KR20100114609A - Lamp driving circuit for a liquid crystal display and driving method thereof - Google Patents

Abstract

PURPOSE: A lamp driving circuit of a liquid crystal display device and a driving method thereof are provided to prevent the deterioration of image quality by removing the afterimage of a previous picture after uniformly delaying the lighting of a lamp from the generation time point of a vertical synchronization signal. CONSTITUTION: A liquid crystal panel(110) includes a pixel pattern which is arranged in a matrix form. A gate driving part(120) sequentially applies a gate voltage to a plurality of gate lines. A data driving part(130) applies a data voltage for the display of an image to a plurality of data lines. A lamp(140) can be used as the light source of a liquid crystal display device. An inverter device(150) generates a driving signal for a lamp.

Description

Lamp driving circuit and driving method of liquid crystal display device {LAMP DRIVING CIRCUIT FOR A LIQUID CRYSTAL DISPLAY AND DRIVING METHOD THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lamp driving circuit and a driving method of a liquid crystal display device, and more particularly, to a lamp driving circuit and a driving method of a liquid crystal display device for controlling the brightness of a lamp in accordance with a PWM method based on a sawtooth oscillation signal.

With the development of information technology, displays are increasing in importance as an information transmission medium. In the field of display, the demand for large screen, light weight, thin, and high quality is increasing to meet the technological development. To meet this demand, the liquid crystal display (LCD) is widely used to replace the conventional cathode ray tube (CRT). It is used.

A liquid crystal display device is typically made of a substrate in which pixels are formed in a matrix form and a substrate opposite thereto, and a liquid crystal material having an anisotropic dielectric constant injected between the two substrates, and applying and applying an electric field between the two substrates. By controlling the intensity of the electric field, the amount of light passing through the liquid crystal material is controlled to display a desired image. When voltage is applied to the liquid crystal through the pixel electrodes provided for each pixel of the liquid crystal display device, the arrangement of the liquid crystals is changed accordingly, and light is passed through the liquid crystal in such a state, thereby obtaining a desired image. Since such a liquid crystal display device is not a self-luminous display device, the lamp provided on the back side is configured to operate as a light source.

The liquid crystal display device is also required to have a dimming function that can adjust the brightness of the lamp in order to increase the quality of the moving image display or to reduce the power consumption. As a method for controlling the brightness of the lamp, an analog method of changing the intensity of the current flowing through the lamp and a change in the on / off duty ratio of the current flowing through the lamp while maintaining a constant magnitude of the lamp current. There is a PWM method. According to the analog system, when the luminance required for the lamp is low, the magnitude of the current supplied to the lamp is too small, and thus the lighting of the lamp may become unstable, thereby causing the lamp to turn off easily. On the contrary, the PWM method has an advantage of easily controlling the amount of light, that is, luminance of the lamp by adjusting the duty ratio of the on / off period without such a problem.

On the other hand, in the liquid crystal display device, in order to change an image signal input thereto and change the image displayed on the screen, the liquid crystal array needs to change from one state to another state. There is a need for adequate response time that can be rearranged. However, if the human eye continues to recognize the liquid crystal, an afterimage of the previous screen may remain on the newly displayed screen while the liquid crystal rearrangement is performed according to the change of the input image signal. This may cause deterioration of image quality, and may be a serious problem, especially when displaying a video. Therefore, when a new image is to be displayed on the screen, it is necessary to prevent the screen being changed for an appropriately determined time in consideration of the characteristics of the liquid crystal material, that is, the response time for rearranging the liquid crystal. In addition, a method of delaying the lighting of the lamp by the response time may be considered as one method for preventing the screen being changed from being recognized by the human eye during the response time required for the liquid crystal rearrangement.

However, when adjusting the brightness of the lamp by the conventional PWM method, there is a problem that it is difficult to delay the lighting of the lamp by a predetermined response time required for the liquid crystal rearrangement. According to the conventional PWM method, the triangular wave oscillation signal is compared with the dimming signal and a PWM signal for driving the lamp is generated according to the comparison result. Both the start and end times of are changed. Therefore, according to the conventional method of generating the PWM signal by using the triangular wave oscillation signal, it is difficult to constantly secure the appropriate liquid crystal rearrangement time in consideration of the liquid crystal characteristics of the liquid crystal display device before the lamp is turned on. do.

