KR20120077574A - Backlight driving circuit and liquid crystal display having the same - Google Patents

Abstract

PURPOSE: A backlight driving circuit and liquid crystal display having the same are provided to supply a driving voltage suited a variety of LED elements having different load characteristics by producing a driving signal of lamp unit corresponding to a compensating feedback signal. CONSTITUTION: A DC-DC converter(321) presses the driving voltage of the lamp unit by receiving power supply voltage. A driver IC(322) controls a current flowing the lamp unit. A sensing circuit(323) senses a feedback signal of the lamp unit from the driver IC. A compensating circuit(324) compensates a sensed feedback signal by the sensing circuit. A MCU(325) controls the driver IC and compensating circuit according to a set-up value.

Description

BACKLIGHT DRIVING CIRCUIT AND LIQUID CRYSTAL DISPLAY HAVING THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight driving circuit, and more particularly to a backlight driving circuit for controlling an LED device having different load characteristics and a liquid crystal display device including the same.

As is well known, a light emitting diode (LED), which is a semiconductor light emitting device, is formed by joining an n-type semiconductor, in which a majority carrier is electrons, and a p-type semiconductor, in which a majority hole is a majority carrier, and applying an electrical signal thereto. It is a device that emits light energy. Such LED devices are packaged and covered with molds such as plastics in order to protect the devices from an impact from the outside, to extract light efficiently, and to have a heat dissipation function. Therefore, it is suitable as a light source of a backlight unit of a passive display device such as a liquid crystal display device.

1 is a view schematically illustrating a configuration of a backlight unit included in a liquid crystal display device using a conventional LED element as a light source.

As illustrated, the conventional backlight unit includes a DC-DC converter 1 for converting a voltage applied from an external power supply unit into a predetermined DC voltage, and a current corresponding to the voltage converted from the DC-DC converter 1. A plurality of LED elements 2 for emitting light, and a driver unit 3 for controlling the light emission timing of the LED element (2).

In detail, the DC-DC converter 1 adjusts the power supply voltage VIN applied from an external power supply source to maintain a constant current flowing in the plurality of connected LED elements 2, and thus requires a driving voltage ( VLED) is generated and provided to the LED device 2.

The plurality of LED elements 2 are connected in series to form one LED string, and the plurality of LED strings are connected in parallel so that the anode terminal is connected to the DC-DC converter 1. Drive with (VLED) applied.

The LED driving circuit unit 3 is connected to the cathode of the above-described LED element 2 and receives a feedback signal FB from each LED string of the LED element 2 to control the DC-DC converter 1 to control the LED. The current flowing through the element 2 is kept constant or the lighting timing of the LED element 2 is adjusted.

The LED device 2 having the above-described structure differs in the number of strings and the number of LED devices connected to one string according to the driving characteristics, size, and model type of each device. Will be present. Accordingly, even when the backlight is configured using the same LED device, the voltage and current values required for lighting should be set differently.

Table 1 below is a table showing an example of the number of LED strings provided for each size (inch) of the general liquid crystal display device, and the corresponding lamp voltage and current values.

Inch LED string count Lighting voltage Drive current 42 ' 12 ea 115 V 55 mA 47 ' 12 ea 136 V 55 mA 55 ' 16 ea 130 V 55 ma

As shown in Table 1, the number of LED strings, the lighting voltage, and the driving current of the backlight unit are different according to the size of the liquid crystal display device, and accordingly, LEDs for controlling the LED string in manufacturing the liquid crystal display device The driving circuit also has the inconvenience of using only those having proper driving characteristics, and has the disadvantage of preparing various types of LED driving circuit during manufacturing.

The present invention has been made in view of the above-mentioned disadvantages, and an object thereof is to provide a backlight driving circuit in which an LED driving circuit is used in common depending on different load characteristics of the LED element and a liquid crystal display including the same.

In order to achieve the above object, a backlight driving circuit according to a preferred embodiment of the present invention, a plurality of lamps are connected in series to form a single LED string, the plurality of LED strings are connected to control the lamp unit in parallel A backlight driving circuit, comprising: a DC-DC converter supplied with a power supply voltage and stepping down to a driving voltage of a lamp unit; A driver IC for controlling a current flowing in the lamp unit; A sensing circuit for sensing a feedback signal of the lamp unit from the driver IC; A compensation circuit for compensating a feedback signal sensed by the sensing circuit; A switching regulator for generating a PWM signal having a duty ratio corresponding to the feedback signal compensated by the compensation circuit and supplying the PWM signal to the DC-DC converter; And an MCU controlling the driver IC and the compensation circuit according to a setting value.

