KR20150061919A - Backlight unit for liquid crystal display device - Google Patents

Abstract

The present invention relates to a backlight unit for a liquid crystal display device using a light-emitting diode as a light source and, specifically, to a backlight unit for a liquid crystal display device, which can realize a quantity of light emitting diodes with an optimal design. The characteristics of the present invention are to be able to realize an optimum light source design for a liquid crystal display device of the present invention by designing one LED string to have a different quantity of LEDs compared to other LED string, with respect to configuring a small number of LEDs with a plurality of strings, when a small quantity of LEDs of a backlight unit corresponds to the optical design. Therefore, the present invention is capable of preventing problems of hot spot generation, power consumption increase, and the like from occurring. Especially, the present invention can accurately detect disconnection and malfunction of an LED string even if the LED string comprises a small number of LEDs by allowing an LED string which has a different quantity among LED strings to be detected for having a broken wire and a defect through a separate comparator having a separate reference voltage. Thus, the present invention is capable of preventing problems that the LED string is damaged by an excessive current and that a driving voltage generation unit, which supplies operational power to the LED strings, is damaged by an excessive voltage.

Description

BACKLIGHT UNIT FOR LIQUID CRYSTAL DISPLAY DEVICE

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit for a liquid crystal display using a light emitting diode as a light source, and more particularly, to a backlight unit for a liquid crystal display capable of realizing an optimum design of a quantity of light emitting diodes.

In recent years, the use of light emitting diodes (LEDs) having features such as small size, low power consumption and high reliability as light sources has been increasing. Such LEDs have been utilized for various lighting purposes, and their use ranges from a display portion of an electronic product to various display devices, a lighting device of a vehicle, and the like.

In particular, LEDs may artificially generate white light to replace fluorescent lamps for general illumination, and LEDs that emit white light are receiving the spotlight as backlight units of liquid crystal displays (LCDs).

Here, when the LED is provided as a light source of the backlight unit of the LCD, the LED is usually comprised of a plurality of LED strings connected in series or in parallel so that the total number of LEDs of the backlight unit of the LCD is * Number of LEDs per string).

On the other hand, the backlight unit having the LED string structure has a problem in that it is difficult to optimally design the quantity of the LED, which is the light source of the backlight unit of the LCD, according to the type and size of the LCD.

That is, since the LED string is formed of the same number of LEDs, in the case of an LCD having an optimal design of the prime number of LEDs, the number of LEDs can not be optimally designed, And the power is increased.

For example, when 23 LEDs are provided for an LCD, it is not possible to provide 23 LEDs as a plurality of LED strings. Therefore, it is necessary to increase the number of LEDs by one or one. When the number is increased by one, the power consumption of the backlight unit is increased. If the number is reduced by one, a hot spot defect occurs in which the portion where the light reaches and the portion where the light does not reach coexist.

This results in a factor that hinders the overall luminance uniformity of the LCD.

In addition, there is no means for checking the current flowing through each of the plurality of LED strings, and when an over-current flows through the LED string and an over-voltage is supplied, there is no means for damaging the LED string and driving voltage The generation part may be damaged by the overvoltage.

SUMMARY OF THE INVENTION It is a first object of the present invention to design an LED quantity as a light source of a backlight unit of an LCD optimally to solve the above problems.

Another object of the present invention is to prevent the damage of the LED string or the damage of the driving voltage generator due to the overvoltage by adjusting the current for each of the plurality of LED strings.

In order to achieve the above object, the present invention provides a plasma display panel comprising: a driving voltage generator; First and second LED strings connected to the driving voltage generating unit and each including a plurality of LEDs; A third LED string connected to the driving voltage generating unit, the third LED string including a plurality of LEDs having different numbers of the first and second LED strings and the LEDs; A first comparator for comparing the first feedback voltage of the first and second LED strings with a first reference voltage to output an output voltage; A second comparator for comparing the second feedback voltage of the third LED string with a second reference voltage to output an output voltage; Wherein the first and third LED strings are connected to the first and second LED strings, and the first and third LED strings are connected to the first and second LED strings, And a control unit for lowering the driving voltage of the driving voltage generating unit or for stopping the generation of the driving voltage.

