JP2008287128A - Lighting display device of fluorescent lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lighting display device of a fluorescent lamp with which the length of the fluorescent lamp can be shortened even when used for a large screen and contrast distribution of a screen can be controlled by decreasing lighting voltage as much as possible to reduce breakdown voltage of an inverter, a terminal, or the like. <P>SOLUTION: The lighting display device is provided with a liquid crystal display panel, quadrangular light source modules B1, B2,... in each of which a plurality of fluorescent lamps are arranged and a polarity switching circuit driving the light source modules B1, B2,... by outputting AC driving voltage having a prescribed frequency, wherein the plurality of light source modules B1, B2,... are prepared and the plurality of light source modules B1, B2,... are disposed so that the light source modules are combined with one another and opposed to the whole rear surface of the liquid crystal display panel. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fluorescent lamp lighting display device capable of lighting a plurality of fluorescent lamps serving as a backlight of a large screen.

As a backlight of various display devices such as a liquid crystal display device, a cold cathode fluorescent tube, which is a kind of fluorescent lamp, is used. Conventionally, a high-frequency lighting method using an inverter has been employed for driving the cold cathode tubes.
FIG. 10 is a circuit diagram showing a conventional high-frequency drive circuit. This high frequency drive circuit includes an inverter circuit 21 for supplying high frequency AC power of several tens of kHz, a main transformer 31, and a plurality of cold cathode tubes having one end connected to the output line of the main transformer 31. 70 and a current equalizing circuit 601 composed of a plurality of transformers, which are connected to the other ends of the plurality of cold cathode tubes 70 and flow an equal current to each of the cold cathode tubes 70.

FIG. 11 shows waveforms at various parts of the high-frequency drive circuit of FIG. FIG. 11A shows a DC input voltage input to the inverter 2. FIG. 11B shows the waveform of the output voltage of the inverter 2, that is, the primary voltage of the main transformer 31. FIG. 11C shows the waveform of the high-frequency voltage on the secondary side of the main transformer 31.
In a liquid crystal display device to which such a high-frequency driving circuit is applied, a cold cathode tube having a length substantially equal to the horizontal width of the display screen is usually used and is installed in the horizontal direction.
JP 2000-294391 A

  For this reason, the length of the cold cathode tube becomes longer as the display screen becomes larger. When the length of the cold cathode tube is increased, not only the cost of the cold cathode tube is increased, but also the lighting voltage is increased, and the withstand voltage of the inverter circuit 21 and the main transformer 31 must be increased. A connector with a high withstand voltage is also required. Thus, the difficulty in design increases. For example, the limit length of current cold cathode tubes that can be manufactured is 1500 mm, and the 1500 mm cold cathode tube lighting voltage is required to be 2000 V or higher and the lighting start voltage is required to be 2500 V or higher. It will be subject to big restrictions.

  Further, high-frequency current leaks due to the parasitic capacitance between the cold cathode tube and the metal plate supporting the cold cathode tube, the parasitic capacitance between the cold cathode tube and the inverter circuit 21 and the main transformer 31, and the parasitic capacitance between the wirings. The brightness distribution of the tube varies. In particular, the tendency becomes stronger as the lighting voltage becomes higher. In particular, the installation location of the inverter circuit 21 and the main transformer 31 is important, and the side of the cold-cathode tube close to the inverter circuit 21 (either the left or right side of the screen) is bright, and conversely, it is dark at the opposite distant position.

Therefore, it is necessary to minimize the variation in brightness between the left and right sides of the liquid crystal screen. To that end, measures such as the addition of an auxiliary light source that ignores energy savings and the twin inverter method that increases costs have been taken, but more effective solutions are required.
By reducing the length of the fluorescent lamp even on a large screen, the present invention reduces the lighting voltage as much as possible, lowers the withstand voltage of the inverter and terminals, etc., and can control the brightness distribution of the screen, thereby reducing the cost. An object of the present invention is to provide a fluorescent lamp lighting display device.

