JP2008234865A - Lighting display device for vertical fluorescent lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lighting display device for a fluorescent lamp which shortens a length of a cold-cathode tube in spite of a laterally-long large screen. <P>SOLUTION: The lighting display device for a fluorescent lamp comprises: a polarity switching-over circuit 5 for outputting low frequency driving voltage with a designated frequency; a plurality of cold cathode tubes 71 to 7n connected with an output circuit of the polarity switching-over circuit 5 at one end; and a uniform flow circuit 6 made of a constant current circuits respectively connected with the other ends of the cold cathode tubes 71 to 7n so as to flow current equivalent to respective cold cathode tubes 71 to 7n. The cold cathode tubes 71 to 7n are arranged to be perpendicular in a longitudinal direction, and the polarity switching-over circuit 5 outputs the low frequency driving voltage having different time duration widths at a positive period and a negative period. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fluorescent lamp lighting display device capable of lighting a long and narrow fluorescent lamp.

A cold cathode fluorescent tube (Cold Cathode Fluorescent Tube), which is a type of fluorescent lamp, is used for backlights of various display devices such as liquid crystal display devices. Conventionally, a high-frequency AC lighting method using an inverter has been adopted for lighting driving of the cold cathode tube.
FIG. 7 is a circuit diagram showing a conventional high-frequency AC lighting device. This high-frequency AC lighting device 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 cathodes connected at one end to the output line of the main transformer 31. A tube 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 cold cathode tube 70, are provided.

The waveform of each part of the high frequency lighting device of FIG. 7 is shown in FIG. FIG. 8A shows a DC input voltage input to the inverter 2. FIG. 8B shows the waveform of the output voltage of the inverter 2, that is, the primary voltage of the main transformer 31. FIG. 8C shows the waveform of the high-frequency voltage on the secondary side of the main transformer 31.
JP 2000-294391 A

In a display device to which such a high-frequency lighting device is applied, the display screen is normally horizontally long, and the cold cathode tubes are horizontally installed in the horizontally long direction of the display screen.
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. In addition, it becomes difficult to maintain the degree of vacuum of the cold cathode fluorescent lamp. Thus, the difficulty in design increases.

  An object of the present invention is to provide a fluorescent lamp lighting display device that can shorten the length of a fluorescent lamp even on a large screen.

  A lighting display device for a vertical fluorescent lamp according to the present invention includes a polarity switching circuit that outputs a low-frequency driving voltage of a predetermined frequency, a plurality of fluorescent lamps connected to the output side of the polarity switching circuit, and each fluorescent lamp. Each of the plurality of fluorescent lamps and the constant current circuit are connected in series, and the plurality of fluorescent lamps are installed so that their longitudinal directions are perpendicular to each other. The polarity switching circuit outputs a low-frequency driving voltage having a different time width between a positive period and a negative period.

With this vertical fluorescent lamp lighting display device, even if a plurality of fluorescent lamps are installed vertically, the polarity switching circuit generates a low frequency drive voltage having a different time width between a positive period and a negative period. By outputting, it is possible to generate a force that electrically pulls up the fluid substance in the tube upward, and it is possible to prevent the fluid substance from being biased due to gravity.
Therefore, even if the fluorescent lamp is installed vertically, the fluid substance in the tube is not biased and uniform light emission is possible. In addition, the “sputtering phenomenon” in which only one of the electrodes is worn is less likely to occur. Therefore, the length of the fluorescent lamp can be shortened on a horizontally long screen, and an increase in driving voltage can be suppressed. If the length of the fluorescent lamp is constant, the backlight and the screen can be enlarged.

The ratio of the positive period to one cycle (referred to as polarity switching time ratio) is preferably more than 0.5 and 0.8 or less.
Moreover, it is preferable to set the polarity switching time ratio to a high value immediately after starting. This is because the fluid substance in the tube may be biased during long-term storage, so that it is desired to increase the homogenization speed after startup and to shorten the time until lighting is stabilized.