The DC-DC converter is characterized in that the switching mode power supply (SMPS) circuit.

The SMPS circuit may be any one of a buck converter, a boost converter, and a single ended primary inductance converter (SEPIC) converter including at least one switching element, an inductor, a diode, and a capacitor.

The driver IC may include: current sinking means for sinking current for sinking current flowing through each of the LED strings under the control of the MCU; And feedback control means for supplying the feedback signal to the sensing circuit.

The driver IC 322 may include at least one comparator connected to a cathode end of the LED string, respectively.

The sensing circuit may include a first resistor connected to an output terminal of the driver IC; A second resistor connected to an output terminal of the DC-DC converter and an input terminal of the lamp unit; And a third resistor to be grounded.

The compensation circuit may include a fourth resistor connected to an output terminal of the sensing circuit; And a second switching element having a base connected to an output terminal of the MCU, a collector connected to the fourth resistor, and an emitter grounded.

In order to achieve the above object, a liquid crystal display device according to an embodiment of the present invention, the interface unit for receiving image data and control signals from an external system; A timing controller configured to generate gate and source control signals in response to the control signals; A gate driver for supplying a gate driving signal to a gate line according to the gate control signal, and a source driver for providing the image data to a data line according to the source control signal; A liquid crystal panel displaying an image according to the gate driving signal and image data; And a backlight unit including the lamp unit providing light to the liquid crystal panel and the backlight driving circuit as a compensation circuit for controlling the lamp unit and compensating the lamp unit for a feedback signal.

According to a preferred embodiment of the present invention, in a backlight unit of a liquid crystal display device using a plurality of LED elements as a light source, the common operation by compensating the feedback signal output from the LED element according to the load characteristics of the LED element to control the LED driving voltage It is possible to provide a backlight driving circuit and a liquid crystal display including the same.

1 is a view schematically illustrating a configuration of a backlight unit included in a liquid crystal display device using a conventional LED package as a light source.
2 is a block diagram illustrating a configuration of a liquid crystal display including a backlight driving circuit according to an exemplary embodiment of the present invention.
3 is a diagram illustrating a structure of a backlight unit of the present invention.
4 is a diagram schematically illustrating an equivalent circuit diagram of a backlight unit of a liquid crystal display according to an exemplary embodiment of the present invention.

Hereinafter, a backlight driving circuit and a liquid crystal display including the same according to a preferred embodiment of the present invention will be described with reference to the drawings.

The drawings referred to for the embodiments of the present specification are not intended to limit the shapes and positions of the components to the forms shown, and in particular, in order to help the understanding of structures and shapes which are technical features of the present invention, some components The scale of is exaggerated or reduced.

2 is a block diagram illustrating a configuration of a liquid crystal display including a backlight driving circuit according to an exemplary embodiment of the present invention.

As shown, the liquid crystal display device of the present invention, the liquid crystal panel 100 for displaying an image, the driving circuit unit 200 for driving the liquid crystal panel 100, and the backlight unit for providing light to the liquid crystal panel 100 300.

The liquid crystal panel 100 crosses a plurality of data lines DL1 to DLm and a plurality of gate lines GL1 to GLn in a matrix form on a substrate using glass, and forms a plurality of pixel regions at intersections. The thin film transistor T and the liquid crystal LC are configured in the pixel region to implement an image through light provided from the backlight unit 300.

The driving circuit unit 200 includes an interface unit 110 for receiving data input from an external system, a timing controller 120 for generating control signals of each driving unit in response to the data received by the interface unit 110, and a liquid crystal. The panel 100 includes a gate driver 140 for providing a gate driving signal and a source driver 150 for providing an image signal.

The interface unit 110 includes a control signal including image data RGB data, a clock signal CLK, a horizontal synchronization signal Hsync, a vertical synchronization signal Vsync, and a data enable signal DE from an external system. These are supplied to the timing controller 120.

Here, the horizontal synchronization signal Hsync represents the time taken to display one line of the screen, and the vertical synchronization signal Vsync represents the time taken to display the screen of one frame. In addition, the data enable signal DE represents a period for supplying data to the actual pixel.

