JP2007280884A - Lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lighting device capable of detecting total current flowing in all discharge tubes with a circuit of simple structure when two-tube serial light sources connecting in series two discharge tubes are connected in parallel a plurality of pieces. <P>SOLUTION: The lighting device uses as a light source a plurality of sets of two-tube serial light sources in which two discharge tubes are arranged in parallel and one of the terminals in the same direction of the two discharge tubes is connected. In the light source, a plurality of sets of two-tube serial light sources are arranged in parallel. Furthermore, at the series connection portion of the respective two discharge tubes of the plurality of sets of two-tube serial light sources, a total current detection circuit is installed in which coils having respectively equal number of windings and the same polarity are connected and the coils connected to the serial connection portion of the respective two discharge tubes and the coil for taking out the total current of the plurality of sets of two-tube serial light sources are wound on the same core. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an illuminating apparatus in which two discharge tubes are arranged in parallel, and a plurality of discharge tubes are simultaneously turned on by a plurality of two-tube series light sources connected to one of the terminals.

  For example, in a display device that does not emit light, such as a liquid crystal display used as a liquid crystal television or a computer display device, an illumination device that illuminates from the back side of the display surface, a so-called backlight device is used. In such an illumination device, a cold cathode fluorescent lamp (CCFL) is often used as an illumination light source. In the above lighting device, as the screen size increases, the length of the cold-cathode tubes used increases and the number thereof increases.

  However, it is generally said that it is difficult to connect two-tube series light sources of cold-cathode tubes in a multistage parallel manner in a plane, that is, to use a plurality of two-tube series light sources arranged in parallel. For example, as shown in FIG. 11, when four cold-cathode tubes (CCFL) are connected in series and two sets of two-tube series light sources are arranged in parallel, a cold-cathode tube is shown as indicated by an arrow. + Side and-side of Since the operating frequency of the cold cathode tube is relatively high, there is a problem that the potential difference at this intersection is large, a leak current is generated, and the overall efficiency is lowered.

  Therefore, when two-stage serial light sources of cold cathode tubes are connected in parallel in multiple stages, it is general to employ a configuration using separate inverters 68 as shown in FIG. 12, for example. However, this requires a plurality of inverters 68, which increases the cost. Further, since the oscillation of each inverter 68 is asynchronous, the influence due to mutual interference cannot be ignored. Further, as shown in FIG. 13, there is a method of causing two inverters 72 to oscillate based on one oscillation circuit 70, but this method further increases the cost.

  In contrast, Patent Document 1 proposes a backlight device as shown in FIG. 14, for example. The backlight device of Patent Document 1 includes an illumination device including an inverter 68 and four cold cathode fluorescent lamps (CCFLs), and a light guide plate 74. Here, two cold-cathode tubes are connected in series by lead wires, and two sets of cold-cathode tube light sources in parallel are arranged in parallel along the upper and lower long sides of the light guide plate 74. . The inverter 68 is disposed on the short side on the left side of the light guide plate 74 and is connected to each cold cathode tube by a lead wire. The short side on the right side of the light guide plate 74 is used for routing the lead wire.

  If it is the method of patent document 1, since the other 2 tube | pipe serial light source is arrange | positioned in parallel so that the circumference | surroundings of one 2 tube | pipe serial light source may be enclosed, without the + side and-side of a cold cathode tube crossing, It is possible to connect two-stage cold-cathode tube serial light sources in parallel.

  Next, in an illuminating device using a plurality of cold cathode tubes, it is necessary to make the tube current flowing through each of the cold cathode tubes substantially uniform and to suppress variations in luminance.

  On the other hand, in Patent Document 2, two coils are connected to the secondary winding of the step-up transformer, and magnetic fluxes generated by these two coils are opposed to each other so that the magnetic fluxes are offset. In the inverter circuit for a discharge tube in which a discharge tube is connected to each of the two coils and the tube current flowing through each discharge tube is balanced, an inverter circuit having an inductance related to the balance of the shunt transformer It is disclosed that the reactance at the operating frequency exceeds the negative resistance of the discharge tube.

  However, in Patent Document 2, since it is necessary to insert a current shunting transformer between the step-up transformer and the discharge tube, it is necessary to install the shunting transformer in the high-pressure portion of the discharge tube. For this reason, it is easily affected by leakage and the like, and the efficiency is reduced. Also, as described in Patent Document 2, there is a method in which a ballast capacitor is inserted into each cold cathode tube, but a voltage loss corresponding to the voltage divided by the ballast capacitor is large, which also causes a reduction in efficiency. There was a problem.

  In addition, in a lighting device using a cold cathode tube, when the abnormality occurs in the cold cathode tube, it is detected and, for example, the operation of the piezoelectric transformer is stopped to prevent the piezoelectric transformer from being destroyed. Safety measures such as providing a circuit are necessary.

