WO2004030421A1

WO2004030421A1 - Discharge lamp lighting device

Info

Publication number: WO2004030421A1
Application number: PCT/JP2003/010832
Authority: WO
Inventors: Norikazu Yamamoto
Original assignee: Matsushita Electric Industrial Co., Ltd.
Priority date: 2002-09-27
Filing date: 2003-08-27
Publication date: 2004-04-08
Also published as: JP2006079830A; AU2003261751A1

Abstract

A discharge lamp lighting device which drives a light emission tube sealed with a rare gas therein and provided with a first electrode inside thereof and a second electrode outside thereof, and which is provided with a lighting circuit between the first and second electrodes to apply an alternating rectangular wave voltage (Va). The lighting circuit outputs a dimming signal (Sa) for controlling an intermittent light emission period (Ton) so as to intermittently emit light at a specified cycle (T) to enable a dimming control, and generates an alternate rectangular wave voltage (Va) starting with a negative rectangular wave voltage (A), based on this dimming signal (Sa) and using the potential of the second electrode as a reference potential during an intermittent light emission period (Ton), for application to the first electrode.

Description

Description Discharge lamp lighting device Technical field

The present invention relates to a discharge lamp device provided with a lighting circuit for applying an alternating rectangular wave voltage to an arc tube having an internal electrode and an external electrode, and a backlight provided with such a discharge lamp device. Background of the Invention

Discharge lamp devices are often required to have brightness according to the ambient illuminance of the environment in which they are used. This is because, if the brightness of the discharge lamp device is kept constant, the brightness may be too high or too low depending on the surrounding illuminance, which may cause discomfort during use. Such a problem becomes particularly apparent when a discharge lamp device is used as a backlight, for example, a backlight of a liquid crystal display device to perform a fine display. Under such circumstances, a backlight for a liquid crystal display device or the like is provided with a dimming function so as to obtain luminance according to the ambient illuminance environment.

In recent years, there has been a demand for a mercury-free mercury-free discharge lamp device to take measures against environmental problems. As a mercury-free discharge lamp device, there is a discharge lamp device using an arc tube filled with a rare gas. Examples of the arc tube containing a rare gas include an internal electrode at one end of the arc tube containing a rare gas composed of at least one of xenon, talypton, and argon, and a tube axis on the outer surface of the arc tube. An arc tube in which an external electrode is formed in a band shape in a direction is known (for example, see Japanese Patent Application Laid-Open No. Hei 6-163005 (page 3, FIG. 1)). In such an arc tube, a high frequency is applied between an internal electrode and an external electrode to generate ultraviolet rays by dielectric barrier discharge, and the phosphor coated on the inner surface of the arc tube is excited by the ultraviolet rays to emit visible light to the outside. To be released. Disclosure of the invention

(Problems to be solved by the invention) FIG. 8 shows a schematic block diagram of a conventional discharge lamp device. The arc tube 1 has an internal electrode 2 provided inside thereof and an external electrode 3 provided outside thereof. External electrode 3 is usually grounded. An applied voltage Va, which is an alternating rectangular wave voltage for causing discharge inside the arc tube 1 to emit light, is applied from the lighting circuit 4 between the internal electrode 2 and the external electrode 3. The reason for applying the alternating rectangular wave voltage is that the overall luminous efficiency (for the entire discharge lamp device) can be increased.

In the lighting circuit 4, the rectangular wave generating circuit 5 generates a rectangular wave signal Sb which is a continuous rectangular wave, and inputs the rectangular wave signal Sb to the drive signal generating circuit 6. The drive signal generation circuit 6 generates a drive signal Sc based on the square wave signal Sb and the dimming signal Sa input from the dimming control circuit 7, and inputs the driving signal Sc to the switching circuit 8. . The switching circuit 8 controls the input to the pulse transformer 9 based on the drive signal Sc, and applies an applied voltage Va, which is an alternating rectangular wave voltage boosted by the pulse transformer 9, between the internal electrode 2 and the external electrode 3. Apply.

9A to 9D are diagrams showing waveforms at various points in the discharge lamp device of FIG. The dimming signal Sa is generated by the dimming control circuit 7, has an intermittent light emission period T on, and is controlled so as to emit light from the arc tube 1 in the intermittent light emission period T on.

