JP2008192318A - Lighting device of discharge lamp, backlight unit, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lighting device or the like capable of downsizing iron core of a transformer without deteriorating transformer efficiency by suppressing occurrence of magnetic saturation of a step-up transformer occurring with the passage of lighting time at the time of blink-dimming lighting, and thereby capable of downsizing the whole device. <P>SOLUTION: This is the lighting device 10 to light by the blink-dimming a discharge lamp 19, and is provided with a step-up transformer 12 which uses a core without a gap in the transformer iron core, a ballast capacitor 13 which is connected in the current route between a secondary side of the step-up transformer 12 and the discharge lamp 19, and a low-frequency reject filter 14 connected between a power supply unit 11 and the discharge lamp 19. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lighting device for a discharge lamp, a backlight unit including the lighting device, and a liquid crystal display device including the backlight unit, and in particular, to reduce the step-up transformer of the lighting device when performing flashing dimming lighting. Related to technology.

At present, liquid crystal display devices are widely used. Especially, most monitors for personal computers have already been replaced with liquid crystal monitors instead of conventional cathode ray tube monitors, and the size of liquid crystal televisions is also increasing.
In such a liquid crystal display device, since the liquid crystal panel does not emit light, a backlight unit is generally provided as a light source on the back surface of the liquid crystal panel.

In addition, the liquid crystal display device is a light source of the backlight unit because it is necessary to change the light emission amount for adjustment according to the brightness of the surroundings and user's preference and correction according to the timely luminance change. The discharge lamp is dimmed.
As a method of dimming and lighting the discharge lamp, there is flashing dimming such as PWM dimming, and in a transmissive liquid crystal display device having a backlight having a flashing dimming function, the dimming range is greatly expanded and a booster circuit Japanese Patent Application Laid-Open No. H10-228867 discloses a technique that enables high efficiency and downsizing.
Japanese Patent No. 3076184

Since the liquid crystal display device is one of the advantages that it is thin, there is a strong demand for downsizing the discharge lamp lighting device.
In the lighting device described above, the step-up transformer is particularly large, and it is particularly effective to reduce the size of the transformer core in order to reduce the size of the step-up transformer.
However, the transformer iron core cannot simply be reduced in size until the characteristics of the transformer are deteriorated, and some device is required.

In addition, when flashing dimming is turned on, the transformer iron core is likely to cause magnetic saturation as the lighting time elapses, and when magnetic saturation occurs, there is a problem that the transformer efficiency is significantly reduced. Otherwise, it is difficult to reduce the size of the transformer core.
The present invention makes it possible to reduce the size of the transformer iron core without reducing the transformer efficiency by suppressing the occurrence of magnetic saturation of the step-up transformer that occurs as the lighting time elapses when the flashing dimming is performed. It is an object of the present invention to provide a discharge lamp lighting device, a backlight unit, and a liquid crystal display device that can be miniaturized.

  In order to achieve the above object, a lighting device according to the present invention includes a step-up transformer using a core without a gap in a transformer core, a secondary side of the step-up transformer, and a discharge A ballast capacitor connected between the lamp and a low-pass filter connected in a current path between a power source and the discharge lamp.

In order to achieve the above object, a backlight unit according to the present invention uses the lighting device.
In order to achieve the above object, a liquid crystal display device according to the present invention includes a backlight unit using the lighting device.

With the configuration described in the means for solving the problems, the DC saturation and low-frequency components of the lamp current during flashing dimming lighting are removed by the low-frequency elimination filter, so that the magnetic saturation of the step-up transformer that occurs with the passage of lighting time Therefore, the transformer efficiency is improved.
Therefore, it is possible to use a core having a low magnetic resistance and no gap in the transformer iron core, and the transformer can be reduced in size without reducing the transformer efficiency.

Here, in the lighting device, the backlight unit, and the liquid crystal display device, the low-frequency elimination filter may be connected between the power source and a primary side of the step-up transformer.
As a result, since the low-frequency elimination filter is connected to the primary side of the step-up transformer, the inflow of the direct current component and the low-frequency component of the current from the power source to the step-up transformer is suppressed.