Therefore, regardless of the change in the dimming signal value, the lamp driving method and apparatus for allowing the lamp lighting to be constantly delayed by a fixed liquid crystal rearrangement time appropriately determined in consideration of the characteristics of the liquid crystal from the time when the vertical synchronization signal occurs It is necessary.

According to the present invention, regardless of the change in the dimming signal value, the lamp driving of the liquid crystal display device which can uniformly delay the lighting of the lamp by a fixed liquid crystal rearrangement time which is appropriately determined in consideration of the response characteristics of the liquid crystal upon screen change. A method and a driving circuit are provided.

According to one aspect of the present invention, a lamp driving circuit in a liquid crystal display device is provided. The lamp driving circuit according to the present invention may include a PWM signal generator for generating a first PWM signal based on a series of vertical synchronization signals and a dimming signal, a switching unit, and a boosting unit. The switching unit may be operated to supply or cut off power to the boosting unit according to the first PWM signal, and the boosting unit may be operated to boost the supplied power to a level suitable for driving the lamp. The PWM signal generator is operated to generate the first sawtooth oscillation signal based on the series of vertical synchronizing signals, and the first sawtooth oscillation signal can be reset every time a predetermined delay time elapses from the time of occurrence of each vertical synchronizing signal. have. The PWM signal generator may be further operable to generate the first PWM signal based on the first sawtooth oscillation signal and the dimming signal.

According to an embodiment of the present invention, the first sawtooth oscillation signal may rise between two adjacent time points among the time points at which the first sawtooth oscillation signal is reset.

According to an embodiment of the present invention, the first sawtooth wave oscillation signal may have a waveform of a substantially right triangle shape.

According to an embodiment of the present invention, the PWM signal generation unit may further include a first capacitor, and the charging voltage of the first capacitor may be used to determine when a predetermined delay time elapses.

According to an embodiment of the present invention, the first capacitor may be instantaneously discharged when the charging is started and the predetermined voltage is reached in synchronization with the timing of generating the vertical synchronization signal.

According to an embodiment of the present invention, the charging voltage of the first capacitor may reach a predetermined voltage when a predetermined delay time elapses from the time of generating the vertical synchronization signal.

According to an embodiment of the present invention, the liquid crystal display may include first and second lamp groups including one or more lamps. In this case, the first PWM signal may be used to control the lighting on / off of lamps belonging to the first lamp group, and the PWM signal generator may shift the phase of the first sawtooth oscillation signal by a predetermined time so that the second sawtooth oscillation signal It can be operated to generate. Here, the second sawtooth oscillation signal is a signal having the same waveform as the first sawtooth oscillation signal and shifted in phase by a predetermined time. The PWM signal generator may be operable to generate a second PWM signal based on the second sawtooth wave oscillation signal and the dimming signal, the second PWM signal being used to control the lighting on / off of lamps belonging to the second lamp group. Can be.

According to still another feature of the present invention, a lamp driving method in a liquid crystal display device is provided. According to the ramp driving method according to the present invention, a series of vertical synchronization signals and dimming signals are received, and a sawtooth oscillation signal that is reset every time a predetermined delay time elapses from the time of generation of each vertical synchronization signal can be generated. . Then, the sawtooth oscillation signal and the dimming signal are compared, and a PWM signal can be generated based on the comparison result. Then, the lighting of the lamp can be controlled based on the PWM signal,

According to an embodiment of the present invention, the generating of the PWM signal based on the comparison result may include turning on the PWM signal in the level where the dimming signal is higher than the sawtooth oscillation signal.

According to an embodiment of the present disclosure, generating the sawtooth wave oscillation signal may include identifying a time point when a predetermined delay time elapses by using voltage charging and discharging of a capacitor.

