KR20120076948A - Apparatus for protecting a light emitting diode, its method and liquid crystal display using the same - Google Patents

Abstract

PURPOSE: A light emitting diode protecting device and method, and a liquid crystal display using the same are provided to steadily drive an LED array by establishing a detection period and applying a detection voltage to a light emitting diode string. CONSTITUTION: A plurality of constant current transistors is respectively connected between a detection resistance and a plurality of LED strings(812) included in an LED array(810). A plurality of detection lines is connected to a node between the constant current transistor and the detection resistance. The plurality of detection lines detects a current flowing in the plurality of constant current transistors. A circuit unit(930) determines whether a disconnected light emitting diode exists in the plurality of LED strings or not. The circuit unit blocks the radiation of the LED string in which the disconnected light emitting diode exists.

Description

Light emitting diode protection device and method and liquid crystal display device using the same {APPARATUS FOR PROTECTING A LIGHT EMITTING DIODE, ITS METHOD AND LIQUID CRYSTAL DISPLAY USING THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode protection device, and more particularly, to a device for protecting a light emitting diode used in a backlight unit of a liquid crystal display device.

Recently, flat panel displays have shown explosive growth. Flat panel displays are widely used in mobile devices that require miniaturization and low power, as well as large digital TVs that require weight and thickness reduction.

Among them, a liquid crystal display (LCD) is most widely used among flat panel displays due to its advantages of being applicable to small devices and large devices.

On the other hand, the liquid crystal display device requires a light source called a backlight unit (BLU) on the back of the liquid crystal panel because the liquid crystal panel does not emit light by itself. That is, the light generated by the backlight unit passes through the liquid crystal layer and the color filter of the liquid crystal panel to show the screen to the outside. Thus, the backlight unit has a significant effect on the performance of the LCD display device.

For example, not only screen quality such as color reproducibility, maximum brightness, contrast ratio, white uniformity, color temperature, etc., but also weight, design, lifespan, and power consumption of the liquid crystal display device may be significantly affected by the backlight unit.

Conventionally, a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), or the like is widely used as a light source of a backlight unit.

Recently, however, light emitting diodes (LEDs) with sufficiently high luminance, low power consumption and low manufacturing cost have been developed to replace the backlights as described above. That is, the backlight unit using the light emitting diode (LED) array does not need to use an expensive diffusion film or the like, and unlike an fluorescent lamp, an inverter is not required, so that manufacturing cost can be reduced, and the size and weight are also advantageous. It is also widely used because it can reduce the power consumption and environmental problems.

In the backlight unit using a light emitting diode, a number of light emitting diodes are configured in the form of a light emitting diode string, and the light emitting diode string is formed of an array of light emitting diodes. Since the light emitting diode array emits light by the light emitting diode, the performance of the light emitting diode array is determined by the method of driving each light emitting diode.

The amount of light emitted by the light emitting diode may be roughly proportional to the magnitude of the driving current passing through the active layer of the light emitting diode, and the driving of the light emitting diode refers to a method of supplying and controlling the driving current.

In general, the light emitting diode driving method may be largely divided into a constant voltage driving method and a constant current driving method.

First, the constant voltage driving method has a simple circuit configuration, but heat is generated when the light emitting diode emits light, and the driving current passing through the light emitting diode active layer is generally a forward voltage drop of the light emitting diode when the temperature increases. Since there is this increasing characteristic, the change in luminance may occur severely as the light emission time increases.

On the other hand, in the constant current driving method, since the driving current is controlled to be constant even when the temperature changes, the amount of emitted light is also kept constant, thereby greatly reducing the luminance change. In this case, the expression that the driving current is constant means that the driving current is continuously variable over time but remains constant on average.

Therefore, in recent years, the constant current driving method is more widely used. In other words, if the light emitting diodes do not emit a constant amount of light, the screen quality may appear blemished, so that the image quality is poor. Therefore, keeping the light emitting diodes constant and emitting light according to the set conditions is very important for the performance of the liquid crystal display device. For this reason, the constant current drive system in which the drive current is controlled constantly is widely used.