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 display device using the vertical fluorescent lamp of the present invention. This display device includes a display device body 101 on which cold cathode tubes 71... 7n are mounted, and a liquid crystal panel 102 that supports a liquid crystal display unit 103. The cold cathode tubes 71... 7n are vertically arranged (n ≧ 2) and vertically. Therefore, the length of the cold cathode tubes 71... 7 n is defined by the height H of the liquid crystal display unit 103. The liquid crystal display unit 103 has a horizontally long shape such as 4: 3, 16: 9, and the like, and the length of the cold cathode tubes 71... 7n is shortened compared to the case where the cold cathode tubes 71. be able to.

FIG. 2 is a circuit diagram of a lighting display device for a vertical fluorescent lamp according to the present invention.
This lighting device includes an inverter 2 that converts DC input into AC, a main transformer 3 that boosts an AC voltage from the inverter 2, and a voltage rectifier circuit that doubles and rectifies the AC voltage output from the main transformer 3. 4, a polarity switching circuit 5 for switching the polarity of the rectified DC voltage, and a plurality (n) of cold cathode tubes 71 respectively connected to the output lines (e) and (f) of the polarity switching circuit 5. .. 7n and a current equalizing circuit 6 connected to the other ends of the plurality of cold cathode tubes 71... 7n for flowing an equal current to each of the cold cathode tubes 71.

  The operation of this apparatus will be described. First, the DC input is converted into an AC frequency optimum for the main transformer 3 by switching of the switching transistor included in the inverter 2. This “optimal AC frequency for the main transformer 3” 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. As a result, it is possible to obtain a DC voltage necessary for lighting the cold cathode tubes 71. The “DC voltage required for lighting the cold cathode tubes 71... 7n” is usually about 1000 V to 2000 V, but the length of the cold cathode tubes 71. This voltage can be set lower than the case where the cold cathode tubes 71.

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.

As will be described later with reference to FIG. 3, the signal width of the on / off signal is not equal but positive and negative and is not uniform. 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.
The current equalization circuit 6 includes electronic circuits (referred to as constant current circuits) 61... 6n that obtain a constant current by using a current flowing between the collector and emitter of the transistor according to the number of cold cathode tubes 71. ing. 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. 2, the npn-type and pnp-type transistors of the constant current circuits 61... 6n are connected in parallel. In the case of the npn type, a resistor R 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 R is substantially equal to the voltage Vb, and the voltage Vb is common to each transistor, the voltage across the resistor R 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 transistor) is also equalized by the same action of the pnp 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.
FIG. 3 is a graph showing waveforms of respective parts of the lighting device of FIG.
FIG. 3A shows a DC input voltage input to the inverter 2. FIG. 3B shows the waveform of the output voltage of the inverter 2, that is, the primary voltage of the main transformer. FIG. 3C 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. 3D shows an 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. 3E 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 shown in FIG. 3E, the positive signal width is t ₁ and the negative signal width is t ₂ . t ₁ is larger 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. 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.
With the configuration of the lighting device of the present invention as described above, the plurality of cold-cathode tubes 71... 7n can be lit at a low frequency with a frequency f.

Here, “low frequency lighting” means lighting while switching the direct current by the polarity switching circuit 5 at a lower frequency f than in the prior art. As described above, the range of the low frequency f is more than 0 Hz and not more than 20 kHz. Preferably it is more than 0 Hz and 10 kHz or less, more preferably more than 0 Hz and 1 kHz or less.
Conventionally, compared to the case where the inverter 2 is turned on by flowing a high frequency current of several tens of kHz to the cold cathode tubes 71... 7 n, the cold cathode tubes 71. By turning on the light, it is possible to reduce the influence of stray capacitance generated between the cold cathode tubes 71... 7n and the wiring connected thereto and the chassis 8, and to make the uniformity of the screen brightness close to ideal. it can. The effect of maintaining the uniformity of the screen luminance becomes more advantageous as the switching frequency f of the polarity switching circuit 5 is lower.