The third LED string may include one or more LEDs in the first and second LED strings, the first reference voltage may be input to an inverting end of the first comparator, The first feedback voltage is input to the non-inverting terminal of the first comparator, the second reference voltage is input to the inverting terminal of the second comparator, and the second feedback voltage is input to the non-inverting terminal of the second comparator.

The second reference voltage is designed to be the first reference voltage VCC +/- X, where X is a voltage VLED (driving voltage for driving one LED) * compared to each of the first and second LED strings And a first voltage detector is provided between the first and second LED strings and the first comparator so that a larger one of the feedback voltages inputted from the first and second LED strings, And transfers the first feedback voltage to the first comparator.

The third comparator may further include a third comparator to which a lowest feedback reference voltage is input as an inversion stage and a low feedback voltage is input as a non-inversion stage of the feedback voltages of the first to third LED strings. A second voltage detector is located between the LED string and the third comparator, and the second voltage detector transmits a small feedback voltage among the feedback voltages input from the first to third LED strings to the third comparator.

A current detection unit is disposed between the first to third LED strings and the control unit to detect currents of the first to third LED strings, and the first to third LED strings are connected to the drive voltage generating unit And the plurality of LEDs of the first to third LED strings are connected in series.

As described above, in the case where the number of LEDs of the backlight unit according to the present invention is an optimal design, a small number of LEDs may be constituted by a plurality of LED strings. In this case, It is possible to realize an optimal light source design for the liquid crystal display device of the present invention. Accordingly, it is possible to prevent the occurrence of problems such as the occurrence of hot spots and the increase in power consumption.

In particular, the number of LED strings of each LED string is detected by detecting a disconnection or defect of the LED string through a separate comparator having a separate reference voltage, so that even if the number of LEDs is small, There is an effect that it can be detected. This has the effect of preventing a problem that the LED string is damaged by the overcurrent or that the driving voltage generating unit that supplies the operating power to the LED string is damaged by the overvoltage.

1 is a view schematically showing a liquid crystal display device according to an embodiment of the present invention.
2 is a schematic view illustrating a driving integrated circuit and a backlight unit connected thereto according to an embodiment of the present invention;

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

1 is a view schematically showing a liquid crystal display device according to an embodiment of the present invention.

1, the liquid crystal display 100 according to the embodiment of the present invention includes a liquid crystal panel 110, a driver, and a backlight unit. The driver includes a timing control circuit 120, a gate driving circuit 130, and a data driving circuit 140, and the backlight unit includes an LED and a backlight driving circuit 160.

The liquid crystal panel 110 includes a plurality of gate lines GL extending in the row direction and a plurality of data lines DL extending in the column direction and includes a plurality of gate lines GL and a plurality of data lines DL intersect each other to define a plurality of pixels P in the form of a matrix.

A thin film transistor T connected to a gate line and data lines GL and DL is formed in each pixel P of the liquid crystal panel 110. The thin film transistor T is connected to a pixel electrode (not shown).

A common electrode (not shown) is formed corresponding to the pixel electrode (not shown), and an electric field is formed between the pixel electrode (not shown) and the common electrode (not shown) to drive the liquid crystal to display an image.

Here, the liquid crystal located between the pixel electrode (not shown) and the common electrode (not shown) and these electrodes constitutes the liquid crystal capacitor Clc.

A storage capacitor Cst is formed in each pixel P of the liquid crystal panel 110. The storage capacitor Cst holds a data voltage applied to a pixel electrode (not shown) until the next frame .

Each pixel P of the liquid crystal panel 110 may include red (R), green (G), and blue (B) pixels, and R, G, B data voltages can be input, and adjacent R, G, and B pixels (P) constitute one image unit.