1 is an exemplary view showing the configuration of a conventional light emitting diode protection device.

In the constant current driving scheme as described above, a light emitting diode driving IC (LED D-IC) (hereinafter simply referred to as an 'LED D-IC') 10 is used to control the light emitting diode with a constant current. The IC consists of a VI converter for constant current control, and the VI converter consists of an OP-AMP and a constant current transistor.

However, in the case where the constant current transistor is configured in the LED D-IC, the unit cost of the LED D-IC and the like increase, so that as shown in FIG. 1, each of the LED strings of the LED array 40 The connected constant current transistor 20 is formed outside the LED D-IC.

That is, in the conventional LED protection apparatus, as shown in FIG. 1, the constant current transistor 20, the LED D-IC 10, and each of the light emitting diodes connected to the ends of each of the LED strings of the LED array 40 are provided. And a diode 30 connected to the LED D-IC and a node between the diode string and the constant current transistor.

On the other hand, the conventional LED protection device as described above, the collector (or the collector (or collector) of the constant current transistor 20 by using the diode 30 for short detection of each light emitting diode string (string). The drain stage sensing is required, and a voltage-resistant process corresponding to the LED short detect level is required in the sensing unit 11 of the LED D-IC (usually 18V or more).

In this case, when the high voltage resistance LED D-IC is used, the unit cost of the LED D-IC manufacturing process increases and the price of the LED D-IC increases, and the number of diodes 30 for sensing the constant current transistors of each LED string is increased. Due to the increase, the number of pins of the LED D-IC increases, which causes a problem that the price of the LED D-IC increases.

That is, the conventional LED protection device generates the above problems by directly sensing the collector terminal of the constant current transistor Tr using the LED D-IC and the diode 30 connected to each LED string. Doing.

In addition, the conventional LED protection apparatus performs control for supplying a constant current after a soft start period for gradually raising the final voltage required for the LED array, that is, during a normal operation period in which the LED is operated by the final voltage. It is detected whether the light emitting diode is shorted in each light emitting diode string.

Therefore, even if the LED is detected in the state where the LED array 40 is driven by the final voltage, the constant current transistor 20 connected to the LED string is already damaged or damaged. For this reason, there arises a problem that even a constant current transistor needs to be replaced.

That is, when the light emitting diode mounted on the light emitting diode string is shorted, the voltage to be applied to the light emitting diode is applied to the constant current transistor connected to the light emitting diode string, and the applied voltage is outside the rated voltage of the constant current transistor. Because of the high possibility, the constant current transistor 20 can be broken or damaged. Therefore, the conventional light emitting diode protection device is accompanied with a breakdown of the constant current transistor together with a short of the light emitting diode, so even if the normal operation is possible by replacing only the light emitting diode, it is necessary to replace the constant current transistor, so the replacement operation for this And cost is added.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and sets a detection period during a soft start period so that a detection voltage set lower than a final voltage is applied to the light emitting diode string during the detection period, and through the light emitting diode string during the detection period. It is a technical object of the present invention to provide a light emitting diode protection device and a method thereof, and a liquid crystal display device using the same, which can determine whether a light emitting diode is shorted in the light emitting diode string by using current.

According to an aspect of the present invention, there is provided a light emitting diode protection device including: a plurality of constant current transistors connected between each of a plurality of LED strings and a detection resistor provided in an LED array; A plurality of detection lines connected to a node between the constant current transistor and the detection resistor for detecting a current flowing through the constant current transistor; And determining whether or not there is a shorted light emitting diode in the LED string to which the detection line is connected, using the amount of current flowing through the detection line during the soft start period for supplying the final voltage to the LED string. And a circuit portion for blocking the LED string with the light emitting diodes from emitting light.

The liquid crystal display device using the light emitting diode protection device according to the present invention for achieving the above technical problem, the light emitting diode protection device; A liquid crystal panel; A data driver for controlling a data line formed in the liquid crystal panel; A gate driver for controlling a gate line formed in the liquid crystal panel; A backlight unit configured of an LED array for irradiating light onto the liquid crystal panel and controlled by the light emitting diode protection device; And a power supply unit for supplying power to the LED array.

