JP2007174881A - Inverter circuit, backlight device, and liquid crystal display device made thereby - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inverter circuit which maintains energy efficiency and ensures less power consumption even with multiple cold-cathode tubes, a backlight device, and a liquid crystal display device made thereby. <P>SOLUTION: An inverter circuit 150 has an inverter transformer 156, and a frequency adjustment means provided to a primary side of the inverter transformer 156. A backlight device 120 comprises this inverter circuit 150, and multiple cold-cathode tubes 122 connected in parallel to the inverter transformer 156 of this inverter circuit. A liquid crystal display device comprises this backlight device 120, a liquid crystal panel, a display unit with data and gate circuits to be connected to this liquid crystal panel, a container storing the display unit and backlight device, and a top chassis. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inverter circuit that can be suitably used in a backlight device having a cold cathode tube, and relates to a backlight device using the inverter circuit, and further to a liquid crystal display device.

  In general, a liquid crystal display device has excellent characteristics such as low voltage drive, low power consumption, light weight, and thinness, and is widely used as a display device for a monitor device, a television receiver, etc. in a personal computer. The demand for computerization is increasing.

  A liquid crystal display device generally includes a backlight device and a display unit disposed in front of the backlight device, the backlight device supplies light to the display panel, and the display unit is a backlight unit. The light supplied from the light device is modulated and displayed as an image.

  Generally, the backlight device includes a reflector, a light source, and an optical sheet, and can supply light to the display unit by applying a current to the light source.

By the way, when a cold cathode tube is used as the light source of the backlight device, an inverter circuit having an inverter transformer is used to light the cold cathode tube. In general, one cold cathode tube is often lit by one transformer. However, as a liquid crystal display device has a large screen, it is necessary to light a plurality of cold cathode tubes in parallel. As a conventional technique, Patent Document 1 below discloses a discharge lamp lighting device in which a plurality of discharge lamps are connected in parallel on the output side of an inverter. In the technique described in Patent Document 1 below, a current detecting means, a switch capable of shutting off power supply, and a variable resistor for adjusting an input voltage to the inverter are further provided between one end and the other end on the output side of the inverter. Further, lighting control means for adjusting on / off of the switch and the resistance in the variable resistance unit is provided.

JP 2002-31593 A

  Certainly, in the prior art described above, since a plurality of discharge lamps are connected and shared with one inverter transformer, the circuit scale can be reduced, and one discharge lamp has an abnormality. It is also useful in preventing the chain of lighting abnormalities.

However, with the above technology, there remains a problem in a decrease in energy efficiency due to an increase in the number of discharge lamps. Specifically, for example, when driving one single discharge lamp serving CCFL inverter transformer, if the equivalent capacitance of the CCFL and C _S, Q value at the resonance frequency ω is represented by the following formula ( Given in 1).
[Equation 1]
Q = 1 / (ωRC _S ) (1)
(Where R is the equivalent resistance of the circuit)

On the other hand, when driving a plurality of cold-cathode tubes with one inverter transformer, assuming that the number of cold-cathode tubes is N, the Q _N value at the resonance frequency ω is given by the following equation (2).
[Equation 2]
Q _N = 1 / (ωRC _S N) (2)

  That is, as the N increases, the Q value at the resonance frequency ω decreases to 1 / N. On the other hand, generally, when the Q value decreases, the energy of resonance decreases, the shape of the sine wave at the resonance point collapses, harmonic current flows through the cold cathode tube, loss that does not contribute to light emission increases, and energy efficiency decreases. .

  Accordingly, the present invention provides an inverter circuit, a backlight device, and a liquid crystal display device using the same, which solve the above problems, maintain energy efficiency, and consume less power even when having a plurality of cold cathode tubes. The purpose is to do.

  As a result of intensive studies on the above problems, the present inventors can adjust the resonance frequency of the entire circuit by providing a frequency adjusting means on the drive primary side of the inverter transformer in order to prevent the shape of the sine wave from collapsing. In view of the above, the present inventors have focused on the point that the Q value can be increased.

  That is, the backlight device according to the present invention includes an inverter circuit having an inverter transformer, and a plurality of cold cathode tubes connected in parallel to the inverter transformer in the inverter circuit. The inverter circuit is disposed on the drive primary side of the inverter transformer. A frequency adjusting means is provided. Here, it is preferable that the frequency adjusting means is realized by using a choke coil and a capacitor. By doing so, the present invention can adjust the resonance frequency of the entire circuit, can increase the Q value at the resonance frequency, and can further suppress an increase in power consumption.