The frequency (rectangular wave frequency) of the square wave signal Sb is set to about 20 to 50 kHz, which is necessary for the arc tube 1 to generate a discharge and emit light efficiently, in consideration of the luminous efficiency of the arc tube 1. It is set. The drive signal generation circuit 6, which receives the square wave signal Sb from the square wave generation circuit 5 and the dimming signal Sa from the dimming control circuit 7, performs logical operation on the dimming signal Sa and the square wave signal Sb as appropriate. By processing, a drive signal Sc is generated. The switching circuit 8 to which the driving signal Sc has been input from the driving signal generating circuit 6 operates in synchronization with the driving signal Sc, and generates an applied voltage Va synchronized with the driving signal Sc from the pulse transformer 9. The applied voltage Va is a peak-to-peak voltage of about 2 kV, that is, an alternating rectangular wave voltage of +1 kV to 11 kV. Since the applied voltage V a applied between the internal electrode 2 and the external electrode 3 is determined by the ratio of the intermittent light emission period T on and the light emission stop period T off as shown in the figure, the first cycle T of the applied voltage V a The waveform direction of a1 is not constant because it becomes a positive rectangular wave or a negative rectangular wave depending on the timing condition. Also, since the external electrode 3 is grounded, the applied voltage Va is also the voltage applied to the internal electrode 2, and the timing condition Also occurs when the voltage sign changes.

10A to 10C are diagrams showing enlarged waveforms of the lamp current when the initial applied voltage becomes a positive rectangular wave voltage in the discharge lamp device of FIG. The applied voltage Va and the lamp current Ia flowing through the arc tube 1 are shown corresponding to the intermittent light emission period T on of the dimming signal Sa. Referring to FIG. 10C, the initial stage of the application of the applied voltage Va applied in response to the intermittent light emission period T on of the dimming signal Sa (particularly, the first cycle Ta 1 and the second cycle Ta 2 Looking at the situation of the lamp current Ia in the third cycle T a3), the current Ia hardly flows in the first cycle T al, the lamp current Ia drops significantly, and the current in several cycles thereafter It can be seen that the state has shifted to a stable state after the value has gradually increased. Note that the peak current value of the lamp current Ia is approximately ± 35 to 4 O mA in a stable state (here, the fourth cycle and thereafter). At this time, the frequency of the square wave signal Sb is about 30 kHz, and the cycle such as the first cycle Ta1 is about 33 microseconds. The specifications of the arc tube 1 are the same as those in FIG. 3 described later.

The lamp current I a in the first cycle T a 1 is remarkably reduced to about 10% of the peak current value in both positive and negative directions, and is extremely unstable even in the discharge state, and the light emission state It seems that the transition to is not sufficient. The lamp current Ia in the second cycle Ta2 is about 50 to 80% of the peak current value in both positive and negative directions, and cannot be said to be in a stable discharge state, and the fluctuation width of the current value is large. It seems that the light emission state is not sufficiently stable. The lamp current Ia in the third cycle Ta3 is about 90% of the peak current value in both positive and negative directions, and it is considered that the lamp current Ia has reached an almost stable discharge state (luminous state).

The decrease and variation of the lamp current Ia at the beginning of the application of the applied voltage Va cause flickering of light emission, especially when the dimming rate α is reduced (the intermittent light emission period ο ο η is shortened). Therefore, the effect becomes larger when the number of alternating rectangular wave pulses of the applied Va decreases.

As described above, the conventional discharge lamp device has a problem in that when the dimming rate is reduced, the light emission flickers. In addition, when such a discharge lamp device is used for a backlight, there is a problem that the display flickers and the display becomes difficult to see. A liquid crystal display that requires a particularly wide range of dimming rate and may make the dimming rate extremely small .

There was a problem that the flicker of light emission became remarkable in the backlight for the 4 'device. (How to solve it)

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a discharge lamp device in which light emission does not flicker even when the dimming rate is reduced. Another object of the present invention is to provide a backlight having a small flicker of light emission even when the dimming rate is reduced, particularly a backlight suitable for a liquid crystal display device.