According to an aspect of the present invention, there is provided a method of protecting a light emitting diode, the method including: maintaining a power applied to an LED array including a plurality of LED strings at a detection voltage having a value lower than a final voltage; Determining whether there is a shorted light emitting diode in each of the plurality of LED strings during a detection period during which the detection voltage is kept constant; According to the determination, blocking the LED string with the shorted LED and controlling the constant current transistor connected to the LED string when there is no shorted LED so that a constant current flows into the LED string; And controlling the constant current transistor to flow a constant current through the LED string after the detection period.

According to the above solution, the present invention provides the following effects.

That is, the present invention sets the detection period during the soft start period so that the detection voltage set lower than the final voltage is applied to the light emitting diode string during the detection period, and whether or not current flows through the light emitting diode string during the detection period. By determining whether the LED is shorted in the LED string, the LED array can be stably driven.

In addition, the present invention can be implemented through some modifications of the conventional constant current driving device, and provides an effect of detecting the short circuit of the light emitting diode without adding a separate circuit.

That is, the present invention can detect whether the light emitting diode of each light emitting diode string is shorted without sensing the collector terminal of the driving transistor by using a detection diode, so that the constant current driver (LED D-IC) The number of pins can be reduced, and the voltage resistance process of the constant current driver can be made 3.3V, which reduces the cost of the constant current driver (LED D-IC).

1 is an exemplary view showing the configuration of a conventional light emitting diode protection device.
2 is a configuration diagram of a liquid crystal display device to which a light emitting diode protection device according to the present invention is applied.
Figure 3 is a configuration diagram of an embodiment of a light emitting diode protection device according to the present invention.
4 is a graph showing a voltage change during a soft start period applied to the LED protection device according to the present invention.
Figure 5 is another embodiment configuration of a light emitting diode protection device according to the present invention.

Hereinafter, with reference to the accompanying drawings will be described in detail an embodiment of the present invention.

2 is a configuration diagram of an LCD device to which a light emitting diode protection device according to the present invention is applied.

As shown in FIG. 2, the LCD including the LED protection device 900 according to the present invention includes a liquid crystal panel 102, a timing controller 108, a data driver 106, a power supply unit 400, and a gate. A driver 104, a backlight unit 800, and a light emitting diode protection device 900 are included.

The liquid crystal panel 102 includes liquid crystal molecules dropped between two glass substrates. In the liquid crystal panel, m × n liquid crystal cells Clc are arranged in a matrix form by the intersection structure of the data lines DL1 to DLm and the gate lines GL1 to GLn.

The lower glass substrate of the liquid crystal panel has m data lines D1 to Dm, n gate lines G1 to Gn, TFTs, pixel electrodes of the liquid crystal cell Clc connected to the TFT, and a storage capacitor Cst. ) Is formed.

The black matrix, the color filter, and the common electrode are formed on the upper glass substrate of the liquid crystal panel. The common electrode is formed on the upper glass substrate in a vertical electric field driving method such as twisted nematic (TN) mode and vertical alignment (VA) mode, and a horizontal electric field such as IPS (In Plane Switching) mode and FFS (Fringe Field Switching) mode. The driving method is formed on the lower glass substrate together with the pixel electrode. A polarizing plate having an optical axis orthogonal to each other is attached to the upper glass substrate and the lower glass substrate of the liquid crystal panel, and an alignment layer for setting the pretilt angle of the liquid crystal is formed on an inner surface of the liquid crystal panel in contact with the liquid crystal.

The timing controller 108 receives timing signals such as vertical / horizontal synchronization signals (Vsync, Hsync), data enable, clock signal (CLK), and the like to operate the data driver 106 and the gate driver 104. Generate control signals for controlling timing. These control signals include a gate start pulse (GSP), a gate shift clock signal (GSC), a gate output enable signal (GOE), and a source start pulse (SSP). , A source sampling clock (SSC), a source output enable signal (SOE), a polarity control signal (POL), and the like. In addition, the timing controller rearranges the input digital video data RGB to the liquid crystal panel 102 and supplies the digital video data RGB to the data driver 106.