Here, in the lighting device, the backlight unit, and the liquid crystal display device, the low-frequency removal filter may be an LC high-pass filter, an LC band-pass filter, or a DC cut capacitor.
Here, in the lighting device, the backlight unit, and the liquid crystal display device, the low-frequency elimination filter may be connected between a secondary side of the step-up transformer and the discharge lamp.

As a result, since the low-frequency elimination filter is connected to the secondary side of the step-up transformer, the inflow of the DC component and low-frequency component of the current from the discharge lamp to the step-up transformer is suppressed.
Here, in the lighting device, the backlight unit, and the liquid crystal display device, the low-frequency removal filter may be a T-type or π-type high-pass filter.
Here, in the lighting device, the backlight unit, and the liquid crystal display device, the power source intermittently supplies the lamp current at the first frequency for lighting the inverter at the second frequency, and the low-frequency elimination filter It is also possible to provide a characteristic in which the first frequency is a pass region and the second frequency is a removal region.

Thus, the frequency component for lighting the inverter can be passed and the frequency component for dimming can be cut off, and the direct current component and the low frequency component of the lamp current at the time of flashing dimming lighting do not flow to the step-up transformer. The iron core is less likely to cause magnetic saturation.
Here, in the lighting device, the backlight unit, and the liquid crystal display device, the transformer core of the step-up transformer may be a toroidal core.

[Embodiment 1]
<Overview>
In Embodiment 1 of the present invention, in a lighting device for flashing and dimming a discharge lamp, a low-frequency elimination filter that passes a frequency component for lighting an inverter and cuts off a frequency component for dimming is used as a power source. By connecting in the current path to the primary side of the step-up transformer, the inflow of the direct current component and low-frequency component of the lamp current from the power source to the step-up transformer is suppressed, and the magnetism of the step-up transformer that occurs as the lighting time elapses By suppressing the saturation, the transformer efficiency is improved and the transformer can be miniaturized.

<Configuration>
FIG. 1 is a diagram showing an outline of a liquid crystal display device according to Embodiment 1 of the present invention.
A liquid crystal display device 100 illustrated in FIG. 1 is, for example, a 32-inch liquid crystal television, and includes a liquid crystal screen unit 101 and a backlight unit 102.
The liquid crystal screen unit 101 includes a color filter substrate, a liquid crystal, a TFT substrate, a drive module and the like (not shown), and forms a color image based on an image signal from the outside.

The backlight unit 102 includes one or a plurality of lighting devices 10 and 16 discharge lamps 19.
The one or a plurality of lighting devices 10 are electronic devices that cause the 16 discharge lamps 19 to blink and dimm.
FIG. 2 is a diagram showing an outline of a circuit of the lighting device 10 according to Embodiment 1 of the present invention.

As shown in FIG. 2, the lighting device 10 according to the first embodiment of the present invention includes a power supply unit 11, a transformer 12, a ballast capacitor 13, and a low-frequency elimination filter 14. Here, the discharge lamp 19 is also shown in FIG.
The power supply unit 11 intermittently supplies a lamp current having a high frequency lighting frequency f1 of about 30 kHz to 100 kHz for lighting the inverter at a blinking dimming frequency f2 of about 60 Hz to 300 Hz.

The transformer 12 is a step-up transformer using a toroidal core with a low magnetic resistance and no gap in the transformer iron core.
The ballast capacitor 13 is connected between the secondary side of the step-up transformer and the discharge lamp, suppresses a change in current due to a change and fluctuation of the lamp voltage, and improves a constant current characteristic.
The low-frequency elimination filter 14 is connected in the current path between the power supply unit 11 and the primary side of the transformer 12, and basically uses the high-frequency lighting frequency f1 as a passing region and the blinking dimming frequency f2 as a removal region. With characteristics.

  The discharge lamp 19 is, for example, a cold cathode fluorescent tube (Cold Cathode Fluorescent Lamp, hereinafter referred to as “CCFL”) or an external electrode fluorescent tube (dielectric barrier discharge lamp: External Electrode Fluorescent Lamp, hereinafter referred to as “EEFL”). This is an arc tube having a lamp outer diameter of about 1.8 to 6.0 mm, which is mainly used in a backlight unit of a liquid crystal display. In the first embodiment, a CCFL will be described as an example. The present invention can be similarly applied to EEFL (in the case of EEFL, the ballast capacitor 13 is built in the lamp) and other discharge lamps (hot cathode fluorescent tube, neon tube, etc.).