  In the backlight device according to the present invention, it is also desirable that there are a plurality of inverter transformers in the inverter circuit. For example, a mode in which currents in opposite phases flow by connecting adjacent cold cathode tubes to different inverter transformers is also possible.

  In the backlight device according to the present invention, when the frequency adjusting means is realized by a choke coil and a capacitor, it is also desirable that these are connected in series.

  In the backlight device according to the present invention, it is also desirable to have a balance circuit connected to each of the plurality of cold cathode tubes in order to keep the current of each cold cathode tube in a more balanced state.

  In addition, the liquid crystal display device according to the present invention can maintain low power consumption as a whole by using the above backlight device. Specifically, a liquid crystal panel, a data circuit connected to the liquid crystal panel, and Display unit having gate circuit, inverter transformer, inverter circuit having frequency adjusting means on drive primary side of inverter transformer, backlight device having a plurality of cold cathode tubes connected in parallel to inverter transformer in inverter circuit, and display It has a storage container and a top chassis which store a unit and a back light device. Here, it is preferable that the frequency adjusting means is realized by using a choke coil and a capacitor. By doing so, the present invention can adjust the resonance frequency of the entire circuit, can increase the Q value at the resonance frequency, and can further suppress an increase in power consumption.

  In the liquid crystal display device according to the present invention, it is also desirable that there are a plurality of inverter transformers in the inverter circuit. For example, a mode in which currents in opposite phases flow by connecting adjacent cold cathode tubes to different inverter transformers is also possible.

  In the liquid crystal display device according to the present invention, when the frequency adjusting means is realized by a choke coil and a capacitor, it is also desirable that these are connected in series.

  In the liquid crystal display device according to the present invention, it is also desirable to have a balance circuit connected to each of the plurality of cold cathode tubes in order to keep the currents of the cold cathode tubes more balanced.

  In addition, the inverter circuit according to the present invention can perform the above function in combination with a plurality of cold cathode fluorescent lamps, but even if it is only an inverter circuit, it is distributed as a component such as a liquid crystal display device or a backlight device in the market. A specific configuration is characterized in that an inverter transformer and frequency adjusting means are provided on the drive primary side of the inverter transformer. Here, it is preferable that the frequency adjusting means is realized by using a choke coil and a capacitor. In this way, the present invention makes it possible to adjust the resonance frequency of the entire circuit of a plurality of cold-cathode tubes connected in parallel, increase the Q value at the resonance frequency, and further increase the power consumption. It will be possible to suppress.

  In the inverter circuit according to the present invention, it is also desirable that there are a plurality of inverter transformers. For example, it is possible to correspond to a mode in which currents in opposite phases are caused to flow by connecting adjacent cold cathode tubes to different inverter transformers in a plurality of cold cathode tubes connected thereto.

  In the inverter circuit according to the present invention, when the frequency adjusting means is realized by a choke coil and a capacitor, it is also desirable that these are connected in series.

  As described above, according to the present invention, a backlight device that maintains high energy efficiency and consumes less power even in the case of having a plurality of cold cathode tubes, a liquid crystal display device using the backlight device, and this backlight device An inverter circuit for realizing this can be provided.

  Embodiments of the present invention will be described below with reference to the drawings. However, the present invention can be implemented in many different modes and should not be construed as being limited to the description of the embodiments described below. Note that in the drawings referred to in this embodiment, the same portions or portions having similar functions are denoted by the same reference numerals, and repetitive description thereof is omitted.

(Embodiment 1)
FIG. 1 is an exploded perspective view of a liquid crystal display device according to the present embodiment (hereinafter referred to as “the present liquid crystal display device”).

  As shown in FIG. 1, the liquid crystal display device 100 includes a display unit 110, a backlight unit 120, a storage container 130 for storing them, and a top chassis 140.

  The display unit 110 further includes a liquid crystal display panel 111 that displays an image, a data circuit 112 that provides a drive signal for driving the liquid crystal display panel 111, and a gate circuit 113. The data circuit 112 and the gate circuit 113 are electrically connected to the liquid crystal display panel 111 through the data circuit tape substrate 114 and the gate circuit tape substrate 115, respectively.

  The liquid crystal display panel 111 further includes a thin film transistor (hereinafter referred to as “TFT”) substrate 116, a color filter (hereinafter referred to as “CF”) substrate 117 disposed opposite to the TFT substrate 116, and a gap between these substrates. The liquid crystal is arranged.

  The TFT substrate 116 is not particularly limited as long as a TFT and an electrode can be formed. For example, a transparent glass substrate can be preferably used, and a plurality of gate electrodes, A plurality of data electrodes arranged crossing the gate electrode and a plurality of TFTs arranged near the intersections of the gate electrode and the data electrode and connected to the gate electrode and the data electrode, And at least a pixel electrode provided to be connected to each other. Note that the common electrode provided corresponding to the pixel electrode may be formed on the TFT substrate 116 or the CF substrate 117.