According to the present invention, when changing the screen display of the liquid crystal display, regardless of the change in the dimming signal value, the ramp from the time of the generation of the vertical synchronization signal for a fixed time required for the liquid crystal rearrangement according to the response characteristics of the liquid crystal It is possible to steadily delay the lighting, so that the afterimage of the previous screen is shown on the newly displayed screen, thereby preventing the problem of deterioration in image quality. The present invention can also achieve more precise time control than controlling the time itself by using the capacitor charging voltage to delay the lighting of the lamp by a fixed time from the time of generating the vertical synchronization signal when changing the screen.

Embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following, when it is determined that there is a risk of unnecessarily obscuring the gist of the present invention, a detailed description of already known functions and configurations will be omitted. In addition, it should be understood that the following description only relates to one embodiment of the present invention, but the present invention is not limited thereto.

1 is a diagram schematically illustrating a configuration of a liquid crystal display device 100 to which the present invention may be applied. As illustrated, the liquid crystal display 100 may include a liquid crystal panel 110, a gate driver 120, a data driver 130, a lamp 140, and an inverter device 150.

The liquid crystal panel 110 includes a pixel substrate having pixel patterns arranged in a matrix form. A plurality of gate lines and a plurality of data lines perpendicular to each gate line are formed in the pixel substrate, and each pixel is formed at an intersection point of each gate line and each data line. Each pixel includes a thin film transistor having a gate electrode and a source electrode connected to one gate line and one data line, respectively, and a pixel electrode is connected to a drain electrode of the thin film transistor. When an electrical signal is applied to the gate electrode of the thin film transistor through the gate line and an electrical signal is applied to the source electrode of the thin film transistor through the data line, the thin film transistor is turned on in response to the input of the electrical signal, and the drain electrode and the pixel connected thereto. An electrical signal for displaying an image is output to the electrode.

The gate driver 120 is a circuit that sequentially applies gate voltages to each of the plurality of gate lines disposed in the liquid crystal panel 110 so that the gate lines can be sequentially selected. The gate driver 120 sequentially scans each gate line in units of one horizontal scanning period based on the horizontal synchronization signal Hsync. That is, the gate driver 120 applies a gate-on voltage to one gate line selected from the plurality of gate lines while applying a gate-off voltage to the remaining gate lines during one horizontal scanning period, and applies the scan process to all the gate lines. Are performed sequentially. When a voltage is applied to the gate line, the thin film transistors of the pixels connected to the gate line are turned on.

The data driver 130 is a circuit for applying a data voltage for displaying an image to each of the plurality of data lines arranged in the liquid crystal panel 110. The data driver 130 sequentially latches image data input from the outside in pixel units and converts the image data into scan line unit data, and then generates a gray voltage signal according to the image data of the corresponding scan line unit to generate one horizontal scanning period. To the data lines on the liquid crystal panel 110. The gray voltage signal supplied to each data line from the data driver 130 is applied to the thin film transistor source electrodes of pixels that are turned on by receiving the gate voltage applied from the gate driver 120 to the pixel electrodes. And a predetermined video display operation is performed accordingly. As such, the data driver 130 applies a gray voltage signal for displaying an image to each data line in units of one horizontal scanning period, and this operation is repeatedly performed for one frame based on one vertical synchronization signal.

The lamp 140 may be disposed under the pixel substrate of the liquid crystal panel 110 to operate as a light source of the liquid crystal display device 100. The lamp 140 may be one of various types of lamps, such as a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), a light emitting diode (LED), and a flat fluorescent lamp (FFL). The lamp 140 may be one lamp group composed of a plurality of lamps.

The inverter device 150 receives a vertical synchronizing signal STV and a dimming signal Vdim indicating the start of one frame from the outside and generates a driving signal for the lamp 140 by using them. According to an embodiment of the present invention, the ramp drive signal is a pulse width modulated signal PWM obtained by comparing the sawtooth oscillation signal oscillated in synchronization with the generation of the vertical synchronization signal STV and the received dimming signal Vdim. Can be determined based on this. The brightness of the lamp 140 may be controlled by adjusting the on / off duty ratio of the lamp driving signal, and the on / off duty ratio of the lamp driving signal may be determined by the on / off duty ratio of the above-described PWM signal. The sawtooth signal according to the present disclosure is a signal having a waveform having a substantially right triangle shape, and may have a waveform having a shape in which the falling edge is substantially vertical on the time axis. According to an embodiment of the present invention, the sawtooth signal may be a waveform signal in which the rise of the waveform is gentle with time while the drop of the waveform is instantaneously sharp. The sawtooth oscillation signal may be reset by the vertical falling edge whenever a predetermined delay time elapses from the time of generation of the vertical synchronization signal STV, and the predetermined delay time is predetermined from the time of generation of the vertical synchronization signal STV. It may have a rising edge that rises gently between the vertical falling edge of the elapsed time point and the new vertical falling edge which occurs after a predetermined predetermined delay time elapses from the new vertical synchronizing signal STV.

