KR100838415B1 - Flat Backlight Driving Circuit of Liquid Crystal Display Device - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mercury-free surface light source driving circuit used in a backlight for a liquid crystal display device. The surface light source driving circuit of a liquid crystal display device newly designed to improve power consumption, light efficiency, and lower cost through energy recovery circuit technology. It is about. According to an aspect of the present invention, there is provided a surface light source driving circuit including: a coupled inductor having a secondary inductor coupled to both terminals of the surface light source and supplying a driving voltage to the surface light source; A source capacitor connected between one end of the primary inductor of the coupled inductor and a ground and storing a predetermined voltage; A first capacitor connected between the other end of the primary inductor of the coupled inductor and a voltage source, and charged or discharged at a predetermined voltage; A first diode having a cathode electrode connected to the voltage source and an anode electrode connected to the other end of the primary side inductor of the coupled inductor; A first switch connected between the voltage source and the other end of the primary inductor of the coupled inductor to perform an on / off switching operation; A second capacitor connected between the other end of the primary inductor of the coupled inductor and a ground, and configured to charge or discharge a predetermined voltage; A second diode having a cathode electrode connected to the other end of the primary inductor of the coupled inductor and an anode electrode connected to the ground; And a second switch connected between the other end of the primary inductor of the coupled inductor and ground to perform an on / off switching operation.

Description

Flat Backlight Driving Circuit of Liquid Crystal Display Device

1 is a block diagram illustrating a surface light source driving circuit of a liquid crystal display according to a first exemplary embodiment of the present invention.

2 is a timing diagram illustrating an operation of a surface light source driving circuit of a liquid crystal display according to a first exemplary embodiment of the present invention.

3 is a block diagram illustrating a surface light source driving circuit of a liquid crystal display according to a second exemplary embodiment of the present invention.

4 is a timing diagram illustrating an operation of a surface light source driving circuit of a liquid crystal display according to a second exemplary embodiment of the present invention.

5 is a configuration diagram illustrating a surface light source driving circuit of a liquid crystal display according to a third exemplary embodiment of the present invention.

6 is a timing diagram illustrating an operation of a surface light source driving circuit of a liquid crystal display according to a third exemplary embodiment of the present invention.

7 is a configuration diagram illustrating a surface light source driving circuit of a liquid crystal display according to a fourth exemplary embodiment of the present invention.

8 is a timing diagram illustrating an operation of a surface light source driving circuit of a liquid crystal display according to a fourth exemplary embodiment of the present invention.

9 is a configuration diagram illustrating a surface light source driving circuit of the liquid crystal display according to the fifth exemplary embodiment of the present invention.

10 is a timing diagram illustrating an operation of a surface light source driving circuit of a liquid crystal display according to a fifth exemplary embodiment of the present invention.

11 is a configuration diagram illustrating a surface light source driving circuit of the liquid crystal display according to the sixth exemplary embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface light source driving circuit of a liquid crystal display, and more particularly, to a surface light source driving circuit of a new liquid crystal display designed to improve power consumption, light efficiency, and lower cost through energy recovery circuit technology. will be.

Future research challenges in the display market include the development of low-cost technologies, high-efficiency technologies for reducing power consumption, fast response speed, and low heat noise. Low cost and high efficiency can be achieved to some extent by the development of a new light source driving circuit of the liquid crystal display device.

In the future, it is necessary to study environmental regulations that are essential for the realization of light sources, and in particular, it is necessary to exclude mercury. Accordingly, new research on various driving methods including the existing mercury method is underway at home and abroad.

Currently available methods use xenon gas instead of mercury, which results in significantly higher drive voltages. In consideration of this point, domestic and overseas lamp makers for liquid crystal display backlight units (LCD BLU) have made various efforts to develop driving circuits.

Cold Cathode Fluorescent Lamp (CCFL), which is used as the back light unit (BLU) light source of the existing LCD screen, is a diffuser plate for utilizing the environmental pollution and ray light source by using mercury as surface light source. (Diffusion layer) has the disadvantage of reducing energy efficiency. On the other hand, in the case of a flat panel type surface light source, mercury is not used, so that it is possible to prepare for the upcoming environmental regulations, and also by reducing the manufacturing cost by not requiring a diffusion plate.

For this purpose, a circuit for driving a surface light source is required, and an energy recovery circuit is essential to increase power conversion efficiency.

Recently, mercury-free flat panel light sources (brand name PLANON) have been introduced in Germany. This product does not need a diffusion plate because the light source is in the form of a flat plate, and because it does not use mercury, it is attracting attention as the next generation LCD BLU when considering the upcoming environmental regulations.

However, in the case of the mercury-type flat surface light source product developed in Germany, the light efficiency is only 271m / W because the driving technology is still in the development stage, and it has not been experimentally verified in large area driving. In this regard, there is no domestic research. Therefore, there is an urgent need to develop a high efficiency driving circuit for such a surface light source.

An object of the present invention is to provide a surface light source driving circuit of an improved mercury-free liquid crystal display device which improves power consumption and light efficiency, which is a problem of the conventional driving method.

It is also an object of the present invention to provide a surface light source driving circuit of a liquid crystal display device capable of driving a large area display of 30 inches or more in the future by realizing high efficiency and low cost of the device through energy recovery circuit technology.

In accordance with one aspect of the present invention, there is provided a surface light source driving circuit of a liquid crystal display device including: a coupled inductor having a secondary inductor coupled to both terminals of the surface light source and supplying a driving voltage to the surface light source; A source capacitor connected between one end of the primary inductor of the coupled inductor and a ground and storing a predetermined voltage; A first capacitor connected between the other end of the primary inductor of the coupled inductor and a voltage source, and charged or discharged at a predetermined voltage; A first diode having a cathode electrode connected to the voltage source and an anode electrode connected to the other end of the primary side inductor of the coupled inductor; A first switch connected between the voltage source and the other end of the primary inductor of the coupled inductor to perform an on / off switching operation; A second capacitor connected between the other end of the primary inductor of the coupled inductor and a ground, and configured to charge or discharge a predetermined voltage; A second diode having a cathode electrode connected to the other end of the primary inductor of the coupled inductor and an anode electrode connected to the ground; And a second switch connected between the other end of the primary inductor of the coupled inductor and ground to perform an on / off switching operation.

