CN1550850A - Discharge lamp lighting device and backlight device using same - Google Patents

Abstract

To light a plurality of discharge lamps so that luminance deviation due to unevenness in stray capacity of load does not occur. A discharge lamp lighting device is provided with a plurality of discharge tubes 1a, 1b, connected in series, and an electromagnetic transformer T having a common primary winding 11 and two secondary windings 12(1), 12(2). One vacant electrode of the plurality of discharge tubes connected in series is connected to a high voltage terminal of one secondary winding of the electromagnetic transformer. The other vacant electrode of the discharge tubes connected in series is connected to a high voltage terminal of the other secondary winding of the electromagnetic transformer. Low voltage terminals of the two second windings are grounded respectively. Each of the high voltage terminals of the two secondary windings are applied with a voltage of an inverted phase respectively. The lighting device is characterised in that, by making magnetic circuit one, luminance deviation (lamp current) can be prevented, even if unevenness in stray capacity of load exists, thus eliminating luminance unevenness on screen, when used as a backlight arranged on the back side of pannel.

Description

Discharge lamp lighting device and backlight device using same

technical field

The present invention relates to a discharge lamp lighting device and a backlight device using the same.

Background technique

Conventionally, a discharge lamp lighting device having a plurality of discharge lamps used as a direct backlight for liquid crystal monitors, liquid crystal televisions, etc. has used the circuit configuration shown in FIGS. 6 and 7 . That is, in order to light two discharge lamps 1a, 1b, the two discharge lamps 1a, 1b are connected in series, and two electromagnetic transformers T1, T2 composed of a primary winding 2 and a secondary winding 3 are used, and these The respective low-voltage terminals of the secondary windings 3, 3 of the electromagnetic transformers T1, T2 are grounded together with the respective low-voltage side electrodes of the two discharge lamps 1a, 1b, and the respective secondary windings 3, 3 of these electromagnetic transformers T1, T2 are connected to the ground. The high-voltage terminals are connected to respective high-voltage-side electrodes of the discharge lamps 1a and 1b through connection terminals CCFL-1 and CCFL-2. Furthermore, the collectors of a pair of transistors 5a, 5b constituting the high-frequency power supply 5 are connected to the primary windings 2, 2 of the respective electromagnetic transformers T1, T2. Moreover, it is connected so that the voltage of mutually opposite phase may be output to discharge lamp 1a, 1b from the high voltage terminal side of each secondary winding 3, 3 of electromagnetic transformer T1, T2.

Also, as a conventional discharge lamp lighting device, as shown in FIG. 8 , it is known that the low-voltage terminals of the secondary windings 3 and 3 of the two electromagnetic transformers T1 and T2 are mutually grounded in order to simplify the structure of the grounding circuit. The discharge lamps 1a and 1b connected in series are connected only between the low-voltage side electrodes without being grounded. Also, as shown in FIG. 9, it is known that two discharge lamps 1a, 1b are replaced by U-shaped curved tubes 10, and the two electromagnetic transformers T1, T2 are connected to each other in the same way as the discharge lamp lighting device shown in FIG. The low-voltage terminals of the secondary windings 3, 3 are grounded to each other, and the two electrodes of the curved tube 10 are respectively connected to the high-voltage terminals of the secondary windings 3, 3 (refer to Japanese Patent No. 3) bulletin; Japanese Patent Application Laid-Open Publication No. 2001-297613 (Fig. 1) or Japanese Patent Laid-Open Publication No. 2003-168310 (Fig. 4, Fig. 7)).

However, in such a conventional discharge lamp lighting device, a bias voltage is generated in the lamp current of each discharge lamp, and when a plurality of discharge lamps are arranged in an array and used as a direct type backlight, there may be a problem on the screen. The problem of uneven brightness. Such luminance unevenness is a serious disadvantage in the backlight device, and improvement has been demanded.

Contents of the invention

The present invention has been made in view of such problems in the prior art, and an object of the present invention is to provide a discharge lamp lighting device capable of lighting a plurality of discharge lamps without causing brightness unevenness, that is, polarization of brightness.

A discharge lamp lighting device according to an embodiment of the present invention is characterized in that it has: an electromagnetic transformer having a shared primary winding and at least first and second secondary windings; an electrode and the first secondary winding of the electromagnetic transformer A first cold cathode discharge lamp connected to the high voltage terminal of the first cold cathode discharge lamp; a second cold cathode discharge lamp with one electrode connected to the other electrode of the first cold cathode discharge lamp and the other electrode connected to the high voltage terminal of the second secondary winding of the electromagnetic transformer For a cathode discharge lamp, the low-voltage terminals of the first and second secondary windings of the electromagnetic transformer are respectively grounded, and the phase-reversed voltages are respectively applied to the high-voltage terminals of the first and second secondary windings of the electromagnetic transformer .

