KR101977968B1 - Liquid Crystal Display Device and Driving Method the same - Google Patents

Abstract

An embodiment of the present invention is a liquid crystal display device comprising: a liquid crystal panel; An LED string including LEDs connected in series to the first power terminal to provide light to the liquid crystal panel; A transistor formed between the cathode electrode of the LED string and the monitor resistor connected to the second power supply terminal and driving the LED string; A constant current supply unit for supplying a driving signal through a base electrode of the transistor and outputting a driving signal by using a first reference voltage and an emitter voltage of the transistor; And a short-circuit detecting unit for detecting the short-circuit current and stopping the output of the constant-current supply unit according to the comparison result.

Description

[0001] The present invention relates to a liquid crystal display device and a method of driving the same,

An embodiment of the present invention relates to a liquid crystal display and a driving method thereof.

As the information technology is developed, the market of display devices, which is a connection medium between users and information, is getting larger. Accordingly, a flat panel display (FPD) such as a liquid crystal display (LCD), an organic light emitting diode (OLED), and a plasma display panel (PDP) Usage is increasing. Among them, liquid crystal display devices capable of realizing high resolution and capable of not only miniaturization but also enlargement are widely used.

The liquid crystal display device includes a liquid crystal panel composed of a transistor substrate formed with a transistor, a storage capacitor, a pixel electrode, and the like, and a liquid crystal layer positioned between a color filter substrate and a color filter substrate on which a color filter and a black matrix are formed.

When a gate signal is supplied from a gate driver to a liquid crystal display device, a liquid crystal layer is driven by a difference between a data voltage supplied from the data driver and a common voltage supplied from the power supply, thereby controlling light incident from the backlight unit So that the image is displayed.

Recently, a light emitting diode (hereinafter, LED) is mainly used as a light source included in the backlight unit. A plurality of LEDs form a unit light source in the form of a string (or a string) connected in series. A plurality of LED strings may be connected in parallel.

On the other hand, a current deviation occurs in the LED string or between the LED strings due to the impedance difference. In addition, the LED may be short-circuited due to various factors. When a short-circuited LED is generated, an overcurrent flows to the LED string, and the LED, as well as the device driving the LED, are destroyed.

Therefore, conventionally, a first terminal for finely adjusting the current of the LED string, a second terminal for monitoring the current of the LED string, and a second terminal for controlling the output of the DC power source based on the monitored current, A driver with three terminals per channel was used to detect shorts and to protect the device like a three-terminal.

However, a structure in which three terminals (or pins) are required as in the conventional driving unit causes a problem of cost increase due to an increase in the number of terminals in the apparatus configuration, and therefore, a method of reducing costs is required.

The embodiment of the present invention for solving the problems of the background art described above can reduce the cost in the device configuration and can be implemented in a discrete element-based manner, excluding the use of a bulky logic element, (IC), and a method of driving the same.

According to an embodiment of the present invention, there is provided a liquid crystal display device comprising: a liquid crystal panel; An LED string including LEDs connected in series to the first power terminal to provide light to the liquid crystal panel; A transistor formed between the cathode electrode of the LED string and the monitor resistor connected to the second power supply terminal and driving the LED string; A constant current supply unit for supplying a driving signal through a base electrode of the transistor and outputting a driving signal by using a first reference voltage and an emitter voltage of the transistor; And a short-circuit detecting unit for detecting the short-circuit current and stopping the output of the constant-current supply unit according to the comparison result.

The short detection unit can stop the output of the constant current supply unit if the second reference voltage is larger than the base voltage of the transistor.

The second reference voltage may be set to a voltage value corresponding to a value between the base voltage value of the transistor before the LEDs are short-circuited and the base voltage value of the transistor after the LEDs are short-circuited.

Wherein the constant current supply unit includes a first comparison unit having an output terminal connected to a base electrode of the transistor and connected to a first reference voltage terminal for supplying a first reference voltage, and a short detection unit connected to the inverting terminal of the first comparison unit, And a second comparator having a non-inverting terminal connected to the second reference voltage terminal for supplying the second reference voltage and an inverting terminal connected to the base electrode of the transistor.