FIG. 2 is a diagram showing the configuration of the inverter device 150 shown in FIG. 1 in more detail. As shown in FIG. 2, the inverter device 150 includes a PWM signal generator 210, a switch 220, a DC power supply 230, and a booster 240.

The PWM signal generator 210 may receive a vertical synchronization signal STV and a dimming signal Vdim from the outside. The PWM signal generator 210 may include a circuit for generating a sawtooth wave oscillation signal having a period equal to a period of the vertical synchronization signal STV. The sawtooth oscillation signal generated by the PWM signal generator 210 may be a signal that is reset when a predetermined time, i.e., a predetermined delay time, elapses from every occurrence of the vertical synchronization signal STV. According to an embodiment of the present invention, the PWM signal generating unit 210 also has a predetermined time delay elapsed from the timing of generating the vertical synchronization signal STV, that is, a delay time for accurately obtaining the reset timing of the sawtooth oscillation signal. A confirmation capacitor can be provided. In such a case, the PWM signal generator 210 charges the delay time checking capacitor at a constant rate from the time when the vertical synchronization signal STV is generated, and checks the delay time when the charging voltage becomes a predetermined voltage. The capacitor can be instantaneously discharged and the sawtooth oscillation signal can be reset.

The PWM signal generator 210 may also compare the generated sawtooth oscillation signal with the dimming signal Vdim, and generate and output a PWM signal based on the comparison result. According to an embodiment of the present invention, the PWM signal is turned on at a level where the sawtooth oscillation signal is greater than the dimming signal Vdim and is turned off at a predetermined level when the sawtooth oscillation signal is less than the dimming signal Vdim. May have an off duty ratio.

The switching unit 220 receives the PWM signal generated by the PWM signal generator 210 and transfers the DC power supply 230 to the booster 240 based on the received PWM signal. That is, the switching unit 220 connects the DC power supply to the booster 240 during the turn-on period of the received PWM signal, and cuts off the connection between the DC power supply and the booster 240 during the turn-off period of the received PWM signal. do.

The booster 240 may receive the on / off level DC power supplied through the switching unit 220 and generate a high voltage sine wave signal using a transformer provided therein. Although not specifically illustrated, the high voltage sine wave signal generated by the booster 240 may be applied to the lamp through the connector and used as the lamp driving signal.

3 is a timing diagram showing a phase change of signals used in an inverter device when according to an embodiment of the present invention. As shown in FIG. 3, the relationship between the generation of the vertical synchronization signal STV, the phase change of the sawtooth oscillation signal, and the lighting of the lamp according to the time axis is well illustrated.

Specifically, FIG. 3A illustrates a vertical synchronization signal STV. The vertical synchronizing signal STV is a synchronizing signal for starting input of a new image signal on a screen of the liquid crystal display, and is repeatedly generated every frame period.

FIG. 3B shows a signal representing the charging voltage of the capacitor for the delay time used to obtain the preset delay time. The delay capacitor starts charging in synchronism with the generation of the vertical synchronizing signal STV, and immediately discharges when the charging voltage reaches a predetermined value Vdelay. Thus, the voltage signal waveform of the capacitor for delay time has a sawtooth wave shape as shown.