The timing control circuit 120 receives a data signal RGB, a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync and a clock signal DCLK from an external system (not shown) such as a TV system or a video card, A control signal such as an enable signal DE can be input.

Although not shown, such a control signal may be input to the timing control circuit 120 via an interface.

The timing control circuit 120 generates a gate control signal GCS for controlling the gate driving circuit 130 and a data control signal DCS for controlling the data driving circuit 140 using the input control signal, .

The gate control signal GCS may include a gate start pulse GSP, a gate shift clock GSC, a gate output enable signal GOE, The data control signal DCS includes a source start pulse SSP, a source shift clock SSC, a source output enable SOE, a polarity POL, And the like.

On the other hand, the timing control circuit 120 can generate the backlight control signal BCS for controlling the backlight driving circuit 160 and generate the light emission data signal LDAT for controlling the light emission luminance of the LED have.

Although not shown, the driving unit may further include a gamma voltage generating circuit and a power supply circuit. The gamma voltage generating circuit divides a high potential voltage and a low potential voltage to generate a plurality of gamma voltages and supplies them to the data driving circuit 140 .

The power supply circuit can generate and supply a driving voltage for driving the components of the liquid crystal display device 100 by receiving a power supply voltage from the outside.

The gate driving circuit 130 sequentially scans a plurality of gate lines GL in units of frames in response to a gate control signal GCS supplied from the timing control circuit 120.

That is, during each scan period, a gate high voltage VGH that turns on the corresponding thin film transistor T is supplied to the gate line GL, and the corresponding thin film transistor T is supplied until the scan period of the next frame. To the gate line GL, a gate-low voltage VGL that turns off the gate line GL.

The data driving circuit 140 supplies the data voltage to the plurality of data lines DL in response to the data control signal DCS supplied from the timing control circuit 120, RGB), and outputs the generated data voltage to the corresponding data line DL.

The backlight unit 150 serves to supply light to the liquid crystal panel 110.

The backlight unit 150 includes a plurality of LED strings 151a, 151b, 151c and 151d (see FIG. 2), and each of the plurality of LED strings 151a, 151b, 151c and 151d .

The backlight driving circuit 160 generates a driving voltage and a driving current and supplies the driving voltage and the driving current to the backlight unit 150. The backlight driving circuit 160 generates a driving voltage and a driving current to be supplied to the plurality of LED strings 151a 151b 151c 151d, And may include a plurality of driving integrated circuits 210 (see FIG. 2) for controlling the driving voltage and the driving current according to the current.

Here, the liquid crystal display device 100 of the present invention can design the quantity of LED of the backlight unit 150 to have the optimum design.

That is, the liquid crystal display 100 of the present invention can provide a small number of LEDs as the LED strings 151a, 151b, 151c, and 151d (see FIG. 2) even if the number of LEDs is a prime number There is no problem such that a hot spot is generated or power consumption is increased.

In particular, even when the number of LEDs is a small number, overcurrent flows to the LED strings 151a, 151b, 151c and 151d (see FIG. 2) (See FIG. 2) of the drive integrated circuit 210 (see FIG. 2) for supplying the operating voltages of the LED strings 151a, 151b, 151c, 151d Can be prevented from being damaged by the overvoltage.

2 is a schematic view illustrating a driving integrated circuit and a backlight unit connected thereto according to an embodiment of the present invention.

As shown, the backlight unit 150 according to the embodiment of the present invention includes a plurality of LED strings 151a, 151b, 151c and 151d. In the present invention, four LED strings 151a, 151b, 151c and 151d ) Will be described as an example.

The first to fourth LED strings 151a, 151b, 151c and 151d are connected to the drive integrated circuit 210. [

Here, the first to fourth LED strings 151a, 151b, 151c and 151d are connected in parallel to each other, and the first to fourth LED strings 151a, 151b, 151c and 151d include a plurality of LEDs connected in series .