  On the other hand, in FIG. 1 of Patent Document 3, a current transformer is provided between the piezoelectric transformer and the cold cathode tube, and a secondary side voltage induced by a change in the primary side current of the high-voltage current path is detected. A piezoelectric transformer driving circuit is disclosed. In addition, FIG. 2 shows an example of applying two cold cathode tubes connected in parallel to each other in a high-voltage current path between the piezoelectric transformer and the two cold cathode tubes. It is disclosed that a current transformer is provided independently.

  However, in Patent Document 3, when a plurality of cold-cathode tubes are used, a current transformer is provided for each cold-cathode tube, and the output of the plurality of current transformers is returned to the operational amplifier for processing. There was a problem that the scale was large.

JP 2002-164185 A JP 2004-335443 A JP 2003-249393 A

  An object of the present invention is to solve the problems based on the prior art, and when all two discharge tubes connected in series are connected in parallel, all discharges can be made with a simple circuit. An object of the present invention is to provide an illuminating device capable of detecting a total current flowing in a tube.

In order to achieve the above object, the present invention provides a plurality of sets of two-tube series light sources in which two discharge tubes are arranged in parallel and one terminal in the same direction of the two discharge tubes is connected as a light source. A lighting device that performs
In the light source, the plurality of sets of two-tube serial light sources are arranged in parallel,
In the series connection portion of the two discharge tubes of each of the plurality of sets of two-tube series light sources, coils having the same number of windings and the same polarity are connected. A total current detection circuit is provided in which a coil connected to a series connection portion of a discharge tube and a coil for taking out a total current of the plurality of sets of two-tube series light sources are wound around the same core. An illumination device is provided.

  Here, in the light source, two discharge tubes of the i + 1-th set (i is a natural number of 1 or more) of two-tube series light sources surround the two discharge tubes of the i-th set of two-tube series light sources. Are preferably arranged in parallel.

Furthermore, a voltage-controlled oscillation circuit that generates a fundamental wave whose oscillation frequency changes according to the current value of the total current supplied from the total current detection circuit;
A drive circuit that generates a drive signal of a predetermined voltage whose oscillation frequency changes according to the frequency of the fundamental wave supplied from the voltage controlled oscillation circuit;
When a drive signal having a predetermined voltage is input from the drive circuit, the transformer includes a transformer that outputs a voltage-transformed signal having a predetermined voltage from the drive signal at a frequency substantially equal to the drive signal that is input to the light source.
Preferably, the voltage controlled oscillation circuit controls the frequency of the fundamental wave in accordance with a current value of the total current so that the total current always becomes a substantially constant value.

  Further, a protection circuit may be provided that controls to stop the output of the drive signal from the drive circuit when the current value of the total current supplied from the total current detection circuit is not within a predetermined range. preferable.

  Moreover, it is preferable that the transformed signal input to the light source is a two-phase signal having a phase difference of about 180 degrees.

  The discharge tube is preferably a cold cathode tube.

  According to the present invention, the total current of a plurality of sets of two-tube series light sources can be detected by the total current detection circuit. The voltage controlled oscillator circuit controls the frequency of the fundamental wave in accordance with the current value of the total current, thereby controlling the total current to be a substantially constant value, and as a result, the luminance of the light source is always set to a substantially constant value. Kept.

  In addition, according to the present invention, by providing the protection circuit, it is possible to prevent the transformer from being destroyed by stopping the output of the drive signal when any abnormality occurs in the discharge tube of the light source. By detecting that a system abnormality has occurred, the system is stopped and various accidents that can occur in a chain can be prevented.

  Below, based on the preferred embodiment shown in an accompanying drawing, the illuminating device of this invention is demonstrated in detail.

  FIG. 1 is a block schematic diagram of an embodiment showing the internal configuration of the illumination device of the present invention. The illuminating device 10 shown in the figure is arranged to arrange two sets of two-tube serial light sources composed of four cold-cathode tubes in parallel, and simultaneously illuminate the four cold-cathode tubes. A drive circuit 14, a voltage controlled oscillation circuit 16, a piezoelectric ceramic transformer 18, a ballast capacitor 20, a light source 22, a balance circuit 24, a total current detection circuit 26, and a current difference detection circuit 28 are provided.

  The power source 12 is a DC power source that outputs a DC voltage DC 24V. This DC voltage DC24V is supplied to the drive circuit 14.

  Note that the DC voltage output from the power supply 12 is not limited to DC24V.

  Subsequently, the voltage-controlled oscillation circuit 16 generates a fundamental wave having an initial frequency of about 40 KHz, and the oscillation frequency depends on the current value of the total current of the cold cathode tubes supplied from the total current detection circuit 26. Change. For example, when the total current is smaller than the reference current amount, the voltage controlled oscillation circuit 16 controls the fundamental wave frequency to be lower than the initial frequency, and conversely, when the total current is larger than the reference current amount. Controls the fundamental frequency to be higher than the initial frequency. This fundamental wave is also supplied to the drive circuit 14.

  The specific configuration of the voltage controlled oscillation circuit 16 is not limited at all, and various configurations of circuits that realize the same function can be used. Further, the frequency of the fundamental wave is not limited to about 40 KHz. The reference current amount can be controlled from the outside and can be varied as necessary.

