JP4537790B2 - LCD backlight lighting device - Google Patents

Description

  The present invention relates to a liquid crystal backlight lighting device disposed adjacent to the back surface of a liquid crystal display panel.

Japanese Patent Laid-Open No. 8-273591 Japanese Patent Laid-Open No. 10-40872 JP 7-105709 A JP 7-45103 A

  In recent years, OA devices such as personal computers have been reduced in size and power consumption, and a liquid crystal display panel is usually used for a display unit of a desktop personal computer as well as a laptop computer and a notebook personal computer. It has become like this. In addition, not only personal computers but also liquid crystal televisions that can reduce the thickness of home televisions are rapidly spreading. Most electrical devices using such a liquid crystal display panel use a backlight in combination to improve visibility. As the backlight, particularly in the case of a color liquid crystal display panel, a white lamp is used so that the influence on the color tone is small. Fluorescent lamps have been widely used as white lamps, but the backlights of personal computers and televisions have a long continuous lighting time, and there is a drawback in that the brightness is quickly reduced with ordinary hot cathode fluorescent lamps. Therefore, as a fluorescent lamp for a backlight, as in Patent Document 1, a cold cathode lamp having a long life, in which electrode consumption is relatively difficult to proceed, is often used.

  However, the cold cathode type fluorescent lamp is not different from the hot cathode type fluorescent lamp in that the electrode is enclosed in the glass discharge tube, and the electrode consumption becomes a problem to some extent. Further, since the electrode terminal is taken out of the tube through the glass wall, it is difficult to avoid that the discharge gas inside the tube leaks slowly from the boundary between the terminal and the tube. It is said that the decrease in luminance due to such factors becomes significant particularly in a region where the cumulative lighting time exceeds 30000 hours.

  In the fluorescent lamp for general-purpose lighting, a slight decrease in luminance is not so much a problem, but in the case of a backlight for a liquid crystal display panel, a new problem that cannot be used for general-purpose lighting occurs. When a moving image is displayed on the liquid crystal display panel, there is an interval period (for example, 20 to 30 ms) in which nothing is displayed between frames that are switched and displayed (that is, the screen becomes dark for a moment). On the other hand, the driving voltage of the liquid crystal pixel is controlled by using the capacitance associated with the pixel (individual capacitor or junction capacitance of a switching transistor), so the switching is performed due to the influence of the discharge time constant related to the capacitance of each pixel. Even after shifting to the interval, the pixel setting state of the previous frame is not immediately reset, and an afterimage may occur.

  Conspicuous afterimages lead to deterioration in display quality, and in recent years, afterimages have been widely reduced by blinking of the backlight. Specifically, the backlight is not constantly illuminated at a constant luminance, but the luminance is reduced during a frame interval period during which the screen becomes dark, so that an afterimage entering the interval period is difficult to see. In this case, it is most effective to reduce the backlight brightness in synchronization with the interval period. However, even if the backlight is blinked asynchronously with a period shorter than the frame switching period, the backlight brightness is reduced with respect to the interval period. If the period of falling can be overlapped with a certain probability, the afterimage reduction effect can be sufficiently enhanced.

  In this case, if the luminance during the interval period is significantly lower than the luminance during normal time (frame display period), the afterimage is less noticeable due to the dark adaptation delay effect of the naked eye. In other words, it can be said that if the luminance at the normal time decreases due to the lifetime of the backlight, it becomes more noticeable than the afterimage in the interval period, and the display quality of the liquid crystal display panel is likely to deteriorate. Therefore, the lifetime determination of the light source for the backlight must be performed from the viewpoint of whether or not a higher level of luminance can be maintained more stably in view of the reduction in the afterimage visibility. The cold-cathode fluorescent lamp generally has a life of about 30000 hours at the most, from the viewpoint of preventing afterimages, luminance deterioration becomes a problem from an earlier stage. In this sense, a light source for a liquid crystal backlight Is still inadequate.

  Therefore, in order to solve the above-described problems, Patent Documents 2 to 4 disclose a liquid crystal backlight configured using an electrodeless discharge lamp having a longer life than a cold cathode fluorescent lamp. An electrodeless discharge lamp is similar to a fluorescent lamp in that it uses a glass tube filled with a discharge gas. However, like a fluorescent lamp, a discharge gas ion is irradiated with a cathode ray from an internal electrode to emit light. Instead, the discharge drive electrode is placed outside the glass tube, and an alternating voltage is applied to the discharge electrode to excite the discharge gas by plasma emission. The wavelength of the excitation light is usually set in the ultraviolet region, and the phosphor applied on the inner surface of the glass tube is irradiated with the excitation ultraviolet light to cause visible light emission, similar to the fluorescent lamp.