In this case, the fourth LED string 151d has a different number of LEDs than the first to third LED strings 151a, 151b and 151c,

That is, the fourth LED string 151d is configured such that the number of one LED is less or more than that of the first to third LED strings 151a, 151b, and 151c.

For example, when the number of LEDs of the backlight unit 150 having the optimum design for driving the liquid crystal display (100 of FIG. 1) of the present invention is 23, the first to third LED strings 151a, 151b, 151c are connected in series with six LEDs, and the fourth LED string 151d is connected in series with five LEDs.

Or the number of LEDs of the backlight unit 150 having the optimum design for driving the liquid crystal display device 100 (FIG. 1) is 21, the first to third LED strings 151a, 151b, and 151c are Five LEDs are connected in series, and the fourth LED string 151d has six LEDs connected in series.

Accordingly, the liquid crystal display (100 of FIG. 1) of the present invention can be configured to have the number of LEDs having the optimum design, thereby increasing the number of LEDs to increase the power consumption, It is possible to prevent a problem that a hot spot is generated from occurring.

A driving integrated circuit (D-IC) 210 includes a driving voltage generator 220, a controller 230, first and second voltage detectors 280 and 290, a current detector 260, 1 to a third comparator 240, 250, and 270, respectively.

The driving voltage generating unit 220 generates and outputs a driving voltage corresponding to the number of the first to fourth LED strings 151a, 151b, 151c, and 151d of the backlight unit 150. [

For example, the driving voltage generator 220 outputs a higher driving voltage as the number of the first through fourth LED strings 151a, 151b, 151c, and 151d increases, and the first through fourth LED strings 151a , 151b, 151c, and 151d, the lower driving voltage can be output.

The driving voltage generating unit 220 boosts the power supply voltage supplied from the outside to a voltage for driving the first to fourth LED strings 151a, 151b, 151c and 151d of the backlight unit 150, And the output voltage of the boost circuit is adjusted in accordance with a PWM (pulse width modulation) duty ratio so that the first to fourth LED strings 151a, 151b, 151c, and 151d of the backlight units 150a and 150b And an adjusting circuit for generating a driving voltage to be supplied.

The first to third comparators 240, 250, and 270 may compare the currents of the first to fourth LED strings 151a, 151b, 151c, and 151d with the first and second reference voltages VCC and VCC + And outputs the feedback voltage by comparing the feedback reference voltage Vsat to the control unit 230. [

The first to third LED strings 151a, 151b and 151c are connected to the first comparator 240. The first to third LED strings 151a, 151b and 151c are connected to a fourth LED The string 151d is connected to the second comparator 250. [

A first voltage detector 280 is disposed between the first comparator 240 and the first to third LED strings 151a, 151b and 151c. The first voltage detector 280 detects the first, The first comparator 240 outputs the largest feedback voltage after detecting the feedback voltage input from the first comparators 151a, 151b, and 151c.

Here, it is possible to detect the occurrence of a short-circuit defect of the first to third LED strings 151a, 151b and 151c through the first voltage detector 280. [

That is, when a short-circuit defect occurs in any one of the first to third LED strings 151a, 151b, and 151c, a voltage higher than the set voltage is caused to flow in the LED string.

Accordingly, the first to third LED strings 151a, 151b, and 151c output the largest feedback voltage among the feedback voltages to the first comparator 240 so that the first to third LED strings 151a, 151b, and 151c can be detected.

The first to fourth LED strings 151a, 151b, 151c and 151d are connected to the second voltage detector 290. The second voltage detector 290 detects the first to fourth LED strings 151a, 151b, 151c, and 151d, and then outputs the smallest feedback voltage to the third comparator 270. [

Here, through the second voltage detector 280, it is possible to detect whether an open defect has occurred in the first to fourth LED strings 151a, 151b, 151c, and 151d.

