JP2007311261A - Discharge tube driving circuit and inverter circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge tube driving circuit for lighting a plurality of discharge tubes with less numbers of parts uniformly. <P>SOLUTION: In this discharge tube driving circuit in which primary windings of a plurality of driving transformers are connected in parallel and in which the discharge lamp connected to a secondary windings of a plurality of the driving transformers is driven, this discharge tube driving circuit is provided with a plurality of balance transformers corresponding to the plurality of driving transformers, the respective primary windings of the plurality of the driving transformers and the respective secondary windings of the corresponding balance transformer are connected in series, and alternate current signals are applied to the respective primary windings of the corresponding balance transformers. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a discharge tube drive circuit and an inverter circuit for controlling lighting of a cold cathode discharge tube such as a fluorescent lamp, and more particularly to a discharge tube drive circuit and an inverter circuit using a plurality of drive transformers.

  As is well known, a cold cathode discharge tube such as a fluorescent lamp is driven by a high-frequency driving voltage generated by an inverter and emits light. Of course, this type of cold cathode discharge tube is used not only for illumination but also recently as a light source for backlights of liquid crystal display panels. The discharge tube drive circuit and the cold cathode discharge tube have a configuration in which a drive transformer is provided on the output side of an inverter included in the discharge tube drive circuit, and an output terminal on the secondary coil side of the drive transformer is connected via a connector. It has become.

  In particular, when a cold cathode discharge tube is used for a backlight of a liquid crystal display panel, it is necessary to use a plurality of cold cathode discharge tubes and to illuminate the plurality of cold cathode discharge tubes uniformly.

  It is already known that the current flowing through a plurality of cold cathode discharge tubes is made constant by connecting a balance coil to the low pressure portion of the cold cathode discharge tube or connecting a balance coil to the high pressure portion of the cold cathode discharge tube. .

  It is also known that the voltage at both electrodes of the cold cathode discharge tube varies due to variations in impedance among the plurality of cold cathode discharge tubes. Therefore, the currents flowing through the plurality of cold cathode discharge tubes have different values, resulting in a difference in light emission luminance. When a plurality of cold cathode discharge tubes are used for a backlight of a liquid crystal display panel, luminance unevenness of the liquid crystal display panel is generated. Therefore, it is necessary to make the current flowing through the plurality of cold cathode discharge tubes constant.

  It is a technique already used by various companies to connect a balance coil to the low-pressure part of the discharge tube or connect a balance coil to the high-pressure part of the discharge tube to make the current flowing through the plurality of discharge tubes constant. Even if the same voltage is applied to the discharge tube due to variations in impedance of the discharge tube or stray capacitance with the panel, the flowing currents are not equal. In the liquid crystal TV, since the screen is getting larger, a plurality of discharge tubes are being used per liquid crystal display panel. Therefore, as described above, luminance unevenness occurs when the amount of current flowing through the discharge tubes changes individually, so that it is essential to match the current flowing through each discharge tube.

  Conventionally, there is a method in which a balance coil is connected to the low-pressure part or the high-pressure part of the discharge tube. Some paths require as many windings as several discharge tubes. (Japanese Patent Laid-Open No. 2003-31383, US Pat. No. 6,781,325). However, in the balance coil with the number of discharge tubes −1, the area occupied by the balance coil increases, and the substrate becomes large. In addition, the balance coil having one magnetic path and the number of windings corresponding to the number of discharge tubes has a problem that the size of the balance coil itself increases.

  In WO2005 / 038828, the primary winding of the balance transformer is connected to the discharge tube, and the secondary winding of each balance transformer is a circuit forming a closed loop. Also, it is disclosed that a plurality of discharge tubes are connected in parallel to the output of the transformer, and when one discharge tube does not ignite, a balance transformer is used to increase the voltage at that point. It is described to work.

  However, if a balance transformer is placed on the secondary winding side, the secondary winding of the drive transformer outputs a high voltage, so insulation must be taken into account, and component placement must be considered in the board design. In addition, the same number of balance transformers as the number of discharge tubes, or half balance transformers with respect to the number of discharge tubes, must be used.