The constant current supply unit includes a first diode connected between the first reference voltage terminal and the non-inverting terminal of the first comparison unit, and a second diode connected between the emitter electrode of the transistor and the inverting terminal of the first comparison unit. And a third diode connected between the inverting terminal of the comparing unit and the output terminal of the second comparing unit.

The short detection unit may include a resistor connected between the base electrode of the transistor and the output terminal of the first comparison unit.

The inverting terminal of the second comparing unit may be connected between the output terminal of the first comparing unit and the resistor.

The transistor driver may comprise an integrated circuit having a base electrode of the transistor and two terminals connected to the emitter electrode of the transistor.

According to another aspect of the present invention, there is provided a method of driving a liquid crystal display, comprising: outputting a driving signal using a first reference voltage and an emitter voltage of a transistor for a transistor driving an LED string including LEDs for providing light to a liquid crystal panel; Comparing the base voltage of the transistor with the second reference voltage to determine whether the LEDs are short-circuited; And stopping the output of the driving signal when the second reference voltage is larger than the base voltage of the transistor as a result of comparing the base voltage of the transistor and the second reference voltage.

The second reference voltage may be set to a voltage value corresponding to a value between the base voltage value of the transistor before the LEDs are short-circuited and the base voltage value of the transistor after the LEDs are short-circuited.

Embodiments of the present invention provide a transistor driver capable of reducing the number of one terminal per LED string to control transistors with two terminals, thereby reducing the cost of device configuration, eliminating the use of bulky logic elements, And it is possible to realize an integrated circuit (IC) with a small volume by implementing it with a discrete element. In addition, the present invention is capable of short-circuit detection by LED string with minimum element arrangement, and a device with high heat such as a transistor (or a switch) is disposed outside and a device with low heat generation is disposed inside, There is an effect that can be increased.

1 is a schematic block diagram of a liquid crystal display device.
2 is a block diagram of a gate driver;
3 is a block diagram of a data driver;
FIG. 4 is a schematic view of a part of a backlight unit driving unit of a liquid crystal display according to a first embodiment of the present invention; FIG.
5 is a diagram showing a driving state of a backlight unit driving unit in normal operation;
6 is a diagram showing a driving state of a backlight unit driving unit when a short occurs.
7 is a view for explaining a transistor driver configured in the form of an integrated circuit;
8 is a schematic view of a part of a backlight unit driving unit of a liquid crystal display device according to a second embodiment of the present invention.
9 is a view for explaining a transistor driving unit configured in the form of an integrated circuit;
10 is a flowchart for explaining a driving method according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic block diagram of a liquid crystal display, FIG. 2 is a block diagram of a gate driver, and FIG. 3 is a block diagram of a data driver.

1, a liquid crystal display includes a timing driver TCN, a liquid crystal panel PNL, a gate driver SDRV, a data driver DDRV, a backlight unit BLU, and a backlight unit driver BDRV. do.

The timing driver TCN receives a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a data enable signal DE, a clock signal CLK and a data signal DATA from the outside. The timing driver TCN supplies data signals to the data driver DDRV and the data driver DDRV using timing signals such as a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a data enable signal DE, and a clock signal CLK. And controls the operation timing of the driving unit SDRV.

The timing driver TCN can count the data enable signal DE in one horizontal period to determine the frame period so that the externally supplied vertical sync signal Vsync and horizontal sync signal Hsync can be omitted. The timing driver TCN generates control signals GDC and DDC for controlling the panel driver for driving the liquid crystal panel PNL such as the gate driver SDRV and the data driver DDRV. The control signals GDC and DDC are supplied with a gate timing control signal GDC for controlling the operation timing of the gate driver SDRV and a data timing control signal DDC for controlling the operation timing of the data driver DDRV. .