The object may also include a first coupled inductor having a secondary side inductor coupled to a positive terminal of the surface light source and supplying a positive driving voltage to the surface light source; A first source capacitor connected between one end of a primary side inductor of the first coupled inductor and a ground and storing a predetermined voltage; A first capacitor connected between the other end of the primary side inductor of the first coupled inductor and a voltage source (Vsource) and charged or discharged to a predetermined voltage; A first diode having a cathode electrode connected to the voltage source and an anode electrode connected to the other end of the primary side inductor of the first coupled inductor; A first switch connected between the voltage source and the other end of the primary side inductor of the first coupled inductor to perform an on / off switching operation; A second capacitor connected between the other end of the primary inductor of the first coupled inductor and a ground, and configured to charge or discharge a predetermined voltage; A second diode having a cathode electrode connected to the other end of the primary inductor of the first coupled inductor and an anode electrode connected to the ground; A second switch connected between the other end of the primary inductor of the first coupled inductor and ground to perform an on / off switching operation; A second coupled inductor coupled to a negative terminal of the surface light source and supplying a negative driving voltage to the surface light source; A second source capacitor connected between one end of a primary side inductor of the second coupled inductor and a ground and storing a predetermined voltage; A third capacitor connected between the other end of the primary side inductor of the second coupled inductor and a voltage source, and charged or discharged to a predetermined voltage; A third diode having a cathode electrode connected to the voltage source and an anode electrode connected to the other end of the primary side inductor of the second coupled inductor; A third switch connected between the voltage source and the other end of the primary side inductor of the second coupled inductor to perform an on / off switching operation; A fourth capacitor connected between the other end of the primary inductor of the second coupled inductor and a ground, and configured to charge or discharge a predetermined voltage; A fourth diode having a cathode electrode connected to the other end of the primary inductor of the second coupled inductor and an anode electrode connected to the ground; And a fourth switch connected between the other end of the primary side inductor of the second coupled inductor and ground to perform an on / off switching operation. have.

In addition, the object is a coupled inductor coupled to the other end of the primary side inductor to form a secondary inductor, the third side inductor is coupled to both ends of the power source terminal of the surface light source to supply a driving voltage to the surface light source; A source capacitor connected between one end of the primary inductor of the coupled inductor and a ground and storing a predetermined voltage; A first capacitor connected between the other end of the primary inductor of the coupled inductor and a voltage source, and charged or discharged at a predetermined voltage; A first diode having a cathode electrode connected to the voltage source and an anode electrode connected to the other end of the primary side inductor of the coupled inductor; A first switch connected between the voltage source and the other end of the primary inductor of the coupled inductor to perform an on / off switching operation; A second capacitor connected between the other end of the secondary inductor of the coupled inductor and a ground, and configured to charge or discharge a predetermined voltage; A second diode having a cathode electrode connected to the other end of the secondary inductor of the coupled inductor and an anode electrode connected to the ground; And a second switch connected between the other end of the secondary inductor and the ground of the coupled inductor to perform an on / off switching operation.

Furthermore, in the surface light source driving circuit of the liquid crystal display device for achieving the above object, the tab inductor is coupled to the other end of the primary inductor to form a secondary inductor, and the tertiary side inductor is coupled to both ends of the power supply terminal of the surface light source. A coupled inductor for supplying a driving voltage to the light source; A source capacitor connected between one end of the primary inductor of the coupled inductor and a ground and storing a predetermined voltage; A first capacitor connected between the other end of the secondary inductor of the coupled inductor and a voltage source and charging or discharging at a predetermined voltage; A first diode having a cathode electrode connected to the voltage source and an anode electrode connected to the other end of the secondary inductor of the coupled inductor; A first switch connected between the voltage source and the other end of the secondary inductor of the coupled inductor to perform an on / off switching operation; A second capacitor connected between the other end of the primary inductor of the coupled inductor and a ground, and configured to charge or discharge a predetermined voltage; A second diode having a cathode electrode connected to the other end of the primary inductor of the coupled inductor and an anode electrode connected to the ground; And a second switch connected between the other end of the primary inductor of the coupled inductor and ground to perform an on / off switching operation.

In addition, the object is a coupled inductor for three inductors are mutually inductively coupled, the tertiary side inductor is coupled across the power supply terminal of the surface light source to supply a driving voltage to the surface light source; A source capacitor connected between one end of the primary inductor of the coupled inductor and a ground and storing a predetermined voltage; A voltage source connected to one end of the secondary inductor of the coupled inductor to apply a voltage; A first capacitor connected between the other end of the secondary inductor of the coupled inductor and a ground and charged or discharged to a predetermined voltage; A first diode having a cathode electrode connected to ground and an anode electrode connected to the other end of the secondary inductor of the coupled inductor; A first switch connected between the other end of the secondary inductor of the coupled inductor and ground to perform an on / off switching operation; A second capacitor connected between the other end of the primary inductor of the coupled inductor and a ground, and configured to charge or discharge a predetermined voltage; A second diode having a cathode electrode connected to the other end of the primary inductor of the coupled inductor and an anode electrode connected to the ground; And a second switch connected between the other end of the primary inductor and the ground of the coupled inductor to perform an on / off switching operation.

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

Example  One

1 is a block diagram illustrating a surface light source driving circuit of a liquid crystal display according to a first exemplary embodiment of the present invention.

Referring to FIG. 1, the surface light source driving circuit of the liquid crystal display includes a coupled inductor 20, three capacitors Cs, C1 and C2, two diodes d1 and d2, and two switches S1 and S2. And a voltage source Vsource.

The coupled inductor 20 is coupled to both ends of the power supply terminal of the surface light source 10 to supply a driving voltage to the surface light source 10. That is, the voltage applied across the primary inductor is induced across the secondary inductor in proportion to the winding ratio of the coupled inductor 20 and applied to the surface light source 10 as a driving voltage.

The source capacitor Cs is connected between one end of the primary inductor of the coupled inductor 20 and the ground and is charged to a predetermined voltage in advance. The source capacitor Cs has a very large capacitance and operates as a voltage source for supplying a voltage to one end of the primary inductor.

The first capacitor C1 is connected between the other end of the primary inductor of the coupled inductor 20 and the voltage source Vsource, and is charged or discharged to a predetermined voltage.

The first diode d1 has a cathode electrode connected to the voltage source Vsource and an anode electrode connected to the other end of the primary inductor of the coupled inductor 20 so that forward current passes and block reverse current.

The first switch S1 is connected between the voltage source Vsource and the other end of the primary inductor of the coupled inductor 20 and periodically performs an on / off switching operation.

The second capacitor C2 is connected between the other end of the primary inductor of the coupled inductor 20 and ground, and is charged or discharged at a predetermined voltage.

The second diode d2 has a cathode electrode connected to the other end of the primary inductor of the coupled inductor 20 and an anode electrode connected to ground to pass forward current and block reverse current.

The second switch S2 is connected between the other end of the primary inductor of the coupled inductor 20 and the ground and periodically performs an on / off switching operation.

An operation of the surface light source driving circuit of the liquid crystal display according to the exemplary embodiment of the present invention configured as described above will be described with reference to FIG. 2.

2 is a timing diagram illustrating an operation of a surface light source driving circuit of a liquid crystal display according to a first exemplary embodiment of the present invention.