The data driver 106 consists of a number of gate drive ICs (not shown) including shift registers, first and second latches, digital-to-analog converters and output buffers that are cascaded between the input and data lines. . The data driver latches data RGB under the control of the timing controller 108 and converts the data into an analog positive / negative gamma compensation voltage to generate a positive / negative data voltage and convert the data voltage to a data line. To Dl to Dm.

The gate driver 104 includes a shift register, a level shifter for converting an output signal of the shift register into a swing width suitable for TFT driving of the liquid crystal cell, and an output buffer connected between the level shifter and the gate lines GL1 to GLn, respectively. A plurality of gate drive integrated circuits sequentially output scan pulses having a pulse width of approximately one horizontal period to the gate lines.

Since the backlight unit 800 does not emit light by itself, the backlight unit 800 is disposed on the rear side of the liquid crystal panel and outputs light in the direction of the liquid crystal panel. The backlight unit 800 is directly aligned with an edge type according to an arrangement method of a light source. It can be classified as (Direct Type). Meanwhile, the present invention uses a light emitting diode (hereinafter, simply referred to as 'LED') as a light source, and the light source using the LED includes a plurality of LED strings in which a plurality of LEDs are arranged side by side. It consists of an array. Therefore, hereinafter, a liquid crystal display using a direct type backlight unit will be described as an example, but the present invention can also be applied to a liquid crystal display using a photometric backlight unit having at least two strings.

The light emitting diode protection device 900 performs a function of allowing a constant current to flow for each LED string, and determining whether the LEDs are short for each LED string, and as a LED string in which a shorted LED is mounted. It cuts off power supply or blocks current from flowing to corresponding LED string.

The power supply unit 400 is to perform a function of supplying power required to the LED array, especially among the backlight units, and to cut off the power supplied to the LED string in which the short is generated from the light emitting diode protection device as described above. When is received, it may perform a function to cut off the power supply to the LED string.

3 is a configuration diagram of an embodiment of a light emitting diode protection device according to the present invention. 4 is a graph showing a voltage change during a soft start period applied to the light emitting diode protection device according to the present invention.

As shown in FIG. 3, the LED protecting apparatus 900 according to the present invention determines whether the LED is shorted in each of the LED strings 812 in which the plurality of LEDs 811 are arranged in series. Each of the plurality of LED strings 812 and the circuit unit 930 to perform a function to cut off the power supply to the LED string in which the shorted light emitting diode is disposed or to block the flow of current through the LED string; A constant current transistor 910 connected between the detection resistors 950 and a gate or base terminal connected to the circuit portion, and a node between the constant current transistor and the detection resistor and the circuit portion to apply a current flowing through the constant current transistor to the circuit portion. And a detection line 940.

As described above, the backlight unit 800 includes an LED array 810 in which a plurality of LED strings 812 are connected in parallel, and a plurality of LEDs 811 are connected in series to each of the plurality of LED strings. It is. The plurality of LEDs may emit, for example, one of primary colors of red, green, and blue, and a color or white light representing a combination of three primary colors.

Although the constant current transistor 910 is illustrated as an example of an N-type BJT transistor in FIG. 3, the constant current transistor 910 may be implemented as a P-type BJT transistor disposed in front of the LED array 810, or in addition to the N-type or P-type MOS transistor. Can be implemented. That is, the constant current transistor performs a function of allowing a constant current to flow in the LED string 812 connected thereto. This function may be performed in the constant current driver, particularly in the circuit part connected to the constant current transistor.