The liquid crystal panel (PNL) includes subpixels arranged in a matrix including a liquid crystal layer positioned between a transistor substrate (hereinafter abbreviated as TFT substrate) and a color filter substrate. A data line, a gate line, a TFT, a storage capacitor and the like are formed on the TFT substrate, and a black matrix, a color filter and the like are formed on the color filter substrate.

The subpixel SP is defined by a data line DL1 and a gate line SL1 which cross each other. The subpixel SP includes a TFT driven by a gate signal supplied through a gate line SL1, a storage capacitor Cst for storing a data signal supplied through the data line DL1 as a data voltage, a storage capacitor Cst And a liquid crystal cell Clc driven by the data voltage stored in the liquid crystal cell Clc.

The liquid crystal cell Clc is driven by the data voltage supplied to the pixel electrode 1 and the common voltage Vcom supplied to the common electrode 2. [ The common electrode is formed on a color filter substrate in a vertical field driving method such as a TN (Twisted Nematic) mode and a VA (Vertical Alignment) mode, and a horizontal electric field such as IPS (In Plane Switching) mode and FFS (Fringe Field Switching) Is formed on the TFT substrate together with the pixel electrode in the driving method. A polarizing plate is attached to the TFT substrate of the liquid crystal panel (PNL) and the color filter substrate, and an alignment film for setting a pre-tilt angle of the liquid crystal is formed. The liquid crystal mode of the liquid crystal panel PNL can be implemented in any liquid crystal mode as well as the TN mode, VA mode, IPS mode, and FFS mode described above.

The gate driver SDRV sequentially generates gate signals to be operated by the transistors of the subpixels SP included in the liquid crystal panel PNL in response to the gate timing control signal GDC supplied from the timing driver TCN . The gate driver SDRV supplies the gate signal generated through the gate lines SL1 to SLm to the subpixels SP included in the liquid crystal panel PNL.

As shown in FIG. 2, the gate driver SDRV is composed of gate drive ICs. The gate drive ICs each include a shift register 61, a level shifter 63, a plurality of AND gates 62 and a gate output enable signal GOE connected between the shift register 61 and the level shifter 63, And an inverter 64 for inverting the inverter 64 and the like. The shift register 61 shifts the gate start pulse GSP sequentially in accordance with the gate shift clock GSC using a plurality of D flip-flops depending thereon. The AND gates 62 logically multiply the output signal of the shift register 61 and the inverted signal of the gate output enable signal GOE to generate an output. The inverter 64 inverts the gate output enable signal GOE and supplies it to the AND gates 62. The level shifter 63 shifts the output voltage swing width of the AND gate 62 to the swing width of the gate voltage at which the transistors included in the liquid crystal panel PNL can operate. The gate signal output from the level shifter 63 is sequentially supplied to the gate lines SL1 to SLm. Although the gate driver SDRV shown in FIG. 2 is configured as an integrated circuit, the gate driver SDRV shown in FIG. 2 may be configured as a gate-in-panel type that is formed directly on the liquid crystal panel PNL.

The data driver DDRV samples and latches the data signal DATA supplied from the timing driver TCN in response to the data timing control signal DDC supplied from the timing driver TCN and converts the sampled data signal into data of a parallel data system . The data driver DDRV converts the data signal DATA in accordance with the gamma reference voltage when converting the data into data of a parallel data system. The data driver DDRV supplies the data signal DATA converted through the data lines DL1 to DLn to the subpixels SP included in the liquid crystal panel PNL.

