JP2006073476A - Discharge lamp lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce resonance of a transformer generated during dimming to stabilize lighting during low dimming by turning on a third switching element, wherein the transformer used for an inverter is parallel connected with a primary winding. <P>SOLUTION: In this discharge lamp lighting device, a cold cathode lamp LP is connected with a secondary winding L3 side of the transformer T in a blink backlight system, a tap is provided to a primary winding side, a first switch S1 and a second switch S2 are provided between each of ends of the primary winding, to which power is supplied through the tap and the ground, respectively, and a flicker preventing circuit 1, wherein an element R1 having a resistance component and a third switch S3 are connected in series is connected in parallel with the ends of the primary winding having the tap. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a discharge lamp lighting device.

  Cold cathode discharge lamps are used as light sources for backlights of liquid crystal display devices used in personal computers and liquid crystal televisions. In addition, a liquid crystal display device that supports moving image reproduction requires a discharge lamp driving device that can produce a video with less blurring when the moving image is reproduced.

  Conventionally, a blink backlight system (BBS) is known as a discharge lamp lighting device that meets such requirements. FIG. 15 shows a conceptual configuration of a general blink backlight system, and FIG. 16 shows operation waveforms. The blink backlight system includes an LCD (Liquid Crystal Display) 10, a backlight unit 20 that illuminates it from the back, and an inverter 30 that supplies power to the backlight unit 20.

  When a blinking backlight system considering moving images is used, the inverter 30 is controlled by the control circuit 31, and the timing when the discharge lamp of the backlight unit (B / L) 30 is turned on as shown in FIG. It is generally known that the lamp is operated at a dimming level of 60% or less in accordance with the synchronizing signal (V-SYNC). This is because the black region 11 is inserted into the moving image by operating at a light control of 60% or less to reduce blur. In the following, an example of 50% light control will be shown. When the blink backlight system is used, as shown in the graph of FIG. 17, the dimming 50% becomes 100% luminance as indicated by the dimming rate-relative luminance line C2. (In the conventional method, as indicated by the dimming rate-relative luminance line C1, the dimming is 100% and the luminance is 100%.) Therefore, to set the luminance to 20%, the dimming needs to be 10%. In the dimming of the conventional liquid crystal backlight that is not compatible with moving images, the dimming rate could be easily adjusted to about 20% because the luminance was only 100% when the dimming rate was 100%. However, in the cold cathode discharge lamp using mercury, it is difficult to perform stable lighting with 10% dimming in the region Re2 in FIG. 17, and there is a problem that flickering occurs.

  A circuit diagram of a conventional discharge lamp lighting device is shown in FIGS. 18 and 19, and a lamp voltage when dimming is shown in FIG. The discharge lamp lighting device shown in FIGS. 18 and 19 includes a control circuit 31 that generates a pair of inverter drive signals (1) SG1 and drive signals (2) SG2. Then, the switching element S1 is switched by the driving signal (1) SG1 of the control circuit 31, the switching element S2 is switched by the driving signal (2) SG2, and the pulse transformer T is switched by the switching operation of these switching elements S1 and S2. The discharge lamp LP is turned on by driving. 18 and 19, C is a capacitor.

FIG. 18 shows a state in which the negative tube current CL1 is generated by turning on the switching element S1 by the drive signal (1) SG1 and turning off the switching element S2 by the drive signal (2) SG2. FIG. 19 shows a state in which the positive tube current CL2 is created by turning off the switching element S1 by the drive signal SG1 and turning on the switching element S2 by the drive signal SG2. That is, the primary winding voltage of the lamp driving transformer T repeats “L → H → L → H → L...” During the ON period of the drive signals SG1 and SG2, thereby being connected to the secondary winding of the transformer T. Positive and negative tube currents CL1 and CL2 are supplied to the cold cathode discharge lamp LP. By repeating these steps, a high-frequency AC voltage is continuously applied to the cold cathode discharge lamp LP to light the lamp LP. In such a conventional discharge lamp lighting device, as can be seen from the lamp voltage waveform of FIG. 20, a resonance RS occurs when the lamp voltage falls, and this resonance causes flickering when the discharge lamp is lit. It was.
JP 2002-313595 A

  The present invention has been made in view of such a conventional technical problem, and is generated at the time of dimming by turning on a third switching element connected in parallel to a transformer primary winding by a transformer used in an inverter. An object of the present invention is to provide a discharge lamp lighting device capable of reducing the resonance of a transformer to perform stable lighting even with dimming 19% to 5%.