The circuit unit 930 determines whether each LED string is shorted by using the current input through each detection line 940 during the detection period of the soft start period for the LED array, and accordingly to the corresponding LED string It cuts the applied power or current, and controls the magnitude of voltage or current applied to each constant current transistor 910 by using the current input through each detection line during the normal operation period after the soft start period. In addition, it performs a function to allow constant current to flow to each LED string. To this end, as illustrated in FIG. 3, the circuit unit 930 includes a constant current driver 933, a switching unit 932, and a controller 931.

As described above, the constant current driver 933 uses the amount of current input through the detection line 940 after passing through the constant current transistor 910 and is greater than a preset current, that is, a voltage higher than or equal to the preset resistance. When this is applied, the constant current transistor is controlled to allow a small current to flow, and when less than the preset current, that is, when a predetermined voltage or less is applied to the detection resistor, the constant current transistor is controlled to allow a large current to flow. It performs the function.

The control unit 931 controls the power supply unit 400 so that the predetermined detection voltage Vd is constantly applied to the LED array during the detection period during the soft start period, and detects that a constant current flows from the constant current driver during the detection period. If it is determined that there is a light emitting diode shorted in the corresponding LED string and performs the function accordingly.

The switching unit 932 performs a function of turning off the constant current transistor so that no current flows through the constant current transistor 910 connected to the LED string in which the shorted light emitting diode is disposed under the control of the controller. On the other hand, the present invention by blocking the power supplied to the LED string is disposed short LED, it is possible to cut off the flow of current to the LED string, in this case, the control unit cuts off the power supply to the LED string The control signal may be transmitted directly to the power supply unit, in which case the switching unit 932 may be omitted.

That is, the circuit unit 930 to be applied to the present invention, during the soft start period of gradually increasing the voltage required to drive the LED array 810 composed of LEDs, more precisely, particularly during the soft start period. During the detection period B in which the detection voltage Vd set to a value smaller than the final voltage Vf supplied to the array is constantly supplied to the LED array, it is determined whether each LED string is shorted, and the soft start period is determined. During the subsequent normal operation period, the constant current transistor is controlled to flow a constant current through each LED string.

Here, the soft start period refers to a section in which the voltage is gradually increased up to the final voltage Vf to prevent inrush current when driving the LED array 810 composed of LEDs. Inrush current refers to a phenomenon in which a lot of current flows instantaneously when the power switch is first turned on.

In detail, the present invention detects a current flowing through the constant current transistor 910 during the detection period B during the soft start period, so that a voltage Vd which is not sufficient to drive the LED string 812 is applied. By checking whether the LED is still running even in the closed state, it is possible to detect the short failure of the LED inside the LED string without adding a peripheral circuit, and the detected level of the shorted LED (LED detect Level) In other words, the detection voltage Vd can be freely set.

Hereinafter, a light emitting diode protection method using a light emitting diode protection device according to the present invention will be described with reference to FIGS. 3 and 4. In addition, a method of protecting a light emitting diode by detecting whether a short is detected with respect to one LED string will be described below. However, the present invention simultaneously shorts all LED strings during a detection period B using the method described below. By detecting whether or not the LED string of the LED string and the constant current transistor can be protected.

First, when power is applied to the liquid crystal display, the power supply unit 400 gradually increases the voltage during the first period A as shown in FIG. 4 to prevent the inrush current as described above.

When the voltage is gradually increased to reach a voltage for LED short detection (hereinafter, simply referred to as 'detection voltage Vd'), the power supply unit maintains the detection voltage Vd for the detection period B. In this case, the function of detecting the detection voltage Vd and maintaining the detection voltage for the detection period B may be performed by the power supply unit itself, or may be performed by the power supply unit under the control of the controller 931.

Here, the detection voltage Vd is smaller than the final voltage Vf supplied to the LED string during the normal operation period, and the detection voltage Vd is a value of the final voltage applied to the LED string and the short of the light emitting diode in the LED array. It may be variously set in consideration of the voltage for determining.

During the detection period B, as in the normal operation period, the constant current driver 933 uses the amount of current input through the detection line 940 through the constant current transistor 910 to be larger than the preset current. That is, when a predetermined voltage or more is applied to the detection resistor 950, the current is controlled to flow less by controlling the constant current transistor, and when less than the preset current, that is, a predetermined voltage or less is applied to the detection resistor. In this case, the constant current transistor is controlled so that a large amount of current flows.