Referring to FIG. 2, the surface light source driving circuit is driven while the four modes are periodically cycled according to the on / off of the first and second switches S1 and S2. That is, in the mode 1, when the first switch S1 is OFF, the second switch S2 is ON, and the mode 2 is both the first and second switches S1 and S2. , Mode 3 is when the first switch S1 is on and second switch S2 is off, and mode 4 is when both the first and second switches S1 and S2 are off again. 4 Next, it starts from mode 1.

First, before the mode 1 starts, the first switch S1 and the second switch S2 are turned off, and the primary current i _primary of the coupled inductor 20 is reversed through the second diode d2. Flows into. At this time, the mode 1 starts while the second switch S2 is turned on.

Mode 1: When the first switch S1 is off and the second switch S2 is on, the source capacitor Cs voltage is applied to the primary inductance of the coupled inductor 20 and the primary current of the coupled inductor 20 is i _primary ) begins to increase. The primary current i _{primary leaves} the source capacitor Cs and flows through the second switch S2. Here, the source capacitor Cs has a very large capacitance and thus operates as a nearly direct current (DC) voltage source.

Mode 2: When the first switch S1 is off and the second switch is off, at the moment when the second switch S2 is off, the primary current i _primary of the coupled inductor 20 is _{changed to} the second switch ( Since it cannot pass through S2), most of them turn to the secondary side of the coupled inductor 20, and as the current is charged in the surface light source, the secondary voltage V _Lamp of the coupled inductor 20 rapidly increases. (The surface light source is equivalent to a capacitor when no light is emitted). A slight current of the primary current i _primary flows to the second capacitor C2 to raise the voltage of the second capacitor C2, and simultaneously flows toward the first capacitor C1 to discharge the charge in the first capacitor. While reducing the voltage of the first capacitor (C1). When the primary side voltage of the coupled inductor 20 is equal to the voltage source Vsource, the first diode d1 is turned on and the _primary side current i _primary of the coupled inductor 20 flows to the voltage source Vsource. As the primary side voltage of the inductor 20 is fixed to the voltage source Vsource, the secondary side voltage V _Lamp of the coupled inductor 20 is also fixed. If the primary side voltage of the coupled inductor 20 is not equal to the voltage source Vsource, if the primary side voltage of the coupled inductor 20 is only close to the voltage source, the first switch S1 is turned on to perform the mode without soft switching. Go to 3.

Mode 3: Soft switching is obtained by turning on the first switch S1 while the first diode d1 is on. Thereafter, the direction of the current is changed, at which time the first diode d1 is turned off and the primary current i _primary of the coupled inductor 20 flows through the first switch S1. The first reason for the change of current is because the voltage source (Vsource) is much higher than the source capacitor (Cs) voltage, so that the primary magnetization inductor is subjected to a reverse voltage and the primary current (i _primary ) decreases and then changes direction. During the mode 3, the surface light source emits light, because the surface light source 10 consumes a lot of power as a resistor, so that current flows into the load.

Mode 4: When the section in which the lamp emits light ends, the first switch S1 is turned OFF. Since the primary current i _primary of the coupled inductor 20 may not pass through the first switch S1 at the moment when the first switch S1 is turned off, the surface light source 10 may be connected through the coupled inductor 20. The secondary voltage V _{lamp of} the coupled inductor 20 decreases rapidly while removing the charge accumulated in the capacitor. In addition, as a small amount of current flows to the first capacitor C1, the voltage of the first capacitor C1 increases, and at the same time, the voltage of the first capacitor C1 also flows toward the second capacitor C2 while discharging the charges in the second capacitor C2. The voltage of the two capacitors C2 decreases. When this voltage reaches near zero, the second diode d2 is turned on and fixed at zero, the coupled inductor 20 primary voltage is fixed at the source capacitor Cs voltage, and the coupled inductor 20 1 The secondary current i _primary is reduced to the source capacitor Cs. If the second switch S2 is turned on (soft switching) while this current flows to the second diode d2, the mode 1 is repeatedly repeated.

According to the surface light source driving circuit of the liquid crystal display according to the embodiment of the present invention operating as described above, it is possible to implement a driving waveform for optimizing the light efficiency of the light source, and has an energy recovery circuit (Energy Recovery Circuit) function, Minimize power consumption and reduce the size and cost of products by simplifying components in circuit fabrication.

1 and 2, the pulse of the output voltage (lamp voltage) is generated only in one direction, but the pulse of the output voltage (lamp voltage) is generated in both directions to extend the life of the surface light source. You may. Hereinafter, the bidirectional driving will be described with reference to FIGS. 3 and 4.

Example  2

3 is a block diagram illustrating a surface light source driving circuit of a liquid crystal display according to a second exemplary embodiment of the present invention.

Referring to FIG. 3, the surface light source driving circuit of the liquid crystal display includes two coupled inductors 30 and 40, three capacitors Cs, C1 and C2, two diodes d1 and d2, and two switches ( S1, S2) and a voltage source Vsource.

The first coupled inductor 30 is connected to the positive power supply terminal of the surface light source 10 to supply a positive driving voltage to the surface light source 10. That is, the voltage applied across the primary side inductor of the first coupled inductor 30 is induced across the secondary side inductor in proportion to the turns ratio of the first coupled inductor 30 to be positive in the surface light source 10. It is applied to the driving voltage.

The source capacitor Cs is connected between one end of the primary side inductor of the first coupled inductor 30 and the ground and is charged to a predetermined voltage in advance. The source capacitor Cs has a very large capacitance and operates as a voltage source for supplying a voltage to one end of the primary inductor.

The first capacitor C1 is connected between the other end of the primary side inductor of the first coupled inductor 30 and the voltage source Vsource, and is charged or discharged at a predetermined voltage.

The first diode d1 has a cathode electrode connected to the voltage source Vsource, and an anode electrode connected to the other end of the primary inductor of the first coupled inductor 30 to pass forward current and block reverse current.

The first switch S1 is connected between the voltage source Vsource and the other end of the primary inductor of the first coupled inductor 30 and periodically performs on / off switching operation.

The second capacitor C2 is connected between the other end of the primary side inductor of the first coupled inductor 30 and ground, and is charged or discharged to a predetermined voltage.

The second diode d2 has a cathode electrode connected to the other end of the primary side inductor of the first coupled inductor 30 and an anode electrode connected to ground to pass forward current and block reverse current.

The second switch S2 is connected between the other end of the primary side inductor of the first coupled inductor 30 and the ground and periodically performs an on / off switching operation.

The second coupled inductor 40 is connected to the negative power supply terminal of the surface light source 10 to supply a negative driving voltage to the surface light source 10. That is, the voltage applied across the primary side inductor of the second coupled inductor 40 is induced across the secondary side inductor in proportion to the turns ratio of the second coupled inductor 40 so as to be negative to the surface light source 10. It is applied to the driving voltage. In the second coupled inductor 40, the polarity indications of the coils of the primary and secondary inductors are reversed, and when a positive voltage is applied to the primary side, a negative voltage is induced to the secondary side.

