KR20060011353A - A inverter for a liquid crystal display device - Google Patents

Abstract

The present invention relates to an inverter for a liquid crystal display device capable of minimizing the variation in resonance frequency by optimizing the capacitance, and an inverter for a liquid crystal display device outputting a driving voltage for driving a light source provided in a backlight of the liquid crystal display device. A power conversion unit for receiving a DC voltage and converting it into an AC voltage to supply to the primary side of the transformer; A plurality of capacitors having a parallel structure, connected between a primary side of the transformer and an output terminal of the power conversion unit; And a plurality of switches having a parallel structure, connected between each one end of each capacitor and the primary side of the transformer.

LCD, Inverter, Resonant Frequency, Lamp, Luminance, Transformer

Description

A inverter for a liquid crystal display device

1 is a circuit diagram of a conventional inverter for a liquid crystal display device

2 is a circuit diagram of an inverter for a liquid crystal display according to an embodiment of the present invention.

3A to 3D are views for explaining a change in capacitance according to the adjustment of the switch of FIG.

* Explanation of symbols on the main parts of the drawings

S1 to S4: First to Fourth Switch 210: Lamp

Q1 to Q4: First to fourth NMOS transistors 200: Power converter

A and B: 1st and 2nd node TF: transformer

222a: primary side 222b: secondary side

C1 to C5: First to fifth capacitors Vdc: Voltage power supply

Llk: Inductance

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to an inverter for a liquid crystal display device which can minimize variation in resonance frequency by optimizing capacitance.                         

In recent years, research on flat panel display devices has been actively conducted. Among them, liquid crystal display devices (LCDs), field emission display devices (FEDs), electro-luminescence display devices (ELDs), and PDPs (PDPs) Plasma Display Pannels).

Among them, LCD is the most widely used as a substitute for CRT (Cathode Ray Tube) for the use of mobile image display device because of the excellent image quality, light weight, thinness, and low power consumption, and mobile type such as monitor of notebook computer. In addition, it is being developed in various ways such as a monitor of a television and a computer for receiving and displaying broadcast signals.

As described above, although various technical advances have been made in order for the liquid crystal display device to serve as a screen display device in various fields, the task of improving the image quality as the screen display device has many advantages and disadvantages.

Therefore, in order to use a liquid crystal display device in various parts as a general screen display device, the key to development is how much high definition images such as high definition, high brightness, and large area can be realized while maintaining the characteristics of light weight, thinness, and low power consumption. It can be said.

Such a liquid crystal display device may be classified into a liquid crystal display panel displaying an image and a driving unit for applying a driving signal to the liquid crystal display panel, wherein the liquid crystal display panel has a space and is bonded to the first and second substrates. And a liquid crystal layer injected between the first substrate and the second substrate.                         

On the other hand, such a liquid crystal display device itself is non-luminescent, so a separate external light source for irradiating light is required.

In particular, in the case of a transmissive liquid crystal display, a separate dimming device that emits light and guides the back of the liquid crystal display panel, that is, a back light device is necessary.

The back light includes an edge type and a direct type.

In the direct type, a light emitting lamp is disposed on a flat surface. Since the shape of the light emitting lamp appears on the liquid crystal panel, the gap between the light emitting lamp and the liquid crystal display panel should be maintained, and light scattering means is disposed for the uniform distribution of light. There is a limit to thinning because it must be.

In addition, as the liquid crystal display panel becomes larger, the area of the light emitting surface of the backlight is also increased. When the direct type backlight is enlarged, the light emitting surface is not flat unless the light scattering means secures a sufficient thickness. For this reason, the thickness of the light scattering means must be sufficiently secured.

On the other hand, the edge type is to install a light emitting lamp on the outside and to distribute the light to the entire surface using a light guide plate, the light emitting lamp is installed on the side, there is a problem that the brightness is low because the light must pass through the light guide plate. In addition, high optical design and processing techniques for the light guide plate are required for uniform distribution of luminance.