  The discharge lamp lighting device in the blink backlight system according to the first aspect of the present invention includes a cold cathode discharge lamp connected to the secondary winding side of the pulse transformer, a tap provided on the primary winding side of the pulse transformer, and the tap A first switching element and a second switching element are provided between both ends of the primary winding to which power is supplied through and the ground, respectively, and resistance components are provided at both ends of the primary winding having the tap. A flicker prevention circuit in which an element having the above and a third switching element are connected in series is connected in parallel.

  According to a second aspect of the present invention, there is provided a discharge lamp lighting device comprising: a cold cathode discharge lamp connected to a secondary winding side of a pulse transformer; a tap provided on the primary winding side of the pulse transformer; A first switching element and a second switching element are provided between both ends of the primary winding to which power is supplied through and the ground, respectively, and the tap of the primary winding and the first or second switching element are provided. A flicker prevention circuit in which an element having a resistance component and a third switching element are connected in series is connected in parallel to the end of the primary winding to which the switching element is connected.

  According to a third aspect of the present invention, there is provided a discharge lamp lighting device comprising: a cold cathode discharge lamp connected to a secondary winding side of a pulse transformer; a tap provided on the primary winding side of the pulse transformer; A first switching element and a second switching element are provided between both ends of the primary winding to which power is supplied through and the ground, respectively, and a third winding is provided on the primary side of the pulse transformer. The one side of the third winding is connected to the ground, and the element having the resistance component and the third switching element are connected in series between the other side of the third winding and the ground. A flicker prevention circuit is connected in parallel.

  According to a fourth aspect of the present invention, there is provided a discharge lamp lighting device comprising: a cold cathode discharge lamp connected to a secondary winding side of a pulse transformer; a tap provided on the primary winding side of the pulse transformer; A first switching element and a second switching element are provided between both ends of the primary winding to which power is supplied through and the ground, respectively, and a third winding is provided on the primary side of the pulse transformer. The one side of the third winding is connected to the ground, and the third switching element is connected as a flicker prevention circuit between the other side of the third winding and the ground.

  According to a fifth aspect of the present invention, in the discharge lamp lighting device in the blink backlight system according to the first to fourth aspects, the first switching element and the second switching element are alternately turned on / off, and the first switching element and the second switching element are turned on when the dimming is performed. 3 is turned on.

  According to a sixth aspect of the present invention, in the discharge lamp lighting device in the blink backlight system according to the first to fifth aspects, a MOSFET, a transistor, or a photocoupler is used as the third switching element, and a resistance as the element having the resistance component is used. It is characterized by using.

  According to a seventh aspect of the invention, in the discharge lamp lighting device in the blink backlight system of the third or fourth aspect, the number of turns of the third winding is 10 turns or less.

  According to the present invention, the transformer used in the inverter turns on the third switching element connected in parallel with the primary winding of the transformer to reduce the resonance of the transformer that occurs during dimming, and the dimming is 19% to 5%. %, Stable lighting is possible.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 and 2 are circuit diagrams of the discharge lamp lighting device according to the first embodiment of the present invention. In the discharge lamp lighting device of the present embodiment, the cold cathode discharge lamp LP is connected to the secondary winding L3 side of the pulse transformer T, and the primary winding side has a tap, and power is supplied through this tap. I have to. By this tap, the primary winding is divided into half of L1 and L2. A first switch S1 and a second switch S2 are connected between both ends of the primary winding of the pulse transformer T and the ground. Further, a flicker prevention circuit 1 in which an element R1 having a resistance component and a third switch S3 are connected in series is connected in parallel to both ends of the primary winding of the pulse transformer T. As the third switch S3, a photo MOSFET as shown in FIG. 3, a MOSFET as shown in FIG. 4, a bipolar transistor, or a photocoupler can be employed.