The timing controller 120 generates a control signal for driving the gate driver 140 including the plurality of driver integrated circuits and the source driver 150 including the plurality of drive integrated circuits using the input control signal. . Also, the data input through the interface 110 is supplied to the source driver 150.

As a control signal of the gate driver 140 generated by the timing controller 120, a gate high signal VGH, a gate low signal VGL, a clock signal CLKS, a start signal VST, a reset signal RST, etc. There is this.

The power supply voltage generator 130 serves to supply a power supply voltage, a reference voltage, and a ground voltage required for operation to each driver, and in particular, the liquid crystal panel 100 supplies a common voltage corresponding to the reference voltage, and provides a backlight. The unit 300 is supplied with a DC power supply VIN required for driving.

The gate driver 140 controls on / off of the thin film transistors T arranged on the liquid crystal panel 100 in response to the above-described control signals of the gate driver from the timing controller 120. The thin film transistors on the liquid crystal panel 100 by outputting the gate driving signals Vg1 to Vgn to enable the gate lines GL1 to GLn on the liquid crystal panel 100 sequentially by one horizontal synchronizing time. The T is sequentially driven line by line so that the image signals supplied from the source driver 150 are applied to the pixels connected to the thin film transistors T.

The gate driver 140 includes a plurality of shift registers. The gate driver 140 has a rear end of the gate driving signals Vg1 to Vgn generated in response to one clock signal selected from the clock signals CLK1 and CLK2 input from the timing controller 122. It is driven by repeating the supply with the start signal Vst for starting operation of the shift register and the reset signal of the previous shift register.

The source driver 150 selects reference voltages of the input data in response to data signals and control signals input from the timing controller 120, and supplies the selected reference voltages to the liquid crystal panel 100 to adjust the rotation angle of the liquid crystal molecules. To control.

The backlight unit 300 is disposed on one surface of the liquid crystal panel 100 and serves to provide light. The backlight unit 300 drives the lamp unit 310 and the lamp unit 310 that are formed of a plurality of point light sources. The circuit unit 320 is included.

The lamp unit 310 provides light to the liquid crystal panel, and packaged LED elements are connected in series to form a single LED string, and a plurality of LED strings are connected in parallel to the LED driving circuit unit 320. It is connected to the structure to drive by receiving the driving voltage. Here, the driving current flowing through the lamp unit 310 is fed back to the LED driving circuit unit 320.

In addition, each of the above-described LED device may be a method of emitting red, green, and blue monochromatic light, or one device may emit white light.

In the case of using an LED device emitting monochromatic light, red, green, and blue monochromatic LED devices are alternately arranged on the substrate at regular intervals, and the monochromatic light emitted therefrom is mixed with white light and then supplied to the liquid crystal panel 100. In the case where the LED device emits white light, the plurality of LED devices are arranged at regular intervals to supply the white light to the liquid crystal panel 100.

The LED driving circuit unit 320 controls the on / off of the lamp unit 310, and the DC power of 24V applied from the power supply voltage generating unit 130 is applied to the LED element driving voltage of about DC 13.3V or less ( VLED) and supplies it to the lamp unit 310, and feeds back a current flowing through the LED string to control the same current to flow through each LED string.

In particular, the above-described LED driving circuit unit 320 further comprises a compensation circuit for adjusting the LED driving voltage (VLED) according to the load characteristics of the LED element by compensating the sensed (sensing) output voltage according to the set value. It is done.

The LED driving circuit unit 320 may be composed of a DC-DC converter, a driver IC, a switching regulator, a compensation circuit, and a MCU for converting the power supplied by the power supply voltage generator 130. ) Will be described later.

Accordingly, the liquid crystal display of the present invention can variably adjust the LED driving voltage according to the load characteristics of the LED element. Hereinafter, a structure of a backlight unit of a liquid crystal display according to an exemplary embodiment of the present invention will be described with reference to the drawings.

3 is a diagram illustrating a structure of a backlight unit of the present invention.

As shown, the backlight unit of the present invention is largely composed of a lamp unit 310 and the LED driving circuit unit 320.

As described above, the lamp unit 310 serves to provide light to the liquid crystal panel, and is configured of an LED string including a plurality of LED elements.