Since the direct type and edge type have their disadvantages, the direct type backlight is mainly used in the liquid crystal display device where brightness is more important than the screen thickness, and the thickness such as a notebook PC or a monitor PC is important. In the liquid crystal display device, an edge type backlight is mainly used. The lamp provided in the backlight receives a voltage output from the inverter. The inverter rectifies alternating current into direct current, and converts it back into alternating current through a switching device.

Hereinafter, a conventional inverter for a liquid crystal display device will be described in detail with reference to the accompanying drawings.

1 is a circuit diagram of a conventional inverter for a liquid crystal display device.

As shown in FIG. 1, the conventional inverter receives a DC voltage and switches it at different points in time to convert the AC voltage into an AC voltage and an AC voltage output from the power converter 100. Transformer TF for transforming the supply to the lamp 110. Here, the power conversion unit 100 is a full bridge circuit, the first NMOS transistor Q1 and the second NMOS transistor Q2 having a source connected to the drain of the first NMOS transistor Q1. And a third NMOS transistor Q3 having a source connected to the source of the first NMOS transistor Q1, a source connected to the drain of the third NMOS transistor Q3, and the second NMOS transistor Q2. A fourth NMOS transistor Q4 having a drain connected to a drain of the first NMOS transistor Q4, and a first connected between a source and a drain of the first, second, third and fourth NMOS transistors Q1, Q2, Q3, and Q4, respectively. , Second, third and fourth diodes D1, D2, D3, and D4. Here, the voltage power supply Vdc connected between the source of the first NMOS transistor Q1 and the drain of the second NMOS transistor Q2 is connected, and the drain and the third of the first NMOS transistor Q1 are connected. The primary side 111a of the transformer TF is connected between the drain of the NMOS transistor Q3, and the first side 111a of the transformer TF is connected between the drain of the first NMOS transistor Q1. One capacitor C1 is connected. In addition, the second capacitor C2 and the lamp 110 are connected in parallel to the secondary side 111b of the transformer TF.

Meanwhile, reference numeral A, which has not been described, is a first in which a drain of the first NMOS transistor Q1, a source of the second NMOS transistor Q2, and one end of the primary side 111a of the transformer TF are commonly connected. Node B, which is not described, has a common drain in the third NMOS transistor Q3, the source of the fourth NMOS transistor Q4, and the other end of the primary side 111a of the transformer TF. The second node B is connected.

On the other hand, a fluorescent lamp 110 (hot cathode, cold cathode) is used as the lamp 110, the fluorescent lamp 110 is less heat generation than a heat radiation type lighting device such as an incandescent lamp, in the form of a line (line) It can be manufactured without length limitation, has a long life, and has various advantages to withstand frequent flashing. The cold cathode ray tube fluorescent lamp 110 having the above-mentioned advantages is characterized in that the ultraviolet rays generated when the electrons spaced across two electrodes (anode and cathode) spaced apart from each other by a high voltage collide with mercury. It is operated by a unique driving method that stimulates and generates visible light.

Referring to the operation of the conventional liquid crystal display inverter configured as described above in detail.

First, when power is applied to the liquid crystal display, a DC voltage of a predetermined level is output from the voltage power supply Vdc, and the DC voltage is applied to each switching element Q1, Q2, Q3, Q4 of the power conversion unit 100. ) Is converted into an AC level with alternating positive and negative DC voltages. To this end, the first NMOS transistor Q1 and the fourth NMOS transistor Q4 are turned on during the first period, and the second NMOS transistor Q2 and the third NMOS transistor Q3 are turned off. In this case, the voltage power source Vdc, the turned-on first NMOS transistor Q1, the first node A, the first capacitor C1, the primary side 111a of the transformer TF, and the A current loop consisting of the second node B and the fourth NMOS transistor Q4 is formed. Here, since the current flowing from the first node A to the second node B along the current loop has a positive polarity, the voltage between the first node A and the second node B is positive. Indicates.