On the other hand, when the detection voltage Vd that has not reached the final voltage Vf is applied to the LED array and the current flows through the detection resistor, the constant current control means that there is a shorted light emitting diode in the LED array. When the current flows from the detection resistor, it may be determined that the light emitting diode of the corresponding LED string is shorted.

This will be described in detail.

For convenience of explanation, hereinafter, the string steady voltage required for each LED string is 96.7V, and the drive steady voltage required for the drive transistor is 3.3V. Therefore, the final voltage (100V) of the voltage supply unit during the normal operation period ( The present invention will be described taking as an example the case where Vf) is applied between each LED string and ground. That is, when a voltage of 100V is applied between the LED string and the ground, the present invention will be described assuming that 96.7V is applied to the LED string by the plurality of LEDs, and the remaining 3.3V is detected through the detection resistor.

In addition, if at least one LED of the LED string is shorted and the string steady voltage is about 1.1V lower than 96.7V, and instead a 1.1V voltage to be applied to the shorted LED is applied to the constant current transistor, the constant current transistor is broken or normal. Assume that it does not work. Therefore, in FIG. 4, the final voltage Vf is 100V and the detection voltage Vd is 98.9V.

Therefore, when the voltage gradually increases during the soft start period to reach 98.9 V, which is the detection voltage Vd, the voltage applied between each LED string and the ground during the detection period B is then fixed to 98.9 V.

At this time, the controller 931 determines whether the current applied through the detection line 940 flows less than the current in the normal operation state.

First, that the current applied through the detection line 940 flows less than the current in the normal operating state means that the current flowing through the LED string 810 is smaller than the current in the normal operating state, which shorts the LED string. It means that there is no light emitting diode. In this case, the current flowing through the detection line corresponds to a very small value compared to the steady state current.

That is, if there is no light emitting diode shorted in the LED string, 98.9V is applied between the string and ground, so that 3.3V, which is a driving normal voltage, is applied to the constant current transistor, and the remaining 95.6V is applied to the LED string.

However, since the string steady voltage for driving the LED string is set to 96.7V, less current flows through the LED string when 95.6V smaller than 96.7V is applied to the LED string. That is, since 95.6V alone cannot drive all the LEDs in the LED string to a normal state, the amount of current is reduced in the LED string.

Therefore, a small current flows through the detection line 940 connected to the LED string. In this case, the controller may determine that the LED string is in a normal state.

Next, if there is a current applied through the detection line 940, and the constant current control is performed by the constant current driver 933, this means that the LED string is shorted in the LED string.

That is, when there is a light emitting diode shorted to the LED string, 98.9V is applied between the string and the ground, so that 3.3V, which is a driving normal voltage, is applied to the constant current transistor, and the remaining 95.6V is applied.

At this time, since the string steady voltage for driving the LED string is set to 96.7V, when 95.6V smaller than 96.7V is applied to the LED string, less current should flow through the LED string. In this case, however, the current flows normally because the LED string is shorted in the LED string, so that the voltage required by the shorted LED is not needed. It means to flow.

That is, when the detection voltage Vd lower than the final voltage Vf is applied between the LED string and the ground during the detection period B, since there is no shorted light emitting diode, the string steady voltage cannot be applied to the LED string. The constant current driver 933 may not perform the constant current control.

However, if there is a shorted light emitting diode and all the light emitting diodes of the LED string are driven even when a voltage lower than the string normal voltage is applied, the current flowing through the LED string is applied to the constant current driver through the detection line. Constant current control is performed.

Therefore, if the current is applied to the constant current driver during the detection period and the constant current driver is performing the constant current control, the controller determines that there is a light emitting diode short-circuited in the LED string. When the constant current control is not performed or the constant current control is weak, it can be determined that the LED string is not shorted in the LED string.