  A fluorescent lamp lighting display device according to the present invention includes a liquid crystal display panel, a light source module in which a plurality of fluorescent lamps are arranged, and a polarity switching circuit that drives the light source module by outputting an AC drive voltage having a predetermined frequency. The plurality of light source modules are prepared, the light source modules are combined, and the plurality of light source modules are arranged so as to face the entire back surface of the liquid crystal display panel.

With this fluorescent lamp lighting display device, a short tube fluorescent lamp capable of lowering the lighting voltage can be disposed in the light source module, and a plurality of the light source modules can be prepared to constitute a large backlight. . Since the lighting voltage can be lowered, the withstand voltage of the inverter and the terminal can be lowered and the cost can be reduced.
The output frequency of the polarity switching circuit is preferably a frequency exceeding 0 Hz and 10 kHz or less, and more preferably a frequency exceeding 0 Hz and 1 kHz or less.

  By performing low-frequency lighting in this way, parasitic capacitance can be reduced, so that there is no restriction on the installation location of the inverter. In addition, since the parasitic capacitance between the wirings is reduced, the degree of freedom in wiring is increased. Further, the cold cathode tube can be brought close to a metal plate that supports the cold cathode tube. Therefore, it is possible to meet the user's desire to make the display device small, light, and thin, and it is possible to realistically cope with an increase in the size of the display screen (energy saving, low cost, reduction in thickness and weight).

  Further, the drive current of each light source module can be individually controlled by using each light source module as a matrix element of the display screen. For example, by increasing the current of the light source module at the center of the screen to make it brighter, the image effect of a large screen can be maximized, and the current of the light source module pixels that may be dark such as the periphery of the screen is reduced to increase the current. Energy saving effect can be achieved.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is an exploded view showing a fluorescent lamp lighting display device of the present invention. This display device includes a display device body 101 on which m rectangular light source modules B1, B2,..., Bm (m ≧ 2) and a liquid crystal panel 102 that supports a liquid crystal display unit 103 are provided. . The light source modules B1, B2,..., Bm are referred to as “light source modules Bi”. The light source module Bi is a small rectangular panel in which n (n ≧ 2) cold cathode tubes 71... 7n are horizontally arranged.

  The liquid crystal display unit 103 has a horizontally long shape such as 4: 3, 16: 9, for example. The structure of the liquid crystal display unit 103 is a well-known structure. For example, the surface-side transparent substrate and the light source-side transparent substrate face each other. The liquid crystal driving method may be a passive matrix type or an active matrix type. Taking the active matrix type as an example, a plurality of matrix-like transparent electrode groups are arranged on the inner surface of the transparent substrate on the front side, and the inner surface of the transparent substrate on the light source side is 1 so as to face the matrix-like transparent electrode group. A semi-transparent electrode is installed. Further, an alignment film made of a resin rubbed in a certain direction is formed on each electrode. Liquid crystal is sealed between the alignment films. In the case of color liquid crystal, a color filter layer is provided on the transparent substrate on the front side.

FIG. 2 is a perspective view showing the structure of the light source module Bi. The n cold cathode tubes 71... 7n are arranged in parallel to the longitudinal direction of the light source module Bi. Lead wires 9 are provided at the end portions of the cold cathode tubes 71... 7n, and these lead wires 9 are connected to the polarity switching circuit 5 through a current equalizing circuit 6 described later.
A plurality of these light source modules Bi are prepared and arranged in a matrix in the longitudinal (horizontal) direction and the longitudinal (vertical) direction, and the display device body 101 is configured as shown in FIG.

  FIG. 4 is a drive circuit diagram of the fluorescent lamp lighting display device main body 101. This drive circuit includes a main transformer 3 that boosts an AC voltage from an inverter 2 that converts a DC input into AC, a voltage doubler rectifier circuit 4 that doubles and rectifies an AC voltage output from the main transformer 3, and a rectifier. Polarity switching circuit 5 for switching the polarity of the direct current voltage, and light source modules Bi (B1, B2,... Bm) connected to the output lines (e) and (f) of the polarity switching circuit 5, respectively. It has.