  The drive circuit 14 generates a two-phase drive signal for driving the piezoelectric ceramic transformer 18 based on the DC voltage DC24V supplied from the power supply 12 and the fundamental wave supplied from the voltage controlled oscillation circuit 16. In the present embodiment, the two-phase drive signal is an AC signal (sine wave) having a phase difference of about 180 degrees at about 650 Vp-p (peak to peak) and about 40 KHz. The frequency of the drive signal changes according to the frequency of the fundamental wave, and the total current of the cold-cathode tube, that is, the luminance of the light source 22 is always kept at a substantially constant value.

  Note that the signal for driving the piezoelectric ceramic transformer 18, that is, the drive signal output from the drive circuit 14, is not limited to two phases, and may be a single-phase signal with one side being ground GND, for example.

  Further, the drive circuit 14 has a current value of the current difference supplied from the current difference detection circuit 28 when the current value of the total current of the cold cathode tubes supplied from the total current detection circuit 26 is not within a predetermined range. A protection circuit 30 is provided for controlling the output of the drive signal from the drive circuit 14 to stop when the upper limit value is exceeded. By providing the protection circuit 30, it is possible to prevent the piezoelectric ceramic transformer 18 from being destroyed in the event that some abnormality occurs in the cold cathode tube of the light source 22, or to detect that a system abnormality has occurred. The system can be shut down and various accidents that can occur in a chain can be prevented.

  Note that specific circuit configurations of the drive circuit 14 and the protection circuit 30 are not limited at all, and various configurations of circuits that realize the same function can be used. Further, the value of the upper limit value of the current difference can be controlled from the outside and can be varied as necessary. For example, the current flowing through each of them may be converted into an absolute amount from the information on the total current and the current difference, and the drive signal may be stopped when the absolute amount exceeds a set upper and lower limit value.

  In the case of this embodiment, the piezoelectric ceramic transformer 18 uses a high-power piezoelectric transformer disclosed in Japanese Patent Application Laid-Open No. 2005-129475 related to one of the present applicants. Its configuration and operation are described in the publication, and will be briefly described below.

  As shown in FIG. 2, the piezoelectric ceramic transformer 18 of the present embodiment includes a piezoelectric ceramic 32, first input electrodes 34a and 34b, second input electrodes 36a and 36b, a first output electrode 38, and a second output. The electrode 40 is configured.

  The piezoelectric ceramic 32 has a rectangular flat plate shape with a predetermined thickness. The length L is 80 mm, the width W is 18 mm, and the thickness t is 4 mm. In the case of the present embodiment, the piezoelectric ceramic 32 is configured such that the ratio W / L of the dimension L in the length direction to the dimension W in the width direction is about 0.2, and the secondary vibration in the length direction during operation. Vibrates in mode (λ mode). Accordingly, the center frequency of vibration is determined by the length dimension L, and the voltage amplification factor is determined by the ratio L / t between the length dimension L and the thickness dimension t.

  The piezoelectric ceramic 32 is divided into a first region 42, a second region 44, a third region 46, a fourth region 48 and a fifth region 50 from the left end in the length direction in FIG. 2 to the right end. The ratio of the length of each region in the length direction is about 2: 2: 1: 2: 2. The second region 44 and the fourth region 48 are input portions for input voltages (drive signals input from the drive circuit 14), and the first region 42 and the fifth region 50 are outputs of two-phase output voltages (transformed signals). The third region 46 is a rigid part.

  The first input electrodes 34a, 34b, the second input electrodes 36a, 36b, the first output electrode 38, and the second output electrode 40 are made of baked silver.

  The first input electrodes 34a and 34b are respectively disposed on both surfaces (upper and lower surfaces in FIG. 2) of the second region 44 of the piezoelectric ceramic 32 in the thickness direction. The first input electrode 34a on the upper surface is an electrode on the plus (+) side of polarization described later, and the first input electrode 34b on the lower surface is an electrode on the minus (−) side. Similarly, the second input electrodes 36a and 36b are respectively disposed on both surfaces of the fourth region 48 of the piezoelectric ceramic 32 in the thickness direction. Conversely, the second input electrode 36a on the upper surface is an electrode having a negative polarity of polarization, and the second input electrode 36b on the lower surface is an electrode on the positive side.

  Further, the first output electrode 38 is disposed on the left surface in the length direction of the piezoelectric ceramic 32 in FIG. 2, and similarly, the second output electrode 40 is disposed on the right surface in the length direction of the piezoelectric ceramic 32. .

  In addition, as indicated by an arrow in FIG. 2, the first region 42 is polarized from the second region 44 side toward the left side in the length direction of the piezoelectric ceramic 32, and similarly, the fifth region 50 is the fourth region. It is polarized from the region 48 side toward the right side in the length direction of the piezoelectric ceramic 32. The second region 44 is polarized from the lower surface side in the thickness direction of the piezoelectric ceramic 32 toward the upper surface side. Conversely, the fourth region 48 is from the upper surface side in the thickness direction of the piezoelectric ceramic 32 to the lower surface side. Polarized towards. The third region 46 is in an unpolarized state.