3, the data driver DDRV includes a shift register 51, a data register 52, a first latch 53, a second latch 54, a converter 55, an output circuit 56 ) And the like. The shift register 51 shifts the source sampling clock SSC supplied from the timing driver TCN. The shift register 51 transfers the carry signal CAR to the shift register of the next source drive IC in the neighboring stage. The data register 52 temporarily stores the data signal DATA supplied from the timing driver TCN and supplies it to the first latch 53. The first latch 53 samples and latches the data signal DATA serially input according to the clocks sequentially supplied from the shift register 51, and outputs the latched data at the same time. The second latch 54 latches the data supplied from the first latch 53 and then latches the latched data in synchronization with the second latch 54 of the other source drive ICs in response to the source output enable signal SOE Simultaneously output. The conversion unit 55 converts the data signal DATA input from the second latch 54 into gamma reference voltages GMA1 to GMAn. The data signal DATA output from the output circuit 56 is supplied to the data lines DL1 to DLn in response to the source output enable signal SOE. The data driver DDRV shown in FIG. 3 is merely an example, and the present invention is not limited thereto.

The backlight unit (BLU) provides light to the liquid crystal panel (PNL). The backlight unit (BLU) may be variously configured as an edge type, a dual type, a direct type, and the like. Here, the edge type is one in which light emitting diodes (hereinafter referred to as LEDs or LEDs) are arranged in a string (or row) shape on one side of a liquid crystal panel PNL. In the dual type, LEDs are arranged on both sides of a liquid crystal panel (PNL) in the form of strings (or strings). In the direct type, light emitting diodes are arranged in a block or matrix form in the lower part of the liquid crystal panel (PNL).

The backlight unit driving unit BDRV drives the backlight unit BLU. The backlight unit driving unit (BDRV) includes a DC power supply unit for supplying DC power to the LED strings, transistors for driving the LED strings, and a transistor driving unit for driving the transistors. On the other hand, the backlight unit driving unit (BDRV) can detect a short when the LED strings are short-circuited to protect the devices from short-circuiting, which will be described in more detail below.

≪ Embodiment 1 >

5 is a diagram illustrating a driving state of the backlight unit driving unit in normal operation, and FIG. 6 is a diagram illustrating a backlight unit driving unit in the backlight unit driving unit of the liquid crystal display device according to the first embodiment of the present invention. FIG. 7 is a view for explaining a transistor driving unit configured in the form of an integrated circuit. FIG.

As shown in FIG. 4, the backlight unit driving unit of the liquid crystal display according to the first embodiment of the present invention includes a transistor TR and a transistor driving unit TDRV. The backlight unit driving unit drives the first LED string LS1 included in the backlight unit by using the transistor TR and the transistor driving unit TDRV.

The first LED string LS1 includes light emitting diodes (LEDs) LED1 to LEDn connected in series to the first power supply terminal VLED.

The transistor TR is formed between the cathode electrode of the nLED LEDn included in the first LED string LS1 and the monitor resistor R _E connected to the second power source terminal VGND and drives the first LED string LS1 do. The transistor TR may be formed of a bipolar junction transistor (BJT) or a field effect transistor (FET). In the embodiment, an example in which the transistor TR is formed of an NPN type BJT will be described as an example.

The transistor drive unit TDRV is provided with a constant current supply unit DRP1 for supplying a drive signal to the transistor TR and a short detection unit SDP1 for stopping the output of the constant current supply unit DRP1 depending on whether the LEDs D1 to Dn are short- .

The constant current supply unit DRP1 supplies the driving signal through the base electrode of the transistor TR and outputs the driving signal by using the first reference voltage and the emitter voltage V _E of the transistor TR.

The short detection unit SDP1 compares the base voltage V _B of the transistor TR with the second reference voltage to determine whether the LEDs LED1 to LEDn are short-circuited and outputs the output of the constant current supply unit DRP1 Stop.

The constant current supply unit DRP1 includes a first comparator OP1 having an output terminal connected to the base electrode of the transistor TR and a non-inverting terminal connected to a first reference voltage Vref1 for supplying a first reference voltage . The constant current supply unit DRP1 includes a first diode D1 connected between a first reference voltage Vref1 and a non-inverting terminal (+) of the first comparator OP1, a first diode D1 connected between the emitter electrode And a second diode D2 connected between the inverting terminal (-) of the first comparing unit OP1.