  The pulse transformer T is driven by a control circuit 32 that outputs a drive signal (1) SG1 and a drive signal (2) SG2 for alternately turning on and off the first switch S1 and the second switch S2, and cold cathode discharge. The power supplied to the lamp LP is controlled. The control circuit 32 alternately turns on / off the first switch S1 by the drive signal (1) SG1 and the second switch S2 by the drive signal (2) SG2 by PWM control, and also turns the third switch S3 by the drive signal ( 3) Switch at SG3.

  FIG. 1 shows a state in which the third switch S3 is held in an off state and operates at a dimming rate of 50% to 20%, and FIG. It shows the operating state in%. Timing charts in the respective operation states are shown in FIGS.

  In dimming 50% to 20%, as shown in FIG. 1, the control circuit 32 keeps the third switch S3 off with the drive signal (3) SG3, and the first switch S1 is driven to the drive signal ( 1) When SG1 and the second switch S2 are alternately turned on / off by the drive signal (2) SG2, the first switch S1 is turned on and the second switch S2 as in the period M1 in the timing chart of FIG. When is turned off, a current flows through half of the primary winding L1 and the first switch S1 via a tap connected to the power source. At this time, the second switch S2 is off and does not operate. On the contrary, when the second switch S2 is on and the first switch Sl is off as in the period M2, the second half L2 of the primary winding and the second switch S2 are connected via the tap connected to the power source. A current flows through the switch S2. At this time, the first switch S1 is off and does not operate. Since the third switch S3 is off, no current flows through the resistor R1. By repeating this state, the voltage output from the transformer T is supplied to the lamp LP, and the lamp LP is turned on.

  In dimming 19% to 5%, as shown in FIG. 2, the control circuit 32 keeps the third switch S3 on with the drive signal (3) SG3, and the first switch S1 is driven with the drive signal ( 1) SG1 and second switch S2 are alternately turned on / off by drive signal (2) SG2. At this time, when the first switch S1 is on and the second switch S2 is off as in the period M1 in the timing chart of FIG. 6, the primary of the transformer T is connected via a tap connected to the power source. Since the current flows through the winding half Ll and the first switch S1 and the third switch S3 is on, the primary winding half L1, the resistance element R1, the third switch S3, and the primary winding. Current also flows through the other half L2 of the line. On the contrary, when the second switch S2 is on and the first switch S1 is off as in the period M2, the half L2 of the primary winding through the tap connected to the power source, the second switch Since the current flows through the switch S2 and the third switch S3 is ON, the current flows through the half L2 of the primary winding, the third switch S3, the resistance element R1, and the remaining half L1 of the primary winding. . The ramp voltage waveform at this time does not resonate after the first switch S1 and the second switch S2 have been alternately operated because the third switch S3 is on. FIG. 7 shows the lamp voltage waveform at this time. It can be seen from the voltage waveform of FIG. 7 that the resonance is reduced when the lamp voltage falls, from the voltage waveform of FIG.

  The operation by the conventional circuit is equivalent to the operation in which the third switch S3 is not turned on as shown in FIG. 1, and the LC resonance circuit constituted by the primary windings (L1, L2) of the transformer T and the capacitor C is configured. Then, resonance occurs at the resonance frequency f given by the equation f = 1 / 2π√ (LC), and the resonance continues even after the first switch S1 and the second switch S2 are turned off. Therefore, the resonance at the rise and fall of the lamp voltage has an effect on the flicker.