  Similarly to the TFT substrate 116, the CF substrate 117 is not particularly limited as long as the CF can be formed. For example, a transparent glass substrate can be preferably used. In the CF formed on the CF substrate, an organic layer containing a dye that transmits one of red (R), green (G), and blue (B) is disposed corresponding to each pixel electrode of the TFT substrate. This can be achieved. In the liquid crystal display device 100, the backlight unit 120 is installed on the back surface, and the light from the backlight device is adjusted using an optical change by the liquid crystal display panel and displayed as an image. Therefore, the TFT substrate 116 and the CF substrate 117 It is a desirable mode that both are transparent substrates.

  The storage container 130 is configured to include a bottom surface 131 and a side wall 132 provided at an end of the bottom surface 131, and stores the display unit 110, the backlight device 120, and the like. The storage container 130 is fitted to the top chassis 140 to fix the display unit 110 and the like stored therein and prevent damage due to external impact.

  FIG. 2 is an exploded perspective view of the backlight unit 120 in the liquid crystal display device 100.

  The backlight unit 120 includes a reflecting plate 121, a plurality of cold cathode tubes 122 arranged substantially in parallel on the reflecting plate 121, and an optical sheet 123 arranged above the plurality of arranged cold cathode tubes. The first electrode 153 connected to the plurality of cold cathode tubes 122 and the plurality of second electrodes 154 provided in each of the plurality of cold cathode tubes. A plurality of cold-cathode tubes in the backlight unit are electrically connected in parallel to form a circuit on the backlight unit side. The plurality of second electrodes 154 are formed on the electrode substrate 155, and a balance circuit described later is formed on the electrode substrate 155.

  Further, an inverter circuit 150 is connected to the backlight unit 120, and the inverter circuit 150 is disposed outside the storage container 130. The inverter circuit 150 generates a discharge voltage for driving the backlight unit 120, and applies a voltage to the backlight unit 120 through the first power supply application line 151 and the second power supply application line 152. Specifically, the first power supply line 151 and the second power supply line 152 are connected to the first electrode 153 and the electrode substrate 155 formed on both sides of the backlight unit 120, respectively. Note that it is possible to appropriately provide at least a part of the inverter circuit 150 side on the backlight unit side. In this specification, in principle, the term “inverter circuit” refers to a circuit that controls the backlight unit in the entire inverter circuit, and the term “backlight device” refers to the control of the backlight unit in the inverter circuit. It shall include the circuit and the backlight unit.

  The optical sheet 123 is provided to improve the characteristics of the light supplied from the backlight device 110. The optical sheet 123 may be a diffusion sheet for diffusing light. It may be a prism sheet for condensing light. The number of cold cathode tubes 122 in the backlight device 120 is not particularly limited, but is preferably 10 or more, more preferably 14 or 16.

  FIG. 3 is a functional block diagram of the liquid crystal display device. As described above, in the present liquid crystal display device, the AC voltage supplied from the external power source is applied to the cold cathode tube 122 via the inverter circuit. The inverter circuit 150 also applies a gate voltage or the like to the gate electrode, the data electrode, and the common electrode in the display unit 110 (however, illustration is omitted).

  FIG. 4 is a functional block diagram of the backlight device according to the present embodiment, and is a diagram for explaining details of the backlight device in FIG.

  The backlight device includes an inverter circuit 150 and a circuit on the backlight side including a plurality of cold cathode tubes 122 connected in parallel to the inverter circuit. The inverter circuit 150 includes a power source, an inverter transformer 156, a capacitor 157 and a choke coil 158 provided on the drive primary side of the inverter transformer 156. Here, the power supply can adopt various known configurations that can generate an alternating current, and is not particularly limited (thus, details are omitted). The circuit on the backlight unit side is connected in series with each of the cold cathode tubes 122 on the side opposite to the side connected to the inverter transformer of the plurality of cold cathode tubes 122 and the plurality of cold cathode tubes. And a balance circuit 124 connected to the. In the present backlight device, by arranging the balance circuit 124, the currents of the respective cold cathode tubes can be kept in balance. An example of an equivalent circuit diagram in a part of the balance circuit according to the present embodiment is shown in FIG.

  The balance circuit shown in FIG. 5 includes a plurality of balance transformers 125, and one of the coils in each of the plurality of balance transformers 125 is connected to each adjacent cold cathode tube 122. On the other hand, the other coil is connected in series with another balance transformer to form a circuit and is grounded. By doing in this way, this balance circuit can keep the current between cold-cathode tubes in balance. Various configurations of the balance circuit are also conceivable.

