KR20080073441A - Backlight unit - Google Patents

Abstract

A backlight unit is provided to reduce a current difference between lamps by detecting current flowing on a first coil of a transformer and controlling output of an inverter through the detected current. A backlight unit(190) comprises a backlight(150) consisting of a plurality of lamps, and an inverter controlling tube current supplied to the backlight. The inverter includes a transformer(166) boosting the voltage of an alternating signal to supply the boosted alternating signal to the lamps, a feedback signal generator(168) detecting alternating current flowing on a first coil of the transformer to generate a feedback signal, a controller(162) generating a switching control signal in response to the feedback signal, a switching unit(164) converting a direct signal supplied from the outside into the alternating signal to supply the alternating signal to the transformer, and an overvoltage detector(169) detecting alternating voltage supplied to the lamps from a secondary coil of the transformer and returning the alternating voltage to the controller. The controller cuts off the alternating signal applied to the lamps by varying a duty rate of PWM(Pulse Width Modulation) to control the switching unit, when receiving an overvoltage detection signal.

Description

Backlight Unit

1 is a view showing a conventional backlight unit.

2 is a block diagram of a liquid crystal display device to which the present invention is applied.

3 is a diagram illustrating a backlight unit according to a first embodiment of the present invention;

4 is a diagram illustrating a backlight unit according to a second embodiment of the present invention;

 <Description of Symbols for Main Parts of Drawings>

110: liquid crystal display panel 120: data driver

130: gate driver 140: gamma reference voltage generator

150: backlight 160: inverter

162: control unit 164: switching unit

166: transformer 166a, 166b: transformer

168, 268: feedback signal generator 169: overvoltage detector

170: common voltage generator 180: timing controller

190: backlight unit Rs: sensing resistor

D, D1, D2: Diodes R, R1, R2: Input Resistance

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a backlight unit configured to reduce current deviation between lamps by controlling an output of an inverter by using a current flowing in a primary coil of a transformer.

In general, liquid crystal displays (hereinafter referred to as "LCDs") have tended to be increasingly wider in application due to features such as light weight, thinness, and low power consumption. According to this trend, LCDs are used for office automation equipment, audio / video equipment, and the like. On the other hand, the LCD is controlled to display the desired image on the screen by adjusting the transmission amount of the light beam according to the image signal applied to the plurality of control switches arranged in a matrix form.

Since the LCD is not a self-luminous display device, a backlight unit including an inverter and a back light is required. There are two types of LCD backlights: direct type and edge type. In the direct type, a plurality of lamps are arranged on a plane, and a diffusion plate is installed between the lamp and the liquid crystal panel to maintain a constant between the liquid crystal panel and the lamp. In the edge type, a lamp is installed outside the flat plate, and light generated from the lamp is incident on the entire surface of the liquid crystal panel using a transparent light guide plate. The inverter controls the tube current supplied to the lamp to adjust the brightness of the liquid crystal display.

1 shows a conventional backlight unit.

Referring to FIG. 1, a conventional backlight unit includes a backlight including a plurality of lamps and an inverter for controlling a tube current supplied to the backlight.

As a backlight, a cold cathode fluorescent lamp (hereinafter referred to as "CCFL") lamp or an external electrode fluorescent lamp (hereinafter referred to as "EEFL") lamp is used. The high voltage AC signal supplied to the lamp is generated by the inverter.

The inverter includes a controller, a switching unit, a transformer, and a feedback signal generator.

The transformer consists of a transformer having a primary coil and a secondary coil. The primary coils are electrically connected to each other, and a plurality of secondary coils are electrically separated from each other. Lamps are connected to one end and the other end of the secondary coils, respectively. The transformer serves to boost the low-voltage AC signal supplied to the primary coil and supply it to the lamps connected to the secondary coil.

The feedback signal generator detects a tube current supplied to the lamp from one of the one end and the other end of the secondary coils, generates a feedback signal, and supplies it to the controller.

The controller generates a switching control signal in a pulse width modulation scheme (PWM) in response to the supplied feedback signal.