<Discussion and detailed design>
Here, the cause of magnetic saturation of the step-up transformer and specific design values that occur with the passage of lighting time when the discharge lamp is turned on and off with dimming will be described.
FIG. 3 is a diagram showing the lamp current when the flashing dimming is turned on.
When one electrode (GND electrode) of the discharge lamp is grounded to make the potential constant and a high frequency voltage is applied to the other electrode (HV electrode) to blink and dimm, as shown in FIG. Starting from a negative voltage often occurs, the current on the secondary side of the step-up transformer is biased to generate direct current and low-frequency current, which are accumulated and cause the step-up transformer to cause magnetic saturation.

  Specifically, for example, when the low-frequency elimination filter 14 is not used, the high frequency lighting frequency f1 in the power supply unit 11 is 50 kHz, the lamp rated voltage is 1000 V, the lamp rated current is 8 mA, the ballast capacitor 13 = 22 pF, and the input to the transformer 12 When the voltage was 30 Vrms and the output voltage from the transformer 12 was 1450 Vrms (Design 1), the discharge lamp was flashed and dimmed at a frequency of 100 Hz.

In (Design 1), when an equivalent resistance was connected instead of the discharge lamp, the magnetic saturation of the transformer did not occur.
This indicates that the magnetic saturation of the step-up transformer is caused by the discharge lamp.
FIG. 4 is a diagram showing an outline of a circuit when the DC cut capacitor 15 is used for the low-frequency elimination filter 14.

The following three examples show design values when the DC cut capacitor 15 is used for the low-pass filter 14.
The high frequency lighting frequency f1 in the power supply unit 11 is 50 kHz, the step-up ratio of the transformer 12 is 50, the lamp rated voltage is 1000 V, the lamp rated current is 8 mA, the ballast capacitor 13 = 22 pF, the DC cut capacitor 15 = 0.18 μF, and the high frequency output voltage. When the transformer output voltage from the transformer 12 is 37 Vrms and the transformer output voltage is 1450 Vrms (Design 2), when the discharge lamp is blinked and dimmed at a frequency of 100 Hz, a sufficient amount of attenuation of the low frequency component can be secured, and magnetic saturation of the transformer 12 occurs. There wasn't.

Further, when the DC cut capacitor 15 = 2.2 μF, the high frequency output voltage is 31 Vrms, and other conditions are the same as in (Design 2) (Design 3), when the discharge lamp is flashed and dimmed at a frequency of 100 Hz, the low frequency component The attenuation was insufficient and magnetic saturation of the transformer 12 occurred.
Further, the ballast capacitor 13 = 47 pF, the DC cut capacitor 15 = 0.12 μF, the high frequency output voltage is 41 Vrms, and other conditions are the same as (Design 2) (Design 4). The discharge lamp is flashed and dimmed at a frequency of 100 Hz. In some cases, a sufficient amount of attenuation of the low frequency component could be secured, and magnetic saturation of the transformer 12 did not occur.

FIG. 5 is a graph showing a signal attenuation characteristic graph with respect to frequency, with the horizontal axis representing frequency and the vertical axis representing gain.
In FIG. 5, the one-dot broken line A shows the attenuation characteristics when the low-frequency elimination filter 14 is not used as in the prior art, and the solid line B shows the respective attenuation characteristics when the DC cut capacitor 15 is used as in the above configuration of the present application. Show.

  In A, since the discharge lamp is designed to be efficiently lit at the high frequency lighting frequency f1, the characteristic is such that the discharge lamp can be lit stably to the maximum extent within the output range of the step-up transformer. Has been determined. Therefore, at the high frequency lighting frequency f1, lighting with high stability can be performed within the output range of the step-up transformer. However, the attenuation amount is insufficient at the blinking dimming frequency f2, and transformer saturation and vibration are likely to occur. . In order to avoid these, a large core must be used, and this makes it impossible to downsize the step-up transformer.