The LED driving circuit unit 320 serves to control the lamp unit 320 and includes a DC-DC converter 321, a driver IC 322, a sensing circuit 323, a compensation circuit 324, and a MCU 325. And a switching regulator 326.

The DC-DC converter 321 receives the power supply voltage of 24V supplied from the power supply unit and steps down according to the duty ratio of the PWM signal input from the switching regulator 325 to supply VLEDs of 13.3V or less. Do it.

The DC-DC converter 321 is preferably implemented by a switching mode power supply (SMPS) circuit, and the above-described SMPS circuit includes a buck converter composed of at least one switching element, an inductor, a diode, and a capacitor, Boost converters and SEPIC (Single Ended Primary Inductance Converter) converters may be used.

The driver IC 322 sinks a current flowing through the lamp unit 310 to control a constant constant current to flow through each LED string, and outputs the LED string through the feedback means, that is, the LED string. The output voltage of the cathode stage of is supplied to the sensing circuit 323.

The sensing circuit 323 receives the output voltage of the lamp unit 310, divides the voltage, and supplies the divided voltage to the switching regulator 326.

The compensation circuit 324 compensates the feedback output voltage supplied by the sensing circuit 323 to the switching regulator 326, and adjusts the range of the output voltage to supply the switching regulator 326.

The MCU 325 controls the range of the constant current that the driver IC 322 sinks according to a set code input by the setter, and the lamp according to the number of LED strings included in the lamp unit 310. When there is a terminal to which the LED string is not connected at the output terminal of the unit 310, the terminal is disabled or enabled when the LED string is connected to the disabled terminal. The compensation circuit 324 is also controlled to adjust the range of the feedback output voltage input to the switching regulator.

The switching regulator 326 generates a PWM signal having a predetermined duty ratio in response to the output voltage fed back from the lamp unit 310, and supplies the same to the DC-DC converter 321 to supply the DC-DC converter 321. It converts the LED driving voltage (VLED) which is an output signal appropriately.

The backlight unit of the preferred liquid crystal display device according to the above-described structure may provide a driving voltage suitable for LED devices having various kinds of load characteristics by compensating a feedback signal of a lamp unit sensed through a setting value of the MCU. Can be. Hereinafter, a detailed circuit structure of a backlight unit of a liquid crystal display according to an exemplary embodiment of the present invention will be described with reference to the drawings.

4 is a diagram schematically illustrating an equivalent circuit diagram of a backlight unit of a liquid crystal display according to an exemplary embodiment of the present invention.

As illustrated, the backlight unit of the present invention includes a lamp unit 310 including a plurality of light emitting diode elements D2 and an LED driving circuit unit 320 for controlling the lamp unit 310.

First, the lamp unit 310 has a structure in which a plurality of LED elements D2 are connected in series to form one LED string, and again, the plurality of LED strings are connected in parallel. Here, the anode end of each LED string is connected to the DC-DC converter 321 of the LED driving circuit unit 320 receives a driving voltage (VLED), the cathode end of the LED string is connected to the driver IC 322 flows Sink the current.

The LED driving circuit unit 320 serves to control the lamp unit 320 and includes a DC-DC converter 321, a driver IC 322, a sensing circuit 323, a compensation circuit 324, and a MCU 325. And a switching regulator 326.

The DC-DC converter 321 includes at least one inductor L1, a switching element T1, a diode D1, and a capacitor C1, and a PWM signal having a duty ratio is input to the switching element T. When the voltage is reduced, the voltage is reduced, but the inductor L1 and the capacitor C1 are used to have an average value and the switching noise is removed. In addition, when the switching device T is turned off, the capacitor C1 is charged through the diode D1 to generate the LED driving voltage VLED.

The driver IC 322 includes a current sinking means 322a for sinking current flowing in each LED string and a feedback control means 322b for providing a feedback signal to the sensing circuit 323 under the control of the MCU 325. By controlling the amount of current to be sinked, a constant current flows through each LED string.

The driver IC 322 includes one or more comparators connected to the cathode ends of the LED strings, and thus, the range of the driving voltage VLED is controlled.