  As described above, two sets of input electrodes, the first input electrodes 34a and 34b and the second input electrodes 36a and 36b, are attached in the thickness direction of the piezoelectric ceramic 32, and the polarization directions with respect to the thickness direction are respectively set. It is about 180 degrees different. Accordingly, the first input electrodes 34a and 34b are configured such that the upper surface is a plus side and the lower surface is a minus side, and the second input electrodes 36a and 36b are arranged such that the upper surface is a minus side and the lower surface is a plus side. .

  The piezoelectric ceramic transformer 18 has a two-phase phase difference of about 180 degrees from the drive circuit 14 to the first input electrode 34a and the second input electrode 36a, and the second input electrode 36b and the first input electrode 34b. Drive signal (sinusoidal AC signal) or a single-phase signal with GND on one side is input.

  Specifically, in the case of two-phase input, one drive signal is input to the input terminal 52a of the first input electrode 34a and the input terminal 54a of the second input electrode 36a, and the input terminal 52b of the first input electrode 34b. And the other drive signal is input to the input terminal 54b of the second input electrode 36b. Further, in the case of single-phase input with one side being ground GND, the drive signal is applied to the input terminal 52a of the first input electrode 34a and the input terminal 54a of the second input electrode 36a, and the input terminal 52b of the first input electrode 34b is What is necessary is just to connect GND to the input terminal 54b of the two input electrodes 36b.

  When a drive signal is given as an input voltage, stress is generated in the piezoelectric ceramic 32 due to the inverse piezoelectric effect, and the second region 44 and the fourth region 48 are mechanically strained in the thickness direction. Then, a potential difference occurs in the polarization direction between the first region 42 and the fifth region 50 due to the piezoelectric effect. As a result, from the first output electrode 38 and the second output electrode 40, a two-phase transformed signal (sine wave AC signal) having a frequency approximately equal to that of the drive signal and having a phase higher by about 180 degrees than the drive signal. Are simultaneously output from the respective output terminals 56 and 58.

  In this embodiment, the input voltage of 650 Vp-p of the drive signal input from the drive circuit 14 is boosted about 10 times, and a two-phase output voltage of 6500 Vp-p is obtained. As will be described later, if the cold cathode tube used has a tube length of 527 mm and a tube outer diameter of about 2.6, it can be lit at a voltage of 1000 to 1200 Vrms, but in the present embodiment, Since two cathode tubes are connected in series, the voltage is increased to a voltage of 2000 to 2400 Vrms necessary for lighting two cold cathode tubes.

  Further, since the unpolarized third region 46 is provided in the central portion of the piezoelectric ceramic 32, the unpolarized portion functions as a rigid rigid body portion that does not vibrate, and vibration in the torsional direction that is generated when a transform signal is output. The mode and the vibration mode in the meandering direction can be more suitably suppressed.

  In the present embodiment, a piezoelectric ceramic transformer capable of 30W class high power output is used as the transformer. However, the present invention is not limited to this, and depending on the application of the lighting device 10, for example, a normal 3W class transformer is used. A piezoelectric ceramic transformer with a low power output may be used, or a wound transformer may be used. Further, the phase shift of the two-phase transformed signal output from the transformer is not limited to about 180 degrees. In short, it is only necessary to use a transformer that can output a voltage and phase transformation signal required by the light source 22.

  Next, the two-phase transformation signal output from the piezoelectric ceramic transformer 18 is input to the light source 22 via the ballast capacitor 20 for matching the output impedance of the piezoelectric ceramic transformer 18 and the negative resistance of the cold cathode tube of the light source 22. Is done. Specifically, one of the transformed signals output from the piezoelectric ceramic transformer 18 is input to the two upper cold cathode tubes of the light source 22 via the upper ballast capacitor in FIG. 1, and the other transformed signal is input to the lower side. The light is input to the two cold cathode tubes below the light source 22 through the ballast capacitor.

  Conventionally, in the combination of a 3W class low-power output piezoelectric ceramic transformer and a cold cathode tube, since the output impedance of the piezoelectric ceramic transformer is large, the cold cathode tube can be driven without using a ballast capacitor. However, in the case of the piezoelectric ceramic transformer 18 of 30 W class high power output as in the present embodiment, the thickness is thicker than before, so the output impedance is reduced, and the balance with the negative resistance of the cold cathode tube is balanced. It becomes difficult to steadily light without taking off.

  This is because the light source 22 does not light stably unless the output impedance on the input side (piezoelectric ceramic transformer 18 side) is larger than the negative resistance on the load side (cold cathode tube side). That is, as in the present embodiment, in the combination of the high-power piezoelectric ceramic transformer 18 and the cold cathode tube, by inserting the ballast capacitor 20 between the output side of the piezoelectric ceramic transformer 18 and the cold cathode tube, It becomes possible to light the cold cathode tube stably.