3C illustrates a sawtooth oscillation signal Vsaw for generating a PWM signal. The sawtooth oscillation signal Vsaw is instantaneously reset at the point when the delay capacitor shown in (b) is discharged, that is, when the charge voltage waveform of the delay capacitor is at the falling edge, and thereafter, the next reset point. Gradually rises. Therefore, the sawtooth oscillation signal having the sawtooth shape repeats the rising and falling with the period of the same magnitude as the vertical synchronizing signal (STV). It should be noted here that the reset of the sawtooth oscillating signal Vsaw may be instantaneous on the time axis, so that the waveform of the sawtooth oscillating signal Vsaw may have a substantially right triangle shape with a vertical falling edge. .

In FIG. 3C, two dimming signals Vdim1 and Vdim2 having different values are also shown. The dimming signal Vdim1 and the dimming signal Vdim2 having a higher value may be maintained at a constant value, respectively. The dimming signal used in the inverter device may vary according to the luminance setting of the liquid crystal display. In FIG. 3C, the dimming signals Vdim1 and Vdim2 having two different values are shown together for comparison. It is.

FIG. 3D illustrates waveforms of the PWM signal PWM1 for lamp lighting control generated based on the sawtooth oscillation signal Vsaw and the dimming signal Vdim1 shown in (c). According to the exemplary embodiment of the present invention, the PWM signal PWM1 is turned on in a section in which the dimming signal Vdim1 is higher than the sawtooth oscillation signal Vsaw according to the comparison of the sawtooth oscillation signal Vsaw and the dimming signal Vdim1. It may have an off level in the interval that does not have. Therefore, according to an embodiment of the present invention, the PWM signal PWM1 is turned on at the time when the sawtooth oscillation signal Vsaw is reset. In addition, in one embodiment of the present invention, when the PWM signal PWM1 is on level, the lamp of the liquid crystal display is turned on, and when the off level is turned off, the lamp of the liquid crystal display may be turned off. Accordingly, the lighting duty ratio of the lamp is determined according to the on / off duty ratio determined by the off timing of the PWM signal PWM1, and thus the brightness of the lamp can be controlled.

FIG. 3E illustrates waveforms of the PWM signal PWM2 for lamp lighting control generated based on the sawtooth oscillation signal Vsaw and the dimming signal Vdim2 shown in (c). Also in the case of the PWM signal PWM2 shown in (e), the dimming signal Vdim2 may have an on level in a section higher than the sawtooth oscillation signal Vsaw and an off level in a section other than the sawtooth oscillation signal Vsaw. As in the case of (d), is turned on when the sawtooth oscillation signal Vsaw is reset. However, since the dimming signal Vdim2 is larger than the dimming signal Vdim1, the time point at which the PWM signal PWM2 is turned off becomes later than that of the PWM signal PWMM, and thus the PWM signal PWM2 is It may have a longer on period than the PWM signal PWM1. This means that the lighting time of the lamp is longer and the luminance of the liquid crystal display becomes brighter by the PWM signal PWM2.

Comparing the PWM signals PWM1 and PWM2 shown in FIGS. 3D and 3E, respectively, when the values of the dimming signals Vdim1 and Vdim2 are changed, that is, when the PWM signals PWM1 and PWM2 are turned on, that is, It can be seen that there is no change when the lamp is turned on. Therefore, the time point at which the PWM signals PWM1 and PWM2 are turned on is fixed to the time when the preset delay time Tdelay has elapsed after the time point of the vertical synchronization signal STV generation, and the PWM signals PWM1 and PWM2 for controlling the luminance of the lamp are fixed. The on / off interval duty ratio of may be determined by a difference in off time points of the PWM signals PWM1 and PWM2. Therefore, according to the exemplary embodiment of the present invention, the lamp lighting of the liquid crystal display is always started with a constant delay from the generation of the vertical synchronization signal STV by a constant delay time regardless of the variation of the set dimming signal value. It can be seen that.

In addition, according to the present embodiment, the time from the time when the vertical synchronization signal STV is generated to the time when discharge of the capacitor for delay time occurs is the delay time Tdealy described above. That is, it may be possible to control the exact time by controlling the charging voltage of the capacitor. In the present specification, a method of using the charging voltage of the capacitor is mainly described for accurate time control, but those skilled in the art will recognize that another method for accurate time control may also be used.