As an example, when the output voltage applied to the output terminal of each LED string is not uniform and the forward voltage Vf and the output voltage Vc are greater than the driving voltage VLED, the above-described comparator outputs a low signal. Accordingly, the first resistor R1 of the sensing circuit 323 is floated to increase the feedback signal. The switching regulator 326 supplies a PWM signal having a small duty ratio to the DC-DC converter 321 in inverse proportion to a large feedback signal when the large feedback signal is supplied, and according to the small duty ratio, the first transistor T1 uses the LED driving signal ( VLED) converts the power supply voltage to have a smaller voltage.

The sensing circuit 323 may include a first resistor R1 connected to the output terminal of the driver IC 322, an output terminal of the DC-DC converter 321, and a second resistor R2 connected to the input terminal of the lamp unit 310, And a third resistor R3 that is grounded, and divides and senses a feedback signal supplied from the driver IC 322.

The compensation circuit 324 is connected to the fourth resistor R4 connected to the output terminal of the sensing circuit 323, the output terminal of the MCU 325 and the base, and the collector is connected to the fourth resistor R4 described above. The emitter is configured to have a second switching element T2 grounded, and compensates the feedback signal by dropping the feedback signal applied to the input terminal of the switching regulator 326 according to the control signal input from the MCU 325.

The MCU 325 controls the driver IC 322 to adjust the amount of current flowing through the lamp unit 310 according to a set value input as a conventional micro controller unit, and also controls the compensation circuit 324 to provide a feedback signal. It serves to compensate.

The switching regulator 326 receives a feedback signal applied from the compensation circuit 324 and generates a PWM signal having a duty ratio corresponding thereto. The switching regulator 326 is connected to the gate of the switching element T1 of the DC-DC converter 321. The voltage applied from the power supply unit is applied to step down the driving signal VLED of the lamp unit 310.

By generating a driving signal corresponding to the feedback signal compensated according to the above-described structure, the LED driving circuit of the present invention can provide a driving voltage suitable for various kinds of LED elements having different load characteristics.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.

310: lamp unit 320: LED driving circuit unit
321: DC-DC converter 322: driver IC
323 sensing circuit 324 compensation circuit
325: MCU 326: switching regulator

Claims (8)

A backlight driving circuit for controlling a lamp unit in which a plurality of lamps are connected in series to form one LED string, and the plurality of LED strings are connected in parallel,
A DC-DC converter receiving a power voltage and stepping down the driving voltage of the lamp unit;
A driver IC for controlling a current flowing in the lamp unit;
A sensing circuit for sensing a feedback signal of the lamp unit from the driver IC;
A compensation circuit for compensating a feedback signal sensed by the sensing circuit;
A switching regulator for generating a PWM signal having a duty ratio corresponding to the feedback signal compensated by the compensation circuit and supplying the PWM signal to the DC-DC converter; And,
MCU controlling the driver IC and the compensation circuit according to a set value
Backlight driving circuit comprising a. The method of claim 1,
The DC-DC converter is a switching mode power supply (SMPS) circuit, characterized in that the backlight drive circuit. The method of claim 2,
The SMPS circuit is any one of a buck converter, a boost converter, and a single ended primary inductance converter (SEPIC) converter including at least one switching element, an inductor, a diode, and a capacitor. Driving circuit. The method of claim 1,
The driver IC may include: current sinking means for sinking current for sinking current flowing through each of the LED strings under the control of the MCU; And,
And a feedback control means for supplying the feedback signal to a sensing circuit. The method of claim 4, wherein
The driver IC 322 includes at least one comparator connected to the cathode terminal of the LED string, respectively. The method of claim 1,
The sensing circuit,
A first resistor connected to the output terminal of the driver IC;
A second resistor connected to an output terminal of the DC-DC converter and an input terminal of the lamp unit; And,
And a third resistor grounded. The method of claim 1,
The compensation circuit,
A fourth resistor connected to the output terminal of the sensing circuit; And,
A second switching element having an output terminal of the MCU connected to a base, a collector connected to the fourth resistor, and an emitter grounded
Backlight driving circuit comprising a. An interface unit for receiving image data and control signals from an external system;
A timing controller configured to generate gate and source control signals in response to the control signals;
A gate driver for supplying a gate driving signal to a gate line according to the gate control signal, and a source driver for providing the image data to a data line according to the source control signal;
A liquid crystal panel displaying an image according to the gate driving signal and image data; And,
And a backlight unit including a lamp unit for providing light to the liquid crystal panel and a backlight circuit for controlling the lamp unit and compensating for the feedback signal.

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