  In the above electrodeless discharge lamp, the drive electrode does not need to be a cathode ray generation source and is arranged outside the glass tube as a simple voltage application means, so that electrode consumption hardly occurs and the electrode terminal that penetrates the glass tube is taken out. Since the structure is also eliminated, there is an advantage that the sealing property of the glass tube against the discharge gas is enhanced and the light emission can be stably continued for a long time. Further, in the case of fluorescent lamps, due to its characteristics, a voltage that is significantly higher than when the discharge is stable is required at the start of lighting, and when a plurality of lamps are connected to one AC power supply circuit, Since much is distributed, there is a problem that disturbs starting of other lamps during that time. Therefore, it is necessary to provide an AC power supply circuit (for example, an inverter) individually for each lamp, and there is a problem that the device cost is likely to increase. However, since the starting voltage itself is not so high, the electrodeless discharge lamp has an advantage that a plurality of lamps are connected to one AC power supply circuit without any problem.

  However, since the electrodeless discharge lamp has an electrode disposed outside the glass tube, the parasitic capacitance of the glass tube interposed between the electrode and the discharge gas is large, and the load impedance is high. As a result, although the starting voltage is low, the driving voltage after entering the stable discharge period is considerably higher than that of a fluorescent lamp and the power consumption is large. Therefore, in the backlight using the electrodeless discharge lamp, in order to reduce the load impedance, the frequency of the alternating current used is increased to a high frequency range (for example, several hundred MHz to several GHz) to suppress power consumption. . However, this higher frequency has the following drawbacks.

(1) When the driving AC of the backlight through which a relatively large current flows is increased in frequency, there is a problem that the electromagnetic wave radiation noise level naturally increases. This problem is also referred to in Patent Document 3 and Patent Document 4, but the method disclosed in these documents is to shield the casing of the backlight device with a conductor, and the shield structure is complicated. The cost increase due to is inevitable and there is no change in adopting a high frequency for driving the lamp, so the generation of electromagnetic radiation noise itself is not suppressed and is not a radical solution.

(2) The main cause of electromagnetic radiation noise in equipment involving high frequency is common mode radiation in the wiring section connecting the load (electrodeless discharge lamp) and the power source. To reduce this, load / power wiring It is effective to shorten the length as much as possible to reduce the stray capacitance generated in parallel on the ground side and to increase the radiation impedance to the ground side. However, even if the layout of the circuit block in the device is taken into consideration, there is a design limit to shortening the wiring length and thus reducing electromagnetic wave radiation noise.

(3) As described above, in order to reduce the afterimage of the liquid crystal display panel, it is effective to dimm the electrodeless discharge lamp used for the backlight intermittently. However, lamp dimming control using a high-frequency current requires complicated waveform control such as pulse width modulation, and has a drawback that the dimming control circuit must be complicated. In addition, the power supply circuit for generating high-frequency alternating current is complicated.

  An object of the present invention is to provide a liquid crystal back that is substantially free from electromagnetic radiation radiation, has a high degree of freedom in designing the wiring length between the lamp and the power supply, and is easy to control light for suppressing afterimages of the liquid crystal display panel. It is in providing the lighting device of a light.

Means for Solving the Problems and Effects of the Invention

The present invention relates to a lighting device for a liquid crystal backlight disposed adjacent to the back surface of a liquid crystal display panel, the translucent insulating tube filled with a discharge gas, and disposed outside the translucent insulating tube. In order to solve the above-mentioned problem, it is used by connecting to an electrodeless discharge lamp having an external electrode for exciting plasma discharge discharge by exciting the enclosed discharge gas and forming a light source of a liquid crystal backlight In addition,
A drive AC generator for applying a light emission drive AC having a low frequency of 30 Hz to 1 kHz to an external electrode of the electrodeless discharge lamp;
A wiring portion that electrically couples the electrodeless discharge lamp and the drive AC generator;
Dimming control means for switching the light emission state of the electrodeless discharge lamp between the first luminance and the second luminance that is darker than the first luminance at a frequency smaller than the driving AC voltage;
In order to reduce the impedance at the time of light emission driving of the electrodeless discharge lamp at the setting frequency of the light emission driving AC voltage, the electrode portion capacitance formed by the external electrode and the translucent insulating tube of the electrodeless discharge lamp and the setting frequency And an impedance adjustment inductance provided so as to form a series resonance circuit.