Subsequently, the first NMOS transistor Q1 and the fourth NMOS transistor Q4 are turned off during the second period, and the second NMOS transistor Q2 and the third NMOS transistor Q3 are turned on. do. In this case, the voltage power source Vdc, the third NMOS transistor Q3, the second node B, the primary side 111a of the transformer TF, the first capacitor C1, and the first node. A current loop consisting of (A) and the second NMOS transistor Q2 is formed. Here, since the current flowing from the first node A to the second node B along the current loop has negative polarity, the voltage between the first node A and the second node B is negative. Indicates. As described above, as the first and fourth NMOS transistors Q1 and Q4 and the second and third NMOS transistors Q2 and Q3 are alternately turned on and off, the first node. The voltage between (A) and the second node (B) alternately has positive and negative polarities every cycle. Subsequently, an AC level voltage applied between the first node A and the second node B of the primary side 111a of the transformer TF is transmitted to the secondary side 111b of the transformer TF. The AC level voltage transmitted to the secondary side 111b is supplied to the lamp 110 to emit the lamp 110.

On the other hand, the voltage output from the inverter configured as described above (voltage output from the secondary side 111b of the transformer TF) is changed by the variation of the resonance frequency, the change of the voltage is the brightness of the lamp 110 Will change. The resonant frequency is generated by a combination of the inductance Llk component inherent in the transformer TF and the capacitance component of the first capacitor C1, and the inductance Llk component of the transformer TF is the same transformer. (TF) has different values. In general, the tolerance of the inductance Llk of the transformer TF is about 25%. However, when the transformer Tf exceeds the tolerance, the deviation of the resonance frequency of the transformer TF increases, whereby the deviation of the voltage output from the inverter increases. This, in turn, causes a problem of deteriorating the quality of the image represented on the liquid crystal panel by changing the brightness of the lamp 110.

The present invention has been made to solve the above problems, to provide an inverter for a liquid crystal display device which can minimize the luminance difference of the lamp by connecting a plurality of capacitors in parallel, and by optimizing the capacitance of the capacitors through a switch. The purpose is.

Inverter for liquid crystal display device according to the present invention for achieving the above object, in the inverter for liquid crystal display device for outputting a driving voltage for driving a light source provided in the backlight of the liquid crystal display device, receiving a DC voltage A power conversion unit converting the AC voltage to supply the primary side of the transformer; A plurality of capacitors having a parallel structure, connected between a primary side of the transformer and an output terminal of the power conversion unit; And a plurality of switches having a parallel structure connected between each one end of each capacitor and the primary side of the transformer.

Hereinafter, an inverter for a liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

2 is a circuit diagram of an inverter for a liquid crystal display according to an embodiment of the present invention.

In the inverter for the liquid crystal display according to the exemplary embodiment of the present invention, as shown in FIG. 2, the power converter 200 which receives a DC voltage, converts the AC voltage, and supplies the DC voltage to the primary side 222a of the transformer TF. ), A plurality of capacitors C1, C2, C3 having a parallel structure, connected between the primary side 222a of the transformer TF and the output terminal of the power conversion unit 200, and each of the capacitors ( Switches S1, S2, S3 having a parallel structure, which are connected between each one end of C1, C2, C3 and the primary side 222a of the transformer, respectively. In addition, the inverter for liquid crystal display according to the embodiment of the present invention, at least any of the capacitors (C2, C2, C3) connected in parallel and connected in series through the switch (S2). One capacitor C4 is included.