That is, when an open defect occurs in any one of the first to fourth LED strings 151a, 151b, 151c, and 151d, a voltage lower than a set voltage is caused to flow in the LED string.

Accordingly, by outputting the smallest feedback voltage among the feedback voltages input from the first to fourth LED strings 151a, 151b, 151c, and 151d to the third comparator 240, the first to fourth LED strings 151a, 151b, 151c, and 151d can be detected.

The current detector 260 detects the feedback currents flowing through the first to fourth LED strings 151a, 151b, 151c and 151d and then compares the feedback current with the current input from the drive voltage generator 220 And outputs the result to the control unit 230.

The control unit 230 may include a conversion unit and a determination unit. The conversion unit may include a plurality of conversion units corresponding to the first through third comparators 240, 250, and 270 and the current detection unit 260, respectively. As the conversion unit, an analog-digital converter (ADC) can be used.

Each analog-to-digital converter converts the input analog feedback voltage and feedback current into a digital feedback signal.

The determination unit determines the states of the LED strings 151a, 151b, 151c, and 151d input by the comparators 240, 250, and 270 and the current detection unit 260 through the feedback signal output from the analog- do.

For example, the determination unit determines whether the feedback signals of the first to third comparators 240, 250, and 270 and the current detection unit 260 meet the conditions of the steady state or the conditions of the abnormal state.

The information detected through the determination unit is transmitted to the driving voltage generation unit 220. At this time, when a defect of the first to fourth LED strings 151a, 151b, 151c, and 151d is detected, the controller 230 interrupts the generation of the driving voltage of the driving voltage generator 220, The driving voltage is not transmitted to the LED strings 151a, 151b, 151c, and 151d, or the driving voltage is lowered.

Also, the correction value is detected for the current to raise or lower the current value.

One end of each of the first to fourth LED strings 151a, 151b, 151c and 151d is commonly connected to the driving voltage generator 220 .

Accordingly, the plurality of LED strings 151a, 151b, 151c, and 151d receive the same driving voltage at their one ends.

The ends of the first to third LED strings 151a, 151b and 151c are connected to the first and second voltage detecting units 280 and 290 and the current detecting unit 260. The first and second current detecting units 280 and 280, And the current detection unit 260 receives the feedback currents of the first and second LED strings 151a, 151b, and 151c. The current detection unit 260 receives the feedback currents of the first and second LED strings 151a, 151b, and 151c, .

The end of the fourth LED string 151d is connected to the second comparator 250 and the current detector 260. The second comparator 250 receives the feedback voltage of the fourth LED string 151d, The detection unit 260 receives the feedback current of the fourth LED string 151d.

At this time, the first reference voltage VCC is inputted to the inverting terminal (-) of the first comparator 240 and the first voltage detecting unit 280 is connected to the non-inverting terminal (+ 151a, 151b, and 151c.

The feedback voltage of the fourth LED string 151d is input to the non-inverting terminal (+) of the second comparator 250 and the second reference voltage (VCC + X) is input to the inverting terminal (-).

The second comparator 270 receives the lowest feedback reference voltage Vsat as the inversion stage and the second voltage detection unit 290 as the non-inverting stage. The lowest feedback voltage among the strings 151a, 151b, 151c, and 151d is input.

The output terminals of the first to third comparators 240, 250 and 270 and the current detector 260 are connected to the controller 230 and are connected to the first to third comparators 240, 250 and 270 and the current detector 260 Is input to the control unit 230. [0053]

The feedback voltage and the feedback current from the first to third comparators 240, 250 and 270 and the current detector 260 are input to the converter of the controller 230.

The feedback process of the first to fourth LED strings 151a, 151b, 151c and 151d of the backlight unit 150 will be described in detail. The feedback voltages of the first to third LED strings 151a, 151b, The first feedback voltage of the first to third LED strings 151a, 151b and 151c applied to the first voltage detection unit is transmitted to the first comparator 240 do.