  As described above, the circuit on the backlight unit side functions as a resonance circuit due to the capacitance of the cold cathode tube, the resistance in the circuit, and the like, and can drive the cold cathode tube with a sinusoidal voltage current through the inverter transformer. On the other hand, in the backlight device according to this embodiment, the capacitor 157 and the choke coil 158 are arranged on the inverter circuit side, and therefore the frequency can be adjusted by appropriately adjusting the constants. That is, as a result, the Q value can be increased, the shape of the sine wave with the harmonic current suppressed at the resonance point can be maintained, the reactive current of the resonance circuit can be suppressed, and the efficient light emission efficiency can be achieved. Power consumption can be reduced. The capacitor is not particularly limited as far as its function is concerned. For example, the capacitor may have a fixed capacity based on a constant obtained when the backlight unit is manufactured, and can be adjusted as needed. The capacity may be variable so that From the viewpoint of frequency adjustment, it is also extremely useful to have a configuration in which the winding direction on the drive primary side of the inverter transformer and the winding direction of the choke coil are connected in opposite directions. As described above, the current value used in the backlight device, the capacitance of the capacitor, and the like can be appropriately adjusted to achieve a desired frequency. For example, the amplitude of the voltage in the inverter circuit is About ± 150 to 200 V, the voltage value in the circuit on the backlight unit side is about ± 1 kV, and the capacitance of the capacitor is preferably about 5 nF to 100 nF. Further, the inductance of the choke coil is preferably about 100 μH to 700 μH.

  As described above, according to the present embodiment, the backlight device that maintains high energy efficiency and consumes less power even when having a plurality of cold cathode tubes, the liquid crystal display device using the backlight device, and the backlight An inverter circuit for realizing the device can be provided.

(Embodiment 2)
FIG. 6 is a functional block diagram of the backlight device according to the present embodiment.
The liquid crystal display device according to the present embodiment is substantially the same as the liquid crystal display device described in the first embodiment, but the circuit configuration of the backlight device is different. More specifically, in the first embodiment, a plurality of cold-cathode tubes are connected in parallel to one inverter transformer and configured as one resonance circuit, whereas in this embodiment, two inverters It is characterized in that it has a transformer, and each of the plurality of cold cathode tubes is connected to an inverter transformer different from the adjacent cold cathode tubes, thereby constituting two resonance circuits. Specifically, in the backlight device according to the present embodiment, the inverter circuit 150 is connected in parallel to a power source, a frequency conversion unit having a capacitor 157 and a choke coil 158 connected to the power source, and the frequency conversion unit. And two inverter transformers 156. As described above, the present embodiment can provide the same effects as those of the first embodiment. In this case, the number of cold cathode tubes connected to the inverter transformer is preferably the same from the viewpoint of current uniformity. When two inverter transformers are provided, the total number of cold cathode tubes may be an even number. preferable. An equivalent circuit diagram in some examples of the balance circuit according to the present embodiment is also shown in FIG.

  The balance circuit shown in FIG. 7 includes a plurality of balance transformers 125, as in the first embodiment, and one of the coils in each of the plurality of balance transformers 125 is connected to the adjacent cold cathode tube 122, respectively. Has been. On the other hand, the other side of the coil is connected in series with another balance transformer to form a circuit and is grounded, but a balance transformer of cold cathode tubes connected to the same inverter transformer is connected to form two circuits. It has become. By doing in this way, this balance circuit can keep the current between cold-cathode tubes in balance.

  As described above, according to the present embodiment as well, a backlight device that maintains high energy efficiency and consumes less power even when having a plurality of cold cathode fluorescent lamps, a liquid crystal display device using the backlight device, and further this backlight device An inverter circuit for realizing the above can be provided.

  In this embodiment, since the conditions such as the number of cold cathode tubes are the same, an example in which one frequency conversion means is arranged for a plurality of inverter transformers is shown. However, as an application example of this embodiment, A configuration in which one frequency conversion means is arranged for each inverter transformer and the frequency is individually adjusted is also possible. In this way, finer adjustment is possible, and a backlight device that is more energy efficient and consumes less power can be realized.