Here, the power conversion unit 200 is a full bridge circuit, the first NMOS transistor Q1 and the second NMOS transistor Q2 having a source connected to the drain of the first NMOS transistor Q1. And a third NMOS transistor Q3 having a source connected to the source of the first NMOS transistor Q1, a source connected to the drain of the third NMOS transistor Q3, and the second NMOS transistor Q2. A fourth NMOS transistor Q4 having a drain connected to a drain of the first NMOS transistor Q4, and a first connected between a source and a drain of the first, second, third and fourth NMOS transistors Q1, Q2, Q3, and Q4, respectively. , Second, third and fourth diodes D1, D2, D3, and D4. Here, the voltage power supply Vdc connected between the source of the first NMOS transistor Q1 and the drain of the second NMOS transistor Q2 is connected, and the drain and the third of the first NMOS transistor Q1 are connected. The primary side 222a of the transformer TF is connected between the drains of the NMOS transistor Q3. The primary side 222a of the transformer TF is connected between the drain of the first NMOS transistor Q1 and the drain of the third NMOS transistor Q3, and the primary side 222a of the transformer TF is connected. ) And the capacitors C1, C2, C3, C4 and the switches S1, S2, S3 are connected between the first NMOS transistor Q1 and the drain of the first NMOS transistor Q1. In addition, the secondary side 222b of the transformer TF is connected in parallel with the capacitor C4 and the lamp 210.

Meanwhile, the non-described reference number A is a first node to which the drain of the first NMOS transistor Q1, the source of the second NMOS transistor Q2, and one end of the primary side 222a of the transformer TF are commonly connected. FIG. 2 is a second node in which the drain of the third NMOS transistor Q3, the source of the fourth NMOS transistor Q4, and the other end of the primary side 222a of the transformer TF are commonly connected. to be.

Here, a fluorescent lamp 210 (hot cathode, cold cathode) is used as the lamp 210, the fluorescent lamp 210 is less heat generation than a heat radiation type lighting device such as an incandescent lamp, in the form of a line (line) It can be manufactured without length limitation, has a long life, and has various advantages to withstand frequent flashing. In the cold cathode fluorescent lamp 210 having the above-described advantages, ultraviolet rays generated when electrons spaced across two electrodes (anode and cathode) spaced apart from each other by a high voltage collide with mercury, thereby absorbing the fluorescent material. It is operated by a unique driving method that stimulates and generates visible light.

An operation of the inverter for a liquid crystal display according to the exemplary embodiment of the present invention configured as described above will be described in detail.

First, when power is applied to the liquid crystal display, a DC voltage of a predetermined level is output from the voltage power supply Vdc, and the DC voltage is the first to fourth NMOS transistors Q1 to Q4 of the power conversion unit 200. And is switched to the AC level having alternating positive and negative DC voltages. To this end, the first NMOS transistor Q1 and the fourth NMOS transistor Q4 are turned on during the first period, and the second NMOS transistor Q2 and the third NMOS transistor Q3 are turned off. In this case, the voltage power source Vdc, the turned-on first NMOS transistor Q1, the first node A, the capacitors C1, C2, C3, C4, the switches S1, S2, A current loop consisting of S3 and S4, the primary side 222a of the transformer TF, the second node B, and the fourth NMOS transistor Q4 is formed. Here, since the current flowing from the first node A to the second node B along the current loop has a positive polarity, the voltage between the first node A and the second node B is positive. Indicates.                     

Subsequently, the first NMOS transistor Q1 and the fourth NMOS transistor Q4 are turned off during the second period, and the second NMOS transistor Q2 and the third NMOS transistor Q3 are turned on. do. In this case, the voltage power source Vdc, the third NMOS transistor Q3, the second node B, the primary side 222a of the transformer TF, the switches S1, S2, S3, and the A current loop consisting of capacitors C1, C2, C3, C4, the first node A, and the second NMOS transistor Q2 is formed. At this time, since the current flowing from the first node A to the second node B along the current loop has negative polarity, the voltage between the first node A and the second node B is negative. Indicates. As described above, as the first and fourth NMOS transistors Q1 and Q4 and the second and third NMOS transistors Q2 and Q3 are alternately turned on and off, the first node. The voltage between (A) and the second node (B) is converted into an alternating current level having alternating positive and negative polarities every cycle. Subsequently, an AC level voltage applied between the first node A and the second node B of the primary side 222a of the transformer TF is transmitted to the secondary side 222b of the transformer TF. The AC level voltage transmitted to the secondary side 222b is supplied to the lamp 210 to emit the lamp 210.