  However, in the discharge lamp lighting device of the present embodiment, for example, when the dimming is less than 20%, the resistor R1 attenuates the resonance of the LC resonance circuit by turning on the third switch S3. Acts as a damping resistor. As a result, linking generated by the LC resonance circuit can be prevented, and as a result, linking in the lamp voltage and lamp current can be prevented and flicker can be suppressed. Therefore, according to the present embodiment, as shown in the graph of FIG. 8, there is no flicker not only in the region Re1 where stable lighting has been possible conventionally, but also in the region Re2, which has been unstable lighting in the conventional circuit. Stable lighting is possible.

  At this time, the resistance value of the resistance element R1 is about 1Ω to 100Ω. When the resistance value of the resistance element R1 is 100Ω or more, it becomes difficult for a current to flow through the resistance element R1, which is the same as a state where the resistance element R1 does not operate. Further, if the resistance value is too low, the loss in the resistance element R1 becomes large. Therefore, the third switch S3 is turned on only when dimming is low. The setting condition for turning on the third switch S3 to prevent resonance at the time of dimming is not limited to the above example, and can be set within a range of about 19% to 5%.

  In this way, the discharge lamp lighting device of the present embodiment can perform stable lighting without flicker even at low brightness (during dimming).

  Next, a discharge lamp lighting device according to a second embodiment of the present invention will be described with reference to FIGS. 9 and 10 are circuit diagrams of the discharge lamp lighting device according to the second embodiment of the present invention. In the discharge lamp lighting device of the present embodiment, the cold cathode discharge lamp LP is connected to the secondary winding L3 side of the pulse transformer T, and the primary winding side has a tap, and power is supplied through this tap. I have to. By this tap, the primary winding is divided into half of L1 and L2. A first switch S1 and a second switch S2 are connected between both ends of the primary winding of the pulse transformer T and the ground. Furthermore, the element R1 having a resistance component and the third element are connected in parallel to either half of the winding (here, L2) to which the tap of the primary winding of the pulse transformer T and the first or second switch are connected. A flicker prevention circuit 1 connected to the switch S3 is provided.

  Next, the operation of the discharge lamp lighting device according to the second embodiment having the above-described configuration will be described. FIG. 9 shows a circuit in the case of operating at 50% to 20% dimming, and the third switch S3 is turned off. The operation timing of the first switch S1 and the second switch S2 in this case is the same as that in the first embodiment, and is as shown in the timing chart of FIG. FIG. 10 shows a circuit in the case of operating at dimming 19% to 5%, and the third switch S3 is turned on. The operation timings of the first switch S1 and the second switch S2 in this case are the same as those in the first embodiment shown in FIG. 2, and are the same as those shown in the timing chart of FIG.

  In the discharge lamp lighting device according to the present embodiment, the resistor element R1 is connected in parallel with the winding L2 between the tap of the transformer T and the end point of the winding L2 on one side, and the waveform diagram shown in FIG. Almost the same result is obtained, linking in the lamp voltage and lamp current can be prevented, and flicker can be suppressed.

  Next, a discharge lamp lighting device according to a third embodiment of the present invention will be described with reference to FIGS. 11 and 12 are circuit diagrams of a discharge lamp lighting device according to the third embodiment of the present invention. In the discharge lamp lighting device of the present embodiment, the cold cathode discharge lamp LP is connected to the secondary winding L3 side of the pulse transformer T, and the primary winding side has a tap, and power is supplied through this tap. I have to. By this tap, the primary winding is divided into half of L1 and L2. A first switch S1 and a second switch S2 are connected between both ends of the primary winding of the pulse transformer T and the ground, and a third winding L6 is further provided on the primary side. The number of turns of the third winding L6 is 10 turns or less, one side of the third winding L6 is connected to the ground, and the element R1 having a resistance component and the third switch are connected between the other side and the ground. The flicker prevention circuit 1 to which S3 is connected in series is connected in parallel.

  Next, the operation of the discharge lamp lighting device according to the third embodiment will be described. FIG. 11 shows a circuit in the case of operating at 50% to 20% dimming, and the third switch S3 is turned off. The operation timings of the first switch S1 and the second switch S2 are the same as those in the first embodiment, and are the same as those in the timing chart of FIG.