FIG. 4 is a diagram illustrating a phase change of signals when an inverter device uses a conventional triangular wave oscillation signal, unlike an inverter device using a sawtooth wave oscillation signal to generate a PWM signal according to an embodiment of the present invention shown in FIG. 3. . Comparing the waveform of each signal shown in FIG. 4 with the case of FIG. 3, when the PWM signal is generated using the triangular wave oscillation signal as in the prior art, all of the on / off start points of the PWM signal are changed according to the change in the dimming signal value. It can be seen that it is not possible to delay the lighting of the lamp by a certain delay time (Tdealy) for the liquid crystal rearrangement from the time when the vertical synchronization signal STV is generated.

FIG. 4A illustrates a vertical synchronization signal STV. As described above, the vertical synchronizing signal STV is a synchronizing signal for starting input of a new video signal on the screen and is repeatedly generated every frame period. (b) shows a triangular wave oscillation signal and a dimming signal Vdima. The generation of the triangular wave oscillation signal may be performed in conjunction with the generation of the vertical synchronization signal STV of (a). (c) shows the PWM signal PWMa derived from the triangular wave oscillation signal and the dimming signal Vdima shown in (b). As shown in the figure, the PWM signal PWMa has an on level in a period in which the dimming signal Vdima is larger than the triangular wave oscillation signal, and on the contrary, in a section in which the dimming signal Vdima becomes a smaller value than the triangular wave oscillation signal. PWM signal PWMa has an off level. The lamp of the liquid crystal display is turned on during the on period of the PWM signal PWM. (d) shows a triangular wave oscillation signal and a dimming signal Vdimb as shown in (b). The dimming signal Vdimb is a higher voltage signal than the dimming signal Vdima and is an input signal given by a brighter lamp brightness request. (e) shows the PWM signal PWM deriving from the triangular wave oscillation signal and dimming signal Vdimb shown in (d). Comparing the PWM signals (PWMa, PWMb) of (c) and (e) shown in FIG. 4 shows that in a liquid crystal display that generates a triangular wave oscillation signal having a constant waveform and phase, when the value of the dimming signal fluctuates. It can be seen that each of the start time point and the end time point of the lighting changes.

Comparing the waveforms of the PWM signals PWM1 and PWM2 shown in FIGS. 3D and 3E with the PWM signal waveforms shown in FIGS. 4C and 4E, the dimming signal Vdim1 in FIG. 3 is compared. , Even when the value of Vdim2) is changed, there is no change at the time when the PWM signals PWM1 and PWM2 are turned on, that is, when the lamp is turned on. In FIG. 4, when the value of the dimming signals Vdima and Vdimb is changed, the PWM signal is changed. It can be seen that (PWMa, PWMb) both on and off times change. Thus, when the inverter device generates the PWM signal using the triangular wave oscillation signal, as shown in FIG. 4, a delay time (Tdealy) of lamp lighting for liquid crystal rearrangement from the time of generating the vertical synchronization signal (STV) can be ensured constantly. In contrast, when the PWM signal is generated using the sawtooth oscillation signal according to the exemplary embodiment of the present invention, a delay time (Tdealy) of lamp lighting for the liquid crystal rearrangement from the vertical sync signal (STV) generation point may be constantly maintained. It can be clearly seen that.

FIG. 5 is a timing diagram illustrating a phase change of signals used in an inverter device and a change in lighting of a lamp according to another embodiment of the present invention. 5 is based on a so-called scanning driving method in which a plurality of lamps included in the liquid crystal display are divided into three lamp groups and each lamp group is sequentially driven. In the present exemplary embodiment, a case in which a plurality of lamps are sequentially driven by dividing into three lamp groups is described. However, the present invention may be applied to a case in which a plurality of lamps are driven in a larger or smaller number of lamp groups. You should know

5A illustrates a vertical synchronizing signal STV input to the inverter device from the outside. As described above, the vertical synchronizing signal STV is a synchronizing signal for starting input of a new image signal on the screen of the liquid crystal display, that is, a signal indicating the start of a frame, and is repeatedly generated every frame period.

