consisting of. The method of claim 9, In response to the control signal of the first logic level, And controlling the tube current of the lamp positioned at the top of the LCD to be reduced, thereby reducing the luminance of the lamp positioned at the top of the LCD.

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