KR20080032440A - Apparatus and method of driving backlight - Google Patents

Abstract

A backlight driving device and a driving method thereof are provided to control brightness of the whole backlight screen uniformly and control characteristics of luminance and color of each part of the whole screen of the backlight minutely. A backlight unit(31) comprises plural light emitting zones(1A,1B,2A,2B) electrically separated from each other. A variable voltage power unit(32) receives power and voltage control signals, and individually outputs controlled voltage to each light emitting zone. A constant current driving unit includes plural constant current circuits(331~334) for receiving a PWM(Pulse Width Modulation) control signal to control amplitude and duty of currents individually which are outputted to each light emitting zone. A terminal voltage measuring unit(34) measures terminal voltage of the constant current circuits. Based on the terminal voltage measured in the terminal voltage measuring unit, a control unit(35) outputs the voltage control signal to the variable voltage power unit and outputs the PWM controls signal to the constant current driving unit.

Description

Backlight driving device and driving method thereof {Apparatus and method of driving backlight}

1 is a view showing an example of a pixel of a TFT-LCD to which a backlight driven by the present invention can be applied.

2 schematically illustrates a configuration of an LCD to which a backlight driven by the present invention can be applied.

3 is a block diagram illustrating a structure of a backlight driving apparatus according to an embodiment of the present invention.

4 is a diagram illustrating another configuration of the backlight unit of FIG. 3.

FIG. 5 is a circuit diagram illustrating an example of a configuration of each constant current circuit in FIG. 3.

FIG. 6 is a waveform diagram illustrating the voltage, current, and power of the collector of the switching device of FIG. 5.

7 is a block diagram illustrating a structure of a backlight driving apparatus according to another embodiment of the present invention.

FIG. 8 is a diagram illustrating a configuration of light emitting diodes included in one light emitting area of FIG. 7.

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

Explanation of symbols on the main parts of the drawings

31: backlight 32: variable voltage power supply

33: constant current driver 331 to 334: constant current circuit

34: terminal voltage measuring unit 35: control unit

36: Measurement channel selector 37: Sensor

The present invention relates to a driving device and a driving method of a backlight, and more particularly, to drive the backlight for controlling the brightness of the entire screen of the backlight uniformly and precisely controlling the brightness and color characteristics of a part of the entire screen. An apparatus and a driving method thereof are provided.

Fluorescent lamps such as Cold Cathode Fluorescent Lamps (CCFLs) are the mainstream backlights for LCDs, but environmentally mercury products have been required. For this reason, LED (Light Emission Diodes) is promising as a light source instead of CCFL in recent years.

In addition to environmental issues, LED backlights are attracting attention as next-generation light sources because they are more energy-saving and semi-permanent than conventional light sources, and research is being actively conducted as the problems of brightness and price are improved.

For use as a backlight, white light is obtained by optically synthesizing the three primary colors by using a white LED or by using a red LED, a green LED, and a blue LED. In particular, since the method of using the three-color LED is easy to balance the color, it is being actively studied for television use.

In a backlight using such a red LED, a green LED, and a blue LED as a light source, the light beams of each of these colors should be optically synthesized at a constant ratio to produce white light of a predetermined chromaticity at all times. Therefore, the amount of light of each color is detected by a photosensor of red, green, and blue, and red, green, and blue are synthesized at a constant ratio by feedback control, and adjusted to white light having a predetermined chromaticity.

However, the conventional backlight driving apparatus has a weak function to uniformly control the brightness of the entire screen of the backlight, and furthermore, it is not possible to precisely control the brightness and color characteristics of each part of the entire screen.

Disclosure of Invention An object of the present invention is to provide a LED driving backlight driving apparatus capable of uniformly controlling the brightness of the entire screen of the backlight, and to precisely control the brightness and color characteristics of each part of the entire screen as necessary, and a driving method thereof. To provide.

The present invention provides a backlight unit including a plurality of light emitting regions electrically separated from each other; A variable voltage power supply unit receiving a power supply and a voltage control signal and separately outputting a voltage controlled to each light emitting area; A constant current driver including a plurality of constant current circuits that receive a PWM control signal and individually adjust the amplitude and duty of the current output to each light emitting area; A terminal voltage measuring unit measuring terminal voltages of the constant current circuits; And a controller which outputs a voltage control signal to the variable voltage power supply unit and outputs a PWM control signal to the constant current driver based on the terminal voltage measured by the terminal voltage measurer.

The backlight driving circuit may further include a measurement channel selector configured to select a constant current circuit in a conductive state among the constant current circuits.

The backlight driving circuit may further include a sensor configured to detect brightness, temperature, or chromaticity of each light emitting area and provide the information to the controller.

Each light emitting region may include white light emitting diodes.

Each of the light emitting zones may include red light emitting diodes, green light emitting diodes, and blue light emitting diodes.