The short detection unit SDP1 has an output terminal connected to the inverting terminal (-) of the first comparing unit OP1 and a non-inverting terminal (+) connected to the second reference voltage terminal Vref2 for supplying the second reference voltage, (-) connected to the base electrode of the second comparator (TR). The short detection unit SDP1 includes a third diode D3 connected between the inverting terminal (-) of the first comparing unit OP1 and the output terminal of the second comparing unit OP2.

According to the above configuration, the constant current supply unit DRP1 performs a constant current function for compensating a current deviation (current deviation between strings) according to the voltage deviation Vf of the LEDs LED1 to LEDn and drives the transistor TR . In addition, the short detection unit SDP1 performs a protection function for protecting the first LED string LS1 from an overcurrent when a short circuit occurs to the LEDs (LED1 to LEDn).

The operation of the constant current supply unit DRP1 and the short detection unit SDP1 will be described below.

As shown in FIG. 5, the constant current supply unit DRP1 drives the constant current using the first reference voltage Vref1 and the emitter voltage V _E of the transistor TR as follows.

The emitter voltage V _E of the transistor TR becomes equal to the first reference voltage Vref1 by the operation of the first comparator OP1. However, if the current increases according to the external environment or device characteristics, the voltage of the inverting terminal (-) of the first comparing unit OP1 becomes high.

The first comparator OP1 always monitors the emitter voltage V _E of the transistor TR and compares it with the first reference voltage Vref1. Therefore, when the voltage of the inverting terminal (-) of the first comparing unit OP1 becomes high, the first comparing unit OP1 outputs a driving signal for lowering the base voltage V _B of the transistor TR so as to reduce the current do.

On the other hand, when the current decreases according to the external environment or device characteristics, the voltage of the inverting terminal (-) of the first comparator OP1 becomes low. The first comparator OP1 monitors the emitter voltage V _E of the transistor TR and compares it with the first reference voltage Vref1. Therefore, when the voltage of the inverting terminal (-) of the first comparing unit OP1 becomes low, the first comparing unit OP1 outputs a driving signal for raising the base voltage V _B of the transistor TR so as to increase the current do.

On the other hand, the current flowing in the first LED string LS1 can be set by the first reference voltage and the monitor resistor R _E. Therefore, the equation is expressed as follows.

ILED = Vref1 / R _E

When the LEDs (LED1 to LEDn) of the first LED string LS1 are normally operated without a short circuit, the base voltage V _B of the transistor TR is output from the second comparator OP2 Is higher than the voltage Vop2_out. Therefore, the input is received only through the second diode D2 connected to the inverting terminal (-) of the first comparing unit OP1, and the short detection unit SDP1 is kept in the inoperative state. On the other hand, the first diode D1 connected to the non-inverting terminal (+) of the first comparator OP1 serves to equalize the voltage deviation Vf which varies depending on the operating temperature. That is, the first and second diodes D1 and D2 are equally connected to both ends (+, -) of the first comparing unit OP1 so that the input of the first comparing unit OP1 is maintained at both ends (Vf) of the voltage Vf.

6, the short detection unit SDP1 compares the base voltage VE of the transistor TR, which is lowered when a short circuit occurs to the LEDs LED1 to LEDn, with the second reference voltage, DRP1 perform the operation of turning off the transistor TR to protect the LEDs LED1 to LEDn.

The second comparing unit OP2 operates as a comparator. When the transistor driving unit TDRV operates normally, the short detection unit SDP1 does not operate. That is, in the normal operation, since the base voltage V _B of the transistor TR is larger than the second reference voltage, the output voltage of the second comparison unit OP2 becomes logic low.

On the other hand, when a short circuit occurs in the LEDs (LED1 to LEDn), the collector voltage (V _C ) of the transistor (TR) becomes high while the base voltage (V _B ) of the transistor (TR) becomes low. On the other hand, the emitter current I _E of the transistor TR is kept constant by the constant current function of the first comparator OP1.