In B, by using the DC cut capacitor 15, the rate of change in attenuation (the slope of the graph) is made larger than A. In the case of A, the rate of attenuation is at most -6 dB / oct. On the other hand, in the case of B, the attenuation rate can be made larger than −6 dB / oct, so that the blinking dimming frequency f2 can be efficiently attenuated.
Here, the DC cut capacitor 15 is preferably about 1 μF to 0.1 μF.

FIG. 6 is a diagram showing an outline of a circuit when the LC high-pass filter 16 is used as the low-frequency elimination filter 14.
The LC high pass filter 16 includes a capacitor 17 and a coil 18.
The following example shows design values when the LC high-pass filter 16 is used as the low-frequency elimination filter 14.

  The high frequency lighting frequency f1 in the power supply unit 11 is 50 kHz, the step-up ratio of the transformer 12 is 50, the lamp rated voltage is 1000 V, the lamp rated current is 8 mA, the ballast capacitor 13 = 22 pF, and the cutoff frequency of the LC high-pass filter 16 is 22 kHz (for example, a capacitor 17 = 0.1 μF, coil 18 = 500 μH), the input voltage is 31 Vrms, the drain output voltage of the transformer 12 is 1450 Vrms, and the discharge lamp is flashed and dimmed at a frequency of 100 Hz (design 5). A sufficient amount of attenuation was secured, and magnetic saturation of the transformer 12 did not occur.

In the design 5, by setting the cut-off frequency to the high frequency lighting frequency f1 or less and the blinking dimming frequency f2 or more, the amount of attenuation required at the flashing dimming frequency f2 is reduced so that the high frequency lighting frequency f1 is not attenuated so much. I try to get it.
FIG. 7 is a graph showing a signal attenuation characteristic graph with respect to frequency, with frequency on the horizontal axis and gain on the vertical axis.

In FIG. 7, the two-dot broken line A indicates the attenuation characteristics when the low-frequency elimination filter 14 is not used as in the conventional case, and the solid line C indicates the respective attenuation characteristics when the LC high-pass filter 16 is used as in the above configuration of the present application. Indicates.
A is the same as in FIG.
In C, by using the LC high-pass filter 16 and setting the cutoff frequency to be the high frequency lighting frequency f1 or lower and the blinking dimming frequency f2 or higher, the rate of attenuation change is made larger than A at the high frequency lighting frequency f1 or lower, and efficiently Not only can the flashing dimming frequency f2 be attenuated, but the input voltage can also be reduced.

Thus, since the attenuation amount of the high-frequency lighting frequency f1 can be reduced in the design 5, the input voltage does not have to be increased compared to the design 2 and the design 4, and the transformer boost ratio is not required. Transformer design is easy and miniaturization is easy.
Note that the low-pass filter 14 is not limited to a DC cut capacitor or an LC high-pass filter, but may be anything as long as it has a characteristic in which the vicinity of the high-frequency lighting frequency f1 is a pass region, for example, an LC band-pass filter.
[Modification 1]
<Overview>
According to the first modification of the present invention, in a lighting device that blinks and dimms a discharge lamp, a low-frequency elimination filter that passes a frequency component for inverter lighting and blocks a frequency component for dimming is provided as a secondary transformer of a step-up transformer. By connecting in the current path between the discharge lamp and the discharge lamp, the inflow of the DC component and low frequency component of the current from the discharge lamp to the step-up transformer is suppressed, and magnetic saturation of the step-up transformer that occurs with the passage of lighting time is suppressed. By suppressing the transformer, the transformer efficiency is improved and the transformer can be miniaturized.

<Configuration>
The first modification of the present invention is different only in that a low-frequency elimination filter 20 is provided instead of the low-frequency elimination filter 14 in the first embodiment, and the other components are the same, so the same components are the same. A number is assigned and description thereof is omitted.
FIG. 8 is a diagram showing an outline of a circuit of the lighting device 10 according to the first modification of the present invention.