The source capacitor Cs' is connected between one end of the primary side inductor of the second coupled inductor 40 and the ground and is charged to a predetermined voltage in advance. The source capacitor Cs' has a very large capacitance and operates as a voltage source for supplying a voltage to one end of the primary inductor.

The third capacitor C3 is connected between the other end of the primary inductor of the second coupled inductor 40 and the voltage source Vsource, and is charged or discharged at a predetermined voltage.

In the third diode d3, a cathode electrode is connected to the voltage source Vsource, and an anode electrode is connected to the other end of the primary inductor of the second coupled inductor 40 to pass forward current and block reverse current.

The third switch S3 is connected between the voltage source Vsource and the other end of the primary side inductor of the second coupled inductor 40 and periodically performs on / off switching operation.

The fourth capacitor C4 is connected between the other end of the primary inductor of the second coupled inductor 40 and ground, and is charged or discharged to a predetermined voltage.

The fourth diode d4 has a cathode electrode connected to the other end of the primary inductor of the second coupled inductor 40 and an anode electrode connected to ground, so that the forward current passes and the reverse current is blocked.

The fourth switch S4 is connected between the other end of the primary side inductor of the second coupled inductor 40 and the ground and periodically performs on / off switching operation.

An operation of the surface light source driving circuit of the liquid crystal display according to the exemplary embodiment of the present invention configured as described above will be described with reference to FIG. 4 to be described later.

4 is a timing diagram illustrating an operation of a surface light source driving circuit of a liquid crystal display according to a second exemplary embodiment of the present invention.

Referring to FIG. 4, in the bidirectional surface light source driving circuit, four modes are periodically cycled in accordance with on / off of the first and second switches S1 and S2 connected to the first coupled inductor 30. Voltage is applied to the surface light source. That is, in the mode 1, when the first switch S1 is OFF, the second switch S2 is ON, and the mode 2 is both the first and second switches S1 and S2. , Mode 3 is when the first switch S1 is on and second switch S2 is off, and mode 4 is when both the first and second switches S1 and S2 are off again. 4 Next, it starts from mode 1.

In addition, the bidirectional surface light source driving circuit has four modes periodically cycled in accordance with the on / off of the third and fourth switches S3 and S4 connected to the second coupled inductor 40, and a negative voltage is applied to the surface. Is applied to the light source. That is, in the mode 1 ', when the third switch S3 is OFF and the fourth switch S4 is ON, the mode 2' is turned off in both the third and fourth switches S3 and S4. Mode 3 'is the first switch S1 is on, and when the second switch S2 is off, the mode 4' is again OFF in both the third and fourth switches S3 and S4. In this case, the mode 4 'is followed by the mode 1' again.

Further, while mode 1 of the driving circuit coupled to the positive terminal of the surface light source 10 proceeds, mode 2 ', mode 3', and mode 4 'of the driving circuit coupled to the negative terminal proceed, and the positive terminal Mode 1 'of the driving circuit coupled to the negative terminal proceeds while Mode 1, Mode 2, and Mode 3 of the driving circuit coupled to.

As shown in FIG. 4, the bidirectional driving operates in the same manner as the operation mode of FIG. 2. The only difference is that the polarity of the voltage applied to the surface light source 10 is positive in mode 3 and negative in mode 3 '. Therefore, the description of FIG. 10 will be omitted since it will be easily understood by those skilled in the art with reference to FIG. 2. Since the electrodes of the surface light source are symmetrical, they turn on equally whether they are positively or negatively applied. By doing so, the life of the surface light source 10 is lengthened.

Example  3

5 is a configuration diagram illustrating a surface light source driving circuit of a liquid crystal display according to a third exemplary embodiment of the present invention.

Referring to FIG. 5, the surface light source driving circuit of the liquid crystal display includes a coupled inductor 22 having a tap inductor coupled to the primary side, three capacitors Cs, C1 and C2, two diodes d1 and d2, It includes two switches S1 and S2 and a voltage source Vsource.

The coupled inductor 22 has a tap inductor coupled to the other end of the primary side inductor to form a secondary side inductor, and the tertiary side inductor is coupled to both ends of the power supply terminal of the surface light source 10 to drive the voltage to the surface light source 10. To supply. That is, the voltage applied across the primary side (or secondary side) inductor is induced across the tertiary side inductor in proportion to the primary: tertiary (or secondary: tertiary) winding ratio of the coupled inductor 22 to the surface. The driving voltage is applied to the light source 10.

The source capacitor Cs is connected between one end of the primary inductor of the coupled inductor 22 and the ground and is charged to a predetermined voltage in advance. The source capacitor Cs has a very large capacitance and operates as a voltage source for supplying a voltage to one end of the primary inductor.

The first capacitor C1 is connected between the other end of the primary inductor of the coupled inductor 22 and the voltage source Vsource, and is charged or discharged to a predetermined voltage.

The first diode (d1) has a cathode electrode is connected to the voltage source (Vsource), an anode electrode is connected to the other end of the primary inductor of the coupled inductor 22 so that forward current passes and reverse Current is cut off.

The first switch S1 is connected between the voltage source Vsource and the other end of the primary inductor of the coupled inductor 22 and periodically performs on / off switching operation.

The second capacitor C2 is connected between the other end of the secondary inductor 22 of the coupled inductor 22 and ground, and is charged or discharged to a predetermined voltage.

The second diode d2 has a cathode electrode connected to the other end of the secondary inductor of the coupled inductor 22 and an anode electrode connected to ground so that forward current passes and reverse current Block it.

The second switch S2 is connected between the other end of the secondary inductor of the coupled inductor 22 and the ground and periodically performs an on / off switching operation.

An operation of the surface light source driving circuit of the liquid crystal display according to the exemplary embodiment of the present invention configured as described above will be described with reference to FIG. 6 to be described later.

6 is a timing diagram illustrating an operation of a surface light source driving circuit of a liquid crystal display according to a third exemplary embodiment of the present invention.

Referring to FIG. 6, the surface light source driving circuit is driven while the four modes are periodically circulated according to the on / off of the first and second switches S1 and S2 as described above. That is, in the mode 1, when the first switch S1 is OFF, the second switch S2 is ON, and the mode 2 is both the first and second switches S1 and S2. , Mode 3 is when the first switch S1 is on and second switch S2 is off, and mode 4 is when both the first and second switches S1 and S2 are off again. 4 Next, it starts from mode 1.

First, before mode 1 starts, the first switch S1 and the second switch S2 are off, and the secondary current i _secondary of the coupled inductor 22 is reversed through the second diode d2. Is flowing in the direction. At this time, the mode 1 starts while the second switch S2 is turned on.