  As described above, the ballast capacitor 20 is not necessary when the output impedance is large, such as a piezoelectric ceramic transformer of 3W class low power output, and is not an essential element in the present invention.

  Subsequently, the light source 22 of this embodiment is configured such that four cold cathode fluorescent lamps (CCFLs) are connected as shown in FIG. That is, the light source 22 uses two sets of two-tube serial light sources. Each two-tube series light source has two cold-cathode tubes arranged in parallel, and one terminal (the right terminal in FIG. 1) in the same direction is connected in series. In addition, two sets of two-tube series light sources include two cold-cathode tubes of one (outer side in FIG. 1) and two cold-cathode tubes of the other (inner side in FIG. 1) two-tube series light source. They are arranged in parallel so as to surround the circumference of the tube, and in the same direction so that the series connection portions of the two cold-cathode tubes do not intersect.

  In this embodiment, the specifications of each cold cathode tube are as follows: tube length 527 mm, tube outer diameter φ2.6, tube inner diameter φ2.0, color temperature around 6500 K, Ni electrode, gas pressure 70 Torr, luminance about 30000 cd / m ^ Two.

  The light source 22 is not limited to four cold-cathode tubes, and may be configured to simultaneously light a plurality of four or more cold-cathode tubes. For example, when six cold cathode tubes are similarly connected and three sets of two-tube series light sources are used, in parallel so as to surround the two cold-cathode tubes of the first set of two-tube series light sources, Two cold-cathode tubes of the second set of two-tube series light sources are arranged so as to be sandwiched from above and below on both sides, as shown in FIG. 1, and further, around the two cold-cathode tubes of the second set of two-tube series light sources Two cold cathode fluorescent lamps of a third set of two-tube serial light sources are arranged in parallel so as to surround the two sides. The same applies when four or more sets of two-tube serial light sources are used.

  A balance circuit 24, a total current detection circuit 26, and a current difference detection circuit 28 are inserted in series in the serial connection portion of each of the two cold-cathode tubes of the two sets of two-tube series light sources of the light source 22. Yes.

  The balance circuit 24 always arranges the tube currents flowing through the cold cathode tubes of the light source 22 almost uniformly. As shown in FIG. 3, the balance circuit 24 is connected in series with two cold-cathode tubes of each of two adjacent two-tube series light sources, as shown in FIG. In each part, coils with the same number of windings and coils of opposite polarity (the direction in which the coils are wound in the opposite direction) are connected, and these coils are wound around one core, and a very simple balance coil (current transformer) It is constituted by.

  Here, in the balance coil shown in FIG. 3 and FIG. 4, when “·” shown in the vicinity of a pair of coils is on the same side, the polarity is the same, and when on the different side, the polarity is Indicates the opposite. The same applies to other drawings.

  In the balance coil, when a current difference is generated between the pair of coils, both generate voltages in opposite directions. A larger current acts to decrease the voltage, and a smaller current acts to increase the voltage. As a result, control is performed so that the larger current becomes smaller and the smaller current becomes larger, and the two are stably balanced where they almost coincide. As a result, even in the case of cold cathode tubes having different VI characteristics, the tube currents of the four cold cathode tubes can be made almost uniform, and the luminance variation can be greatly reduced to within 2-3%. Can do.

  In the illuminating device 10 of this embodiment, the balance circuit 24 realizes simultaneous lighting of the four cold cathode tubes while balancing the tube currents of the cold cathode tubes of the two sets of two-tube serial light sources. . In the above-mentioned Patent Document 2, a shunt transformer must be installed in the high pressure portion of the discharge tube. On the other hand, the balance circuit 24 is not easily affected by leakage or the like because the balance coil is inserted in the series connection portion of the two cold cathode tubes of each of the two sets of two-tube series light sources, that is, the low-voltage portion. There is a feature that efficiency does not decrease.

  When two or more sets of two-tube series light sources are used, the balance coils can be connected in multiple stages. This point will be described later.

  Here, as shown in FIG. 1, the arrangement of the two-tube series light source of the light source 22 is such that the two cold cathode tubes of the i + 1-th set (i is a natural number of 1 or more) of the two-pipe series light sources are Most preferably, they are arranged in parallel so as to surround the two cold cathode tubes of the two-tube series light source. However, the present invention is not limited to this, and it is only necessary that two cold cathode tubes of each of a plurality of sets of two-tube serial light sources are arranged in parallel. In other words, the arrangement order of the two cold cathode tubes of each of the plurality of sets of two-tube serial light sources may be arranged in any order.

  For example, as shown in FIG. 11, the wirings may be arranged to intersect at the input side (left side in FIG. 11) of each of the two cold-cathode tubes of a plurality of sets of two-tube series light sources. As shown in FIG. 5, the arrangement may be such that the wiring intersects at the series connection portion (right side in FIG. 5) of the two cold cathode tubes. Further, the arrangement is not limited to these examples, and the wiring may be arranged in any way. As described above, it is needless to say that it is preferable to arrange the wires so that the wires do not intersect at the input side or the serial connection portion of the two cold cathode tubes of the two-tube series light source.