  Although the above-mentioned liquid crystal backlight lighting device of the present invention uses an electrodeless discharge lamp as a backlight light source, the generation level of electromagnetic wave radiation noise is essentially reduced by keeping the light emission driving AC at a low frequency of 30 Hz to 1 kHz. The shield structure can be omitted or simplified at the time of the device. In addition, by providing an impedance adjustment inductance that is coupled in series resonance with the electrode capacitance, the overall impedance of the lamp during light emission driving can be greatly reduced at the driving frequency, even though the light emission driving alternating current has been lowered. , Power consumption can be kept low. Furthermore, since the drive frequency is low, even if the wiring length connecting the drive AC generator and the electrodeless discharge lamp is somewhat longer, common mode radiation is less likely to occur, so the lamp / drive AC generator (power supply) is not connected. The degree of freedom in designing the wiring length can also be increased. Since the drive frequency is low, the light control for reducing the afterimage visibility on the liquid crystal display panel can be more easily performed without using complicated PWM control or the like.

  When the frequency of the light emission driving AC is less than 30 Hz, the liquid crystal display panel is likely to flicker, and even if the dimming control of the lamp is performed at a frequency lower than that, the effect of preventing the afterimage visibility hardly occurs. On the other hand, if the frequency of the light emission drive alternating current exceeds 1 kHz, the effect of reducing the generation level of electromagnetic wave radiation noise is not significant, and the convenience of simply performing the light control is also reduced. The frequency of the light emission drive AC is more desirably set to 50 Hz or more and 500 Hz or less. In addition, the wiring length connecting the drive AC generator and the electrodeless discharge lamp is set to 10 cm or more (preferably 20 cm or more) from the viewpoint of increasing the design flexibility of general-purpose liquid crystal equipment such as a liquid crystal television and a personal computer monitor. It is desirable. When a plurality of lamps are provided and there are a plurality of wiring paths that connect the drive AC generator and the lamp, the longest one may be set to 10 cm or more (preferably 20 cm or more). Of course, it is not hindered that the wiring length of the lamp of the part becomes less than 10 cm. On the other hand, the upper limit of the wiring length is not limited, but excessively long wiring length is undesirable from the viewpoint of reducing the weight and downsizing of the device. 100 cm).

  The drive AC generator can be configured to include a winding transformer that boosts the power supply voltage to a voltage necessary for driving the electrodeless discharge lamp. In this case, the impedance adjustment inductance can be formed by the secondary coil of the winding transformer and the auxiliary coil provided separately from the secondary coil on the wiring from the secondary coil to the external electrode. By using a part of the inductance also as the secondary coil of the winding transformer, there is an advantage that the size of the coil newly provided for realizing the series resonance circuit can be reduced.

  The dimming control means includes a phase control circuit that performs dimming control for reducing the light emission state of the electrodeless discharge lamp from the first luminance to the second luminance by phase chopper control of light emission driving AC using a semiconductor switching element. It can be configured as having. By making the electrodeless discharge lamp drive at a low frequency as in the present invention, dimming control of the electrodeless discharge lamp is a problem by phase chopper control with a simple circuit configuration without using troublesome and complicated PWM control. Can be done without. In the phase control circuit, a semiconductor switch element for chopping the light emission driving AC can be configured by, for example, a triac. In a conventional liquid crystal backlight using an electrodeless discharge lamp using a high frequency of several hundred MHz to several GHz band, it is difficult to realize a triac itself that operates in such a frequency band, and phase chopper control using this is technically I didn't want to. However, the adoption of the present invention enables simple phase chopper control using a triac.

  In the present invention, an electrodeless discharge lamp having a relatively low starting voltage is used as the light source of the liquid crystal backlight. Therefore, even if a plurality of electrodeless discharge lamps are connected in parallel to the driving AC generator, there is an advantage that the lamp can be lit without problems . In this case, a plurality of electrodeless discharge lamps may be dimmed and dimmed at the same time to suppress afterimages. However, considering that the frequency is low, the dimming control means may control the plurality of electrodeless discharge lamps. Among them, some of them are set to the second brightness, the remaining lamps more than that are set to the first brightness, and a set of lamps set to the second brightness is set for the entire plurality of lamps. It is more desirable to configure as switching periodically in a fixed order within the array. Thereby, even if the frequency is low as described above, it is possible to effectively suppress the afterimage visibility of the liquid crystal display panel. In this case, in order to uniformly illuminate the screen of the liquid crystal display panel, a plurality of electrodeless discharge lamps, each of which is formed horizontally long, along the panel surface of the liquid crystal display panel, the scanning line direction of the liquid crystal display panel It is desirable to arrange them parallel to each other so that their longitudinal directions coincide with each other. And if the light control control means employ | adopts the system which switches the lamp set to 2nd brightness | luminance sequentially from the 1st end side to the 2nd end side of an arrangement | sequence, it will raise especially the afterimage visual recognition suppression effect. be able to.