A discharge lamp device according to the present invention is a discharge lamp device for driving an arc tube in which a rare gas is sealed, a first electrode is provided inside, and a second electrode is provided outside, and the first electrode and the second electrode are provided. A lighting circuit for applying an alternating rectangular wave voltage is provided between them. The lighting circuit includes a dimming control circuit that outputs a dimming signal for controlling the intermittent light emitting period, and a dimming control from the dimming control circuit in order to realize dimming control by intermittently emitting light at a predetermined cycle. A circuit for generating an alternating rectangular wave voltage starting from a negative rectangular wave voltage based on the signal and using the potential of the second electrode as a reference potential in an intermittent light emitting period, and applying the generated voltage to the first electrode.

A plurality of the second electrodes may be arranged apart from each other in the tube axis direction of the arc tube. Further, the first electrode may be cylindrical.

A backlight according to the present invention includes at least one arc tube and the above-described discharge lamp device.

The backlight may further include a light guide plate to be arranged on the back surface of the liquid crystal display element. In this case, it is preferable that an arc tube is arranged to face the light guide plate. The arc tube may have an L-shape, in which case it is preferable that the arc tube is arranged to face the side surface of the light guide plate.

(Advantageous effect over conventional technology)

According to the present invention, during the intermittent light emission period for dimming control, the voltage applied to the internal electrode of the arc tube is set to an alternating rectangular wave voltage starting from a negative rectangular wave voltage, so that the intermittent light emission period Since the lamp current (discharge current) at the initial stage of the application of the alternating rectangular wave voltage can be increased, the fluctuation (variation) of the lamp current when the dimming rate is particularly low can be reduced, and stable dimming control with less flicker of light emission can be achieved. Possible A discharge lamp device can be realized.

Further, by using the discharge lamp device of the present invention for a backlight, for example, a backlight for a liquid crystal display device, it is possible to realize a backlight capable of performing a wide range of dimming control with a small amount of flickering of light emission, and having a small flickering of display A display device capable of dimming control (for example, a liquid crystal display device) can be realized. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic block diagram of a discharge lamp device according to the present invention.

FIG. 2A is a waveform diagram of the dimming signal Sa output from the dimming control circuit in the discharge lamp device.

FIG. 2B is a waveform diagram of a rectangular wave signal Sb output from a rectangular wave generation circuit in the discharge lamp device.

FIG. 2C is a waveform diagram of the drive signal Sc output from the drive signal generation circuit in the discharge lamp device.

FIG. 2D is a waveform diagram of the applied voltage Va output from the pulse transformer in the discharge lamp device.

FIG. 3A is an enlarged waveform diagram of the dimming signal Sa output from the dimming control circuit. FIG. 3B is an enlarged waveform diagram of the applied voltage Va output from the pulse transformer. FIG. 3C is an enlarged waveform diagram of the lamp current Ia.

FIG. 4A is a side view showing a structural example of the arc tube and the external electrodes in the discharge lamp device according to the present invention.

FIG. 4B is a cross-sectional view showing a structural example of the arc tube and the external electrode in the discharge lamp device according to the present invention.

FIG. 5 is a diagram illustrating a configuration example of a switching circuit and a pulse transformer.

FIG. 6 is a plan view of a backlight according to the present invention.

FIG. 7 is a diagram showing the relationship between the dimming rate and the flickering feeling for a backlight using a conventional discharge lamp device and a backlight using the discharge lamp device of the present invention.

FIG. 8 is a schematic block diagram of a conventional discharge lamp device.

9A to 9D are diagrams showing waveforms of respective parts in the conventional discharge lamp device of FIG. 10A to 10C show the dimming signal S a, the applied voltage V a at which the voltage at the start of application becomes a positive rectangular wave voltage, and the increase of the lamp current I a in the conventional discharge lamp device of FIG. It is a figure showing a waveform. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of a discharge lamp device and a backlight according to the present invention will be described with reference to the accompanying drawings. Embodiment 1

The discharge device includes a lighting circuit 4 for lighting the arc tube 1.

The arc tube 1 includes an internal electrode 2 provided inside and an external electrode 3 provided so as to contact or adhere to the outside. The external electrode 3 is normally grounded and set to OV. Between the internal electrode 2 and the external electrode 3, the lighting circuit 4 applies an applied voltage Va, which is an alternating rectangular wave voltage for causing a discharge inside the arc tube 1 to emit light. The reason for applying the alternating rectangular wave voltage is that the overall luminous efficiency (as the entire discharge lamp device) can be increased.