Each light source module Bi is connected to a plurality (n) of cold-cathode tubes 71... 7n and one ends of the plurality of cold-cathode tubes 71. A current equalizing circuit 6 for flowing is provided.
The operation of this drive circuit will be described. First, AC power generated by the inverter 2 is supplied to the main transformer 3. The AC frequency of this AC power is a frequency at which sufficient conversion efficiency is obtained for the main transformer 3, and is usually several tens of kHz to several hundreds of kHz. If the frequency is too lower than this range, the main transformer 3 needs to be enlarged, and the entire device becomes large and heavy. When the frequency is higher than this range, the influence of the parallel capacitance generated inside the main transformer 3 becomes large, resonance occurs, and conversion efficiency decreases.

  Next, the AC voltage is boosted at a predetermined boosting ratio by the main transformer 3 having a predetermined winding number and winding ratio. Further, the voltage doubler rectifier circuit 4 performs rectification and boosting. Thereby, it is possible to obtain a DC voltage necessary for lighting the cold cathode tubes 71... 7n of each light source module Bi. In the present invention, the cold cathode tubes 71... 7n are installed for each light source module Bi, and the length of the cold cathode tubes 71... 7n is substantially equal to the length of the long side of the light source module Bi. ing. Therefore, the direct-current voltage required for lighting the cold cathode tube installed over the entire length of the liquid crystal panel 102 is usually about 1000 V to 2000 V. However, in the present invention, the length of the cold cathode tube is short, and therefore a fraction of that is required. Will be enough.

This direct current voltage is converted into alternating current by turning on and off the switching transistor of the polarity switching circuit 5. The control circuit 51 controls on / off of the switching transistor. The control circuit 51 controls on / off of each switching transistor by supplying an on / off signal to the gate of each switching transistor.
The range of the frequency f of the on / off signal may be more than 0 Hz and 20 kHz or less. If possible, more than 0 Hz and 10 kHz or less are preferable, and more preferably more than 0 Hz and 1 kHz or less.

  The current equalization circuit 6 is installed for each light source module Bi, and electronic circuits (constant current circuits) 61... 6n for obtaining a constant current using current flowing between the collector and the emitter of the transistor are connected to each light source module Bi. It is provided according to the number of cold cathode tubes 71. The cold cathode tubes 71... 7n and the constant current circuits 61. A series circuit of the cold cathode tubes 71... 7n and the constant current circuits 61... 6n (the number of the cold cathode tubes 71... 7n is as many) as two output lines (e), ( connected to f).

  As shown in FIG. 4, the npn type and the pnp type of the transistors of each constant current circuit 61... 6n are connected in parallel. In the case of the npn type, a resistor Ri (i = 1 to m) is connected between the emitter and the ground. The bases of the transistors are connected to each other in common. This common base voltage is expressed as Vb. Since the voltage across the resistor Ri is substantially equal to the voltage Vb, and the voltage Vb is common to each transistor, the voltage across the resistor Ri is substantially equal in each of the constant current circuits 61. For this reason, the currents flowing in the respective constant current circuits 61... 6n in one direction (from the collector of the npn transistor to the emitter) are substantially equal, and a constant current is obtained. The current flowing in the reverse direction (from the emitter to the collector of the pnp type transistor) is also equalized by the same action of the pnp type transistor, and a constant current is obtained.

As described above, the constant current is realized by using the constant current circuits 61... 6 n including the transistors, so that the size reduction and the weight reduction can be achieved as compared with the current equalization circuit 601 using a plurality of transformers as in the past. It becomes possible.
Moreover, the brightness | luminance of each light source module Bi is individually controllable by setting the value of resistance Ri separately for every light source module Bi. For example, by increasing the current of the current-equalizing circuit 6 of the light source module Bi in the center of the screen, the middle of the screen is brightened to maximize the video effect, and the current-equalizing circuit of the light source module which may be dark such as the periphery of the screen By reducing the current of 6, a large energy saving effect can be achieved.

  In order to control the illuminance (dimming) of each light source module Bi, there are a case where it is based on an image signal and a case where the brightness of the screen is sensed by an external sensor and the signal is fed back to each light source module Bi. As an external sensor, there are a method of monitoring brightness with a sensor that divides a liquid crystal screen (matrix) and a method of monitoring a remote control toward the liquid crystal screen.