The variable voltage power supply unit includes a variable voltage power supply unit for a red light emitting diode, a variable voltage power supply unit for a green light emitting diode, and a variable voltage power supply unit for a blue light emitting diode, and the respective constant current circuits are electrically connected to respective light emitting diodes in the respective light emitting regions. Can be.

The constant current circuit may include an amplifier that receives a PWM control signal and generates a shaped waveform, and a switching element that receives the shaped control signal.

According to an aspect of the present invention, there is provided a method of driving a backlight driving apparatus, the method comprising: measuring terminal voltage of each constant current circuit supplying current to each light emitting area; Individually outputting the controlled voltages to the respective light emitting zones based on the measured terminal voltages; And individually adjusting the amplitude and the duty of the current output to each of the light emitting zones based on the measured terminal voltages.

The measurement of the terminal voltage of each constant current circuit may be performed by selecting a constant current circuit in a conductive state among the constant current circuits.

The backlight driving method may further include detecting brightness, temperature, or chromaticity of each light emitting area.

Each step of the backlight driving method may be separately performed for the red light emitting diodes, the green light emitting diodes, and the blue light emitting diodes included in each light emitting area.

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

1 is a view showing an example of a pixel of a TFT-LCD to which a backlight driven by the present invention can be applied.

Referring to FIG. 1, each pixel of the liquid crystal display device has a drain electrode and a common electrode of a TFT 10 and a TFT 10 having a source electrode connected to a data line Dm and a gate electrode connected to a scan line Sn. A liquid crystal capacitor Cl connected between the Vcom and a storage capacitor Cst connected to the drain electrode of the TFT 10 is included.

The TFT 10 provides the pixel electrode (not shown) with the data voltage Vd supplied from the data line Dm in response to a scan signal from the scan line Sn. The electric field corresponding to the difference between the data voltage provided to the pixel electrode (ie, the pixel voltage Vp and the common voltage Vcom applied to the common electrode (not shown) is equivalent to that of the liquid crystal capacitor (FIG. 1). The liquid crystal adjusts the transmittance of light in response to the intensity of the applied electric field, and the storage capacitor Cst converts the pixel voltage provided to the liquid crystal capacitor Cl to the next data voltage Vd. The light is transmitted for a predetermined time by maintaining it until it is supplied.

2 schematically illustrates a configuration of an LCD to which a backlight driven by the present invention can be applied.

Referring to FIG. 2, the liquid crystal display includes a lower substrate 101 having a TFT array (not shown) arranged with a plurality of gate lines, a plurality of data lines, and a plurality of switching thin film transistors connected to a plurality of common lines. Liquid crystal having an upper substrate 103 having a common electrode (not shown) for providing a common voltage to the line, and a liquid crystal (not shown) injected between the upper substrate 103 and the lower substrate 101. The panel 100 is provided.

In addition, the liquid crystal display device includes a gate line driver circuit 110 for providing a scan signal to a plurality of gate lines of the liquid crystal panel 100, and a data line driver circuit 120 for providing a data signal to the data line. And a backlight 130 for providing light to the liquid crystal panel 100.

The backlight 130 includes a white LED or a red LED, a green LED, and a blue LED to provide white light, and a light guide plate for providing light emitted from the LED to the liquid crystal of the liquid crystal panel 100.

3 is a block diagram illustrating a structure of a backlight driving apparatus according to an embodiment of the present invention.

Referring to FIG. 3, a backlight driving apparatus according to an embodiment of the present invention includes a backlight unit 31, a variable voltage power supply unit 32, a constant current driver 33, a terminal voltage measurement unit 34, a controller 35, Measurement channel selector 36 and sensor 37 are included.

The backlight unit 31 includes a plurality of light emitting regions electrically separated from each other. In FIG. 3, the backlight unit 31 includes four light emitting regions 1A, 1B, 2A, and 2B.

The light emitting zones 1A, 1B, 2A, and 2B each comprise white light emitting diodes as a backlight. Although not shown, the light emitting diodes may be connected in series with each other.

4 is a diagram illustrating another configuration of the backlight unit of FIG. 3.

Referring to FIG. 4, the backlight unit includes 16 light emitting zones 1A, 1B, 1C, 1D, 2A, 2B, 2C, 2D, 3A, 3B, 3C, 3D, 4A, 4B, 4C, and 4D. . In the present invention, the number and shape of the light emitting zones constituting the backlight unit may be variously modified by application conditions.

The variable voltage power supply unit 32 receives power from the outside, receives a voltage control signal from the control unit 35, and individually outputs the voltages controlled to the light emitting regions 1A, 1B, 2A, and 2B.