  Further, in the conventional method, the secondary current of the driving transformer is used as constant current control as an F / B signal. However, when a plurality of outputs are performed by one IC, only one output can be controlled. The output varied greatly. For this reason, in the multi-lamp type discharge tube backlight drive circuit, in order to suppress variations in the discharge tube current, the characteristics of the drive transformer and the output capacitor capacity are selected.

  However, this method has a limit in suppressing variations in discharge tube current due to variations in stray capacitance among liquid crystal display panels. In addition, it may be necessary to connect a ballast capacitor and set the resonance frequency on the secondary side, leading to an increase in cost due to the use of highly insulating parts. Moreover, in order to reduce the variation in the discharge tube current, the balance tube is used to adjust the discharge tube current flowing individually, but there is a problem that the number of balance transformers increases.

Japanese Patent Laid-Open No. 2005-5059 is disclosed as a circuit in which a resonance capacitor (filter capacitor) is connected in parallel to a discharge tube. In this circuit, since a rectangular wave is input to the primary winding of the drive transformer, a capacitor is arranged in the secondary winding of the drive transformer, and an LC filter is formed by the secondary inductance and the capacitor of the drive transformer. It was configured to form an alternating current (ideally a SIN wave). However, since it is connected to the secondary winding side of the drive transformer, a capacitor with a high withstand voltage must be used, leading to an increase in cost. In recent years, the number of discharge lamps used per unit has increased due to the increase in the size of liquid crystal TVs. Therefore, the number of discharge tubes or the number of transformers required capacitors, so the area of the substrate can be reduced. Increased. Moreover, since the rectangular wave is converted by a transformer, the efficiency is deteriorated.
JP 2003-31383 A US Pat. No. 6,781,325 JP-T-2004-506294 JP 2005-005059 A

  In the present invention, by connecting a balance transformer to the primary winding side, the currents on the primary side are combined, the currents of each discharge tube are combined indirectly, and an alternating current (ideally a SIN wave) current is generated in the sub-circuit. By inputting to the primary side of the main circuit, the filter capacitor is eliminated and the efficiency is improved. In addition, since the balance transformer is arranged on the primary winding side, it is not necessary to consider insulation for the component arrangement, and the board design can be very useful. Also, the number of parts of the balance transformer can be reduced and driven, which is practical.

  Accordingly, an object of the present invention is to provide a discharge tube driving circuit and an inverter circuit capable of uniformly emitting light from a plurality of discharge tubes despite the use of a small number of balance transformers.

  In addition, since alternating current (ideally, a sine wave) is directly applied to the primary winding of the drive circuit, the efficiency is improved compared to driving with a rectangular current. Another object of the present invention is to provide a discharge lamp drive circuit and an inverter circuit that can reduce the cost because it is not necessary to connect a capacitor for a filter to the secondary winding side of the drive transformer.

In order to achieve the above object, a discharge tube driving circuit according to an embodiment of the present invention includes at least first and second driving transformers each having a primary winding and a secondary winding, and the first and second driving transformers. A first switching unit connected to each primary winding of each of the drive transformers, and a control unit for controlling the first switching unit, each secondary of the first and second drive transformers In a discharge tube driving circuit for driving a discharge tube connected to a winding,
At least first and second balance transformers each having a primary winding and a secondary winding;
A second switching unit,
The primary winding of the first drive transformer and the secondary winding of the first balance transformer are connected in series, and the primary winding of the second drive transformer and the second balance transformer The secondary winding is connected in series,
An AC signal generated in the second switching unit is applied to the primary windings of the first and second balance transformers, respectively.

In order to achieve the above object, a discharge tube drive circuit according to another embodiment of the present invention includes a discharge in which primary windings of a plurality of drive transformers are connected in parallel and connected to secondary windings of the plurality of drive transformers. In a discharge tube driving circuit for driving a tube,
A plurality of balance transformers corresponding to the plurality of drive transformers,
Each primary winding of the plurality of drive transformers and each secondary winding of the corresponding balance transformer are connected in series,
An AC signal is applied to each primary winding of the corresponding balance transformer.