FIG. 5 is a graph showing waveforms at various parts of the drive circuit of FIG.
FIG. 5A shows a DC input voltage input to the inverter 2. FIG. 5B is a waveform of the output voltage of the inverter 2, that is, the primary voltage of the main transformer 3. FIG. 5C shows the waveform of the secondary side voltage of the main transformer 3. The secondary side voltage of the main transformer 3 is boosted according to the turn ratio of the main transformer 3 with respect to the primary side voltage of the main transformer 3. FIG. 5D shows the output waveform of the voltage doubler rectifier circuit 4. This output voltage further rises above the secondary voltage of the main transformer 3, and at the same time is rectified into a pulsating flow. FIG. 5E shows an output waveform of the polarity switching circuit 5. The polarity switching circuit 5 switches the DC output rectified into a pulsating flow so as to be positive and negative alternately. This switched output current is supplied to each cold cathode tube 71. Of the switched signal time width of the output current, a positive signal is applied to the electrodes above the cold cathode tubes 71... 7n, and a negative signal is applied to the electrodes below the cold cathode tubes 71. Applied.

As described above, the range of the frequency f of the polarity switching circuit 5 exceeds 0 Hz and is 20 kHz or less. Preferably it is more than 0 Hz and 10 kHz or less, more preferably more than 0 Hz and 1 kHz or less.
Conventionally, the cold cathode fluorescent lamps 71... 7n are connected to the cold cathode fluorescent lamps 71. By turning on the light, it is possible to reduce the influence of stray capacitance generated between the cold cathode tubes 71... 7n of the light source module Bi and the cold cathode tubes 71. . Further, it is possible to reduce the influence of stray capacitance generated between the cold cathode tubes 71... 7n of each light source module Bi and the chassis of the light source module Bi that supports the cold cathode tubes 71.

Since the main transformer 3 can be driven at a high frequency regardless of the switching frequency f of the polarity switching circuit 5, the size of the main transformer 3 can be considerably reduced.
With the configuration of the drive circuit of the present invention as described above, the cold cathode tubes 71... 7n of the plurality of light source modules Bi can be lit at a low frequency with the frequency f.
Therefore, if this drive circuit is used for a backlight such as a fluorescent lamp lighting display device, the entire drive circuit can be reduced. In addition, lighting the cold cathode tube using low frequency can reduce the effect of stray capacitance, so the cold cathode tube and the chassis supporting it can be brought to infinity, and the thickness of the fluorescent lamp lighting display device The thickness can be reduced.

Moreover, the length of the fluorescent lamp of each light source module Bi can be shortened, and an increase in driving voltage can be suppressed. If the length of the fluorescent lamp is constant, the backlight can be further increased in size and a large screen can be realized.
Next, a second embodiment of the present invention will be described. FIG. 6 is a perspective view showing the structure of the light source module Bi according to this embodiment. The n cold cathode tubes 71... 7n are arranged perpendicular to the longitudinal direction of the light source module Bi. These light source modules Bi are arranged vertically and horizontally to constitute a display device main body 101 as shown in FIG. As a result, the light source of the display device main body 101 can be realized by the vertically installed cold cathode tubes 71.

When the cold cathode tubes 71... 7n are driven in a vertical state, the positive / negative signal width ratio of the drive signal is not positive and negative and the same width as described later with reference to FIG. It is even. This is to prevent the fluid substance (such as mercury) contained in the cold cathode tubes 71... 7n from collecting on one side due to gravity.
FIG. 8 is a graph showing waveforms of respective portions of the drive circuit of the lighting display device for a vertically placed cold cathode tube. The circuit diagram of the drive circuit is the same as that shown in FIG. 4, but the output waveform of the polarity switching circuit 5 is t _{1 with} a positive signal width and a negative signal width as shown in FIG. and it is referred to as t _2, more of t ₁ is greater than t _2. That is, the polarity switching time ratio t ₁ / (t ₁ + t ₂ ) is set to exceed 0.5. The optimum value of the polarity switching time ratio is such that the fluid substance (mercury etc.) contained in the cold cathode tubes 71... 7n is evenly distributed in the tube without being accumulated by gravity during steady lighting. It is good to decide. For example,
0.5 <t ₁ / (t ₁ + t ₂ ) ≦ 0.8
Select from the range. If it exceeds 0.8, the emission intensity of the cold cathode tubes 71... 7n will decrease (particularly the lower end will become dark). Therefore, preferably,
0.5 <t ₁ / (t ₁ + t ₂ ) ≦ 0.7
Select from the range of. In experiments under certain conditions, 0.6 was the optimum value.