On the other hand, the manufacturer of the liquid crystal display device can set the short detection level by adjusting the detection voltage Vd. That is, as the detection voltage Vd is adjusted, the voltage of the LED array in which the constant current control is performed can be changed, so that the manufacturer treats the rated voltage of one LED and the case where several LEDs are shorted. After determining whether or not to protect the circuit, the detection voltage Vd can be set in various ways accordingly.

On the other hand, if it is determined that there is a light emitting diode shorted as described above, the control unit controls the switching unit (932). By turning off the constant current transistor connected to the string, it is possible to protect the LEDs arranged in the LED string by preventing current from flowing in the LED string, and protect the constant current transistor.

In this case, as described above, the controller may directly control the power supply unit to cut off the power supplied to the corresponding LED string, or cut off the power applied to the entire LED array. In other words, when a short occurs in any one of the LED strings, only the corresponding LED strings may be blocked, but the entire LED array may be blocked to prevent the backlight unit from emitting light.

On the other hand, the above function is performed for all LED strings during the detection period B, and that is, after that, during the soft start period, the second voltage C after the detection period and the final voltage thereafter are driven. During the normal operation period, the present invention can control the constant current to flow to each LED string by the constant current driver 933. This constant current drive control can be applied to the general method currently being made, a detailed description thereof will be omitted.

Meanwhile, among the above components, each component constituting the circuit unit 930 may be configured as one integrated circuit (LED D-IC) or may be separately configured.

5 is a configuration of yet another embodiment of a light emitting diode protection device according to the present invention.

Here, in the light emitting diode protection device according to the present invention shown in FIG. 5, each of the plurality of voltage detection diodes 960 is connected to one voltage detection line 970 connected to a circuit part in common. The configuration is the same as that shown in FIG. 4 except that it is connected to the LED string. Therefore, hereinafter, the same contents as those described in FIG. 4 will be omitted or simply described.

That is, in the present invention, since the voltage detection diodes 960 are connected to one voltage detection line 970 as shown in FIG. 5, the voltage measured from the voltage detection diodes is applied to each constant current transistor. One of the voltages has a minimum voltage.

Therefore, when the voltage measured from the voltage detecting diodes is equal to or higher than the driving normal voltage of the constant current transistor, the controller may control the power supply to lower the final voltage Vf to a predetermined level.

That is, in the above example, in the normal operation period after the soft start period, 100 V as the final voltage Vf is applied, 96.7 V is applied to the LED string, and 3.3 V is applied to the constant current transistor.

However, while the LEDs generate heat, the driving voltage drops so that the LED string can operate normally even below 96.7V.

Thus, the remaining voltage in the LED string is applied to the constant current transistor.

For example, in the normal operation period, 100V is applied between the LED array and ground, 96.7V is applied to the LED string, and 3.3V is applied to the constant current transistor.

However, since the driving voltage of the LED falls during the normal operation period, the LED string may operate normally even if a value smaller than 96.7V, for example, 96V, is applied. At this time, since 0.7V is applied to the constant current transistor, the voltage applied to the constant current transistor is 4V in total.

Therefore, if the minimum voltage of all the constant current transistor voltage is 4V and this voltage is detected through the voltage detecting diode, it can be seen that all the LED strings are driven at a voltage of at least 0.7V less than 96.7V.

Therefore, in this case, the control unit 931 may control the power supply to apply the minimum voltage of 99.3V instead of 100V, thereby preventing unnecessary power consumption.

It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Therefore, it is to be understood that the embodiments described above are exemplary in all respects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description and all changes or modifications derived from the meaning and scope of the claims and their equivalents are to be construed as being included within the scope of the present invention do.