Mode 1: When the first switch S1 is OFF and the second switch S2 is ON, the source capacitor Cs is applied to the primary and secondary inductances of the coupled inductor 22 and coupled. Inductor 22 secondary current i _secondary begins to increase. The secondary current i _secondary flows out of the source capacitor Cs and through the second switch S2. At this time, the primary current (i _primary ) does not flow, and the secondary current (i _secondary ) is reduced by the turn ratio in the primary current flows. Here, the source capacitor Cs has a very large capacitance and thus operates as a nearly direct current (DC) voltage source.

Mode 2: When the first switch S1 is off and the second switch is off, at the moment when the second switch S2 is off, the secondary current i _secondary of the coupled inductor 22 is _{reduced to} the second switch ( Since it cannot pass S2, the secondary current i _secondary stops (strictly speaking, a small amount of current flows into the second capacitor C2, raising the voltage of the second capacitor C2 and increasing the secondary current i). _secondary ) is stopped), and this current is mostly charged into the surface light source 10 through the coupled inductor 22, so that the tertiary side voltage V _Lamp rapidly rises (the surface light source 10 emits no light). Is equivalent to a capacitor). When the primary side voltage of the coupled inductor 22 is equal to the voltage source Vsource, the first diode d1 is turned on and the _primary side current i _primary of the coupled inductor 22 flows to the voltage source Vsource. As the primary voltage of the inductor 22 is fixed to the voltage source Vsource, the coupled inductor 22 tertiary voltage V _Lamp is also fixed. At this time, since the number of turns of the secondary and the primary is different, the primary current flows by reducing the turn ratio (primary: secondary) from the secondary current through the first switch S1.

Mode 3: Soft switching is obtained by turning on the first switch S1 while the first diode d1 is on. At this time, the primary current (i _primary ) flowing is the current amplified by the turn ratio in the tertiary current. In addition, the direction of the _primary current i _primary is changed, at which time the first diode d1 is off and the primary current i _primary of the coupled inductor 22 flows through the first switch S1.

Mode 4: When the section in which the lamp emits light ends, the first switch S1 is turned OFF. Since the coupled inductor primary current i _primary cannot pass through the first switch S1 at the moment when the first switch S1 is turned off, the primary current is stopped (strictly speaking, a small amount of current is the first). Flowing through the capacitor C1 raises the voltage of the first capacitor C1 and stops the primary current), and this current mostly turns to the internal coupled inductor 22, which is the surface light source 10 The third voltage V _Lamp of the coupled inductor 22 is rapidly decreased while discharging. When the secondary voltage reaches near zero, the second diode d2 turns on and is fixed at zero, the coupled inductor 22 is fixed at the source capacitor (Cs) voltage, and the coupled inductor 22 is The secondary current i _secondary is reduced to the source capacitor Cs. If the second switch S2 is turned on (soft switching) while this current flows to the second diode d2, the mode 1 is repeatedly repeated.

The surface light source driving circuit according to the third embodiment of the present invention has an advantage that the conduction loss of the switch can be reduced by reducing the current flowing through the second switch S2 by increasing the inductance.

Example  4

7 is a configuration diagram illustrating a surface light source driving circuit of a liquid crystal display according to a fourth exemplary embodiment of the present invention.

Referring to FIG. 7, the surface light source driving circuit of the liquid crystal display includes a coupled inductor 24 having a tap inductor coupled to the primary side, three capacitors Cs, C1 and C2, two diodes d1 and d2, It includes two switches S1 and S2 and a voltage source Vsource.

The coupled inductor 24 has a tap inductor coupled to the other end of the primary side inductor to form a secondary side inductor, and the tertiary side inductor is coupled to both ends of a power terminal of the surface light source 10 to drive the voltage to the surface light source 10. To supply. That is, the voltage applied across the primary side (or secondary side) inductor is induced across the tertiary side inductor in proportion to the primary: tertiary (or secondary: tertiary) winding ratio of the coupled inductor 24 to the surface. The driving voltage is applied to the light source 10.

The source capacitor Cs is connected between one end of the primary inductor of the coupled inductor 24 and the ground and is charged to a predetermined voltage in advance. The source capacitor Cs has a very large capacitance and operates as a voltage source for supplying a voltage to one end of the primary inductor.

The first capacitor C1 is connected between the other end of the secondary inductor of the coupled inductor 24 and the voltage source Vsource, and is charged or discharged to a predetermined voltage.

The first diode (d1) has a cathode electrode is connected to the voltage source (Vsource), an anode electrode is connected to the other end of the secondary inductor of the coupled inductor 24 so that forward current passes and reverse Current is cut off.

The first switch S1 is connected between the voltage source Vsource and the other end of the secondary inductor of the coupled inductor 24 and periodically performs an on / off switching operation.

The second capacitor C2 is connected between the other end of the primary inductor of the coupled inductor 24 and ground, and is charged or discharged to a predetermined voltage.

The second diode d2 has a cathode electrode connected to the other end of the primary inductor of the coupled inductor 24, and an anode electrode connected to ground so that the forward current passes and the reverse current passes. Blocks.

The second switch S2 is connected between the other end of the primary inductor of the coupled inductor 24 and the ground and periodically performs an on / off switching operation.

An operation of the surface light source driving circuit of the liquid crystal display according to the exemplary embodiment of the present invention configured as described above will be described with reference to FIG. 8 to be described later.

8 is a timing diagram illustrating an operation of a surface light source driving circuit of a liquid crystal display according to a fourth exemplary embodiment of the present invention.

Referring to FIG. 8, the surface light source driving circuit is driven while the four modes are periodically circulated in accordance with the on / off of the first and second switches S1 and S2 as described above with reference to FIGS. 2 and 4. That is, in the mode 1, when the first switch S1 is OFF, the second switch S2 is ON, and the mode 2 is both the first and second switches S1 and S2. , Mode 3 is when the first switch S1 is on and second switch S2 is off, and mode 4 is when both the first and second switches S1 and S2 are off again. 4 Next, it starts from mode 1.

First, before the mode 1 starts, the first switch S1 and the second switch S2 are turned off, and the primary current i _primary of the coupled inductor 24 is reversed through the second diode d2. Flows into. At this time, the mode 1 starts while the second switch S2 is turned on.

Mode 1: When the first switch S1 is OFF and the second switch S2 is ON, the source capacitor Cs is applied to the primary inductance of the coupled inductor 24 and the coupled inductor ( 24) The primary current i _primary begins to increase. The primary current i _{primary leaves} the source capacitor Cs and flows through the second switch S2. At this time, the secondary current (i _secondary ) does not flow, and the primary current (i _primary ) is amplified by the turn ratio in the secondary current flows. Here, the source capacitor Cs has a very large capacitance and thus operates as a nearly direct current (DC) voltage source.