As shown in FIG. 8, the lighting device 10 according to the first modification of the present invention includes a power supply unit 11, a transformer 12, a ballast capacitor 13, and a low-frequency elimination filter 20. FIG. 8 also shows the discharge lamp 19.
The low-pass elimination filter 20 is connected in the current path between the secondary side of the transformer 12 and the discharge lamp 19, and basically uses the high-frequency lighting frequency f1 as a pass region and the blinking dimming frequency f2 as a removal region. With characteristics.

A T-type or π-type high-pass filter is effective as the low-frequency elimination filter 20.
In Modification 1, a capacitor is used for the ballast, but a coil may be used.
<Summary>
As described above, according to the first embodiment and the first modification of the present invention, the lapse of the lighting time is obtained by removing the direct current component and the low frequency component of the lamp current at the time of the flashing dimming lighting by the low-frequency elimination filter. Since the magnetic saturation of the step-up transformer that occurs together with this can be suppressed, the transformer efficiency is improved.

  Therefore, a toroidal core with low magnetic resistance and no gap can be used for the transformer iron core, so the transformer can be downsized without reducing the transformer efficiency, and the transformer output waveform distortion is reduced and the lighting state is stable. The effect of doing is obtained.

  The present invention can be widely applied to any discharge lamp lighting device, and is particularly effective in a backlight unit for a liquid crystal display device. According to the present invention, the transformer iron core can be miniaturized without reducing the transformer efficiency, and the power supply unit can be miniaturized. Therefore, the liquid crystal display device can be miniaturized, and its industrial utility value is extremely high. .

It is a figure which shows the outline | summary of the liquid crystal display device in Embodiment 1 of this invention. It is a figure which shows the outline | summary of the circuit of the lighting device 10 in Embodiment 1 of this invention. It is a figure which shows the lamp current at the time of blink dimming lighting. FIG. 5 is a diagram showing an outline of a circuit when a DC cut capacitor 15 is used for the low-frequency elimination filter 14. It is the figure which took the frequency on the horizontal axis, took the gain on the vertical axis, and showed the attenuation characteristic graph of the signal with respect to frequency. FIG. 3 is a diagram showing an outline of a circuit when an LC high-pass filter 16 is used as the low-frequency elimination filter 14. It is the figure which took the frequency on the horizontal axis, took the gain on the vertical axis, and showed the attenuation characteristic graph of the signal with respect to frequency. It is a figure which shows the outline | summary of the circuit of the lighting device 10 in the modification 1 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Lighting device 11 Power supply unit 12 Transformer 13 Ballast capacitor 14 Low frequency removal filter 15 DC cut capacitor 16 LC high pass filter 17 Capacitor 18 Coil 19 Discharge lamp 20 Low frequency removal filter 100 Liquid crystal display device 101 Liquid crystal screen unit 102 Backlight unit

Claims (9)

In a lighting device that flashes and dimms a discharge lamp,
A step-up transformer using a core without gap in the transformer core;
A ballast capacitor connected between the secondary side of the step-up transformer and the discharge lamp;
A lighting device, comprising: a low-pass filter connected in a current path between a power source and the discharge lamp. The low-pass removal filter is
The lighting device according to claim 1, wherein the lighting device is connected between the power source and a primary side of the step-up transformer. The low-pass removal filter is
The lighting device according to claim 1, wherein the lighting device is an LC high-pass filter, an LC band-pass filter, or a DC cut capacitor. The low-pass removal filter is
The lighting device according to claim 1, wherein the lighting device is connected between a secondary side of the step-up transformer and the discharge lamp. The low-pass removal filter is
The lighting device according to claim 4, wherein the lighting device is a T-type or π-type high-pass filter. The power supply intermittently supplies the lamp current at the first frequency for lighting the inverter at the second frequency,
The low-pass removal filter is
The lighting device according to claim 1, wherein the lighting device has a characteristic in which the first frequency is a pass region and the second frequency is a removal region. The lighting device according to any one of claims 1 to 6, wherein the transformer iron core of the step-up transformer is a toroidal core. A backlight unit using the lighting device according to any one of claims 1 to 7. A liquid crystal display device comprising a backlight unit using the lighting device according to claim 1.

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