In FIG. 5B, the sawtooth wave oscillation signal Vsaw1 for driving the first lamp group is shown by a solid line. In FIG. 5B, the sawtooth oscillation signal Vsaw2 for driving the second lamp group is also shown by a dashed-dotted line. The sawtooth oscillation signal Vsaw2 is delayed by a predetermined x value than the sawtooth oscillation signal Vsaw1. Has In FIG. 5B, the sawtooth oscillation signal Vsaw3 for driving the third lamp group is also shown by the dashed-dotted line. The sawtooth oscillation signal Vsaw3 is delayed by a predetermined x value than the sawtooth oscillation signal Vsaw2. Has Specific methods and circuits for obtaining the sawtooth oscillation signal Vsaw2 and the sawtooth oscillation signal Vsaw3 through the phase shift from the sawtooth oscillation signal Vsaw1 are described in detail in another patent application specification held by the present applicant. Detailed description will be omitted in the specification.

The sawtooth oscillation signal Vsaw1 shown in FIG. 5B is periodically reset every time a predetermined delay time (Tdealy) has elapsed from the time of generating the vertical synchronization signal SVT, and the next reset time point from the reset time point. Gradually rises. That is, the sawtooth oscillation signal Vsaw1 may basically have the same waveform as the sawtooth oscillation signal Vsaw shown in FIG. 3C, and a detailed description thereof will be omitted. The sawtooth oscillation signal Vsaw2 is a signal obtained by delaying the phase of the sawtooth oscillation signal Vsaw1 by a predetermined x value, and the sawtooth oscillation signal Vsaw3 delays the phase of the sawtooth oscillation signal Vsaw2 by a predetermined x value. Is the signal obtained. Therefore, the sawtooth oscillation signals Vsaw2 and Vsaw3 all have the same waveform as the sawtooth oscillation signal Vsaw1, but have a phase difference of the x and 2x values with the sawtooth oscillation signal Vsaw1, respectively. That is, the sawtooth oscillation signal Vsaw2 is periodically reset from the time when the vertical synchronizing signal STV is generated by a time elapsed by the delay time (Tdealy) plus the x value, and the sawtooth oscillation signal Vsaw3 is the vertical synchronizing signal. It is periodically reset every time that the delay time (Tdealy) is added by 2 times from the time of occurrence of (STV).

5B also shows a dimming signal Vdim having a constant value on the time axis. The dimming signal Vdim may be used to determine the on / off timing of the PWM signal for the lamp group lighting control together with the sawtooth oscillation signals Vsaw1, Vsaw2, and Vsaw3.

In FIG. 5C, the on / off section of the first lamp group is illustrated. The rectangular part shown in (c) of FIG. 5 represents a section in which the first lamp group is lit. In a section in which the dimming signal Vdim is higher than the sawtooth oscillation signal Vsaw1, the first lamp group remains on and in the section in which the dimming signal Vdim is lower than the sawtooth oscillation signal Vsaw1. As shown, the first lamp group is turned on every time the delay time Tdelay has elapsed from the time of generation of the vertical synchronization signal STV.

In FIG. 5D, the on / off section of the second lamp group is illustrated. The rectangular part shown in (d) of FIG. 5 represents a section in which the second lamp group is lit. The second lamp group remains on in the period when the dimming signal Vdim is higher than the sawtooth oscillation signal Vsaw2 and is turned off in the period when the dimming signal Vdim is lower than the sawtooth oscillation signal Vsaw2. As shown, the second lamp group is turned on every time the delay time Tdelay and the x value elapse from the time of generating the vertical synchronization signal STV.

In FIG. 5E, the on / off section of the third lamp group is illustrated. The rectangular portion illustrated in FIG. 5E represents a section in which the third lamp group is lit. The third lamp group remains on in the section in which the dimming signal Vdim is higher than the sawtooth oscillation signal Vsaw3, and is turned off in the section in which the dimming signal Vdim is lower than the sawtooth oscillation signal Vsaw3. As shown, the third lamp group is turned on every time the delay time Tdelay and the 2x value have elapsed from the time of generating the vertical synchronization signal STV. As shown in FIG. 5, even when a plurality of lamps included in the liquid crystal display are divided into a plurality of lamp groups and a scanning driving method for sequentially driving each lamp group is performed, a sawtooth oscillation signal is used to determine each lamp group. By generating a PWM signal for lighting, it can be seen that the lighting can be started after a predetermined time is constantly delayed from the time of generating the vertical sync signal STV for each lamp group.