  When the drive AC generator includes the above-described winding transformer and the impedance adjustment inductance is formed by the secondary coil of the winding transformer and the above-described auxiliary coil, a plurality of electrodeless discharge lamps Can be provided with auxiliary coils in a one-to-one correspondence. When connecting a plurality of lamps to a transformer in parallel, the main part of all the inductances necessary to realize a series resonant circuit can be shared by one secondary coil of the winding transformer. Since it is only necessary to form a supplemental inductance to ensure the inductance necessary for series resonance, the effect of downsizing the device is further enhanced. If the inductance of the secondary coil coincides with the inductance necessary for series resonance, the auxiliary coil can be omitted.

  In the above case, the dimming control means performs dimming control for reducing the light emission state of the electrodeless discharge lamp from the first luminance to the second luminance by the phase chopper control of the light emission driving AC using the semiconductor switching element. In this case, the inductances of the plurality of auxiliary coils only need to be set to be equivalent to each other, and the load impedances of the plurality of electrodeless discharge lamps can be made uniform, so that impedance matching with the driving AC generator can be easily performed, thereby increasing efficiency. be able to. In this case, since each electrodeless discharge lamp is driven with an alternating current of the same frequency, the aforementioned step-up winding transformer is a self-excited resonance inverter for converting a power supply voltage into a light emission drive alternating voltage having a set frequency. When incorporated in the circuit, the booster circuit and the inverter as the frequency converter can be shared, and the device configuration can be further simplified.

  On the other hand, the drive AC generator may be configured to input drive AC having a different set frequency for each of the plurality of electrodeless discharge lamps. In this case, the inductances of the plurality of auxiliary coils are set to different values so that the resonance frequencies of the series resonance circuit are different from each other in accordance with the set frequency of each lamp. The drive AC generator is configured to have a multiple AC generator that generates a multiple AC in which a plurality of AC waveforms having frequencies corresponding to different set frequencies are superimposed. The plurality of electrodeless discharge lamps are driven to emit light by extracting an alternating current component having a frequency corresponding to a set frequency from multiple alternating currents by using a series resonance circuit as a bandpass filter. In this case, the dimming control means performs the dimming control for reducing the light emission state of the electrodeless discharge lamp from the first luminance to the second luminance. This can be done by attenuating the AC component corresponding to the set frequency of the discharge lamp. According to this method, waveform control for dimming is essentially unnecessary, and the circuit configuration can be further simplified.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an example of a liquid crystal display device provided with a liquid crystal backlight lighting device of the present invention. A liquid crystal backlight device 3 is disposed adjacent to the back surface of the liquid crystal display panel 2. As shown in FIG. 2, the liquid crystal backlight device 3 includes a plurality of electrodeless discharge lamps 13 serving as light sources, and these electrodeless electrodes are formed in a horizontally long shape to uniformly light up the screen of the liquid crystal display panel 2. The discharge lamps 13 are arranged in parallel with each other along the panel surface of the liquid crystal display panel 2 so that the scanning line direction and the longitudinal direction coincide with each other. As shown in FIG. 1, the liquid crystal display panel 2 and the liquid crystal backlight device 3 are integrally incorporated in a housing 4.

  FIG. 3 shows a schematic configuration of the electrodeless discharge lamp 13, a translucent insulating tube 14 in which a discharge gas is enclosed, and a discharge gas that is disposed outside the translucent insulating tube 14 and enclosed therein. And an external electrode 15 for plasma discharge discharge. The translucent insulating tube 14 is made of, for example, a glass tube, and the discharge gas is a heavy inert gas such as Kr or Xe with a relatively small binding energy of outer shell electrons so that it can be easily converted into plasma at a low frequency. Metal vapor such as mercury is used. In view of the principle of plasma excitation by cyclotron resonance, it is desirable that the directions of the oscillating electric field and the induced magnetic field applied to the external electrode 15 by application of alternating current are orthogonal to each other. From this point of view, the external electrode 15 is made of the translucent insulating tube 14. However, as shown in FIG. 4, the planar electrode 15jt can provide an effect close to that of the coil due to the eddy current effect. If the electrodes 15jt provided at both ends of the lamp are inserted into the socket 15j2, the assembly of the electrodeless discharge lamp 13 is facilitated. In FIG. 4, one socket 15j2 is urged by a spring 20 so that it can advance and retreat in the lamp axis direction, and the electrodeless discharge lamp 13 is mounted while pushing back the socket 15j2 against the urging force of the spring 20. Yes.

In the electrodeless discharge lamp 13, direct excitation light by plasma is ultraviolet light, and in order to convert this into white visible illumination light, a known phosphor material (for example, calcium halophosphate (3Ca) is provided on the inner surface of the translucent insulating tube. ₃ (PO ₄ ) ₂ · CaFCl / Sb, Mn), and white light of various color temperatures can be obtained by adjusting the amounts of F and Cl, Sb and Mn).