  Subsequently, the total current detection circuit 26 outputs the total current of two sets of two-tube serial light sources, and is conceptually shown in FIG. 3, but in this embodiment, a ring-shaped core includes 3 A toroidal coil in which two coils are wound is used. The two coils are connected in series to the pair of coils of the balance circuit 24, that is, the same polarity connected to the series connection portion of two cold cathode tubes in each of two sets of two-tube series light sources. The total current of the tube currents flowing through the balance circuit 22 is calculated. Another coil is a coil for extracting the total current.

  The total tube current output from the total current detection circuit 26 is fed back to the voltage controlled oscillation circuit 16 and the protection circuit 30 in the drive circuit 14 described above. The operation of the voltage controlled oscillator 16 and the protection circuit 30 when the total current is supplied is as described above.

  In this embodiment, the total current of two sets of two-tube series light sources is obtained. However, as shown in FIG. 6, for example, one core has two sets of two sets of two-tube series light sources. It is also possible to obtain the total current of three sets of two-tube series light sources by winding the same coil with the same number of windings connected to the series connection portion of the cold cathode tubes. Similarly, the total current of four or more sets of two-tube DC light sources can be obtained.

  The current difference detection circuit 28 outputs a current difference (difference current) between two sets of two-tube series light sources. As shown in FIG. 3, the current difference detection circuit 28 is connected in series to a pair of coils of the total current detection circuit 26, that is, two cold tubes in each of two sets of two-tube series light sources. A pair of coils having the same number of windings of opposite polarity connected to the series connection portion of the cathode tube is wound around the core, and another coil for taking out a current difference is wound around the same core.

  The current difference output from the current difference detection circuit 28 is fed back to the protection circuit 30 in the drive circuit 14 described above.

  When an abnormality occurs in a cold cathode tube or the like, for example, even when an abnormality occurs in one cold cathode tube of one set of two tube serial light sources out of two sets of two tube serial light sources, The balance circuit 22 described above works to make the tube currents of the two sets of two-tube series light sources substantially uniform. If the total current increases as a result of the alignment, the total current detection circuit 26 detects an abnormality. However, when the balance circuit 24 does not align as normal, the total current may not deviate significantly from the set reference value. In that case, the abnormality cannot be detected with this. Therefore, a means for monitoring each of the tube currents of each set of two-tube series light sources is required.

  In general, in order to ensure insulation, a method of feeding back each current to the protection circuit 30 in the drive circuit 14 with a photocoupler or the like can be considered. In the present embodiment, the current difference detection circuit 28 of the winding type detects the current difference in the serially connected portions of the two cold cathode tubes of each of the two sets of two-tube series light sources. This current difference is supplied to the protection circuit 30. When an abnormality is detected in the protection circuit 30, output of the drive signal from the drive circuit 14 is stopped. Based on the relative information of the total current and the current difference, the absolute amount of the current flowing through each tube may be specified to determine whether each tube is abnormal. A portion for determining the state of each tube from the combination of the two information is included in the protection circuit 30. When an abnormality is detected, the output of the drive signal is stopped.

  Note that the balance circuit 24, the total current detection circuit 26, and the current difference detection circuit 28 are not limited to the circuit configuration shown in FIG. 3, and can be implemented by any other configuration that performs the same function. This point will also be described later. In FIG. 1, the balance circuit 24, the total current detection circuit 26, and the current difference detection circuit 28 are connected in series in this order, but the arrangement order is not limited.

  Next, the balance circuit 24 when the number of cold cathode tubes used in the light source 22 is increased will be described.

  When four cold cathode fluorescent lamps are turned on simultaneously, it is as described in the above embodiment. However, in applications such as backlight devices for liquid crystal televisions, even a 22-inch liquid crystal television has a planar light source structure using about 10 to 12 cold cathode tubes. In that case, it is necessary to make the tube currents of all the cold cathode tubes uniform. Even in that case, it is possible to light up more cold cathode tubes at the same time and to make the tube current uniform by adding a little contrivance to the above-mentioned four simultaneous lighting circuit.

  First, in the example shown in FIG. 7, two sets of two-tube serial light sources shown in FIG. 4 are simply arranged in parallel. Even with this configuration, it is possible to double the number of two-tube series light sources to be used. Similarly, when the number of two-tube series light sources is increased to n times, the inverter (drive circuit 14, voltage-controlled oscillator 16) of the preceding stage is used. , The number of piezoelectric ceramic transformers 18 etc.) is also required, leading to an increase in cost. Further, since each balance circuit 24 is located far away, it is inconvenient to arrange a total current circuit 26 connected in series to the overall tube current balance circuit 24.

  On the other hand, in the example shown in FIG. 8, in the light source 22 shown in FIG. 4, the second set of two-tube series light sources is arranged in parallel so as to surround the first set of two-tube series light sources. It is a summary. With this configuration, it is very easy to increase the number of two-tube series light sources, and even if the number of two-tube series light sources is increased n times, one inverter is always required. In addition, since the positions of the balance circuits 24 are also close, it is easy to arrange a total current circuit 26 connected in series to the overall tube current balance circuit 24. For example, when a multi-stage total current detection circuit as shown in FIG. 6 is provided in series with the balance circuit 24, a plurality of total current detection circuits 26 can be concentrated on a part, and wiring becomes easy.