Mode 2: When the first switch S1 is off and the second switch is off, at the moment when the second switch S2 is off, the primary current i _primary of the coupled inductor 24 is _{changed to} the second switch ( Cannot pass through S2), the primary current stops (strictly speaking, a small amount of current flows into the second capacitor C2, raising the voltage of the second capacitor C2 and the primary current i _primary ) This current is mostly turned to the coupled inductor 24, and as the current is charged in the surface light source 10, the tertiary side voltage V _Lamp rapidly increases (the surface light source 10 Equivalent to a capacitor when no light is emitted). When the secondary voltage of the coupled inductor 24 is equal to the voltage source Vsource, the first diode d1 is turned on and the secondary inductor 24 secondary current i _secondary flows to the voltage source Vsource. As the secondary voltage of the inductor 24 is fixed to the voltage source Vsource, the coupled inductor 24 third voltage V _Lamp is also fixed. At this time, since the number of turns of the secondary and the primary is different, the secondary current is amplified by the turn ratio (secondary: first) from the primary current through the first switch S1. If the secondary side voltage of the coupled inductor 24 is not equal to the voltage source Vsource, when the primary side voltage is only close to the voltage source Vsource, the first switch S1 is turned on to mode 3 without soft switching. Passing

Mode 3: Soft switching is obtained by turning on the first switch S1 while the first diode d1 is on. At this time, the secondary current (i _secondary ) flowing is the current amplified by the turn ratio in the _primary current (i _primary ). In addition, the direction of the _secondary current (i _secondary ) is changed, at which time the first diode (d1) is off and the secondary current (i _secondary ) of the coupled inductor 24 flows through the first switch (S1).

Mode 4: When the section in which the lamp emits light ends, the first switch S1 is turned OFF. Since the coupled inductor secondary current i _secondary cannot pass through the first switch S1 at the moment when the first switch S1 is turned off, this current is mostly turned to the internal coupled inductor 24. As the current discharges the surface light source 10, the tertiary side voltage V _Lamp of the coupled inductor 24 rapidly decreases (the surface light source is equivalent to a capacitor when no light is emitted). When the primary side voltage of the coupled inductor 24 reaches near zero, the second diode d2 is turned on and fixed at zero, and the coupled inductor 24 primary side voltage is fixed at the source capacitor Cs voltage, Coupled inductor 24 _primary side current i _primary is reduced to source capacitor Cs. If the second switch S2 is turned on (soft switching) while this current flows to the second diode d2, the mode 1 is repeatedly repeated.

Example  5

9 is a configuration diagram illustrating a surface light source driving circuit of the liquid crystal display according to the fifth exemplary embodiment of the present invention.

Referring to FIG. 9, the surface light source driving circuit of the liquid crystal display includes a tertiary coupled inductor 26 having three inductors coupled to each other, three capacitors Cs, C1 and C2, and two diodes d1 and d2. ), Two switches S1 and S2 and a voltage source Vsource.

In the tertiary coupled inductor 26 in which three inductors are induced, a tertiary side inductor is coupled to both ends of a power supply terminal of the surface light source 10 to supply a driving voltage to the surface light source 10. That is, the voltage applied across the primary side (or secondary side) inductor is induced across the tertiary side inductor in proportion to the primary: tertiary (or secondary: tertiary) winding ratio of the coupled inductor 26 to provide the surface light. The circle 10 is applied as a driving voltage. A voltage source Vsource is connected between the other end of the secondary inductor of the coupled inductor 26 and the ground.

The source capacitor Cs is connected between one end of the primary inductor of the coupled inductor 26 and the ground and is charged to a predetermined voltage in advance. The source capacitor Cs has a very large capacitance and operates as a voltage source for supplying a voltage to one end of the primary inductor.

The first capacitor C1 is connected between one end of the secondary inductor of the coupled inductor 26 and the ground, and is charged or discharged to a predetermined voltage.

The first diode d1 has a cathode electrode connected to ground and an anode electrode connected to one end of the secondary inductor of the coupled inductor 26 so that forward current passes and reverse current. Blocks.

The first switch S1 is connected between one end of the secondary inductor of the coupled inductor 26 and the ground and periodically performs an on / off switching operation.

The second capacitor C2 is connected between the other end of the primary inductor of the coupled inductor 26 and ground, and is charged or discharged to a predetermined voltage.

The second diode d2 has a cathode electrode connected to the other end of the primary inductor of the coupled inductor 26, and an anode electrode connected to ground so that forward current passes and reverse current. Blocks.

The second switch S2 is connected between the other end of the primary inductor of the coupled inductor 26 and the ground and periodically performs an on / off switching operation.

An operation of the surface light source driving circuit of the liquid crystal display according to the exemplary embodiment of the present invention configured as described above will be described with reference to FIG. 10 to be described later.

10 is a timing diagram illustrating an operation of a surface light source driving circuit of a liquid crystal display according to a fifth exemplary embodiment of the present invention.

Referring to FIG. 10, the surface light source driving circuit is driven while the four modes are periodically circulated according to the on / off of the first and second switches S1 and S2 as described above with reference to FIGS. 2, 4, and 6. do. That is, in the mode 1, when the first switch S1 is OFF, the second switch S2 is ON, and the mode 2 is both the first and second switches S1 and S2. , Mode 3 is when the first switch S1 is on and second switch S2 is off, and mode 4 is when both the first and second switches S1 and S2 are off again. 4 Next, it starts from mode 1.

First, before the mode 1 starts, the first switch S1 and the second switch S2 are turned off, and the primary current i _primary of the coupled inductor flows in the reverse direction through the second diode d2. . At this time, the mode 1 starts while the second switch S2 is turned on.

Mode 1: When the first switch S1 is OFF and the second switch S2 is ON, the source capacitor Cs is applied to the primary inductor of the coupled inductor 26 and the coupled inductor ( 26) The primary current i _primary begins to increase. The primary current i _{primary leaves} the source capacitor Cs and flows through the second switch S2. At this time, the secondary current (i _secondary ) does not flow, and the primary current (i _primary ) is reduced by as much as the turn ratio in the secondary current flows. Here, the source capacitor Cs has a very large capacitance and thus operates as a nearly direct current (DC) voltage source.