In order to achieve the above object, a discharge tube driving circuit according to still another embodiment of the present invention includes a driving transformer,
A first switching unit connected to a primary winding of the drive transformer;
A control unit for supplying a control signal to the first switching unit;
A second switching unit,
The second switching unit is configured to superimpose an AC signal generated in the second switching unit on a signal flowing through the primary winding.

In order to achieve the above object, an inverter circuit according to still another embodiment of the present invention includes:
In an inverter circuit for lighting a plurality of discharge lamps equipped with a switching unit and a step-up transformer,
A first drive transformer section in which primary windings of at least two drive transformers are connected in series;
A second drive transformer section in which primary windings of at least two drive transformers are connected in series;
The secondary winding and the primary winding of the balance transformer connected in series to each of the first drive transformer unit and the second drive transformer unit are connected in series so that an AC signal is applied. It is characterized by comprising.

In order to achieve the above object, an inverter circuit according to still another embodiment of the present invention includes:
In an inverter circuit including a drive transformer, a balance transformer, and an LC resonance circuit,
An alternating current formed by the LC resonance circuit is applied to a primary winding of the balance transformer that shares a magnetic path with a secondary winding of the balance transformer connected in series to the drive transformer. And

  In the present invention, by connecting the primary winding of the balance transformer in series, the current flowing through the primary winding of the drive transformer can be made constant. In addition, AC current can be applied to the primary winding of the drive transformer, so that it is not necessary to provide a capacitor on the secondary side, and not only cost can be reduced but also efficiency can be increased. In addition, the number of capacitors used can be reduced, so that the board area can be reduced and the cost can be reduced.

<Example 1>
First, a discharge tube drive circuit for driving two discharge tubes FL1 and FL2 according to Embodiment 1 of the present invention will be described with reference to FIG. The discharge tube driving circuit in the embodiment of the present invention basically includes a main circuit 6 and a sub circuit 7. In FIG. 1, a DC power source Vin is applied between power source terminals 1 and 2. The power supply terminal 2 is connected to the ground potential. Further, the DC power source Vin is supplied as an operation power source to the control circuit 5 and the switching circuit 8 via the fuse 3. Reference numeral 4 denotes a smoothing capacitor.

  The switching circuit 8 is composed of a plurality of switching elements, is composed of a full bridge, a half bridge, or the like, is included in the main circuit 6, and is controlled by switching pulses from the control circuit 5. The output of the switching circuit 8 is boosted to a high voltage by drive transformers DT1 and DT2 included in the main circuit 6 described later, and is applied to the discharge tubes FL1 and FL2 as a high frequency high voltage to drive the discharge tubes FL1 and FL2. .

  As is well known, the control circuit 5 includes therein a variable frequency oscillation circuit, a PWM modulation circuit, or the like, and the oscillation frequency of the variable frequency oscillation circuit or the output pulse width of the PWM modulation circuit is a discharge tube. Is controlled by an IF / B signal related to the current flowing through the VF / B signal and a VF / B signal related to the voltage applied to the discharge tube. As a result, the discharge tube to be lit can emit light stably and stably.

  Two drive transformers DT1 and DT2 are used in the main circuit 6 of the discharge tube drive circuit shown in FIG. That is, the main circuit 6 includes two drive transformers DT1, DT2, and secondary windings CT1-2 and CT2-2 of two balance transformers CT1 and CT2.

  As illustrated, the primary winding DT1-1 of the drive transformer DT1 and the secondary winding of the balance transformer CT1 are connected in series, and both ends thereof are connected to the switching circuit 8. Similarly, the primary winding DT2-1 of the drive transformer DT2 and the secondary winding of the balance transformer CT2 are connected in series, and both ends thereof are connected to the switching circuit 8. The primary windings DT1-1 and DT2-1 of the drive transformers DT1 and DT2 are connected in parallel and connected to the switching circuit 8, respectively.

  The two secondary windings DT1-21 and DT1-22 of the drive transformer DT1 are connected in series, the middle point is grounded, and both ends are connected to the discharge tube FL1. Similarly, the two secondary windings DT2-21 and DT2-22 of the drive transformer DT2 are connected in series, the midpoint is grounded, and both ends are connected to the discharge tube FL2.