  The electrodeless discharge lamp 13 as described above is connected to the lighting device 18. FIG. 5 shows a first example of the circuit configuration of the lighting device 18. The main part of the circuit includes a drive AC generator 12 (inverter) and a lighting control circuit 11. Each of the electrodeless discharge lamps 13 connected to the lighting control circuit 11 is electrically coupled by the driving AC generator 12 and the wiring part 13k at the external electrode 15, and the driving AC generator 12 causes the low frequency of 30 Hz to 1 kHz. A light emission driving alternating current with a frequency is applied.

  The driving AC generator 12 includes a winding transformer 114 that boosts the voltage of an external power source (commercial AC power source 5: connected by a plug (not shown)) to a voltage necessary for driving the electrodeless discharge lamp 13. ing. The winding transformer 114 is incorporated in a self-excited resonance inverter circuit for converting a power supply voltage into a light emission drive AC voltage having a set frequency. By adopting the resonant inverter circuit, the light emission drive AC can be a sine wave AC.

  Specifically, the alternating current from the external power source 5 is converted into a direct current by a known AC / DC converter 111 and input to the primary coil S1 of the winding transformer 114 while being AC modulated by the push-pull transistors 110 and 112. The primary coil S1 is divided by a tap T, one of which is connected to the collector of the transistor 110 that handles the positive half-wave and the other is the collector of the transistor 112 that handles the negative half-wave. Thus, the oscillation frequency on the input side is determined. The push-pull transistors 110 and 112 constitute an amplifier circuit in combination with the current detection resistors 116 and 118, and a self-excited oscillation circuit is configured by feeding back the oscillation frequency of the primary coil S1 with the search coil S3. The oscillation frequency (that is, the set frequency of the light emission driving AC voltage) is preferably determined in the range of 30 Hz to 1 kHz, preferably 50 Hz to 500 Hz, depending on the circuit constant setting of the primary coil S1 and the capacitor 120. In this embodiment, it is determined in the range of 60 Hz to 200 Hz.

  As shown in FIG. 6, the electrodeless discharge lamp 13 has the electrode 15 disposed outside the translucent insulating tube 14, so that the parasitic capacitance of the insulating tube 14 interposed between the electrode 15 and the discharge gas 16 is reduced. large. The equivalent circuit when the parasitic capacitances at the electrodes 15 at both ends of the tube are 2Cx and the series resistance of the discharge gas is Rx is shown in the figure, and it is understood that the load impedance in the low frequency region is increased as it is. it can. Therefore, in order to reduce the impedance at the time of light emission driving of the electrodeless discharge lamp 13 at the set frequency of the light emission driving AC voltage, as shown in FIG. An electrode portion capacitance Cx formed by the insulating tube 14 and an impedance adjustment inductance Lx provided so as to form a series resonance circuit SR at a set frequency are provided.

  If the set frequency of the light emission drive AC voltage is fx, the resonance frequency of the series resonance circuit SR can be matched to this fx, so that the load impedance can be greatly reduced. The lamp 13 can be driven to emit light sufficiently. Specifically, as shown in FIG. 5, the impedance adjustment inductance Lx is formed on the secondary side coil S2 of the winding transformer 114 and on the wiring from the secondary side coil S2 to the external electrode 15. The auxiliary coil 6 is provided separately from S2. The auxiliary coil 6 constitutes a component of the lighting control circuit 11.

  As described above, by using a part of the inductance also as the secondary coil S2 of the winding transformer 114, the size of a coil newly provided for realizing the series resonance circuit SR can be reduced. In the present embodiment, a plurality of electrodeless discharge lamps 13 are provided, and the auxiliary coils 6 are also provided in a form corresponding to them one to one. The plurality of electrodeless discharge lamps 13 are connected in parallel to the secondary coil S2 of the winding transformer 114 by the wiring portion 13k. In any of the electrodeless discharge lamps 13, the main part of the total inductance necessary for realizing the series resonance circuit SR is shared by one secondary coil S <b> 2 of the winding transformer 114. Accordingly, each auxiliary coil 6 forms a supplemental inductance obtained by subtracting the inductance of the secondary coil S2 out of all the inductances necessary for series resonance, so that the size may be small. When the inductance of the secondary coil S2 coincides with the inductance necessary for series resonance, the auxiliary coil 6 on each path can be omitted.