In the voltage device for a liquid crystal display device of the present invention configured as described above, it will be described how the magnitude of the total capacitance of the capacitor is changed by adjusting the switch.

3A to 3D are diagrams for describing a change in capacitance according to the adjustment of the switch of FIG. 2.                     

First, for convenience of description, a plurality of capacitors connected in parallel will be described as being divided into a first capacitor C1, a second capacitor C2, and a third capacitor C3, and are serially connected to the second capacitor C2. The capacitors connected to each other will be referred to as a fourth capacitor C4, and the switches will be referred to as a first switch S1, a second switch S2, and a third switch S3.

In addition, the inverter for the liquid crystal display device of the present invention configured as described above has a state in which only the first switch S1 is turned on by default, and the capacitances of the first to fourth capacitors C1 to C4 are all the same. Suppose you have a size. In this case, when a deviation occurs in the resonance frequency of the transformer TF, the variation of the resonance frequency may be minimized by adjusting the magnitude of the capacitance as follows.

That is, if the capacitance is to be maximized, as shown in FIG. 3A, the first, second, and third switches S1, S2, and S3 are all turned on. In addition, if the size of the capacitance is to be minimized, only the second switch S2 is turned on and the other switches are turned off, as shown in FIG. 3B. In addition, as shown in FIG. 3C, only one of the first switch S1 or the third switch S3 is turned on and the other switches are turned off, thereby causing a value between the maximum value and the minimum value. The magnitude of the capacitance can be adjusted to have. Of course, as shown in FIG. 3d, the first switch S1 and the second switch S2 are turned on, the third switch S3 is turned off, or the second switch ( By turning on S2) and the third switch S3 and turning off the first switch S1, the magnitude of the capacitance may be adjusted to have a value between the maximum value and the minimum value.

On the other hand, the inverter for the liquid crystal display of the present invention is configured using three switches (S1, S2, S3) and four capacitors (C1, C2, C3, C4), but the number of the switches and the number of the capacitors By configuring more, the deviation of the resonance frequency can be further minimized.

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, and it is common in the art that various substitutions, modifications, and changes can be made without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

As described above, the inverter for liquid crystal display according to the present invention has the following effects.

Inverter for liquid crystal display according to the present invention can adjust the magnitude of the capacitance by using a switch, it is possible to effectively minimize the deviation of the resonance frequency.

Claims (6)

In the inverter for liquid crystal display device for outputting a driving voltage for driving a light source provided in the backlight of the liquid crystal display device, A power conversion unit which receives a DC voltage and converts the AC voltage into a primary voltage of the transformer; A plurality of capacitors having a parallel structure, connected between a primary side of the transformer and an output terminal of the power conversion unit; And a plurality of switches having a parallel structure connected between each one end of each capacitor and the primary side of the transformer. The method of claim 1, The power converter includes a first NMOS transistor; A second NMOS transistor having a source connected to a drain of the first NMOS transistor; A third NMOS transistor having a source connected to a source of the first NMOS transistor; A fourth NMOS transistor having a source connected to the drain of the third NMOS transistor and a drain connected to the drain of the second NMOS transistor; And a diode connected between the source and the drain of the first, second, third and fourth NMOS transistors, respectively. The method of claim 2, And a primary side of the transformer is connected between the drain of the first NMOS transistor and the drain of the third NMOS transistor. The method of claim 3, wherein And the capacitors and the switches of the parallel structure are connected between the primary side of the transformer and the drain of the first NMOS transistor. The method of claim 4, wherein And any one of the capacitors connected in parallel and at least one capacitor connected in series through the switch. The method of claim 1, And a capacitor connected in parallel with the secondary side of the transformer, wherein the capacitor is connected in parallel with the light source.

Images