  Next, the sub circuit 7 will be described. The sub circuit 7 basically includes a switching circuit 9, a drive transformer LT, and primary windings CT1-1 and CT2-1 of two balance transformers CT1 and CT2. The switching circuit 9 is composed of a plurality of switching elements, shows a full bridge, a half bridge, etc., operates with a DC power supply Vin supplied from power supply terminals 1 and 2, and is controlled by a switching pulse from the control circuit 5. .

  The output of the switching circuit 9 is supplied to the primary winding LT1 of the drive transformer LT. One terminal of the secondary winding LT2 of the drive transformer LT is grounded via a resistor R. At this time, the connection midpoint between one terminal of the secondary winding LT2 of the drive transformer LT and the resistor R is fed back to the control circuit 5 as an IF / B signal. The other terminal of the secondary winding LT2 of the drive transformer LT is connected in series with the coil L and the primary windings CT1-1 and CT2-1 connected in series with the balance transformers CT1 and CT2.

  The midpoint of connection between the coils L and the primary windings CT1-1 and CT2-1 connected in series is grounded via two capacitors C1 and C2. The connection midpoint between the two capacitors C1 and C2 is related to the voltage applied to each of the drive transformers DT1 and DT2, and is fed back to the control circuit 5 as a VI / F signal.

  Specifically, it serves as overvoltage protection. For example, when the discharge tube FL1 is opened, the impedance of the system rises and the primary current of the drive transformer DT decreases. Therefore, the current of the balance transformer CT1 of the system also decreases. That is, the impedance of the balance transformer is increased. When the impedance of the balance transformer rises, the Q of the LC resonance circuit of the sub circuit 7 rises, so that the capacitor voltage also rises. The load open is detected by the voltage rise of this capacitor.

  Next, the operation of the discharge tube driving circuit according to the first embodiment will be described. First, in the main circuit 6, when the switched voltage Vin is output from the switching circuit 8, a voltage is applied to the primary windings DT1-1 and DT2-1 of the drive transformers DT1 and DT2, respectively. The voltage switched from the switching circuit 9 is also output to the sub circuit and input to the primary winding LT1 of the drive transformer LT. In the secondary winding LT2 of the drive transformer LT, an alternating current (ideally a sine wave) current is generated at the resonance frequency of the LC resonance circuit formed by the coil L, the capacitor C1, and the capacitor C2. And applied to the primary windings CT1-1 and CT2-1 of the balance transformers CT1 and CT2, respectively.

  Here, since the balance transformers CT1-1 and CT2-1 are connected in series, an equal current flows. The currents of the primary windings DT1-1 and DT2-1 of the drive transformers DT1 and DT2 are equalized by being supplied to the secondary windings CT1-2 and CT2-2 of the balance transformer in accordance with the current value. Become. In addition, an alternating current (ideally, a sine wave) current is forced to flow through the primary winding of the drive transformer by a balance transformer, so that boosting is possible with an alternating current (ideally, a sine wave) current. . Further, discharge tube drive signals are generated in the secondary windings DT1-21, DT1-22, DT2-21, and DT2-22 of the drive transformers DT1 and DT2, respectively, to drive the discharge tubes FL1 and FL2.

  The voltage generated across the resistor R of the sub-circuit 7 is related to the current flowing through the primary windings DT1-1 and DT2-1 of the drive transformers DT1 and DT2, and is supplied to the control circuit 5 as an IF / B signal. The voltage that is fed back and generated at the connection midpoint of the capacitors C1 and C2 is related to the voltage applied to the primary windings DT1-1 and DT2-1 of the drive transformers DT1 and DT2, and is a VF / B signal. As feedback to the control circuit 5. By controlling the variable frequency oscillation circuit, the PWM modulation circuit, etc. included in the control circuit 5 by the feedback IF / B signal and VF / B signal, the light emission luminance of the discharge tubes FL1, FL2 can be made constant. It becomes possible.

  In the discharge tube drive circuit shown in the first embodiment of FIG. 1, the discharge tube drive circuit using the two drive transformers DT1 and DT2 has been described. However, the present invention is not necessarily limited to this configuration. For example, it is possible to connect three or more drive transformers in parallel to obtain the same effect. For example, when three drive transformers are used, three balance transformers are also used. The secondary windings of the three balance transformers are respectively connected in series with the primary windings of the three drive transformers, and the primary windings of the three balance transformers are connected in series so that the coil L is connected between the ground and the ground. It is good also as a discharge tube drive circuit comprised by inserting.