  The example shown in FIG. 9 is similar to the example shown in FIG. 7, but the number of two-tube serial light sources is doubled and the number of inverters is one. The connection state of the upper and lower two-tube series light sources is almost the same as in the example of FIG. 7, but one of the two-phase transformation signals of the piezoelectric ceramic transformer 18 is input to the four cold-cathode tubes in the center. In addition, another inverter signal is input to four cold cathode tubes arranged in parallel in the vertical direction in FIG.

  In the example shown in FIG. 9, the balance circuit 24 is arranged in the serial connection portion of the two cold cathode fluorescent lamps of the upper two sets of two-tube series light sources, and the lower two sets of two-tube series light sources are two. The balance circuit 24 is also arranged in the serial connection portion of the cold cathode tubes. As a result, the tube currents of the upper and lower four cold cathode tubes are substantially uniform. Further, a balance circuit 24 is also inserted in the series connection portion of the two cold cathode tubes of the upper outer two-tube series light source and the series connection portion of the two cold cathode tubes of the lower outer two-tube series light source. As a result, the tube currents of all eight cold cathode tubes are made almost uniform.

  In the circuit configurations shown in FIGS. 7 and 8, it is possible to make the tube currents of all the cold cathode tubes substantially uniform in the same manner as the circuit configuration shown in FIG. Further, in the figures of the above examples, only the balance circuit 24 is shown. However, when the total current detection circuit 26 and the current difference detection circuit 28 are further provided in these circuits, the upper outer side shown in FIG. It may be provided in series with the balance circuit 24 arranged in the series connection part of the two cold cathode tubes of the two-tube series light source and the series connection part of the two cold cathode tubes of the lower outer two-tube series light source. good.

  In addition, although the case where the number of cold-cathode tubes was doubled to eight (the number of two-tube serial light sources was four) was described as an example, the number of cold-cathode tubes is not limited to four or eight, It is also possible to configure an illumination device that simultaneously lights a required number of cold-cathode tubes as required.

  Next, another embodiment of the balance circuit 24, the total current detection circuit 26, and the current difference detection circuit 28 will be described.

  For example, the circuit shown in FIG. 10 is an example in which the balance circuit 24, the total current detection circuit 26, and the current difference detection circuit 28 are configured as one circuit.

  Two coils of the same polarity are connected in series to the serial connection portion of the two cold cathode tubes of the two-tube series light source on the left side in FIG. Each coil is wound around the core, and coils having the same number of windings of the same polarity are wound around the same core to constitute current transformers 60 and 62, respectively. Similarly, two coils having the same polarity are connected in series to the serial connection portion of the two cold cathode tubes of the right two-tube series light source. Each coil is wound around a core, and coils having the same number of windings of the same polarity are wound around the same core, thereby forming current transformers 64 and 66, respectively.

  The two inner coils constituting the upper left and right current transformers 60 and 64 have one terminal (the lower terminal in FIG. 10) connected to each other and the other terminal (the upper terminal in FIG. 10) is , Respectively, are connected to the portions marked “difference”. On the other hand, the two inner coils constituting the lower left and right current transformers 62, 66 are one terminal of the right coil (lower terminal in FIG. 10) and the other terminal of the left coil (FIG. 10). The middle terminal is connected to each other, and the other terminal of the right coil (upper terminal in FIG. 10) and one terminal of the left coil (lower terminal in FIG. 10) are described as “sum”, respectively. Is connected to the part that is.

  In FIG. 10, the two-tube series light source on the right side and the two-tube series light source on the left side are connected to each other via the respective current transformers 60, 62, 64, 66, so that the tube current flowing in both the left and right two-tube series light sources. Is controlled to be substantially uniform. That is, the same function as the balance circuit 24 shown in FIG. 3 is realized.

  In addition, since the terminals of the two inner coils constituting the left and right current transformers 62 and 66 on the lower side in FIG. 10 are connected so as to cross each other, from the portion described as “sum” on the lower side Can extract a total current equal to the total current output from the total current detection circuit 26 shown in FIG. 3 via the impedance element. That is, the same function as the total current detection circuit 26 shown in FIG. 3 is realized.

  On the other hand, since the terminals of the inner two coils constituting the upper left and right current transformers 60 and 64 are connected so as not to cross each other, the impedance element is similarly applied from the portion described as “difference” on the upper side. The current difference equal to the current difference output from the current difference detection circuit 28 shown in FIG. That is, the same function as the current difference detection circuit 28 shown in FIG. 3 is realized.

  In the example shown in FIG. 10, the balance circuit 24, the total current detection circuit 26, and the current difference detection circuit 28 are configured as one circuit. However, the present invention is not limited to this example, and the same function is realized. Various circuits having other configurations can be employed.