Mode 2: When the first switch S1 is off and the second switch is off, at the moment when the second switch S2 is off, the primary current i _primary of the coupled inductor 26 is _{changed to} the second switch ( Since it cannot pass through S2), the primary current stops (strictly speaking, a small amount of current flows into the second capacitor C2, raising the voltage of the second capacitor C2 and stopping the _primary current i _primary ). This current is mostly turned to the internal coupled inductor 26, and as the current is charged in the surface light source 10, the tertiary side voltage V _Lamp rapidly increases (surface light source 10). Is equivalent to a capacitor when no light is emitted). When the secondary voltage of the coupled inductor 26 is equal to the voltage source Vsource, the first diode d1 is turned on and the coupled inductor 26 secondary current i _secondary flows to the voltage source Vsource. As the secondary voltage of the inductor 26 is fixed to the voltage source Vsource, the coupled inductor 26 third voltage V _Lamp is also fixed. At this time, since the number of turns of the secondary and the primary is different, the secondary current is amplified by the turn ratio (secondary: first) from the primary current through the first switch S1. If the secondary side voltage of the coupled inductor 26 is not equal to the voltage source Vsource, if the primary side voltage is only close to the voltage source Vsource, the first switch S1 is turned on to mode 3 without soft switching. Passing

Mode 3: Soft switching is obtained by turning on the first switch S1 while the first diode d1 is on. At this time, the secondary current (i _secondary ) flowing is the current amplified by the turn ratio in the _primary current (i _primary ). In addition, the direction of the _secondary current (i _secondary ) is changed, at which time the first diode (d1) is off and the secondary current (i _secondary ) of the coupled inductor 26 flows through the first switch (S1).

Mode 4: When the section in which the lamp emits light ends, the first switch S1 is turned OFF. Since the coupled inductor 26 secondary current i _secondary cannot pass through the first switch S1 at the moment when the first switch S1 is turned off, this current is mostly internally coupled inductor 26. The third side voltage V _Lamp of the coupled inductor 26 decreases rapidly while this current discharges the surface light source 10 (the surface light source is equivalent to a capacitor when no light is emitted). When the primary side voltage of the coupled inductor 26 reaches near zero, the second diode d2 is turned on and fixed at zero, and the coupled inductor 26 primary side voltage is fixed at the source capacitor Cs voltage. Coupled inductor 26 _primary side current i _primary is reduced to source capacitor Cs. If the second switch S2 is turned on (soft switching) while this current flows to the second diode d2, the mode 1 is repeatedly repeated.

The surface light source driving circuit according to the fifth embodiment of the present invention has an advantage of driving the first switch S1 based on ground.

Example  6

11 is a configuration diagram illustrating a surface light source driving circuit of the liquid crystal display according to the sixth exemplary embodiment of the present invention.

The surface light source driving circuit of FIG. 11 is a circuit in which a boost-up circuit 50 is further added to the surface light source driving circuit of FIG. 1. That is, the boost up circuit 50 includes a diode and a second voltage source Vsource2 connected in series across the source capacitor Cs.

The reason why the second voltage source Vsource2 is further added is that in case regenerative energy loss occurs when the turn ratio of the coupled inductor 20 increases, the soft switching of the first switch S1 fails, as shown in FIG. 11. Soft switching can be achieved by applying an additional voltage source (Vsource2) to compensate for the losses.

Since the circuit operation of FIG. 11 is the same as that of FIG. 1, detailed descriptions thereof will be omitted. In addition, although FIG. 11 adds the boost up circuit 50 to the circuit of FIG. 1, it is applicable to all other surface light source drive circuits (FIGS. 3, 5, 7, and 9), The figure and description are If omitted, those skilled in the art can easily understand.

The present invention can implement a drive waveform for optimizing the light efficiency of the surface light source.

In addition, the present invention can perform the function of the energy recovery circuit (Drive Energy Recovery Circuit) that has driven the optimum efficiency when driving the surface light source.

In addition, the present invention minimizes power loss occurring in the drive circuit and the energy recovery circuit.

Furthermore, the present invention can minimize the size and cost of the product by simplifying the components put into the circuit fabrication.

Claims (17)