  FIG. 12 shows a circuit in the case of operating at dimming 19% to 5%. A third winding L6 is formed on the primary side of the transformer T, one side thereof is connected to the ground, and the other side is connected to the third switch S3 via the resistance element R1. At this time, the third winding L6 wound around the transformer T obtains a voltage and is turned on by the third switch S3, so that the waveform diagram shown in FIG. 7 is almost the same as in the first embodiment. Similar results are obtained, linking in the lamp voltage and lamp current can be prevented, and flicker can be suppressed.

  The resistance element R1 used at this time is 100Ω or less, and the number of turns of the third winding L6 is 10 turns or less. When the resistance value is 100Ω or more and the number of turns exceeds 10 turns, the influence of the voltage on the secondary winding L3 that directly drives the discharge lamp LP becomes large, and stable lighting becomes difficult. As a result, the lamp LP does not emit light uniformly and emits light unevenly.

  Next, a discharge lamp lighting device according to a fourth embodiment of the present invention will be described with reference to FIGS. 13 and 14 are circuit diagrams of a discharge lamp lighting device according to the fourth embodiment of the present invention. In the discharge lamp lighting device of the present embodiment, the cold cathode discharge lamp LP is connected to the secondary winding L3 side of the pulse transformer T, and the primary winding side has a tap, and power is supplied through this tap. I have to. By this tap, the primary winding is divided into half of L1 and L2. A first switch S1 and a second switch S2 are respectively connected between both ends of the primary winding of the transformer T for supplying power through the tap and the ground, and a third switch is connected to the primary side of the transformer T. Winding L6 is provided. The number of turns of the third winding L6 is 10 turns or less, one side of the third winding L6 is connected to the ground, and the third switch S3 is connected to the other side to constitute the flicker prevention circuit 1. Yes.

  Next, the operation of the discharge lamp lighting device according to the fourth embodiment having the above-described configuration will be described. FIG. 13 shows a circuit in the case of operating with dimming 50% to 20%, and the third switch S3 is turned off. The operation timings of the first switch S1 and the second switch S2 are the same as those in the first embodiment, and are the same as those in the timing chart of FIG.

  FIG. 14 shows a circuit in the case of operating at dimming 19% to 5%. A third winding L6 is formed on the primary side of the transformer T, one side thereof is connected to the ground, and the other side is directly connected to the third switch S3. At this time, the third winding L6 wound around the transformer T obtains a voltage and is turned on by the third switch S3, so that the waveform diagram shown in FIG. 7 is almost the same as in the first embodiment. Similar results are obtained, linking in the lamp voltage and lamp current can be prevented, and flicker can be suppressed.

  As described above, according to the embodiment of the present invention, when the cold cathode discharge lamp LP is dimmed and lit, the vibration of the lamp voltage is prevented by preventing resonance of the transformer at the rise and fall of the dimmed lamp voltage. Stable lighting without flicker is possible even when the light control rate is 10%.