Further, since the main transformer 3 can be driven at a high frequency irrespective of the switching frequency f of the polarity switching circuit 5, the size of the main transformer 3 can be reduced.
Even if the cold cathode tubes 71... 7n are placed vertically, 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.
Therefore, if this lighting device is used for a backlight such as a liquid crystal display device, the entire lighting device can be made small. Moreover, since the influence of the stray capacitance can be reduced by lighting the cold cathode tube using a low frequency, the cold cathode tube and the chassis supporting it can be brought to infinity. Therefore, the thickness of the liquid crystal display device can be reduced. In particular, in a horizontally long screen, the length of the fluorescent lamp 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.

Hereinafter, a circuit modification example of the lighting display device of the vertical fluorescent lamp will be described.
FIG. 4 is a circuit diagram of a main part of a transformerless lighting device in which the main transformer 3 is omitted. In this circuit, an AC voltage is directly obtained by a resonance circuit 2 'using a coil and a transistor with respect to a DC input. The AC voltage obtained by the resonance circuit is about 10 times the DC input, for example, 240 V, and the frequency is 200 kHz. By passing this AC voltage through the voltage doubler rectifier circuit 4, a predetermined voltage, for example, a DC voltage of 1500 V is obtained. The configuration subsequent to the voltage doubler rectifier circuit 4 is the same as that shown in FIG.

With this configuration, the main transformer 3 can be eliminated, so that the lighting device can be further reduced in size.
FIG. 5 omits the inverter circuit 2 and the main transformer 3, and the main circuit showing a configuration in which the inverter circuit 2 and the main transformer 3 of a device (for example, a television receiver) 10 in which the lighting device is incorporated is used. FIG. An AC voltage is obtained from the secondary winding of the power transformer of the device 10 and is passed through the voltage doubler rectifier circuit 4 to be boosted and rectified. With this configuration, the inverter 2 and the transformer dedicated to the cold cathode tubes 71.

FIG. 6 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 that shown in FIG. 2, 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 display apparatus using the vertical fluorescent lamp of this invention. It is a circuit diagram of the lighting display device of the vertical fluorescent lamp of the present invention. It is a graph which shows the waveform of each part of the lighting device of FIG. It is a principal part circuit diagram of the transformerless lighting device which abbreviate | omitted the main transformer. It is a principal part circuit diagram which shows the structure which abbreviate | omits the inverter circuit 2 and the main transformer 3, and diverts the inverter circuit and transformer of the apparatus 10 in which this lighting device is incorporated. 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 alternating current lighting device. It is a graph which shows the waveform of each part of the high frequency lighting device of FIG.

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 10 Equipment 51 Control circuit 101 Display device body 102 Liquid crystal panel 103 Liquid crystal display Part

Claims (4)

A polarity switching circuit that outputs a low frequency driving voltage of a predetermined frequency;
A plurality of fluorescent lamps connected to the output side of the polarity switching circuit and each constant current circuit for flowing an equal current to each fluorescent lamp;
The plurality of fluorescent lamps and the constant current circuit are each connected in series,
The plurality of fluorescent lamps are installed such that the longitudinal direction thereof is vertical,
A lighting display device for a vertical fluorescent lamp, wherein the polarity switching circuit outputs a low-frequency driving voltage having a different time width between a positive period and a negative period.   The lighting display device for a vertical fluorescent lamp according to claim 1, wherein a ratio of the positive period (referred to as a polarity switching time ratio) to one cycle of the low-frequency driving voltage is set to a constant value.   The lighting display device for a vertical fluorescent lamp according to claim 2, wherein the certain value is set to exceed 0.5 and not more than 0.8.   The lighting display device for a vertical fluorescent lamp according to claim 2, wherein the polarity switching time ratio is set to be greater than the predetermined value immediately after starting.

Images