<Example 2>
Next, Embodiment 2 of the present invention will be described with reference to FIG. FIG. 2 shows a sub-circuit 7 ′ obtained by modifying the sub-circuit 7 of the first embodiment shown in FIG. The other circuit parts have the same configuration as that of the first embodiment shown in FIG. 1, and are omitted. Further, in the subcircuit 7 ′, the same parts as those of the first embodiment shown in FIG. The description which overlaps is abbreviate | omitted.

  In the sub-circuit 7 'of FIG. 2, one terminal of the secondary winding LT2 of the drive transformer LT is directly grounded. The other terminal of the secondary winding LT2 is connected to the coil L, the capacitor C, the primary windings CT1-1 and CT2-1 of the balance transformers CT1 and CT2 connected in series, and the resistor R in series and grounded. The The IF / B signal is taken out from the connection midpoint between the resistor R and the primary winding CT2-1 of the balance transformer CT2, and from the connection midpoint between the capacitor C and the primary winding CT1-1 of the balance transformer CT1. The VF / B signal is taken out and fed back to the control circuit 5 in FIG.

  Also in the second embodiment using the sub-circuit 7 ′ configured as described above, the same effect as the first embodiment shown in FIG. 1 can be obtained. Further, the discharge tube driving circuit according to the second embodiment using the sub-circuit 7 ′ can be implemented with a modification similar to the discharge tube driving circuit according to the first embodiment. That is, when three drive transformers are used, three balance transformers are also used. And it is good also as a discharge tube drive circuit comprised by connecting the primary winding of three balance transformers in series, and inserting between the capacitor | condenser C and earth | ground.

<Example 3>
Next, Embodiment 3 of the present invention will be described with reference to FIG. FIG. 3 shows a main circuit 6 ′ obtained by modifying the main circuit 6 of the first embodiment shown in FIG. The other circuit parts have the same configuration as that of the first embodiment shown in FIG. 1, and are omitted. Further, in the main circuit 6 ′, the same parts as those of the first embodiment shown in FIG. The description which overlaps is abbreviate | omitted.

  In the main circuit 6 ′ of FIG. 3, the main circuit 6 ′ is configured to use four drive transformers DT <b> 1 to DT <b> 4. That is, the primary windings DT1-1 and DT2-1 of the drive transformers DT1 and DT2 are connected in series and connected in series with the secondary winding CT1-2 of the balance transformer CT1. The both ends are connected to the switching circuit 8. One end of the secondary winding DT1-2 of the drive transformer DT1 is grounded, and the other end is grounded via the discharge tube FL1 and the resistor R1. Similarly, one side of the secondary winding DT2-2 of the drive transformer DT2 is grounded, and the other side is grounded via the discharge tube FL2 and the resistor R2.

  Similarly, the primary windings DT3-1 and DT4-1 of the drive transformers DT3 and DT4 are connected in series and connected in series with the secondary winding CT2-2 of the balance transformer CT2. The both ends are connected to the switching circuit 8. One end of the secondary winding DT3-2 of the drive transformer DT3 is grounded, and the other end is grounded via the discharge tube FL3 and the resistor R3. Similarly, one side of the secondary winding DT4-2 of the drive transformer DT4 is grounded, and the other side is grounded via the discharge tube FL4 and the resistor R4. The discharge tube drive circuit according to the third embodiment configured as described above can achieve the same effect as the discharge tube drive circuit according to the first embodiment. In the discharge tube drive circuit employing the third embodiment shown in FIG. 3, the discharge tube drive circuit using two sets of drive circuits in which two drive transformers are connected in series has been described. It is not limited to. For example, it is possible to obtain the same effect by using three or three or more drive circuits in which two drive transformers are connected in series.