The variable voltage power supply unit 32 is a power supply circuit for supplying current to the LEDs 1A, 1B, 2A, and 2B. The power supply of an LED may require a high voltage to connect and illuminate the LEDs in series. The variable voltage power supply unit 32 is a power supply circuit for precisely controlling the required voltage. Since LEDs are semiconductors whose electrical characteristics are sensitive to changes in temperature, in order to maintain an optimal operating state, the variable power supply voltage must continuously compensate the voltage by the change in the characteristics of the LED.

The magnitude of the voltage is determined by the value sent from the controller 35. In other words, since the voltage-current characteristics vary depending on the temperature, the power supply voltage must be adjusted for optimal power consumption. The variable voltage power supply unit 32 performs this adjusting role. This output voltage is used in the LED and the constant current driver 33. When the voltage is increased, the heat loss of the constant current driver 33 increases, and the temperature of the portion rises, thereby detecting the voltage of the constant current driver 33 to minimize the voltage. It outputs from the control part 33 so that it may be maintained.

The constant current driver 33 receives a PWM control signal from the controller 35 and individually adjusts the amplitude and duty of the current output to each of the light emitting zones 1A, 1B, 2A, and 2B, respectively, 331, 332, 333, 334. ).

FIG. 5 is a circuit diagram illustrating an example of a configuration of each constant current circuit in FIG. 3.

Referring to FIG. 5, each of the constant current circuits 331, 332, 333, and 334 includes an amplifier for receiving a PWM control signal and generating a shaped waveform, a switching element for receiving the shaped control signal, and a resistor connected to the emitter of the switching element. ).

In more detail, the PWM waveform sent from the controller 35 is distorted due to the PWM influence of the long connection line and the other channel. This waveform is shaped by a constant current circuit to input a more complicated PWM waveform to the base of the transistor. In a constant current circuit, this PWM waveform is shaped and precisely adjusts its amplitude to control the current magnitude of the transistor. The current value is determined by the resistance of the emitter of the transistor. If the amplification ratio of the transistor is about the same, the current value can be precisely adjusted.

Each constant current circuit (331, 332, 333, 334) not only precisely controls the magnitude of the current, but also when the LED temperature rises and its voltage-current characteristic changes, the waveform of the turned-on current flows as close to a square wave as possible, and the amount of current is kept constant. It can also be controlled to protect the LEDs.

In other words, the amount of current can be precisely controlled by the resistor connected to the emitter of the transistor and the terminal voltage (VDD) of the amplifier functioning waveform shaping.

The measurement channel selector 34 selects a constant current circuit in a conductive state among the constant current circuits 331, 332, 333, and 334, and the terminal voltage measuring unit 34 measures the terminal voltage of the selected constant current circuit among the constant current circuits 331, 332, 333, 334. The terminal voltage measurer 34 may be an analog-digital converter (ADC).

The factors for determining the voltage of the variable voltage power supply output from the variable voltage power supply unit 32 are the required voltage of the LED and the terminal voltage of the constant current circuits 331, 332, 333, 334. In the present invention, since the voltage of the LED is determined by the device itself, the method of measuring the terminal voltage of the constant current circuits 331, 332, 333, 334 and calculating the necessary value in the variable voltage power supply 32 using the value is adopted.

FIG. 6 is a waveform diagram illustrating the voltage, current, and power of the collector of the switching device of FIG. 5.

Referring to FIG. 6, the collector voltages of the switching elements of the constant current circuits 331, 332, 333, and 334 are composed of a turn-on state and a turn-off state, which are conductive states of the switching element. At this time, the value for determining the power supply voltage refers to the terminal voltage when the transistor is turned on, and the terminal voltage refers to the collector voltage of the desired constant current circuit using a semiconductor switch that selects a measurement channel when the transistor is turned on. 34). The voltage of the variable voltage power supply unit 32 is adjusted by the controller 35 so that the measured voltage becomes an optimal value.

The sensor 37 detects the brightness, temperature or chromaticity of each LED or LED array included in each of the light emitting zones 1A, 1B, 2A, and 2B, and provides the information to the controller 35.

The control unit 35 uses the terminal voltage information of the constant current circuits 331, 332, 333, 334 measured by the terminal voltage measuring unit 34, and information such as brightness, temperature, or chromaticity sensed by the sensor 37 to obtain a voltage control signal. The variable voltage power supply unit 32 outputs the PWM control signal to the constant current driver 33.

As a result, the luminance and color characteristics of each of the light emitting zones 1A, 1B, 2A, and 2B can be precisely controlled, and therefore, the luminance and color characteristics of the entire backlight unit 31 can be uniformly controlled.

The controller 35 performs feedback control to precisely control the LED current for every zone by using the information of the brightness of the light transmitted from all the sensors and the temperature of each part in order to maintain the brightness of each part of the backlight set by the user. do.