The internal electrode 2 has a rod shape and is made of nickel, tungsten, or the like. The plurality of external electrodes 3 are appropriately spaced apart in the tube axis direction on the outer surface of the arc tube 1. By dividing into a plurality of parts, contraction discharge is suppressed, and higher luminance and higher efficiency can be achieved. Although the external electrodes 3 are uniformly spaced, the distance between them may be narrower as the distance from the internal electrodes 2 increases. With such an arrangement, the luminance distribution can be controlled even at a position distant from the internal electrode 2. In addition, in order to prevent light from being shielded by the external electrode 3, it is preferable that the length of the external electrode 3 in the circumferential direction of the arc tube 1 be less than half the circumference of the arc tube 1! ,. In the present embodiment, the internal electrode 2 is not limited to a specific shape, but may have a rod shape, a cylindrical shape, or other various shapes. The internal electrodes 2 may be provided not only at one end as in the present embodiment but also at both ends. In addition, the external electrode 3 is not limited to a specific shape, and may be formed in a band shape in the tube axis direction in addition to the above-described ones. Object, spirally formed in the tube axis direction, mesh-shaped object, etc., as long as they are electrically connected to the outside of the arc tube 1 by contact, connection, printing, etc., length, size, number Is not limited.

The arc tube 1 is a so-called mercury-free fluorescent tube which uses a rare gas as a discharge medium and does not contain mercury. “Mercury-free” means that it is not contained to the extent that main light emission is obtained by rare gas discharge.

The lighting circuit 4 includes a rectangular wave generating circuit 5, a driving signal generating circuit 6, a dimming control circuit 7, a switching circuit 8, and a pulse transformer 9.

The rectangular wave generation circuit 5 generates a rectangular wave signal Sb which is a continuous rectangular wave, and inputs the rectangular wave signal Sb to the drive signal generation circuit 6. The dimming control circuit 7 outputs a dimming signal Sa for controlling dimming.

The drive signal generation circuit 6 generates a drive signal Sc based on the square wave signal Sb and the dimming signal Sa input from the dimming control circuit 7, and inputs the driving signal Sc to the switching circuit 8. . The switching circuit 8 controls the input to the pulse transformer 9 based on the drive signal Sc, and applies an applied voltage Va, which is an alternating rectangular wave voltage boosted by the pulse transformer 9, between the internal electrode 2 and the external electrode 3. Apply. The rectangular wave generation circuit 5, the drive signal generation circuit 6, and the dimming control circuit 7 are composed of an oscillation circuit, a logic circuit, and the like, and include a dimming signal Sa, a square wave signal Sb, and a driving signal Sc. Phase adjustment and the like may be performed by the usual logic design technique.

The drive signal generation circuit 6 includes an inversion phase adjustment circuit 6 m as phase control means. In particular, the inverting phase adjustment circuit 6 m applies the drive signal Sc that has been phase-controlled (logically controlled to “1” or “0”) so that the first cycle of the applied voltage Va starts from a negative rectangular wave voltage. appear. In other words, the drive signal Sc is controlled so that the applied voltage Va, which is an alternating rectangular wave voltage, always starts from a negative rectangular wave voltage at the start of application during the light emission period controlled during dimming, and is supplied to the switching circuit 8. Is done. The inverted phase adjustment circuit 6 m is a logic circuit of any form as long as it generates a drive signal Sc controlled so that the first cycle in the light emission period of the applied voltage Va starts from a negative rectangular wave voltage. It may be. When the drive signal generation circuit 6 does not include the inversion phase adjustment circuit 6 m, the switching circuit 8 is controlled so that the applied voltage Va starts from a negative rectangular wave voltage. A similar operation is possible by providing a circuit as phase control means. The rectangular wave generation circuit 5, the drive signal generation circuit 6, and the dimming control circuit 7 are controlled by a microcomputer so that the first cycle of the applied voltage Va starts from a negative square wave voltage. Needless to say, the drive signal Sc adjusted to the above may be generated. The operation of the discharge lamp device will be described with reference to FIGS.