  In the circuit of FIG. 5, since the frequency of the drive AC is low, even if the length of the wiring 13k connecting the drive AC generator 12 and the electrodeless discharge lamp 13 is somewhat longer, common mode radiation is less likely to occur. Therefore, it is not necessary to forcibly shorten the wiring length in order to reduce electromagnetic noise radiation, and the degree of freedom in designing the wiring length between the lamp 13 and the drive AC generator 12 (power source) is increased. In the present embodiment, the wiring length is defined as the wiring distance between the drive AC generator (winding transformer 114) 12 and the electrode 15 of the electrodeless discharge lamp 13 for each path of the electrodeless discharge lamps 13 connected in parallel. (There are two electrodes 15 for each electrodeless discharge lamp 13, and the wiring length is determined for each electrode 15, and the sum is not added). There are a plurality of wiring paths that connect the drive AC generator 12 and the lamp 13, but those that are located near the drive AC generator 12 do not necessarily have a longer wiring, so they are farthest from the drive AC generator 12. Of the two electrodes 15 of the lamp 13 positioned at a distance, the length of the wiring portion 13k having a longer path to the terminal of the drive AC generation portion 12 is defined as the maximum wiring length. In the present embodiment, even when the maximum wiring length is set to 10 cm or more (preferably 20 cm or more), electromagnetic noise radiation hardly poses a problem, and the layout of the drive AC generator 12 and each electrodeless discharge lamp 13 is also good. It can be determined freely.

  Next, the lighting control circuit 11 switches the light emission state of the electrodeless discharge lamp 13 between the first luminance and the second luminance that is darker than the first luminance at a frequency smaller than the driving AC voltage. A dimming control circuit (dimming control means) 9 is provided. Since the drive frequency is low, the light control for reducing the afterimage visibility on the liquid crystal display panel 2 can be more easily performed without using complicated PWM control or the like.

  Specifically, the dimming control circuit 9 performs dimming control for reducing the light emission state of the electrodeless discharge lamp 13 from the first luminance to the second luminance, and is a phase chopper for light emission driving AC using a semiconductor switching element. It has a phase control circuit 8 that is controlled. By controlling the electrodeless discharge lamp 13 at a low frequency, the dimming control of the electrodeless discharge lamp 13 can be performed without problems by phase chopper control with a simple circuit configuration without using troublesome and complicated PWM control. Can do.

  As shown in FIG. 11, in the phase control circuit 8, the semiconductor switch element that chops the light emission drive alternating current can be configured by two thyristors for the positive half wave and for the negative half wave as shown in (a). However, if the bidirectional triac 121 is configured as shown in (b), only one trigger terminal (gate) is required, and the control circuit can be further simplified. The amount of light during dimming can be arbitrarily adjusted by the phase (ignition angle) at which each half wave is chopped. In this embodiment, the trigger input of the triac 121 is generated by the breakdown waveform of the diac 122, and the breakdown timing can be determined by the time constant of the trigger activating circuit formed by the resistor 123 and the capacitor 124. . To reduce the amount of light during dimming, increase the value of the resistor 123 or increase the capacitance of the capacitor 124, and increase the time until the terminal voltage of the capacitor 124 reaches the breakdown voltage of the diac 122. Thus, the firing angle in FIG. 11 may be shifted to the high angle side (the reverse is necessary when the amount of light during dimming is to be increased).

  Since the starting voltage of the electrodeless discharge lamp 13 is relatively low, even if a plurality of electrodeless discharge lamps 13 are connected in parallel to the driving AC generator 12, they can be lit without problems. In the present embodiment, the dimming control circuit 9 sets a part of the plurality of electrodeless discharge lamps 13 to the second luminance (for example, 0% to 50% of the first luminance), and More than the remaining lamps 13 are set to the first luminance, and the set of the lamps 13 set to the second luminance is periodically switched in a predetermined order within the entire array of the plurality of lamps 13. It is configured as. Thereby, even if the frequency is low as described above, it is possible to effectively suppress the afterimage visibility of the liquid crystal display panel 2. Specifically, in FIG. 2, the lamps 13 set to the second luminance are arranged from the first end side (upper screen side of the liquid crystal display panel 3 in this embodiment) to the second end side (also lower screen side). Adopt a method of switching in the form of moving sequentially toward the.

  For this switching, for example, the switch group 7 composed of the switches 7S provided corresponding to each electrodeless discharge lamp 13 is controlled by a control signal SS1 (a parallel level signal having a bit number equal to the number of switches). Can be implemented. Specifically, each switch 7S connects the electrodeless discharge lamp 13 to either the first path 13p connected to the phase control circuit 8 or the second path 13q bypassing the phase control circuit 8. When the corresponding bit of the control signal SS1 is L, it is a connection state to the first path 13p (a dimming state by the second luminance), and when it is H, the connection to the second path 13q State (non-dimming state by the first luminance). FIG. 10 shows an example of a switching sequence of the control signal SS1 given to the switch group 7 (7S = SW1, SW2,... SWn). The individual electrodeless discharge lamps 13 are set so that the switching frequency is lower than the driving AC frequency.