The switching unit includes a plurality of switch elements that are switched in accordance with a switching control signal. The DC signal supplied from the outside by the switching operation of the switch elements is converted into an AC signal and supplied to the primary coils of the transformer part.

Such a conventional backlight unit detects a lamp current at any point A of a plurality of secondary coils each connected to a lamp as shown in FIG. 1 to generate a feedback signal. However, due to the leakage capacitance of the lamp itself, the currents at points A, B, C and D have different magnitudes, so the feedback signal generated through a specific point is the average brightness of the lamps connected to each point. Cannot be controlled. This problem is greater with larger monitors. In general, a large monitor using 16 lamps (for example, 26 inches or 30 inches) controls the brightness of the lamps in units of blocks including four lamps, and there is a large variation in the lamp current between the feedback point and the other points. In this case, it is difficult to control the output current of the inverter evenly, resulting in a luminance defect such as a horizontal band.

In addition, the conventional backlight unit has a problem in that an inverter circuit wiring is complicated by lengthening a feedback path by detecting a lamp current at any point A of the secondary coil.

Accordingly, an object of the present invention is to provide a backlight unit capable of reducing current deviation between lamps and simplifying inverter circuit wiring by detecting a current flowing in a primary coil of a transformer and controlling the output of the inverter using the same. There is.

In order to achieve the above object, the backlight unit according to an embodiment of the present invention comprises a plurality of lamps; A transformer unit having at least one secondary coil connected to the lamps, and a primary coil connected to the secondary coils and electrically connected to each other; A feedback signal generator for detecting an alternating current flowing through the primary coil and generating a feedback signal; A controller configured to vary a switching control signal in response to the feedback signal; And a switching unit which is switched according to the switching control signal and converts a DC signal supplied from the outside into an AC signal and supplies it to the transformer unit.

The feedback signal generator may include a sensing resistor connected between the primary coil and the switching unit to convert the primary AC current into a feedback AC voltage; And a rectifier for rectifying the feedback AC voltage to generate a feedback DC voltage.

The rectifier includes at least one diode connected between one side of the sensing resistor and the controller.

The feedback signal generation unit may include: a current sensing transformer connected between the primary coil and the switching unit to convert the primary AC current into a predetermined ratio; A rectifier for rectifying the primary AC current converted at the predetermined ratio to generate a DC current; And a sensing resistor for converting the DC current into a feedback DC voltage.

The rectifier includes a diode connected between one end of the secondary coil of the current sensing transformer and the controller.

The sensing resistor is connected between the other end of the secondary side coil of the current sensing transformer and the cathode electrode of the diode.

The feedback signal generator further includes at least one input resistor connected between the output terminal of the rectifier and the controller to stabilize the feedback DC voltage.

The transformer unit includes a plurality of transformers electrically separated to drive different lamps; Two or more lamps are connected to the secondary coil of each transformer.

The lamps connected adjacent to the secondary coils are supplied with tube currents of opposite phase to each other.

The switching control signal is generated in a pulse width modulation scheme and its duty ratio is changed by the feedback signal.

The switching unit includes a plurality of field effect transistors switched by the switching control signal.

The backlight unit according to an exemplary embodiment of the present invention further includes an overvoltage detector configured to detect an AC voltage supplied from the secondary coil of the transformer to the lamp and feed it back to the controller.

Other objects and features of the present invention in addition to the above object will be apparent from the description of the embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 2 to 4.

2 is a block diagram of a liquid crystal display device to which the present invention is applied.