As will be appreciated by those skilled in the art, the present invention is not limited to the examples described herein but may be variously modified, reconfigured and replaced without departing from the scope of the present invention. Accordingly, all modifications and changes that fall within the true spirit and scope of the present invention are intended to be covered by the following claims.

1 is a view schematically showing a configuration of a liquid crystal display device to which the present invention can be applied;

FIG. 2 is a view showing in more detail the configuration of the inverter device shown in FIG. 1; FIG.

3 is a timing diagram showing a phase change of signals used in an inverter device when according to an embodiment of the present invention;

4 is a diagram illustrating a phase change of signals in a conventional case using a triangular wave oscillation signal in an inverter device unlike in the case of an embodiment of the present invention shown in FIG.

5 is a timing diagram showing a phase change of signals used in an inverter device and a lighting change of a lamp accordingly according to another embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

110: liquid crystal panel 120: gate driver

130: data driver 140: lamp

150: inverter device 210: PWM signal generator

220: switching unit 230: DC power

240: booster

Claims (10)

As a lamp driving circuit in a liquid crystal display device, A PWM signal generator configured to generate a first PWM signal based on the series of vertical synchronization signals and the dimming signal; Switching unit; And Including a booster, The switching unit is operated to supply or cut off power to the boosting unit according to the first PWM signal, and the boosting unit is operated to boost the supplied power to a level suitable for driving a lamp, The PWM signal generator is operated to generate a first sawtooth oscillation signal based on the series of vertical synchronizing signals, wherein the first sawtooth oscillation signal is a time point at which a predetermined delay time elapses from the occurrence of the respective vertical synchronizing signals. Every time, And the PWM signal generator is further operable to generate the first PWM signal based on the first sawtooth oscillation signal and the dimming signal. The method of claim 1, And the first sawtooth oscillation signal rises between two adjacent time points of the time points at which the first sawtooth oscillation signal is reset. The method of claim 2, And the first sawtooth wave oscillation signal has a waveform of substantially right triangle shape. The method of claim 1, The PWM signal generator further includes a first capacitor, the lamp driving circuit is used to determine the time when the charging voltage of the first capacitor elapses the predetermined delay time. The method of claim 4, wherein And the first capacitor discharges instantaneously when charging starts and reaches a predetermined voltage in synchronism with the time when the vertical synchronizing signal is generated. The method of claim 5, And a charging voltage of the first capacitor reaches the predetermined voltage when the predetermined delay time elapses from the time of generating the vertical synchronization signal. The method of claim 1, The liquid crystal display includes a first and a second lamp group consisting of one or more lamps, The first PWM signal is used to control the lighting on / off of the lamp belonging to the first lamp group, The PWM signal generator is further operated to generate a second sawtooth oscillation signal by shifting the phase of the first sawtooth oscillation signal by a predetermined time, The second sawtooth oscillation signal is a signal having the same waveform as the first sawtooth oscillation signal and shifted in phase by the predetermined time, The PWM signal generator is operable to generate a second PWM signal based on the second sawtooth wave oscillation signal and the dimming signal, and the second PWM signal controls to turn on / off a lamp belonging to the second lamp group. Lamp driving circuit used to. As a lamp driving method in a liquid crystal display device, Receiving a series of vertical synchronization signals and a dimming signal; Generating a sawtooth oscillation signal which is reset every time a predetermined delay time elapses from the time of generation of each vertical synchronization signal; Comparing the sawtooth oscillation signal with the dimming signal; Generating a PWM signal based on the comparison result; And Controlling lighting of the lamp based on the PWM signal Lamp driving method comprising a. The method of claim 8, The generating of the PWM signal based on the comparison result may include turning the PWM signal on at a level in which the dimming signal is higher than the sawtooth oscillation signal. The method of claim 8, The generating of the sawtooth wave oscillating signal may include identifying a time point at which the predetermined delay time elapses using voltage charging and discharging of a capacitor.

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