According to the current equation of the NPN type BJT, I _E = I _B + I _C , I _E is constant and I _C is increased, so that I _B is decreased by the increment. That is, when the LEDs (LED1 to LEDn) are short-circuited, the base current (I _B ) and the base voltage (V _B ) of the transistor (TR) become small.

When the base voltage V _B of the transistor TR becomes smaller, the second reference voltage and the base voltage V _B condition Vref2> V _B of the transistor TR are established and the output of the second comparison unit OP2 becomes logic And becomes high. Therefore, the short detection unit SDP1 stops the output of the constant current supply unit DRP1 if the second reference voltage is larger than the base voltage V _B of the transistor TR.

When the above condition is satisfied, the voltage supplied through the third diode D3, that is, the output voltage Vop2_out of the second comparator OP2 becomes higher than the voltage supplied through the second diode D2. Therefore, the logic high signal outputted from the second comparing unit OP2 is supplied to the inverting terminal (-) of the first comparing unit OP1.

When a logic high signal is supplied to the inverting terminal (-) of the first comparing unit OP1, the first comparing unit OP1 outputs a driving signal for turning off the transistor TR And the LEDs (LED1 to LEDn) are protected.

In the above description, the first reference voltage supplied through the first reference voltage stage Vref1 serves to determine the current value flowing through the LEDs (LED1 to LEDn). That is, the emitter voltage V _E of the transistor TR and the first reference voltage are set equal (or similarly), and the current is set to the emitter voltage V _E of the transistor TR and the monitor resistor R _E ) V _E / R _E.

On the other hand, the second reference voltage supplied through the second reference voltage stage Vref2 can turn the output of the second comparison unit OP2 into a logic high signal when a short circuit occurs in the LEDs LED1 to LEDn . That is, the second reference voltage is set to a voltage value between the base voltage value of the transistor before the LEDs D1 to Dn is short-circuited and the base voltage value of the transistor after the LEDs are short-circuited. Therefore, the equation is expressed as follows.

VB_before_short> Vref2> VB_before_short

The transistor driver TDRV described above shows a configuration for driving one first LED string LS1. However, since the liquid crystal panel requires a backlight unit and a backlight unit driving unit configured in various sizes and structures, the transistor driving unit (TDRV) can be configured as follows.

7, the backlight unit and the backlight unit driving unit according to the first embodiment include a plurality of LED strings LS1 to LSn, a plurality of transistors TR and a plurality of transistors TR connected thereto, And a plurality of transistor drivers TDRV1 to TDRVn connected to the gate of the transistor.

More specifically, one transistor driver TDRV1 is composed of an integrated circuit (IC) having two terminals P1 and P2 connected to the base electrode of the transistor TR and the emitter electrode of the transistor TR.

Since the plurality of transistor drivers TDRV1 to TDRVn according to the first embodiment have no terminals shared among the plurality of LED strings LS1 to LSn, it is possible to detect shorts separately.

In the example shown in FIG. 7, the plurality of transistor drivers TDRV1 to TDRVn are formed of integrated circuits (ICs), but they may be integrated into N (N is an integer of 2 or more) tiers.

≪ Embodiment 2 >

FIG. 8 is a diagram illustrating a part of a backlight unit driving unit of a liquid crystal display device according to a second embodiment of the present invention, and FIG. 9 is a view for explaining a transistor driving unit configured in the form of an integrated circuit.

As shown in FIG. 8, the backlight unit driving unit of the liquid crystal display according to the second embodiment of the present invention includes a transistor TR and a transistor driving unit TDRV. The backlight unit driving unit drives the first LED string LS1 included in the backlight unit by using the transistor TR and the transistor driving unit TDRV.

The transistor driver TDRV of the second embodiment is similar to the transistor driver TDRV of the first embodiment. However, the short detection unit SDP1 of the transistor drive unit TDRV includes a resistor Rb connected between the base electrode of the transistor TR and the output terminal of the first comparison unit OP1. The inverting terminal (-) of the second comparing unit OP2 is connected between the output terminal of the first comparing unit OP1 and the resistor Rb.