Referring to FIG. 2, a liquid crystal display device includes a thin film transistor (“Thin Film Transistor”) for driving the liquid crystal cell Clc at an intersection thereof with the data lines DL1 to DLm and the gate lines GL1 to GLn intersecting each other. A liquid crystal display panel 110 having a TFT ", a data driver 120 for supplying a data voltage to the data lines DL1 to DLm of the liquid crystal display panel 110, and a liquid crystal display panel 110. A gate driver 130 for supplying scan pulses to the gate lines GL1 to GLn of the gate lines, a gamma reference voltage generator 140 for generating a gamma reference voltage and supplying it to the data driver 120, and a liquid crystal display panel A backlight unit 190 including a backlight 150 for irradiating light to the 110 and an inverter 160 for applying an AC signal to the backlight 150, and a common voltage Vcom are generated to generate a liquid crystal cell ( A common voltage generator 170 for supplying the common electrode of Clc) And a timing controller 180 for controlling the portion 120 and the gate driver 130.

In the liquid crystal display panel 110, liquid crystal is injected between two glass substrates. The data lines DL1 to DLm and the gate lines GL1 to GLn are orthogonal to the lower glass substrate of the liquid crystal display panel 110. TFTs are formed at intersections of the data lines DL1 to DLm and the gate lines GL1 to GLn. The TFT supplies the data voltages on the data lines DL1 to DLm to the liquid crystal cell Clc in response to the scan pulse. For this purpose, the gate electrodes of the TFTs are connected to the gate lines GL1 to GLn, and the source electrodes of the TFTs are connected to the data lines DL1 to DLm. The drain electrode of the TFT is connected to the pixel electrode of the liquid crystal cell Clc and the storage capacitor Cst.

The data driver 120 samples and latches the digital video data RGB supplied from the timing controller 180, and then, based on the gamma reference voltage supplied from the gamma reference voltage generator 140, the data driver 120 of the liquid crystal display panel 110. The liquid crystal cell Clc is converted into a data voltage capable of expressing gray scale and supplied to the data lines DL1 to DLm.

The gate driver 130 sequentially generates scan pulses and supplies them to the gate lines GL1 to GLn in response to the gate control signal GDC supplied from the timing controller 180. The scan pulse is swinged between the gate high voltage for turning on the TFT and the gate low voltage for turning off the TFT.

The gamma reference voltage generator 140 generates a positive gamma reference voltage and a negative gamma reference voltage by dividing a high potential power voltage VDD from a power generator (not shown) through a resistance string, and generates the data driver 120. )

The backlight 150 is disposed on the rear surface of the liquid crystal display panel 110 and emits light emitted by an AC signal supplied from the inverter 160 to emit light to each pixel of the liquid crystal display panel 110. The backlight 150 may be implemented in a direct type method in which a plurality of lamps are disposed on a plane and a diffusion plate is installed between the lamp and the liquid crystal panel to maintain a constant space between the liquid crystal panel and the lamp. In addition, the backlight 150 may be implemented in an edge type manner in which a lamp is installed outside the flat plate and light emitted from the lamp is incident on the entire surface of the liquid crystal panel using a transparent light guide plate.

The inverter 160 generates a pulse width modulation (PWM) signal having a different duty ratio by using a dimming signal generated from a dimming circuit (not shown) and a signal fed back from the transformer side of the inverter 160. By controlling the internal switching circuit by using the control to adjust the size of the AC signal supplied to the backlight (150). Here, the dimming circuit converts the square wave signal generated therein into a triangular wave signal and compares the triangular wave signal with a DC power supply voltage to generate a burst dimming signal proportional to the comparison result. In particular, the inverter 160 according to the present invention can minimize the difference in tube current between a plurality of lamps by using a signal fed back from the primary side of the transformer to control the switching circuit. This will be described in detail with reference to FIGS. 3 and 4.

The common voltage generator 170 receives the high potential power voltage VDD to generate the common voltage Vcom and supplies the common voltage Vcom to the common electrodes of the liquid crystal cells Clc of each pixel of the liquid crystal display panel 110.

The timing controller 180 supplies the digital video data RGB supplied from the digital video card (not shown) to the data driver 120. In addition, the timing controller 180 generates the data control signal DDC and the gate control signal GDC using the horizontal / vertical synchronization signals H and V according to the clock signal CLK, respectively. And the gate driver 130. The data control signal DDC includes a source shift clock SSC, a source start pulse SSP, a polarity control signal POL, a source output enable signal SOE, and the gate control signal GDC. And a gate start pulse GSP, a gate shift clock GSC, a gate output enable signal GOE, and the like.