  In the circuit of FIG. 5, the dimming control of each lamp 13 is performed by the phase chopper control as described above, the frequency of the drive AC applied to each lamp 13 is the same, and the inductances of the plurality of auxiliary coils 6 are also equivalent to each other. It has been established. Therefore, the load impedance of the plurality of electrodeless discharge lamps 13 can be made uniform, and impedance matching with the drive AC generator 12 can be easily performed, so that the efficiency can be increased. The electrodeless discharge lamps 13 connected in parallel may be input with an alternating current having a common frequency. As a result, the step-up winding transformer 114 can be incorporated into the self-excited resonance inverter circuit. Since the winding transformer 114, which is a booster circuit, and the inverter, which is a frequency converter, are shared, further downsizing of the device has been promoted.

Hereinafter, modifications of the lighting circuit will be described.
In the configuration of the lighting device 18 in FIG. 8, the drive AC generator 12 is configured to input drive AC having a different set frequency for each of the plurality of electrodeless discharge lamps 13. The inductances of the plurality of auxiliary coils 6 are set to different values so that the resonance frequencies of the series resonance circuit SR (see FIG. 7) are different from each other in accordance with the set frequency of each lamp 13. The drive AC generation unit 12 includes a multiple AC generation unit 131 that generates a multiple AC in which a plurality of AC waveforms having frequencies corresponding to different set frequencies are superimposed. The multiple alternating current generator 131 has a configuration in which a plurality of oscillators 132 (which may be either sine waves or square waves) having different oscillation frequencies are connected in parallel, and alternating currents of the respective frequencies are combined and output as multiple alternating currents. . The plurality of electrodeless discharge lamps 13 are driven to emit light by extracting an alternating current component having a frequency corresponding to a set frequency from multiple alternating currents by using the series resonance circuit SR as a bandpass filter.

  The dimming control means performs dimming control for reducing the light emission state of the electrodeless discharge lamp 13 from the first luminance to the second luminance. The AC component corresponding to 13 set frequencies is attenuated. In the present embodiment, in the multiple AC generator 13, a control signal SS2 (a similar signal can be obtained by opening the switch at the L level in FIG. 10) to the switch group 133 provided on the combined path of each oscillator 132. The above-described control is performed by selectively disconnecting the oscillator 132 having a frequency to be attenuated by providing a configuration. In this case, the winding transformer 114 does not need to serve as a self-excited oscillation circuit, and as shown in the figure, the primary side coil configuration is a simple configuration in which search coils, tapping, and feedback amplification circuits are omitted. It can be configured.

  On the other hand, as shown in FIG. 9, it is possible to employ a light control means other than the phase control circuit 8 while adopting a power supply configuration similar to the circuit configuration of FIG. In FIG. 9, a switch 132 similar to that in FIG. 8 is provided on the electrodeless discharge lamp 13 side, and a plurality of electrodeless discharge lamps 13 to be dimming controlled are selectively connected to the choke coil 135. The inductance of the series resonance circuit SR (FIG. 7) for impedance reduction changes when the choke coil 135 is connected, and the resonance point deviates from the frequency of the drive AC, so that the load impedance of the electrodeless discharge lamp 13 increases and decreases. The light can be dimmed in the light direction. In this case, since the load impedance increases as the phase shift of the resonance point with respect to the frequency of the drive AC increases, the degree of dimming (that is, the second point) (that is, the resonance point can be adjusted by the inductance of the choke coil). Brightness) can be adjusted. If the second luminance is set to be completely extinguished, the choke coil 135 is omitted, and the electrodeless discharge lamp 13 to be dimmed (that is, extinguished) is opened by a switch and separated from the lighting circuit. It is also possible to do.

The side surface cross-sectional schematic diagram which shows an example of the liquid crystal display device incorporating the backlight apparatus of this invention. Similarly front schematic diagram. Schematic of the lighting circuit of an electrodeless discharge lamp. Sectional drawing which concretely shows the assembly structure of an electrodeless discharge lamp. The circuit diagram which shows the 1st specific structural example of a lighting circuit. The equivalent circuit explanatory drawing of the load impedance of an electrodeless discharge lamp. An explanatory view of a series resonance circuit formed by impedance adjustment inductance. The circuit diagram which shows the 2nd specific structural example of a lighting circuit. The circuit diagram which shows the 3rd specific structural example of a lighting circuit. The timing diagram of the switching signal used for dimming control. The conceptual explanatory drawing of the phase chopper control used for light control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 Liquid crystal display panel 3 Liquid crystal backlight apparatus 6 Auxiliary coil 8 Phase control circuit 12 Drive alternating current generation part 13 Electrodeless discharge lamp 13k Wiring part 14 Translucent insulating tube 15 External electrode 16 Discharge gas 18 Lighting device Lx Impedance Adjustment inductance SR Series resonance circuit 114 Winding transformer S2 Secondary coil 121 Triac 131 Multiple AC generator