The dimming control circuit 7 outputs a dimming signal Sa which is a control signal for dimming control as shown in FIG. 2A. The dimming signal Sa has an intermittent light emission period T on, and is intermittently controlled so as to generate light emission of the arc tube 1 during this intermittent light emission period To n. The frequency (dimming frequency) of the dimming signal Sa is set to a frequency of about 100 to 300 Hz in order to avoid flickering due to the repetition of the intermittent light emission period Ton and the light emission stop period Toίf. Preferably. One cycle T (= Ton + Toff) is constituted by the intermittent light emission period Ton and the light emission stop period Toff. In one cycle T determined by the dimming frequency, if the intermittent light emission period Ton is made longer than the light emission stop period Toff, the brightness of the arc tube 1 can be increased. If the intermittent light emission period T on is shortened, the brightness of the arc tube 1 can be reduced. The value obtained by the formula: H = (T on / T) X I 00 (%) is defined as a dimming rate α (%). In other words, a dimming rate of 100% indicates a continuous light emission state, a dimming rate of 0% indicates a light emission stop state, and a dimming rate of 50% indicates a state in which the light emission period and the light emission stop period are equal. .

The square wave generating circuit 5 outputs a square wave signal Sb as shown in FIG. The frequency (square wave frequency) of the square wave signal Sb is set to about 20 to 50 kHz necessary for the arc tube 1 to generate a discharge and emit light in consideration of the luminous efficiency of the arc tube 1. Is preferred. If the external electrode 3 is an electrode that is appropriately spaced apart in the tube axis direction on the outer surface of the arc tube 1, the emission efficiency can be further increased by setting the rectangular wave frequency to about 30 to 45 kHz. It was confirmed.

The drive signal generating circuit 6 receives the rectangular wave signal Sb from the rectangular wave generating circuit 5 and the dimming signal Sa from the dimming control circuit 7, and converts these signals Sa and Sb into an inversion phase adjusting circuit 6. By performing a predetermined logical operation on m, a drive signal Sc as shown in FIG. 2C is generated. In the present embodiment, the predetermined logical operation is to logically invert the dimming signal Sa, and calculate the logical sum of the logically inverted dimming signal Sa and the rectangular wave signal Sb. Drive signal S c Is set to maintain, for example, logic “1” in the light emission stop period T off, but becomes a signal synchronized with the rectangular wave signal S b in the intermittent light emission period T on.

The switching circuit 8 receives the drive signal Sc from the drive signal generation circuit 6, operates in synchronization with the drive signal Sc, and switches the pulse transformer 9 appropriately. Thereby, the pulse transformer 9 generates an applied voltage Va synchronized with the drive signal Sc as shown in FIG. 2D. In the present embodiment, the drive signal Sc is described as having a logic "1" during the light emission stop period Toff and having the same logic as the rectangular wave signal Sb during the intermittent light emission period Ton. However, the present invention is not limited to this. For example, by incorporating a logic inversion circuit in the switching circuit 8, it is also possible to configure a logic signal using the same logic signal as in the related art. In other words, if the applied voltage Va can be controlled so that the applied voltage Va starts from the negative rectangular wave voltage (A) in the transition to the intermittent light emission period Ton, the configuration of the logic circuit as the phase control means Can be configured in any way. Further, the phase control means may be constituted by a method other than the logic circuit. Applied voltage Va output from pulse transformer 9 is about 2 k peak-to-peak voltage

V, that is, an alternating rectangular wave voltage of +1 kV to 1 kV. The applied voltage V a applied between the internal electrode 2 and the external electrode 3 is, in contrast to the prior art shown in FIG. 9D, a negative square wave voltage (A) and an alternating square wave voltage starting from Is controlled so that That is, the first cycle Ta1 of the applied voltage Va always starts with a negative rectangular wave voltage and ends with a positive rectangular wave voltage. Since the external electrode 3 is grounded, the applied voltage Va is also the voltage applied to the internal electrode 2, and a negative voltage is always applied to the internal electrode 2 first.

3A to 3C are diagrams showing enlarged waveforms of the applied voltage and the lamp current in the discharge lamp device of the present embodiment. FIG. 3B shows the applied voltage Va and FIG. 3C shows the lamp current flowing through the arc tube 1 corresponding to the intermittent light emission period Ton in the light control signal Sa for light control shown in FIG. 3A. Ia is shown respectively. The applied voltage Va is about 2 kV in peak-to-peak value. Initial stage of the start of application of the applied voltage Va generated in response to the intermittent light emission period Ton of the dimming signal Sa (particularly, the first cycle Ta1, the second cycle Ta2, and the third cycle Ta3). Looking at the situation of the lamp current I a in the first cycle T a 1 Indicates that almost no current flows at the time of the negative rise, but the current that flows when shifting from the negative square wave voltage to the positive square wave voltage is about 50% of the peak current value, and shifts from negative power to positive. In this case, the current flowing during the operation is greatly increased as compared with the prior art. Since the lamp current I a in the second cycle Ta 2 is about 90% of the peak current value in both positive and negative directions, it is considered that the lamp has almost reached a stable discharge state (luminous state). It is.