The first feedback voltage transmitted to the first comparator 240 is compared with the first reference voltage VCC so that if the first feedback voltage is higher than the first reference voltage VCC, .

At this time, the first reference voltage VCC is preferably smaller than the driving voltage of one LED.

The feedback voltage is applied to the second voltage detector 290 from the first to fourth LED strings 151a, 151b, 151c and 151d and the first to fourth feedback signals The lowest one of the voltages 151a, 151b, 151c, and 151d is transmitted to the third comparator 270.

The feedback voltage transmitted to the third comparator 270 is compared with the lowest feedback reference voltage Vsat and when the feedback voltage is lower than the lowest feedback reference voltage Vsat, the feedback voltage is transmitted to the controller 230.

The fourth LED string 151d transmits the third feedback voltage directly to the second comparator 250. The fourth LED string 151d is connected to the first through third LED strings 151a 151b 151c, The second comparator 250 compares the first reference voltage VCC with a second reference voltage VCC +/- X that is different from the first reference voltage VCC.

Here, X of the second reference voltage VCC + X is greater than the number of LEDs of the first to third LED strings 151a, 151b, and 151c that apply the first feedback voltage to the first comparator 240 It is preferable that the fourth LED string 151d with a small quantity corresponds to the number of added or deleted LEDs.

That is, the second comparison voltage VCC + X can be defined by the following equation (1).

(VCC + X) = VCC ± (VLED * number of LEDs deleted or added)

Here, the VLED represents a driving voltage for driving one LED.

For example, when a driving voltage for driving one LED of the first to third LED strings 151a, 151b and 151c is 3V and six LEDs are serially connected to the respective LED strings 151a, 151b and 151c, A driving voltage of 20V is applied to drive the LED strings 151a, 151b, and 151c.

At this time, the first reference voltage is designed to be 2V, 18V is used to drive substantially six LEDs, and 2V is transmitted to the first comparator 240 as a first feedback voltage.

The first feedback voltage and the first reference voltage VCC transmitted to the first comparator 240 are compared by the first comparator 240 and then transmitted to the controller 230. The first comparator 240, It is judged whether the first feedback signal of the first feedback signal meets the condition of the steady state or the condition of the abnormal state.

Here, since the first feedback voltage is equal to the first reference voltage VCC, it can be confirmed that the LED strings 151a, 151b, and 151c are in a normal state.

When the number of LEDs is smaller than that of the first to third LED strings 151a, 151b and 151c, the second reference voltage VCC +/- X is designed to be 5V do.

Accordingly, even if the fourth LED string 151d is connected in series with the five LEDs, the same driving voltage of 20V as that of the first to third LED strings 151a, 151b, and 151c is applied to the fourth LED string 151d Where 15V is used to drive substantially five LEDs, and 5V is passed to the second comparator 250 as a second feedback voltage.

The second feedback voltage and the second reference voltage VCC ± X transmitted to the second comparator 250 are compared by the second comparator 250 and then transmitted to the controller 230 to output a second feedback signal Is in conformity with the condition of the steady state or with the condition of the abnormal condition.

At this time, the second feedback voltage of 5V delivered to the second comparator 250 is equal to the second reference voltage (VCC + X) of 5V, thereby confirming that the fourth LED string 151d is in a normal state.

Conversely, when five LEDs are connected in series to the first to third LED strings 151a, 151b and 151c and six LEDs are connected in series to the fourth LED string 151d, the first reference voltage VCC) is designed to 5V, and the second reference voltage (VCC + X) is designed to be 3V.

Accordingly, 21V is applied to each of the first to fourth LED strings 151a, 151b, 151c and 151d. At this time, 15V of the 21V applied to the first to third LED strings 151a, 151b and 151c is substantially 5V is used to drive the five LEDs, and the 5V is transmitted to the first comparator 240 as the first feedback voltage.