The circuit diagram at the time of 50%-20% dimming operation | movement of the discharge lamp lighting device of the 1st Embodiment of this invention. The circuit diagram at the time of 19%-5% dimming operation | movement of the discharge lamp lighting device of the 1st Embodiment of this invention. The circuit diagram of the photoMOSFET used as a 3rd switch in the said embodiment. The circuit diagram of MOSFET used as a 3rd switch in the said embodiment. The timing chart which shows the drive signal and switch operation at the time of 50%-20% light control operation | movement by the said embodiment. The timing chart which shows the drive signal and switch operation | movement at the time of 19%-5% dimming operation | movement by the said embodiment. The wave form diagram of the lamp voltage at the time of 19%-5% dimming operation | movement by the said embodiment. The graph which shows the operating characteristic of the said embodiment. The circuit diagram at the time of 50%-20% dimming operation | movement of the discharge lamp lighting device of the 2nd Embodiment of this invention. The circuit diagram at the time of 19%-5% dimming operation | movement of the discharge lamp lighting device of the 2nd Embodiment of this invention. The circuit diagram at the time of 50%-20% dimming operation | movement of the discharge lamp lighting device of the 3rd Embodiment of this invention. The circuit diagram at the time of 19%-5% dimming operation | movement of the discharge lamp lighting device of the 3rd Embodiment of this invention. The circuit diagram at the time of 50%-20% dimming operation | movement of the discharge lamp lighting device of the 4th Embodiment of this invention. The circuit diagram at the time of 19%-5% dimming operation | movement of the discharge lamp lighting device of the 4th Embodiment of this invention. A block diagram of a general blink backlight system. The wave form diagram of each part at the time of 50% light control by the conventional discharge lamp lighting device. The operation characteristic figure of the conventional discharge lamp lighting device. The circuit diagram (1) of the conventional discharge lamp lighting device. The circuit diagram (2) of the conventional discharge lamp lighting device. The wave form diagram of the lamp voltage at the time of dimming operation of 19%-5% by the conventional discharge lamp lighting device.

Explanation of symbols

1 flicker prevention circuit 32 control circuit SG1 drive signal (1)
SG2 drive signal (2)
SG3 drive signal (3)
S1 1st switch S2 2nd switch S3 3rd switch T Transformers L1, L2 Half of primary winding L3 Secondary winding L6 3rd winding LP Discharge lamp R1 Resistance element

Claims (7)

  A cold cathode discharge lamp is connected to the secondary winding side of the pulse transformer, a tap is provided on the primary winding side of the pulse transformer, both ends of the primary winding to which power is supplied through the tap, The first switching element and the second switching element are provided between the two, and a flicker is obtained by connecting an element having a resistance component and a third switching element in series at both ends of the primary winding having the tap. A discharge lamp lighting device in a blink backlight system, wherein prevention circuits are connected in parallel.   A cold cathode discharge lamp is connected to the secondary winding side of the pulse transformer, a tap is provided on the primary winding side of the pulse transformer, both ends of the primary winding to which power is supplied through the tap, The first switching element and the second switching element are respectively provided between the taps of the primary winding and the end of the primary winding to which the first or second switching element is connected. A discharge lamp lighting device in a blink backlight system, wherein a flicker prevention circuit in which an element having a resistance component and a third switching element are connected in series is connected in parallel.   A cold cathode discharge lamp is connected to the secondary winding side of the pulse transformer, a tap is provided on the primary winding side of the pulse transformer, both ends of the primary winding to which power is supplied through the tap, The first switching element and the second switching element are provided between the first winding element, the third winding is provided on the primary side of the pulse transformer, one side of the third winding is connected to the ground, A blink backlight system, wherein a flicker prevention circuit in which an element having a resistance component and a third switching element are connected in series is connected in parallel between the other side of the winding 3 and the ground. Discharge lamp lighting device.   A cold cathode discharge lamp is connected to the secondary winding side of the pulse transformer, a tap is provided on the primary winding side of the pulse transformer, both ends of the primary winding to which power is supplied through the tap, The first switching element and the second switching element are provided between the first winding element, the third winding is provided on the primary side of the pulse transformer, one side of the third winding is connected to the ground, A discharge lamp lighting device in a blink backlight system, wherein a third switching element is connected as a flicker prevention circuit between the other side of the winding 3 and the ground.   5. The blink according to claim 1, wherein the first switching element and the second switching element are alternately turned on / off to turn on the third switching element at the time of low dimming. A discharge lamp lighting device in a backlight system.   The blink backlight system according to any one of claims 1 to 5, wherein a MOSFET, a transistor, or a photocoupler is used as the third switching element, and a resistor is used as the element having the resistance component. Discharge lamp lighting device. The discharge lamp lighting device in a blink backlight system according to claim 3 or 4, wherein the number of turns of the third winding is 10 turns or less.

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