3 shows a backlight unit 190 according to a first embodiment of the present invention.

The backlight unit 190 according to the first embodiment of the present invention includes a backlight 150 including a plurality of lamps and an inverter 160 for controlling a tube current supplied to the backlight 150.

As the backlight 150, a CCFL lamp or an EEFL lamp is mainly used. Whereas CCFL lamps use the principle of secondary electron emission from the electrodes in the lamp (sputtering of the electrodes due to high voltages), EEFL lamps are walled by charging and discharging at an external electrode (usually a metal coating on a glass tube). Use a method of inducing charge.

The inverter 160 detects an alternating current flowing through the transformer 166 that boosts the AC signal having a low voltage and supplies it to the lamps of the backlight 150, and detects an alternating current flowing through the primary coil of the transformer 166. A feedback signal generator 168 for generating a signal, a control unit 162 for generating a switching control signal Swc in response to the feedback signal Sfb, and a DC signal switched from the outside in response to the switching control signal Swc. The switching unit 164 converts the AC signal into an AC signal and supplies it to the transformer unit 166, and an overvoltage detector detecting the AC voltage supplied from the secondary coil of the transformer unit 166 to the lamp and feeding it back to the control unit 162. 169).

The transformer 166 includes first and second transformers 166a and 166b that are electrically separated to drive different lamps. One end of the primary coil L11 of the first transformer 166a is connected to the switching unit 164, and the other end of the primary coil L11 of the first transformer 166a is the primary side of the second transformer 166b. It is electrically connected to the coil L21. One end and the other end of the secondary coil L12 of the first transformer 166a are connected one-to-one to the lamps of the backlight 150, respectively. Since the other ends of the two lamps, one end of which is connected to the secondary coil L12 of the first transformer 166a, are grounded, the AC signals supplied to the two lamps connected to the secondary coil L12 may have opposite phases. Have. One end of the primary coil L21 of the second transformer 166b is connected to the switching unit 164, and the other end of the primary coil L21 of the second transformer 166b is the primary side of the first transformer 166a. It is electrically connected to the coil L11. One end and the other end of the secondary coil L22 of the second transformer 166b are connected one-to-one to the lamps of the backlight 150, respectively. Since the other end of the two lamps, one end of which is connected to the secondary coil L22 of the second transformer 166b, is grounded, the AC signals supplied to the two lamps connected to the secondary coil L22 may have opposite phases. Have.

The feedback signal generator 168 is connected between the first node n1 and the switching unit 164 to detect an AC current flowing through the primary coils L11 and L21 of the transformer unit 166 into a feedback AC voltage. First and second diodes D1 and D2 connected between the resistor Rs, both ends of the sensing resistor Rs, and the second node n2 to rectify the converted feedback AC voltage to generate a feedback DC voltage. And an input resistor R for stabilizing the feedback DC voltage applied to the second node n2. The feedback signal generator 168 may be formed between one end of the primary coil L21 of the second transformer 166b and the switching unit 164 as shown, and the primary coil of the first transformer 166a. It may be formed between the L11 and the switching unit 164. The current flowing through the primary coils L11 and L21 of the transformer unit 166 is an average value of the tube currents (currents flowing through the secondary coils L12 and L22 of the transformer unit 166) supplied to the respective lamps. Have Therefore, the feedback signal generator 168 connected to the primary side of the transformer 166 generates the feedback signal Sfb using the average current of the lamp tube currents having different values, so that a current deviation between the lamps is generated. Solve the problem.

The controller 162 generates the switching control signal Swc using the burst dimming signal generated from the dimming circuit (not shown) and the feedback signal Sfb from the feedback signal generator 168. The switching control signal Swc is generated by the pulse width modulation PWM method and its duty ratio is changed by the feedback signal Sfb.