As described above, the decrease phenomenon of the lamp current Ia in the early stage of the start of the application of the applied voltage Va disappears earlier than in the related art, and the lamp current Ia shifts to a substantially stable state in the second cycle. Therefore, the flicker of the arc tube 1 can be greatly improved as compared with the related art. The reason why the decrease in the lamp current Ia is small and the lamp current Ia recovers quickly is that the internal electrode 2 operates as a cathode first, so that the discharge of electrons into the arc tube 1 is stable and sufficient. It is thought to be done. Note that it is more effective if the surface area of the internal electrode 2 is smaller than the surface area of the external electrode 3.

The peak current value of the lamp current Ia is about 35 to 4 OmA in a stable state (here, the third cycle or later). In addition, the rectangular wave frequency of the rectangular wave signal Sb at this time is about 30 kHz, and the cycle such as the first cycle Ta1 is about 33 microseconds. Similar characteristics were obtained when the square wave frequency was about 20 to 50 kHz. Further, the period of transition to the stable state and the like vary depending on the applied voltage Va, the specifications of the arc tube 1, and other conditions, and are not limited to this example.

The specifications of the arc tube 1 used for measuring the characteristics shown in FIGS. 3A to 3C are as follows. The arc tube 1 is processed into an L-shape, and has a diameter of 2.6 mm, an inner diameter of 2. Omm, and a length of 252 mm. The sealed gas is a mixed gas of Xe and Ar (Xe: Ar = 6: 4), and the sealed gas pressure is 13.3 kPa to 26 kPa. The shape of the internal electrode 2 is a rod made of tungsten. When the internal electrode 2 is formed in a cylindrical shape (cup shape, hollow shape), the surface area of the internal electrode 2 increases, and the number of electrons emitted from the internal electrode 2 into the tube can be increased. Since the initial lamp current Ia can be increased and the stability of the lamp current Ia can be increased, the flicker of light emission can be further reduced. The external electrodes 3 are arranged outside the arc tube 1 with a width of 1 to 3 mm and at an interval of 1 to 5 mm, and are grounded. As described above, according to the discharge device or the like of the present embodiment, the lamp current Ia can be reduced and its variation can be improved at the initial stage of the application of the applied voltage Va. In the case where the number of pulses of the applied voltage Va is reduced by shortening Ton), the improvement effect becomes remarkable.

4A and 4B are views showing an example of the structure of the arc tube and the external electrode 3 in the discharge lamp device of the present embodiment.

FIG. 4A is a side view of the arc tube 1, and FIG. 4B is a cross-sectional view taken along line BB in FIG. 4A. The arc tube 1 is formed of a cylindrical glass tube, in which a mixed gas of Xe-Ar is sealed as a discharge medium. A phosphor layer (not shown) is provided on the inner surface of the glass tube. Inside the end of the arc tube 1, an internal electrode 2 made of tungsten is provided, led out to the outside by a lead wire 2a, and is connectable to a lighting circuit 4. The external electrode 3 is composed of a plurality of divided electrode portions 3a spaced apart from each other in the tube axis direction and a connecting portion 3b for connecting them to each other, and can be connected to the lighting circuit 4 by the lead wire 3c. Has been. The connecting portion 3b has two functions of an electrical function of connecting the divided electrode portions 3a to each other and a mechanical function of connecting and holding the divided electrode portions 3a to each other. The external electrode 3 is made of an elastic phosphor bronze plate, and each of the divided electrode portions 3a is in contact with the glass tube in the circumferential direction of the glass tube, and a plurality of external electrodes are arranged in the direction of the tube axis of the arc tube 1. The cross-sectional shape is formed to be uneven so as to act as. The connecting portion 3b is arranged at a position away from the circumferential direction of the glass tube so as not to contact the glass tube. In addition, the internal electrodes 2 may be provided at both ends of the arc tube 1, which can further reduce and reduce the lamp current la, and especially when the length of the arc tube 1 is long, the internal electrode 2 is large. It works. The arc tube 1 is pressed by a light guide plate (not shown) from the direction of arrow 1p so that the glass tube and the external electrode 3 are pressed against each other.