  For example, if the discharge tube drive circuit uses three sets of drive circuits in which two drive transformers are connected in series, three balance transformers are also used. The sub-circuit 7 shown in FIG. 1 may be a discharge tube driving circuit configured by connecting the primary windings of three balance transformers in series. In addition, although it demonstrated as a drive circuit which connected two drive transformers in series, it suffices to connect three or more drive transformers in series and increase the number of sets by the number of necessary discharge tubes.

  Further, the connection method between the driving transformer and the discharge tube of the main circuit shown in FIGS. 1 to 3 is not necessarily limited to this configuration. The discharge tube may be a U-shaped tube or a pseudo U-shaped tube instead of a straight tube.

  Further, the balance transformers CT1 and CT2 are not particularly limited in shape, but the condition is that the primary winding and the secondary winding have a common magnetic path. Further, the shape of the drive transformer is not limited. A drive transformer with a built-in balance transformer may also be used.

  The first to third embodiments of the discharge tube driving circuit according to the present invention and the modifications thereof have been described above. However, the discharge tube driving circuit according to the present invention is not limited to the above-described embodiments and modifications. Various aspects can be changed. That is, the sub-circuit 7 'according to the second embodiment and the main circuit 6' according to the third embodiment may be used to form a discharge tube driving circuit according to a new embodiment.

It is a figure which shows the circuit diagram of the discharge tube drive circuit in Example 1 of this invention. It is a figure which shows the circuit diagram of the subcircuit of the discharge tube drive circuit in Example 2 of this invention. It is a figure which shows the circuit diagram of the main circuit of the discharge tube drive circuit in Example 3 of this invention.

Explanation of symbols

1, 2 Power supply terminal 5 Control circuit 8, 9 Switching circuit 6, 6 'Main circuit 7, 7' Sub circuit DT1 to DT4 Drive transformer DT1-1 to DT4-1 Primary winding DT1-2 to DT4-2 Secondary winding Line CT1, CT2 Balance transformer CT1-1, CT2-1 Primary winding CT1-2, CT2-2 Secondary winding LT Drive transformer LT1 Primary winding LT2 Secondary winding R Resistance L Coils C, C1, C2 Capacitors

Claims (5)

At least first and second drive transformers each having a primary winding and a secondary winding; and a first switching unit connected to each primary winding of the first and second drive transformers; A control unit that controls the first switching unit, and a discharge tube drive circuit that drives a discharge tube connected to each secondary winding of the first and second drive transformers,
At least first and second balance transformers each having a primary winding and a secondary winding;
A second switching unit,
The primary winding of the first drive transformer and the secondary winding of the first balance transformer are connected in series, and the primary winding of the second drive transformer and the second balance transformer The secondary winding is connected in series,
A discharge tube driving circuit, wherein an alternating current signal generated by the second switching unit is applied to the primary windings of the first and second balance transformers. In a discharge tube driving circuit for driving a discharge tube connected to the primary windings of a plurality of drive transformers in parallel and connected to secondary windings of the plurality of drive transformers,
A plurality of balance transformers corresponding to the plurality of drive transformers,
Each primary winding of the plurality of drive transformers and each secondary winding of the corresponding balance transformer are connected in series,
A discharge tube driving circuit, wherein an AC signal is applied to each primary winding of the corresponding balance transformer. A driving transformer,
A first switching unit connected to a primary winding of the drive transformer;
A control unit for supplying a control signal to the first switching unit;
A second switching unit,
2. The discharge tube driving circuit according to claim 1, wherein the second switching unit is configured to superimpose an AC signal generated by the second switching unit on a signal flowing through the primary winding. In an inverter circuit for lighting a plurality of discharge lamps equipped with a switching unit and a step-up transformer,
A first drive transformer section in which primary windings of at least two drive transformers are connected in series;
A second drive transformer section in which primary windings of at least two drive transformers are connected in series;
The secondary winding and the primary winding of the balance transformer connected in series to each of the first drive transformer unit and the second drive transformer unit are connected in series so that an AC signal is applied. An inverter circuit characterized by comprising. In an inverter circuit including a drive transformer, a balance transformer, and an LC resonance circuit,
An alternating current formed by the LC resonance circuit is applied to a primary winding of the balance transformer that shares a magnetic path with a secondary winding of the balance transformer connected in series to the drive transformer. Inverter circuit.

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