At this time, since the first feedback voltage of 5V transmitted to the first comparator 240 is the same as the first reference voltage VCC of 5V, the first to third LED strings 151a, 151b, .

18V of the 21V applied to the fourth LED string 151d is used to drive substantially six LEDs and 3V is transmitted to the second comparator 250 as a third feedback voltage, The third feedback voltage of 3V transmitted to the second LED string 250 is the same as the second reference voltage VCC + X of 3V. Accordingly, it can be confirmed that the fourth LED string 151d is in a normal state.

That is, when the number of LEDs of the backlight unit 150 is an optimal design, the number of the LED strings 151a, 151b, 151c, and 151d in the liquid crystal display 100 of the present invention It is possible to realize an optimal light source design for the liquid crystal display of the present invention (100 in FIG. 1) by designing one LED string differently from the other LED strings in the number of LEDs.

Thus, it is possible to prevent the occurrence of problems such as occurrence of hot spots and increase in power consumption.

Particularly, the LED string 151d having a different quantity among the LED strings 151a, 151b, 151c, and 151d is disconnected through a separate comparator 250 having a separate reference voltage VCC ± X, It is possible to detect whether the LED strings 151a, 151b, 151c, and 151d are broken or not, even if the number of LEDs is a prime number.

Accordingly, the drive voltage generating unit 220, in which the LED strings 151a, 151b, 151c and 151d are damaged by the overcurrent or the operating strings of the LED strings 151a, 151b, 151c and 151d, Can be prevented.

That is, any one of the feedback voltages input from the first to third comparators 240, 250, and 270 as a result of the determination by the controller 230 may be applied to the reference voltages VCC and VCC ± X and the minimum feedback reference voltage Vsat The LEDs 151a, 151b, 151c, and 151d for inputting the feedback voltage to the first to third comparators 240, 250, and 270, respectively, Which means that a defect has occurred.

If any one of the feedback voltages input from the first to third comparators 240, 250, and 270 is in an abnormal state, the entire backlight unit 150 is adversely affected. Therefore, the backlight unit 150 The operation of protecting the backlight unit 150 may be performed by blocking the generation of the driving voltage of the driving voltage generator 220 or by lowering the driving voltage.

Here, when an open defect occurs in the LED strings 151a, 151b, 151c, and 151d, the LED string in which the open defect occurs has a lower voltage than the other LED strings. Accordingly, the third comparator 270 The open-defect of the LED occurs when a voltage significantly lower than the lowest feedback reference voltage Vsat is detected.

As such, if an open defect of the LED occurs, an overvoltage is caused to flow through the LED string that has not suffered an open defect, thereby causing damage to the LED of the normal LED string.

In order to protect the backlight unit 150 in such an overvoltage condition, it is desirable to lower the overvoltage flowing through the LED strings 151a, 151b, 151c and 151d. The control unit 230 transmits the signal to the driving voltage generator 220 to stop or lower the generation of the driving voltage so that the overvoltage state of the normal LED string is relaxed, Can be protected.

When a short defect occurs in any one of the LED strings 151a, 151b, 151c, and 151d, a current higher than the set current flows in the LED string in which the short defect occurs.

When the first and second feedback voltages inputted to the first and second comparators 240 and 250 are compared with the first and second reference voltages VCC and VCC ± X and a significantly higher voltage is detected, Short-circuiting defect of "

If a short-circuit defect occurs in this manner, an overvoltage may flow in the LED string where a short-circuit defect occurs, which may lead to damage of the normal LED in the LED string. Therefore, the backlight unit 150 can be protected by lowering the driving voltage so as to relax the overvoltage state of the LED string having the short-circuit defect.

As described above, when the open / short defect is determined to have occurred in at least one LED string, it is possible to protect the backlight unit 150 by mitigating the overvoltage flowing through the LED string.

By displaying on the liquid crystal panel (110 in FIG. 1) that a defect has occurred in the backlight unit 150 in addition to the method of adjusting the voltage flowing through the LED strings 151a, 151b, 151c and 151d as described above, So that the backlight unit 150 can be protected.