811: LED 812: LED string
810: LED array 950: detection resistor
910: constant current transistor

Claims (16)

A plurality of constant current transistors connected between each of the plurality of LED strings and the detection resistor provided in the LED array;
A plurality of detection lines connected to a node between the constant current transistor and the detection resistor for detecting a current flowing through the constant current transistor; And
During the soft start period for supplying the final voltage to the LED string, it is determined whether there is a shorted light emitting diode in the LED string to which the detection line is connected by using the amount of current flowing through the detection line. A light emitting diode protection device comprising a circuit portion for blocking the LED string with the light emitting diode to emit light. The method of claim 1,
The circuit portion,
During the soft start period, during the detection period in which a detection voltage having a voltage lower than the final voltage is kept constant, the presence or absence of the shorted light emitting diode is determined and the light emitting diode of the LED string is blocked accordingly. Protection. The method of claim 2,
The circuit portion.
And a power supply unit for supplying power to the LED array such that the detection voltage is maintained during the detection period. The method of claim 2,
The circuit portion,
A constant current driver for constantly controlling the amount of current flowing through the constant current transistor using the amount of current input through the detection line during the detection period and the normal operation period after the detection period; And
When the current is applied to the constant current driver during the detection period to control the constant current, the LED string connected to the detection line is judged to have a shorted light emitting diode, and the LED string is shut off. And a control unit for determining that there is no short-circuit LED in the LED string when a small current is applied and constant current driving is not performed. The method of claim 4, wherein
The circuit portion,
And a switching unit capable of turning off the constant current transistor connected to the LED string when it is determined that the LED string is shorted in the LED string. The method of claim 2,
The circuit portion,
If it is determined that there is a light emitting diode shorted in the LED string, a power supply for supplying power to the LED string, the control signal to cut off the power supply to the LED string or to cut off the power supply to the LED array Light emitting diode protection device, characterized in that for transmitting. The method of claim 2,
The detection voltage is,
And the final voltage minus a voltage that can be recognized as the short. The method of claim 1,
And a plurality of voltage detection diodes connected to each of the one voltage detection line connected to the circuit unit and the LED string, respectively. The method of claim 8,
The circuit portion,
And controlling the power supply to lower the level of the final voltage when the minimum voltage detected through the plurality of voltage detection diodes is equal to or higher than a driving normal voltage of the constant current transistor. The light emitting diode protection device according to any one of claims 1 to 10;
A liquid crystal panel;
A data driver for controlling a data line formed in the liquid crystal panel;
A gate driver for controlling a gate line formed in the liquid crystal panel;
A backlight unit configured of an LED array for irradiating light onto the liquid crystal panel and controlled by the light emitting diode protection device; And
Liquid crystal display using a light emitting diode protection device including a power supply for supplying power to the LED array. Maintaining a power applied to an LED array consisting of a plurality of LED strings at a detection voltage having a value lower than a final voltage;
Determining whether there is a shorted light emitting diode in each of the plurality of LED strings during a detection period during which the detection voltage is kept constant;
According to the determination, blocking the LED string with the shorted light emitting diode, and if there is no shorted light emitting diode, controlling a constant current transistor connected to the LED string to allow a constant current to flow into the LED string; And
And controlling the constant current transistor to flow a constant current through the LED string after the detection period. The method of claim 11,
Determining whether the shorted light emitting diode is present,
If a constant current is controlled by applying a current through a detection line connected to the LED string during the detection period, it is determined that there is a light emitting diode short-circuited in the LED string to which the detection line is connected. If a small current is not applied to drive the constant current, it is determined that there is no light-emitting diode shorted to the LED string. The method of claim 11,
Blocking the LED string,
And when it is determined that the LED string is shorted in the LED string, turning off the constant current transistor connected to the LED string. The method of claim 11,
Blocking the LED string,
If it is determined that there is a light emitting diode shorted in the LED string, a power supply for supplying power to the LED string, the control signal to cut off the power supply to the LED string or to cut off the power supply to the LED array Light emitting diode protection method, characterized in that for transmitting. The method of claim 11,
The detection voltage is,
And the final voltage minus a voltage that can be recognized as the short. The method of claim 11,
After the detection period, detecting a minimum voltage among voltages applied to constant current transistors connected to each of the LED strings to constantly control a current flowing through the LED strings; And
And lowering the level of the final voltage when the minimum voltage is equal to or higher than a driving normal voltage of the constant current transistor.

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