In the driving circuit for emitting the surface light source of the liquid crystal display device, A coupled inductor having a secondary inductor coupled to both terminals of the surface light source and supplying a driving voltage to the surface light source; A source capacitor connected between one end of the primary inductor of the coupled inductor and a ground and storing a predetermined voltage; A first capacitor connected between the other end of the primary inductor of the coupled inductor and a voltage source, and charged or discharged at a predetermined voltage; A first diode having a cathode electrode connected to the voltage source and an anode electrode connected to the other end of the primary side inductor of the coupled inductor; A first switch connected between the voltage source and the other end of the primary inductor of the coupled inductor to perform an on / off switching operation; A second capacitor connected between the other end of the primary inductor of the coupled inductor and a ground, and configured to charge or discharge a predetermined voltage; A second diode having a cathode electrode connected to the other end of the primary inductor of the coupled inductor and an anode electrode connected to the ground; A second switch connected between the other end of the primary inductor of the coupled inductor and a ground to perform an on / off switching operation to linearly increase or decrease the current flowing in the primary inductor of the coupled inductor; And And a second voltage source for supplying a predetermined voltage across both of the source capacitors. The method of claim 1, In the surface light source driving circuit, four driving modes are sequentially and repeatedly operated according to on / off states of the first and second switches. The four driving modes A first driving mode in which the first switch is OFF and the second switch is ON; A second drive mode in which the first switch is OFF and the second switch is OFF; A third drive mode in which the first switch is ON and the second switch is OFF; and A surface light source driving circuit of a liquid crystal display device, wherein the first switch is OFF and the second switch is OFF. delete In the driving circuit for emitting the surface light source of the liquid crystal display device, A first coupled inductor having the other end of the secondary inductor coupled to the positive terminal of the surface light source and supplying a positive driving voltage to the surface light source; A first source capacitor connected between one end of a primary side inductor of the first coupled inductor and a ground and storing a predetermined voltage; A first capacitor connected between the other end of the primary side inductor of the first coupled inductor and a voltage source (Vsource) and charged or discharged to a predetermined voltage; A first diode having a cathode electrode connected to the voltage source and an anode electrode connected to the other end of the primary side inductor of the first coupled inductor; A first switch connected between the voltage source and the other end of the primary side inductor of the first coupled inductor to perform an on / off switching operation; A second capacitor connected between the other end of the primary inductor of the first coupled inductor and a ground, and configured to charge or discharge a predetermined voltage; A second diode having a cathode electrode connected to the other end of the primary inductor of the first coupled inductor and an anode electrode connected to the ground; A second switch connected between the other end of the primary inductor of the first coupled inductor and ground to perform an on / off switching operation; One end of the secondary inductor is coupled to the negative terminal of the surface light source, and the other end of the secondary inductor is connected to one end of the secondary side inductor of the first coupled inductor, and supplies a negative driving voltage to the surface light source. A second coupled inductor; A second source capacitor connected between one end of a primary side inductor of the second coupled inductor and a ground and storing a predetermined voltage; A third capacitor connected between the other end of the primary side inductor of the second coupled inductor and a voltage source, and charged or discharged to a predetermined voltage; A third diode having a cathode electrode connected to the voltage source and an anode electrode connected to the other end of the primary side inductor of the second coupled inductor; A third switch connected between the voltage source and the other end of the primary side inductor of the second coupled inductor to perform an on / off switching operation; A fourth capacitor connected between the other end of the primary inductor of the second coupled inductor and a ground, and configured to charge or discharge a predetermined voltage; A fourth diode having a cathode electrode connected to the other end of the primary inductor of the second coupled inductor and an anode electrode connected to the ground; And And a fourth switch connected between the other end of the primary side inductor of the second coupled inductor and a ground to perform an on / off switching operation. The method of claim 4, wherein In the second coupled inductor, when a voltage is applied to the other end of the primary inductor based on each end of the primary inductor and the secondary inductor, the voltage having the opposite polarity of the applied voltage is induced at the other end of the secondary inductor. The surface light source driving circuit of the liquid crystal display device. The method of claim 4, wherein The surface light source driving circuit Four driving modes (A) are sequentially and repeatedly operated according to the on / off states of the first and second switches, and four driving modes (B) according to the on / off states of the third and fourth switches. Operates repeatedly in sequence, The four driving modes (A) The first driving mode A in which the first switch is OFF and the second switch is ON; The second driving mode A in which the first switch is OFF and the second switch is OFF; A third driving mode A in which the first switch is ON and the second switch is OFF; and The fourth drive mode A in which the first switch is OFF, the second switch is OFF, The four driving modes (B) The first driving mode B in which the third switch is OFF and the fourth switch is ON; The second driving mode B in which the third switch is OFF and the fourth switch is OFF; The third driving mode B in which the third switch is ON and the fourth switch is OFF; and A surface light source driving circuit of a liquid crystal display device, wherein the third switch is OFF and the fourth switch is OFF. The method of claim 6, When the first driving mode A is operated, the second to fourth driving modes B are operated. And the first driving mode (B) is operated when the second to fourth driving modes (A) are operated. The method of claim 4, wherein A second voltage source supplying a predetermined voltage across the first source capacitor; And a third voltage source configured to supply a predetermined voltage at both ends of the second source capacitor. In the driving circuit for emitting the surface light source of the liquid crystal display device, The tap inductor is coupled to the other end of the primary inductor, one end of which forms a secondary inductor connected to the other end of the primary inductor, and the tertiary side inductor is coupled to both ends of the power terminal of the surface light source to supply a driving voltage to the surface light source. Coupled inductors; A source capacitor connected between one end of the primary inductor of the coupled inductor and a ground and storing a predetermined voltage; A first capacitor connected between the other end of the primary inductor of the coupled inductor and a voltage source, and charged or discharged at a predetermined voltage; A first diode having a cathode electrode connected to the voltage source and an anode electrode connected to the other end of the primary side inductor of the coupled inductor; A first switch connected between the voltage source and the other end of the primary inductor of the coupled inductor to perform an on / off switching operation; A second capacitor connected between the other end of the secondary inductor of the coupled inductor and a ground, and configured to charge or discharge a predetermined voltage; A second diode having a cathode electrode connected to the other end of the secondary inductor of the coupled inductor and an anode electrode connected to the ground; And And a second switch connected between the other end of the secondary inductor and the ground of the coupled inductor to perform an on / off switching operation. The method of claim 9, In the surface light source driving circuit, four driving modes are sequentially and repeatedly operated according to on / off states of the first and second switches. The four driving modes A first driving mode in which the first switch is OFF and the second switch is ON; A second drive mode in which the first switch is OFF and the second switch is OFF; A third drive mode in which the first switch is ON and the second switch is OFF; and A surface light source driving circuit of a liquid crystal display device, wherein the first switch is OFF and the second switch is OFF. The method of claim 9, And a second voltage source for supplying a predetermined voltage across both of the source capacitors. In the driving circuit for emitting the surface light source of the liquid crystal display device, A tap inductor is coupled to the other end of the primary inductor, one end of which forms a secondary inductor connected to the other end of the primary inductor, and the tertiary side inductor is coupled to both ends of the power terminal of the surface light source to supply a driving voltage to the surface light source. Coupled inductors; A source capacitor connected between one end of the primary inductor of the coupled inductor and a ground and storing a predetermined voltage; A first capacitor connected between the other end of the secondary inductor of the coupled inductor and a voltage source and charging or discharging at a predetermined voltage; A first diode having a cathode electrode connected to the voltage source and an anode electrode connected to the other end of the secondary inductor of the coupled inductor; A first switch connected between the voltage source and the other end of the secondary inductor of the coupled inductor to perform an on / off switching operation; A second capacitor connected between the other end of the primary inductor of the coupled inductor and a ground, and configured to charge or discharge a predetermined voltage; A second diode having a cathode electrode connected to the other end of the primary inductor of the coupled inductor and an anode electrode connected to the ground; And And a second switch connected between the other end of the coupled inductor and the ground of the coupled inductor to perform an on / off switching operation. The method of claim 12, In the surface light source driving circuit, four driving modes are sequentially and repeatedly operated according to on / off states of the first and second switches. The four driving modes A first driving mode in which the first switch is OFF and the second switch is ON; A second drive mode in which the first switch is OFF and the second switch is OFF; A third drive mode in which the first switch is ON and the second switch is OFF; and A surface light source driving circuit of a liquid crystal display device, wherein the first switch is OFF and the second switch is OFF. The method of claim 12, And a second voltage source for supplying a predetermined voltage across both of the source capacitors. In the driving circuit for emitting the surface light source of the liquid crystal display device, A coupled inductor having three inductors coupled to each other, and a tertiary side inductor coupled across a power supply terminal of the surface light source to supply a driving voltage to the surface light source; A source capacitor connected between one end of the primary inductor of the coupled inductor and a ground and storing a predetermined voltage; A voltage source connected to one end of the secondary inductor of the coupled inductor to apply a voltage; A first capacitor connected between the other end of the secondary inductor of the coupled inductor and a ground and charged or discharged to a predetermined voltage; A first diode having a cathode electrode connected to ground and an anode electrode connected to the other end of the secondary inductor of the coupled inductor; A first switch connected between the other end of the secondary inductor of the coupled inductor and ground to perform an on / off switching operation; A second capacitor connected between the other end of the primary inductor of the coupled inductor and a ground, and configured to charge or discharge a predetermined voltage; A second diode having a cathode electrode connected to the other end of the primary inductor of the coupled inductor and an anode electrode connected to the ground; And And a second switch connected between the other end of the coupled inductor and the ground of the coupled inductor to perform an on / off switching operation. The method of claim 15, In the surface light source driving circuit, four driving modes are sequentially and repeatedly operated according to on / off states of the first and second switches. The four driving modes A first driving mode in which the first switch is OFF and the second switch is ON; A second drive mode in which the first switch is OFF and the second switch is OFF; A third drive mode in which the first switch is ON and the second switch is OFF; and A surface light source driving circuit of a liquid crystal display device, wherein the first switch is OFF and the second switch is OFF. The method of claim 15, And a second voltage source for supplying a predetermined voltage across both of the source capacitors.

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