Claims (10)

A lighting device for a liquid crystal backlight disposed adjacent to a back surface of a liquid crystal display panel, a translucent insulating tube in which a discharge gas is sealed, and disposed outside the translucent insulating tube and sealed An external electrode for exciting the discharge gas and causing plasma emission discharge to be used, connected to an electrodeless discharge lamp forming a light source of the liquid crystal backlight,
A drive AC generator for applying a light emission drive AC having a low frequency of 30 Hz to 1 kHz to the external electrode of the electrodeless discharge lamp;
A wiring portion that electrically couples the electrodeless discharge lamp and the driving AC generator;
Dimming control means for switching the light emission state of the electrodeless discharge lamp between a first luminance and a second luminance that is darker than the first luminance at a frequency smaller than the driving AC voltage;
In order to reduce impedance at the time of light emission driving of the electrodeless discharge lamp at a set frequency of the light emission driving AC voltage, an electrode portion capacitance formed by the external electrode and the light-transmitting insulating tube of the electrodeless discharge lamp; An impedance adjusting inductance provided to form a series resonant circuit at the set frequency ,
A plurality of the electrodeless discharge lamps are connected in parallel to the drive AC generator,
The dimming control means sets a part of the plurality of electrodeless discharge lamps to the second luminance, sets the remaining lamps more than that to the first luminance, and A lighting device for a liquid crystal backlight , wherein a set of lamps set to the second luminance is periodically switched in a predetermined order within an array of a plurality of whole lamps .   The lighting device of the liquid crystal backlight according to claim 1, wherein a wiring length for connecting the driving AC generator and the electrodeless discharge lamp is set to 10 cm or more.   The drive AC generator includes a winding transformer that boosts a power supply voltage to a voltage necessary for driving the electrodeless discharge lamp, and the impedance adjustment inductance includes a secondary coil of the winding transformer, The lighting device for a liquid crystal backlight according to claim 1, wherein the lighting device is formed by an auxiliary coil provided separately from the secondary coil on a wiring from the secondary coil to the external electrode.   The dimming control means performs dimming control for reducing the light emission state of the electrodeless discharge lamp from the first luminance to the second luminance by phase chopper control of the light emission driving AC using a semiconductor switching element. The lighting device for a liquid crystal backlight according to any one of claims 1 to 3, further comprising a phase control circuit for performing the operation.   The liquid crystal backlight lighting device according to claim 4, wherein the phase control circuit includes a triac of semiconductor switch elements that chop the light emission drive AC. The plurality of electrodeless discharge lamps, each of which is formed horizontally long, are arranged in parallel with each other along the panel surface of the liquid crystal display panel so that the scanning line direction and the longitudinal direction of the liquid crystal display panel coincide with each other. 6. The light control unit according to claim 1, wherein the dimming control means switches the lamps set to the second luminance in such a manner that the lamps are sequentially moved from the first end side to the second end side of the array. A lighting device for a liquid crystal backlight according to claim 1 . 7. The liquid crystal back according to claim 1, wherein the auxiliary coil is provided in a form corresponding to the requirement according to claim 3 and corresponding to the plurality of electrodeless discharge lamps on a one-to-one basis. Light lighting device. The inductances of the plurality of auxiliary coils are determined to be equivalent to each other, and the dimming control means performs dimming control for reducing the light emission state of the electrodeless discharge lamp from the first luminance to the second luminance. The liquid crystal backlight lighting device according to claim 7 , wherein the light emission driving AC phase chopper control using a switching element is performed . 9. The liquid crystal backlight lighting device according to claim 8 , wherein the winding transformer is incorporated in a self-excited resonance inverter circuit for converting the power supply voltage into a light emission drive AC voltage having the set frequency . The drive AC generator is configured to input drive AC having a different set frequency for each of the plurality of electrodeless discharge lamps, and the resonance frequency of the series resonant circuit is different from each other corresponding to the set frequency of each lamp. The inductances of the plurality of auxiliary coils are set to different values from each other,
The drive AC generation unit includes a multiple AC generation unit that generates a multiple AC in which a plurality of AC waveforms having frequencies corresponding to the different set frequencies are superimposed, and the plurality of electrodeless discharge lamps includes the series resonant circuit Is used as a band-pass filter to extract the AC component of the frequency corresponding to the set frequency from the multiple AC and is driven to emit light,
The dimming control means performs dimming control for reducing the light emission state of the electrodeless discharge lamp from the first luminance to the second luminance. 8. The liquid crystal backlight lighting device according to claim 7, wherein an AC component corresponding to a set frequency of the discharge lamp is attenuated .

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