FIG. 5 is a diagram illustrating a configuration example of the switching circuit 8 and the pulse transformer 9. The switching circuit 8 is composed of switching elements 8A and 8B composed of MOS FETs and a switching control circuit 8C for controlling the switching elements 8A and 8B. Switching element 8 A and switching element 8 B are connected to respective ends of the primary winding of pulse transformer 9. In the center of the primary winding of pulse transformer 9 Is supplied with DC voltage DC. The switching control circuit 8C to which the driving signal Sc is input turns on the switching element 8A and the switching element 8B alternately in synchronization with the driving signal Sc, and supplies a current to the primary winding of the pulse transformer 9. By flowing the current, a boosted alternating rectangular wave voltage is induced in the secondary winding of the pulse transformer 9. The internal electrode 2 and the external electrode 3 of the arc tube 1 are connected to the secondary winding of the pulse transformer 9, and an alternating rectangular wave voltage is applied between the internal electrode 2 and the external electrode 3.

For example, when the switching element 8A is turned on, a current flows in the direction indicated by the arrow A, and a current is induced in the secondary winding of the pulse transformer 9 in the direction indicated by the arrow C. In this case, since the internal electrode 2 has a higher potential than the external electrode 3, a positive rectangular wave voltage is applied to the internal electrode 2. Conversely, when the switching element 8B is turned on, a current flows in the direction indicated by the arrow B, and a current is induced in the secondary winding of the pulse transformer 9 in the direction indicated by the arrow D. In this case, since the external electrode 2 has a low level and a potential with respect to the external electrode 3, a state in which a negative rectangular wave voltage is applied to the internal electrode 2 is shown. The current direction of the secondary winding of the pulse transformer 9 varies depending on the winding direction, and is not limited to the illustrated case. That is, depending on the winding direction of the pulse transformer 9, the connection of the electrodes (the internal electrode 2 and the external electrode 3) of the arc tube 1 may be reversed. In short, the connection may be made such that the first period & 1 of the applied voltage &, which is an alternating rectangular wave voltage generated corresponding to the intermittent light emission period T on, starts from a negative rectangular wave voltage. The circuit configuration is not limited to this, as long as the same rectangular wave voltage can be applied to the arc tube 1 by controlling the drive signal generation circuit 6, and a half-bridge circuit, a full-bridge circuit, etc. It may be something. Embodiment 2

FIG. 6 is a plan view showing a schematic configuration of a backlight according to the present invention including the above lighting circuit. The backlight includes a light guide plate 10 having a predetermined shape for a backlight, two arc tubes 1 (arc tubes l a and l b) processed into an L shape, and a lighting circuit 4. The specifications of the arc tube 1 (the arc tubes l a and l b) and the lighting circuit 4 in FIG. 6 are the same as those of the discharge lamp device in the first embodiment.

Opposite to the end side surface of the light guide plate 10, two arc tubes 1 (light emitting Light tubes la, lb) are symmetrically arranged. FIG. 6 shows a so-called edge light type backlight configuration, but it is also possible to use a direct type backlight in which the arc tube 1 is arranged to face the light guide plate 10 in the plane direction. In any case, a useful effect of reducing flicker can be obtained. Since the arc tubes la and 11) are in a V-shape, they can be opposed to the four sides of the light guide plate 10 with only two tubes. In addition, the arc tubes la and 1b are provided with internal electrodes 2 at both ends, whereby the internal electrode 2 of the arc tube 1a and the internal electrode 2 of the arc tube 1b are adjacent to each other when they are arranged to face each other. The adjacent internal electrodes 2 are commonly connected to each other and connected to a predetermined terminal of the lighting circuit 4. As for the external electrode 3 as well, the light emitting tubes 1a and 1b are commonly connected to each other and connected to the other terminal of the lighting circuit 4, so that the lighting circuit 4 can be composed of only one circuit. Although the internal electrode 2 on the side to which the lighting circuit 4 is not connected is not shown, if the internal electrode 2 is provided here and the lighting circuit 4 is connected, the effect of reducing flicker is further enhanced, and It is possible to cope with the enlargement of the light plate 10 (lengthening of the arc tube 1).