The transistor driver TDRV of the second embodiment is an extension of the sensing range by inserting a resistor Rb between the base electrode of the transistor TR and the first comparator OP1.

The transistor driver TDRV of the second embodiment has the following differences with respect to the transistor driver TDRV of the first embodiment when a normal operation and a short circuit occur.

The change of the output voltage Vop1_out of the first comparator OP1 is larger than the change of the base voltage V _B of the transistor TR. Therefore, since the output voltage Vop1_out of the first comparing unit OP1 is sensed, which is not the base voltage V _B of the transistor TR, the second reference voltage supplied through the second reference voltage terminal Vref2 is wider Range. ≪ / RTI >

Therefore, when the resistor Rb is inserted as in the second embodiment, there is an advantage that the short-time sensing voltage range can be widened. However, when the resistor Rb is inserted as in the second embodiment, additional power consumption occurs. Therefore, it is necessary to properly set the resistance value of the resistor Rb.

9, the backlight unit and the backlight unit driving unit according to the second embodiment also include a plurality of LED strings LS1 to LSn, a plurality of transistors TR and a plurality of transistors TR connected thereto, And a plurality of transistor drivers TDRV1 to TDRVn connected to the gate of the transistor.

More specifically, one transistor driver TDRV1 is composed of an integrated circuit (IC) having two terminals P1 and P2 connected to the base electrode of the transistor TR and the emitter electrode of the transistor TR.

Since the plurality of transistor drivers TDRV1 to TDRVn according to the second embodiment also have no terminals shared among the plurality of LED strings LS1 to LSn, it is possible to detect shorts separately.

In the example shown in FIG. 9, the plurality of transistor drivers TDRV1 to TDRVn are each formed of integrated circuits (ICs), but they may be integrated into N (N is an integer of 2 or more) tiers.

Hereinafter, a driving method for the embodiments of the present invention described above will be described.

10 is a flowchart illustrating a driving method according to an embodiment of the present invention.

As shown in FIG. 10, the driving method according to the embodiment of the present invention will be described with reference to FIG. 1 and FIG. 4 together with the transistor driver TDRV included in the backlight unit driving unit.

First, the LED is driven (S110). In the step of driving the LED, a first reference voltage Vref1 and a second reference voltage Vref2 are applied to the transistor TR driving the first LED string LS1 including the LEDs LED1 to LEDn that provide light to the liquid crystal panel PNL, And outputs a driving signal using the emitter voltage of the transistor TR.

Next, it is determined whether or not the LED is short-circuited (S120). In the step of determining whether the LED is short-circuited, the base voltage V _B of the transistor TR is compared with the second reference voltage Vref2 to determine whether the LEDs LED1 to LEDn are short-circuited.

Next, the driving of the LED is continuously maintained according to the comparison result between the base voltage V _B of the transistor TR and the second reference voltage Vref2 (S110), and the driving of the LED is stopped (S130). When the base voltage V _B of the transistor TR is smaller than the second reference voltage Vref2 (N) in the step of continuously driving the LEDs. On the other hand, when the driving of the LED is stopped, the second reference voltage Vref2 is higher than the base voltage V _B of the transistor TR (Y). Therefore, when the second reference voltage Vref2 is higher than the base voltage V _B of the transistor TR (Y), the output of the driving signal is stopped, and the LED stops driving.

On the other hand, in order to satisfy the above driving condition, the second reference voltage Vref2 is set so that the base voltage value (VB_before_short) of the transistor before the LEDs (LED1 to LEDn) And the base voltage value (VB_after_short)

The present invention provides a transistor driver capable of controlling a transistor with two terminals by reducing one terminal per LED string, thereby reducing the cost of device configuration, eliminating the use of bulky logic elements, ) Device, it is possible to realize an integrated circuit (IC) with a small volume. In addition, the present invention is capable of short-circuit detection by LED string with minimum element arrangement, and a device with high heat such as a transistor (or a switch) is disposed outside and a device with low heat generation is disposed inside, There is an effect that can be increased.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood that the invention may be practiced. It is therefore to be understood that the embodiments described above are to be considered in all respects only as illustrative and not restrictive. In addition, the scope of the present invention is indicated by the following claims rather than the detailed description. Also, all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