The switching unit 164 is switched according to the switching control signal Swc and converts a DC signal supplied from the outside into an AC signal and supplies it to the transformer unit 166. The switching unit 164 includes a plurality of field effect transistors switched by the switching control signal Swc.

The overvoltage detector 169 detects the AC voltage supplied from the secondary coil of the transformer 166 to the lamp for each lamp and feeds back the overvoltage detection signal Sovp to the controller 162. When the overvoltage detection signal Sovp is fed back, the controller 162 blocks the AC signal applied to the lamps by controlling the switching unit 164 by varying the duty ratio of the pulse width modulation PWM.

4 shows a backlight unit 190 according to a second embodiment of the present invention.

The backlight unit 190 according to the second embodiment of the present invention includes a backlight 150 including a plurality of lamps and an inverter 160 for controlling a tube current supplied to the backlight 150.

As the backlight 150, a CCFL lamp or an EEFL lamp is mainly used. Whereas CCFL lamps use the principle of secondary electron emission (electrode sputtering due to high voltage) at the electrodes in the lamp, EEFL lamps are caused by charging and discharging at an external electrode (usually a metal coating on a glass tube). Use a method of inducing wall charge.

The inverter 160 detects an alternating current flowing through the transformer 166 that boosts the AC signal having a low voltage and supplies it to the lamps of the backlight 150, and detects an alternating current flowing through the primary coil of the transformer 166. A feedback signal generation unit 268 for generating a signal, a control unit 162 for generating a switching control signal Swc in response to the feedback signal Sfb, and a DC signal supplied from the outside by being switched according to the switching control signal Swc. The switching unit 164 converts the AC signal into an AC signal and supplies it to the transformer unit 166, and an overvoltage detector detecting the AC voltage supplied from the secondary coil of the transformer unit 166 to the lamp and feeding it back to the control unit 162. 169).

The transformer 166 includes first and second transformers 166a and 166b that are electrically separated to drive different lamps. One end of the primary coil L11 of the first transformer 166a is connected to the switching unit 164, and the other end of the primary coil L11 of the first transformer 166a is the primary side of the second transformer 166b. It is electrically connected to the coil L21. One end and the other end of the secondary coil L12 of the first transformer 166a are connected one-to-one to the lamps of the backlight 150, respectively. Since the other end of the two lamps, one end of which is connected to the secondary coil L12 of the first transformer 166a, is grounded, the AC signals supplied to the two lamps connected to the secondary coil L12 may have opposite phases. Have. One end of the primary coil L21 of the second transformer 166b is connected to the switching unit 164, and the other end of the primary coil L21 of the second transformer 166b is the primary side of the first transformer 166a. It is electrically connected to the coil L11. One end and the other end of the secondary coil L22 of the second transformer 166b are connected one-to-one to the lamps of the backlight 150, respectively. Since the other end of the two lamps, one end of which is connected to the secondary coil L22 of the second transformer 166b, is grounded, the AC signals supplied to the two lamps connected to the secondary coil L22 may have opposite phases. Have.

The feedback signal generator 268 is connected between the primary coils L11 and L21 of the transformer 166 and the switching unit 164 to convert a primary AC current into a predetermined ratio, and a predetermined current sensing transformer. A diode (D) for rectifying the primary side AC current converted into a ratio and generating a DC current, a sensing resistor (Rs) for converting the DC current to a feedback DC voltage, and an input resistor (R1, for stabilizing the feedback DC voltage). R2)). The primary coil Lk1 of the current sensing transformer is connected between the primary coils L11 and L21 of the transformer 166 and the switching unit 164. The secondary coil Lk2 of the current sensing transformer is connected to ground and a diode. It is connected to the anode electrode of (D). The anode electrode of the diode D is connected to one end of the secondary coil Lk2 of the current sensing transformer, and the cathode electrode of the diode D is connected to the first node n1. The sense resistor Rs is connected between ground and the first node n1. The first input resistor R1 is connected between the first node n1 and the second node n2, and the second input resistor R2 is connected between the second node n2 and the ground. As illustrated, the feedback signal generator 268 may be formed between one end of the primary coil L21 of the second transformer 166b and the switching unit 164, and 1 of the first transformer 166a. It may be formed between the vehicle side coil L11 and the switching unit 164. The current flowing through the primary coils L11 and L21 of the transformer unit 166 is an average value of the tube currents (currents flowing through the secondary coils L12 and L22 of the transformer unit 166) supplied to the respective lamps. Have Therefore, the feedback signal generator 268 connected to the primary side of the transformer 166 generates the feedback signal Sfb using the average current of the lamp tube currents having different values, whereby the current deviation between the lamps is increased. Resolve the problem that occurred.