In addition, in order to minimize the total power consumption of the backlight driving circuit, the controller 35 measures the terminal voltage while the control transistor conducts the constant current of the backlight driving circuit to maintain an optimum voltage value at the terminal of the transistor. A value for adjusting the power supply voltage is calculated and provided to the variable voltage power supply unit 32 as a voltage control signal to adjust the output voltage of the circuit.

7 is a block diagram illustrating a structure of a backlight driving apparatus according to another embodiment of the present invention. In FIG. 7, the light emitting regions 711,..., 711N are overlapped for convenience, but are actually configured as shown in FIG. 3.

FIG. 8 is a diagram illustrating a configuration of light emitting diodes included in one light emitting area 711,..., 711N of FIG. 7.

7 and 8, each light emitting zone 711,..., 711N includes red light emitting diodes, green light emitting diodes, and blue light emitting diodes.

The variable voltage power supply unit 72 includes a variable voltage power supply unit 721 for a red light emitting diode, a variable voltage power supply unit 722 for a green light emitting diode, and a variable voltage power supply unit 723 for a blue light emitting diode. 732, 733, 734, 7351, and 736 are electrically connected to respective light emitting diodes in each of the light emitting zones 711,..., 711N.

The control unit 75 receives the brightness of the light sent from each sensor 77 and the temperature of each part and the signal of the user's input to determine the brightness of the three-color LED of red, blue, and green in each compartment.

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

9, a backlight driving method using the backlight driving apparatus according to the present invention includes a terminal voltage measuring step 91, a light emitting area information detecting step 92, a control voltage output step 93, and an amplitude and duty of a current. Control step 94.

The terminal voltage measuring step 91 measures the terminal voltage of each constant current circuit for supplying current to each light emitting area of the backlight driving apparatus. The measurement of the terminal voltage of each constant current circuit may be performed by selecting a constant current circuit in a conductive state among the constant current circuits.

The light emitting area information detecting step 92 detects the brightness, temperature or chromaticity of each light emitting area.

The control voltage outputting step 93 individually outputs the voltage controlled to each light emitting area based on the measured terminal voltage and the detected light emitting area information.

The amplitude and duty control step 94 of the current individually adjusts the amplitude and duty of the current output to each of the light emitting zones based on the measured terminal voltage.

Each of the above steps may be performed separately for the red light emitting diodes, the green light emitting diodes, and the blue light emitting diodes included in each light emitting area.

The present invention having the above-described configuration achieves the following effects.

First, by using the backlight driving apparatus and the driving method thereof, the brightness of the entire screen of the backlight can be uniformly controlled.

Second, it is possible to precisely control the characteristics of the brightness and color of each part of the entire screen of the backlight.

Although the present invention has been described with reference to the embodiments shown in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims (11)

A backlight unit including a plurality of light emitting regions electrically separated from each other; A variable voltage power supply unit receiving a power supply and a voltage control signal and separately outputting a voltage controlled to each light emitting area; A constant current driver including a plurality of constant current circuits that receive a PWM control signal and individually adjust the amplitude and duty of the current output to each light emitting area; A terminal voltage measuring unit measuring terminal voltages of the constant current circuits; And And a controller configured to output a voltage control signal to the variable voltage power supply unit and to output a PWM control signal to the constant current driver based on the terminal voltage measured by the terminal voltage measurer. The method of claim 1, And a measurement channel selector for selecting a constant current circuit in a conductive state among the constant current circuits. The method of claim 1, And a sensor configured to detect brightness, temperature, or chromaticity of each light emitting area and provide the information to the controller. The method of claim 1, And each of the light emitting zones comprises red light emitting diodes, green light emitting diodes, and blue light emitting diodes. The method of claim 1, And each of the light emitting zones comprises white light emitting diodes. The method of claim 5, The variable voltage power supply unit includes a variable voltage power supply unit for a red light emitting diode, a variable voltage power supply unit for a green light emitting diode, and a variable voltage power supply unit for a blue light emitting diode, and each of the constant current circuits is electrically connected to respective light emitting diodes in the respective light emitting regions. And a backlight driving circuit. The method of claim 1, The constant current circuit includes an amplifier configured to receive a PWM control signal and generate a shaped waveform, and a switching device receiving the shaped control signal. In the method of driving the backlight driving device according to any one of claims 1 to 7, Measuring a terminal voltage of each constant current circuit for supplying current to each light emitting area; Individually outputting a controlled voltage to each of the light emitting zones based on the measured terminal voltages; And Individually adjusting the amplitude and duty of the current output to each of the light emitting zones based on the measured terminal voltages. The method of claim 8, The measurement of the terminal voltage of each constant current circuit is performed by selecting a constant current circuit in a conductive state among the constant current circuits. The method of claim 8, And detecting the brightness, temperature, or chromaticity of each light emitting area. The method of claim 8, Wherein each step is performed separately for red light emitting diodes, green light emitting diodes, and blue light emitting diodes included in each light emitting area.

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