TCN: timing driver PNL: liquid crystal panel
SDRV: Gate driver DDRV: Data driver
BLU: Backlight Unit BDRV: Backlight Unit Driver
TR: transistor TDRV: transistor driver
LS1: first LED string DRP1: constant current supply section
SDP1: short detection unit OP1: first comparison unit
OP2: second comparing units D1 to D3: first to third diodes
Vref1: first reference voltage stage Vref2: second reference voltage stage
Rb: Resistor

Claims (11)

A liquid crystal panel;
An LED string including LEDs connected in series to a first power terminal to provide light to the liquid crystal panel;
A transistor formed between a cathode electrode of the LED string and a monitor resistor connected to the second power terminal, the transistor driving the LED string;
A constant current supply unit supplying a driving signal through a base electrode of the transistor and outputting the driving signal by using a first reference voltage and an emitter voltage of the transistor; And a short-circuit detecting unit for determining whether the LEDs are short-circuited and stopping the output of the constant-current supply unit when the second reference voltage is larger than the base voltage of the transistor,
Wherein the constant current supply unit includes a first comparator having an output terminal connected to a base electrode of the transistor and a non-inverting terminal connected to a first reference voltage terminal for supplying the first reference voltage,
Wherein the short detection unit includes a second comparison unit having an output terminal connected to an inverting terminal of the first comparison unit and a non-inverting terminal connected to a second reference voltage terminal for supplying the second reference voltage and an inverting terminal connected to the base electrode of the transistor . delete The method according to claim 1,
The second reference voltage
And a voltage value between a base voltage value of the transistor before the LEDs are short-circuited and a base voltage value of the transistor after the LEDs are short-circuited. delete The method according to claim 1,
The constant current supply unit
A first diode connected between the first reference voltage terminal and the non-inverting terminal of the first comparator, and a second diode connected between the emitter electrode of the transistor and the inverting terminal of the first comparator,
And the short detection unit includes a third diode connected between an inverted terminal of the first comparison unit and an output terminal of the second comparison unit. The method according to claim 1,
The short-
And a resistor connected between the base electrode of the transistor and the output terminal of the first comparator. The method according to claim 6,
The inverting terminal of the second comparator
And the second comparator is connected between the output terminal of the first comparator and the resistor. The method according to claim 1,
The transistor driver
And an integrated circuit having a base electrode of the transistor and two terminals connected to the emitter electrode of the transistor. delete delete A liquid crystal panel;
An LED string including LEDs connected in series to a first power terminal to provide light to the liquid crystal panel;
A transistor formed between a cathode electrode of the LED string and a monitor resistor connected to the second power terminal, the transistor driving the LED string;
A constant current supply unit supplying a driving signal through a base electrode of the transistor and outputting the driving signal by using a first reference voltage and an emitter voltage of the transistor; And a short-circuit detecting unit for determining whether the LEDs are short-circuited and stopping the output of the constant-current supply unit when the second reference voltage is larger than the base voltage of the transistor,
Wherein the constant current supply unit includes a first comparator having an output terminal connected to a base electrode of the transistor and a non-inverting terminal connected to a first reference voltage terminal for supplying the first reference voltage,
Wherein the short detection unit includes a second comparison unit having an output terminal connected to an inverting terminal of the first comparison unit and a non-inverting terminal connected to a second reference voltage terminal for supplying the second reference voltage and an inverting terminal connected to the base electrode of the transistor Including,
The constant current supply unit
A first diode connected between the first reference voltage terminal and the non-inverting terminal of the first comparator, and a second diode connected between the emitter electrode of the transistor and the inverting terminal of the first comparator,
And the short detection unit includes a third diode connected between an inverted terminal of the first comparison unit and an output terminal of the second comparison unit.

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