The controller 162 generates the switching control signal Swc using the burst dimming signal generated from the dimming circuit (not shown) and the feedback signal Sfb from the feedback signal generator 168. The switching control signal Swc is generated by the pulse width modulation PWM method and its duty ratio is changed by the feedback signal Sfb.

The switching unit 164 is switched according to the switching control signal Swc and converts a DC signal supplied from the outside into an AC signal and supplies it to the transformer unit 166. The switching unit 164 includes a plurality of field effect transistors switched by the switching control signal Swc.

The overvoltage detector 169 detects the AC voltage supplied from the secondary coil of the transformer 166 to the lamp for each lamp and feeds back the overvoltage detection signal Sovp to the controller 162. When the overvoltage detection signal Sovp is fed back, the controller 162 blocks the AC signal applied to the lamps by controlling the switching unit 164 by varying the duty ratio of the pulse width modulation PWM.

As described above, the backlight unit according to the present invention can reduce the current deviation between the lamp by detecting the current flowing in the primary coil of the transformer, and controlling the output of the inverter using this.

In addition, the backlight unit according to the present invention can reduce the feedback path by simplifying the inverter circuit wiring by detecting and feeding back a current flowing in the primary coil of the transformer.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (12)

Multiple lamps; A transformer unit having at least one secondary coil connected to the lamps, and a primary coil connected to the secondary coils and electrically connected to each other; A feedback signal generator for detecting an alternating current flowing through the primary coil and generating a feedback signal; A controller configured to vary a switching control signal in response to the feedback signal; And And a switching unit which switches according to the switching control signal and converts a DC signal supplied from the outside into an AC signal and supplies the converted signal to the transformer unit. The method of claim 1, The feedback signal generator, A sensing resistor connected between the primary coil and the switching unit to convert the primary AC current into a feedback AC voltage; And And a rectifier for rectifying the feedback AC voltage to generate a feedback DC voltage. The method of claim 2, And the rectifier includes at least one diode connected between one side of the sensing resistor and the controller. The method of claim 1, The feedback signal generator, A current sensing transformer connected between the primary coil and the switching unit to convert the primary AC current into a predetermined ratio; A rectifier for rectifying the primary AC current converted at the predetermined ratio to generate a DC current; And And a sensing resistor for converting the DC current into a feedback DC voltage. The method of claim 4, wherein And the rectifier includes a diode connected between one end of the secondary coil of the current sensing transformer and the controller. The method of claim 5, wherein And the sensing resistor is connected between the other end of the secondary coil of the current sensing transformer and the cathode electrode of the diode. The method according to claim 2 or 4, And the feedback signal generator further includes at least one input resistor connected between an output terminal of the rectifier and the controller to stabilize the feedback DC voltage. The method of claim 1, The transformer unit, Having a plurality of transformers electrically isolated to drive different lamps; Two or more lamps are connected to the secondary coil of each transformer. The method of claim 8, And the lamps connected adjacent to the secondary coil are supplied with tube currents of opposite phases to each other. The method of claim 1, And the switching control signal is generated in a pulse width modulation scheme and its duty ratio is varied by the feedback signal. The method of claim 1, And the switching unit includes a plurality of field effect transistors switched by the switching control signal. The method of claim 1, And an overvoltage detector configured to detect an AC voltage supplied from the secondary coil of the transformer to the lamp and feed it back to the controller.

Images