As described above, in the liquid crystal display (100 of FIG. 1) of the present invention, when the number of LEDs of the backlight unit 150 is a prime number design, a small number of LEDs are divided into a plurality of LED strings 151a, 151b and 151c And 151d, the number of LEDs 151a, 151b and 151c is designed to be different from that of the other LED strings 151a, 151b and 151c, The light source design of FIG.

Thus, it is possible to prevent the occurrence of problems such as occurrence of hot spots and increase in power consumption.

In particular, the LED string 151d having a different quantity among the LED strings 151a, 151b, 151c, and 151d is connected to the LED strings 151a, 151b, 151c through a separate comparator 250 having a separate reference voltage VCC + 151c and 151d of the LED strings 151a, 151b, 151c and 151d are detected, it is possible to detect whether the LED strings 151a, 151b, 151c and 151d are open or not, even if the number of LEDs is small.

Accordingly, the drive voltage generating unit 220, in which the LED strings 151a, 151b, 151c and 151d are damaged by the overcurrent or the operating strings of the LED strings 151a, 151b, 151c and 151d, Can be prevented.

The present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention.

150: Backlight unit
151a, 151b, 151c and 151d: first to fourth LED strings
210: drive integrated circuit
220: driving voltage generating unit
230:
240, 250: first and second comparators
260: current detector
270: third comparator
280, 290: first and second voltage detecting units
VCC: first reference voltage
VCC 占:: Second reference voltage
Vsat: lowest feedback reference voltage

Claims (9)

A driving voltage generator;
First and second LED strings connected to the driving voltage generating unit and each including a plurality of LEDs;
A third LED string connected to the driving voltage generating unit, the third LED string including a plurality of LEDs having different numbers of the first and second LED strings and the LEDs;
A first comparator for comparing the first feedback voltage of the first and second LED strings with a first reference voltage to output an output voltage;
A second comparator for comparing the second feedback voltage of the third LED string with a second reference voltage to output an output voltage;
Wherein the first and third LED strings are connected to the first and second LED strings, and the first and third LED strings are connected to the first and second LED strings, A control unit for lowering the driving voltage of the driving voltage generating unit,
And a backlight unit for backlighting the liquid crystal display device.
The method according to claim 1,
Wherein the third LED string has one or fewer LEDs than the first and second LED strings.
The method according to claim 1,
Wherein the first reference voltage is input to the inverting terminal of the first comparator, the first feedback voltage is input to the non-inverting terminal of the first comparator, and the second reference voltage is input to the inverting terminal of the second comparator And the second feedback voltage is input to the non-inverting terminal of the second comparator.
The method of claim 3,
The second reference voltage is designed with the first reference voltage VCC +/- X, where X is a voltage VLED (a driving voltage for driving one LED), or is added to each of the first and second LED strings And the number of LEDs that have been removed.
The method according to claim 1,
And a first voltage detector is provided between the first and second LED strings and the first comparator to transmit the first larger feedback voltage among the feedback voltages input from the first and second LED strings to the first comparator And a backlight unit for a liquid crystal display device.
The method according to claim 1,
Further comprising a third comparator to which a lowest feedback reference voltage is input as an inversion stage and a low feedback voltage of a feedback voltage of the first to third LED strings is inputted as a non-inverting stage.
The method according to claim 6,
A second voltage detector is located between the first to third LED strings and the third comparator and the second voltage detector detects a small feedback voltage among the feedback voltages inputted from the first to third LED strings, And transmits it to the comparator.
The method according to claim 1,
And a current detection unit is disposed between the first to third LED strings and the control unit to detect currents of the first to third LED strings.
The method according to claim 1,
Wherein the first to third LED strings are connected in parallel with the drive voltage generating unit and the plurality of LEDs of the first to third LED strings are connected in series.

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