(Embodiment 3)
FIG. 8 is a functional block diagram of the backlight device according to the present embodiment.
The liquid crystal display device according to the present embodiment is substantially the same as the liquid crystal display device described in the second embodiment, but the circuit configuration of the backlight device is different. More specifically, in the second embodiment, two inverter transformers are provided, and each of the plurality of cold cathode tubes is connected to an inverter transformer different from the adjacent cold cathode tubes, and two resonant circuits are provided. In contrast to this, in the present embodiment, there is one inverter transformer, but there is one drive primary coil, two secondary coils, and a common drive primary coil. The point is different. By doing in this way, the same effect as Embodiment 2 can be acquired. In particular, according to the present embodiment, since the inverter transformer can be realized by one, there is an advantage that downsizing can be achieved. In this case, the number of cold cathode tubes in each resonance circuit is preferably the same, and as a result, the total number of cold cathode tubes is preferably an even number. Note that the equivalent circuit diagrams in some examples of the balance circuit according to the present embodiment can be the same as those in the second embodiment. That is, it can be the same as FIG.

  As described above, according to the present embodiment as well, a backlight device that maintains high energy efficiency and consumes less power even when having a plurality of cold cathode fluorescent lamps, a liquid crystal display device using the backlight device, and further this backlight device An inverter circuit for realizing the above can be provided.

  As described above, the backlight device according to the present invention can be suitably used for a liquid crystal display device. The liquid crystal display device is useful as a display device such as a monitor device in a personal computer, a television receiver, and the like, and the inverter circuit is useful as these components. Therefore, the present invention has industrial applicability. .

1 is a developed perspective view of a liquid crystal display device according to Embodiment 1. FIG. 1 is an exploded perspective view of a backlight device according to Embodiment 1. FIG. 3 is a functional block diagram of the liquid crystal display device according to Embodiment 1. FIG. 1 is a schematic diagram of an equivalent circuit of a backlight device according to Embodiment 1. FIG. 3 is an equivalent circuit diagram of a balance circuit of the backlight device according to Embodiment 1. FIG. 6 is a schematic diagram of an equivalent circuit of a backlight device according to Embodiment 2. FIG. 6 is an equivalent circuit diagram of a balance circuit of a backlight device according to Embodiment 2. FIG. 6 is a schematic diagram of an equivalent circuit of a backlight device according to Embodiment 3. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Liquid crystal display device 110 ... Display unit 111 ... Liquid crystal display panel 112 ... Data circuit 113 ... Gate circuit 114 ... Tape substrate for data circuits 115 ... Tape substrate for gate circuits 116 ... TFT substrate 117 ... CF substrate 120 ... Backlight unit 121 Reflector 122 ... Cold cathode tube 123 ... Optical sheet 124 ... Balance circuit 130 ... Storage container 131 ... Bottom surface 132 ... Side wall 140 ... Top chassis 150 ... Inverter circuit 151 ... First power supply line 152 ... Second power supply line 153 ... 1st electrode 154 ... 2nd electrode 155 ... Electrode substrate 156 ... Inverter transformer 157 ... Capacitor 158 ... Choke coil

Claims (14)

  An inverter circuit comprising an inverter transformer and frequency adjusting means on a drive primary side of the inverter transformer.   The inverter circuit according to claim 1, wherein there are a plurality of inverter transformers.   The inverter circuit according to claim 1, wherein the frequency adjusting unit includes a choke coil and a capacitor.   4. The inverter circuit according to claim 3, wherein the choke coil and the capacitor are connected in series. An inverter circuit having an inverter transformer, and a backlight device having a plurality of cold cathode tubes connected in parallel to the inverter transformer in the inverter circuit,
The inverter circuit is provided with a frequency adjusting means on the drive primary side of the inverter transformer.   6. The backlight device according to claim 5, wherein there are a plurality of inverter transformers in the inverter circuit.   The backlight device according to claim 5, wherein the frequency adjusting unit includes a choke coil and a capacitor.   The backlight device according to claim 7, wherein the choke coil and the capacitor are connected in series.   The backlight device according to claim 5, further comprising a balance circuit connected to each of the plurality of cold cathode tubes. A liquid crystal panel, a display unit having a data circuit and a gate circuit connected to the liquid crystal panel, and
An inverter transformer, an inverter circuit having frequency adjusting means on the drive primary side of the inverter transformer, a backlight device having a plurality of cold cathode tubes connected in parallel to the inverter transformer in the inverter circuit;
A liquid crystal display device comprising: a storage container for storing the display unit and the backlight device; and a top chassis.   The liquid crystal display device according to claim 10, wherein there are a plurality of inverter transformers in the inverter circuit.   The liquid crystal display device according to claim 10, wherein the frequency adjusting unit includes a choke coil and a capacitor.   The liquid crystal display device according to claim 10, wherein the choke coil and the capacitor are connected in series.   12. The liquid crystal display device according to claim 10, further comprising a balance circuit connected to each of the plurality of cold cathode tubes.

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