The light guide plate 10 has a size corresponding to a 7-inch wide size liquid crystal display device, and has a long side of 16 O mm and a short side of 97 mm. A silk-printed dot pattern (not shown) was used for light distribution control. As the optical sheet, one diffusion sheet was arranged on the light guide plate 10.

FIG. 7 is a diagram showing a result of comparing the relationship between the dimming rate and the flickering feeling for backlights using the lighting device of the present invention and the conventional technique. The degree of flicker when the dimming rate α was changed for the conventional technology and the backlight according to the present invention was examined as a flickering feeling for 10 subjects. The dimming rate α was changed every 10% between 100 and 10%, and every 1% between 100% and 1%. There were four evaluation levels: (Α) flicker was not felt at all, (らない) flicker was not a concern, (C) flicker was somewhat worried, and (D) flicker was felt. Rating level 記号 or B is indicated by the symbol “〇” when 10 people answered, and rating A or B is indicated by the symbol “△” when 5 or more (9 or less) responded. If the number of respondents who answered A or B is 4 or less, it is indicated by the symbol “X”. In the conventional case, the dimming rate was “〇 |” at 100 to 10%, “mm” at 9 to 8%, and “X” at 7% or less. Against this According to the present invention, however, the dimming rate was “〇” at 100 to 5%, “△” at 4 to 3%, and “X” at 2% or less. In other words, while the conventional device shows some flicker when the dimming ratio is 9% or less, the present invention only shows some flicker when the dimming ratio is 4% or less. It can be seen that the flicker (feeling of flicker) is greatly improved as compared with.

If the backlight according to the present invention is used in a liquid crystal display device as a backlight for a liquid crystal display device, it is sufficient even when an extremely small dimming rate is required, for example, in a vehicle-mounted navigator using the liquid crystal display device. It is possible to realize a liquid crystal display device with little flickering of luminescence which can be used for a liquid crystal display. Note that it is naturally possible to use the backlight directly as a backlight without using the light guide plate 10, and in this case as well, a backlight with less flickering of light emission can be realized. Industrial potential

INDUSTRIAL APPLICABILITY The discharge lamp device of the present invention can be applied to a lighting device for an arc tube having an internal electrode and an external electrode, and can realize a wide range of dimming control with reduced light emission flicker. In addition, the lighting device of the present invention can be applied to a backlight (for example, a backlight for a liquid crystal display device), and can realize a backlight capable of performing a wide range of dimming control with a small amount of flicker of light emission and a small amount of flicker of a display. A display device capable of dimming control (for example, a liquid crystal display device) can be realized. Although the present invention has been described with respect to particular embodiments, many other variations, modifications, and other uses will become apparent to those skilled in the art. Therefore, the present invention is not limited to the specific disclosure herein, but only by the appended claims. This application is related to a Japanese patent application, Japanese Patent Application No. 2002-28283169 (submitted on Sep. 27, 2002), the contents of which are incorporated herein by reference. Incorporated in.

Claims

The scope of the claims

1. A discharge lamp device for driving an arc tube in which a rare gas is sealed, a first electrode is provided inside, and a second electrode is provided outside,

A lighting circuit for applying an alternating rectangular wave voltage between the first electrode and the second electrode;

A dimming control circuit that outputs a dimming signal for controlling the intermittent light emitting period in order to realize dimming control by intermittently emitting light at a predetermined cycle;

Based on the dimming signal from the dimming control circuit, an intermittent light emitting period is used to generate an alternating rectangular wave voltage starting from a negative rectangular wave voltage with the electric potential of the second electrode as a reference potential, to the first electrode. Circuit to apply

Discharge lamp device characterized by the above-mentioned.

2. The discharge lamp device according to claim 1, wherein a plurality of the second electrodes are spaced apart in a tube axis direction of the arc tube.

3. The discharge device according to claim 1, wherein the first electrode has a cylindrical shape.

4. A backlight comprising at least one arc tube and the discharge lamp device according to any one of claims 1 to 3.

5. The backlight according to claim 4, further comprising a light guide plate to be arranged on the back surface of the liquid crystal display element, wherein the arc tube is arranged to face the light guide plate.

6. The backlight according to claim 5, wherein the arc tube has an L shape, and is arranged to face a side surface of the light guide plate.