  Moreover, each said embodiment shows an example of the illuminating device of this invention, and this invention is not limited to the said structure. Moreover, the illuminating device of this invention may contain various components other than each component shown, for example in FIG. The lighting device of the present invention can be suitably used as a backlight device such as a liquid crystal display used as a display device for a liquid crystal television or a computer, but is not limited thereto, and can be used as various lighting devices. .

  The light source is not limited to the cold cathode tube of the above embodiment, and various discharge tubes including a hot cathode tube, a fluorescent tube, a neon tube, an external electrode tube, and the like may be used. In the above embodiment, the voltage is boosted by the piezoelectric ceramic transformer, but this is not limited, and the voltage may be boosted by using various transformers, or may be stepped down, or the same voltage may be output. You may do it. That is, you may transform to a predetermined voltage as needed.

The present invention is basically as described above.
The lighting device of the present invention has been described in detail above. However, the present invention is not limited to the above-described embodiment, and various improvements and modifications may be made without departing from the spirit of the present invention. .

It is the block schematic diagram of one Embodiment showing the internal structure of the illuminating device of this invention. It is a perspective view showing the piezoelectric ceramic transformer shown in FIG. It is the schematic showing the balance circuit, total current detection circuit, and current difference detection circuit which are shown in FIG. It is the schematic showing the structure of the balance circuit shown in FIG. 1 simply. It is the schematic showing the modification of a balance circuit. It is the schematic showing the modification of a total current detection circuit. It is the schematic showing the modification of a balance circuit. It is the schematic showing the modification of a balance circuit. It is the schematic showing the modification of a balance circuit. It is the schematic showing the modification of the balance circuit shown in FIG. 1, a total current detection circuit, and a current difference detection circuit. In the conventional illuminating device, it is the schematic showing the example of a connection at the time of arranging two sets of 2 series light sources which connected two cold cathode tubes in series in parallel. In the conventional illuminating device, it is the schematic showing another connection example at the time of arranging two sets of 2 series light sources which connected two cold cathode tubes in series in parallel. In the conventional illuminating device, it is the schematic showing another connection example at the time of arranging two sets of 2 series light sources which connected two cold cathode tubes in series in parallel. In the conventional illuminating device, it is the schematic showing another connection example at the time of arranging two sets of 2 series light sources which connected two cold cathode tubes in series in parallel.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Illuminating device 12 Power supply 14 Drive circuit 16 Voltage control oscillation circuit 18 Piezoelectric ceramic transformer 20 Ballast capacitor 22 Light source 24 Balance circuit 26 Total current detection circuit 28 Current difference detection circuit 30 Protection circuit 32 Piezoelectric ceramics 34a, 34b 1st input electrode 36a, 36b Second input electrode 38 First output electrode 40 Second output electrode 42 First region 44 Second region 46 Third region 48 Fourth region 50 Fifth region 52a, 52b, 54a, 54b Input terminal 56, 58 Output terminal 60 62, 64, 66 Current transformer 68, 72 Inverter 70 Oscillation circuit 74 Light guide plate

Claims (6)

Two lighting tubes are arranged in parallel, and a lighting device using a plurality of sets of two-tube series light sources connected to one terminal in the same direction of the two discharging tubes as a light source,
In the light source, the plurality of sets of two-tube serial light sources are arranged in parallel,
In the series connection portion of the two discharge tubes of each of the plurality of sets of two-tube series light sources, coils having the same number of windings and the same polarity are connected. A total current detection circuit is provided in which a coil connected to a series connection portion of a discharge tube and a coil for taking out a total current of the plurality of sets of two-tube series light sources are wound around the same core. A lighting device.   The light sources are arranged in parallel so that the two discharge tubes of the i + 1-th set (i is a natural number of 1 or more) of the two-tube series light source surround the two discharge tubes of the i-th set of two-tube series light sources. The lighting device according to claim 1, wherein the lighting device is arranged. Furthermore, a voltage-controlled oscillation circuit that generates a fundamental wave whose oscillation frequency changes according to the current value of the total current supplied from the total current detection circuit;
A drive circuit that generates a drive signal of a predetermined voltage whose oscillation frequency changes according to the frequency of the fundamental wave supplied from the voltage controlled oscillation circuit;
When a drive signal having a predetermined voltage is input from the drive circuit, the transformer includes a transformer that outputs a voltage-transformed signal having a predetermined voltage from the drive signal at a frequency substantially equal to the drive signal that is input to the light source.
The voltage-controlled oscillation circuit controls the frequency of the fundamental wave in accordance with a current value of the total current so that the total current always becomes a substantially constant value. 2. The illumination device according to 2.   And a protection circuit that controls to stop the output of the drive signal from the drive circuit when the current value of the total current supplied from the total current detection circuit is not within a predetermined range. The lighting device according to claim 3.   The lighting device according to claim 3 or 4, wherein the transformed signal input to the light source is a two-phase signal having a phase difference of about 180 degrees.   The lighting device according to claim 1, wherein the discharge tube is a cold cathode tube.

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