In particular, at the time of starting after long-term storage, the fluid substance accumulates downward. Therefore, the value is set to a large value (for example, 0.7) only at the time of starting. The optimum value (for example, 0.6) may be set. This post-start time is preferably determined experimentally. For example, it takes about 1 to 5 minutes.
Thus, even if the cold cathode tubes 71... 7n are vertically arranged, it is possible to prevent the fluid substance in the tube from being biased by gravity by adjusting the polarity switching time ratio of the drive current.

Hereinafter, a circuit modification of the fluorescent lamp lighting display device will be described.
FIG. 9 is a circuit diagram showing another example of the current-equalizing circuit. In this current equalization circuit, a circuit 6a for flowing a constant current in one direction and a circuit 6b for flowing in the other direction are separated from each other and installed on both sides of the cold cathode tube. The operations of the constant current circuits 6a and 6b are the same as described with reference to FIG. According to this current equalization circuit, all npn transistors can be used, which is advantageous in terms of cost.

  Although the embodiment of the present invention has been described so far, it is needless to say that the present invention is not limited to the embodiment. For example, the voltage doubler rectifier circuit 4 rectifies and boosts the output of the main transformer 3. However, step-up and rectification may be separated, and step-up may be performed by a main transformer, and rectification may be performed by a simple rectifier circuit that is not a double voltage. Further, the circuit example of the current sharing circuit is not limited to those shown in FIGS. 4 and 9, and an arbitrary constant current circuit using a transistor may be used. Further, the present invention is not limited to the cold cathode tube used in the above embodiment, and can be applied to general fluorescent lamps.

It is an exploded view which shows the structure of the display apparatus using the fluorescent lamp of this invention. It is a perspective view which shows the structure of one light source module Bi. It is a block diagram of the display apparatus main body 101 which has arrange | positioned light source modules Bi in matrix form. It is a drive circuit diagram of the lighting display device of the fluorescent lamp of the present invention. It is a graph which shows the waveform of each part of the drive circuit concerning a 1st embodiment. It is a perspective view which shows the structure of light source module Bi which has arrange | positioned the fluorescent lamp vertically. It is a block diagram of the display apparatus main body 101 which has arrange | positioned light source modules Bi in matrix form. It is a graph which shows the waveform of each part of the drive circuit concerning a 2nd embodiment. It is a circuit diagram which shows the other example of a current equalization circuit. It is a circuit diagram which shows the conventional high frequency drive circuit. 11 is a graph showing waveforms at various parts of the high-frequency drive circuit of FIG. 10.

Explanation of symbols

2 Inverter 3 Main transformer 4 Voltage doubler rectifier circuit 5 Polarity switching circuit 6 Current equalizing circuit 61... 6 n Constant current circuit 71... 7 n Cold cathode tube 8 Chassis 9 Lead wire 51 Control circuit 101 Display device body 102 Liquid crystal panel 103 Liquid crystal Display section

Claims (4)

A liquid crystal display panel;
A light source module in which a plurality of fluorescent lamps are arranged;
A polarity switching circuit for driving the light source module by outputting an AC drive voltage of a predetermined frequency,
A plurality of the light source modules are prepared, the light source modules are combined, and the plurality of light source modules are arranged so as to face the entire back surface of the liquid crystal display panel. .   2. The fluorescent lamp lighting display device according to claim 1, wherein an output frequency of the polarity switching circuit is a frequency exceeding 0 Hz and not exceeding 10 kHz.   The lighting display device for a fluorescent lamp according to claim 2, wherein an output frequency of the polarity switching circuit is a frequency exceeding 0 Hz and 1 kHz or less.   2. The fluorescent lamp lighting display device according to claim 1, wherein the drive current of the polarity switching circuit can be individually controlled for each light source module.