Furthermore, in the above-mentioned discharge lamp lighting device, it is characterized in that the high-frequency power supply circuit has emitters that are commonly grounded and collectors that are respectively connected to the high-voltage terminals of the first and second secondary windings of the electromagnetic transformer. 1 pair of transistors, the electromagnetic transformer has a 3rd winding, and the 3rd winding is connected to the base of the 1 pair of transistors.

Also, the backlight device according to the embodiment of the present invention is characterized in that a plurality of the cold cathode discharge lamps are arranged on a common reflector.

In the discharge lamp lighting device configured in this way or the backlight device including the lighting device, even when unbalance occurs on the high-voltage sides of the first and second secondary windings due to variations in the parasitic capacitance of the load, Since the magnetic circuit including the primary winding of the electromagnetic transformer is shared, when one lamp current fluctuates, the other fluctuates similarly, and as a result, the same brightness can be maintained.

Another embodiment of the discharge lamp lighting device of the present invention is characterized in that it has: an electromagnetic transformer with a common primary winding and at least the first and second secondary windings; The high-voltage terminal of the first secondary winding is connected, and the other electrode is connected to the high-voltage terminal of the second secondary winding of the electromagnetic transformer. The bent cold cathode discharge tube makes the first and second secondary of the electromagnetic transformer The low-voltage terminals of the windings are respectively grounded, and voltages with mutually reversed phases are respectively applied to the high-voltage terminals of the first and second secondary windings of the electromagnetic transformer.

In addition, in the above-mentioned discharge lamp lighting device of the present invention, it is characterized in that the high-frequency power supply circuit is formed on a substrate provided with a high-voltage high-frequency output land (land), and is connected with the bent The electrode leads of the cold cathode discharge lamp are connected.

Also, the backlight device according to the embodiment of the present invention is characterized in that a plurality of the curved cold cathode discharge lamps are arranged on a common reflector.

In this discharge lamp lighting device or backlight device, since the magnetic circuit including the primary winding of the electromagnetic transformer is also shared, the dispersion of the parasitic capacitance in each part of the cold cathode discharge tube caused by bending, the first time When a voltage fluctuation occurs in the primary winding, approximately the same fluctuation occurs in the second secondary winding, which can prevent the occurrence of polarization of the lamp current on different parts of the curved discharge tube, and can be used as a directly below type. Eliminates brightness unevenness on the screen when illuminating.

That is, the inventors of the present invention investigated the cause of occurrence of brightness unevenness in such a direct-type backlight device, and as a result found the following fact.

Generally, as shown in the above-mentioned conventional devices, in a direct-type backlight device using a plurality of discharge lamps, a reflector made of metal provided in the backlight device or a housing of the backlight device itself A parasitic capacitance is formed between the body and each discharge lamp. In addition, parasitic capacitance is formed between the harness for supplying high-frequency power from the high-frequency power supply to the electrodes of each discharge lamp, the reflector, the casing of the backlight device itself, and the environment around the discharge lamp. Furthermore, each discharge lamp has a parasitic capacitance due to its structure. In addition, these parasitic capacitances have different capacitance values depending on the position of each discharge lamp or the environment of surrounding structures.

Due to the presence of such parasitic capacitances, when a high-frequency voltage exceeding 1 kV is supplied from a high-frequency power supply to each discharge lamp at a frequency of 30 to 60 kHz, a part of high-frequency current leaks through these parasitic capacitances. Therefore, since the tube current flowing through the discharge lamp differs for each discharge lamp depending on the magnitude of the parasitic capacitance, it becomes a cause of brightness unevenness.

In the present invention, since the primary winding of the electromagnetic transformer T is shared for the cause of brightness unevenness, the deviation of the output current caused by the parasitic capacitance generated in each secondary winding of the electromagnetic transformer T can be averaged. , and by supplying approximately the same current to the first and second cold cathode discharge lamps 1a, 1b, it is possible to reduce brightness unevenness.

Description of drawings

Fig. 1 is a block diagram of a discharge lamp lighting device according to Embodiment 1 of the present invention.

Fig. 2 is a circuit diagram of the discharge lamp lighting device shown in Fig. 1 .

Fig. 3 is a block diagram of a discharge lamp lighting device according to Embodiment 2 of the present invention.

Fig. 4 is a plan view showing the connection structure of the curved tube discharge lamp to the frame of the power supply unit according to Embodiment 2 of the present invention.

Fig. 5 is a plan view showing a connection structure of a wire harness between a curved tube discharge lamp according to Embodiment 2 of the present invention and a housing of a power supply unit.

Fig. 6 is a block diagram of a conventional discharge lamp lighting device.

Fig. 7 is a circuit diagram of the conventional discharge lamp lighting device shown in Fig. 6 .

Fig. 8 is a block diagram of another conventional discharge lamp lighting device.

Fig. 9 is a block diagram of yet another conventional discharge lamp lighting device.

Detailed ways

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Example 1

A discharge lamp lighting device according to Embodiment 1 of the present invention will be described with reference to FIGS. 1 and 2 . The discharge lamp lighting device of the present embodiment is composed of a common primary winding 11, two secondary windings 12(1), 12(2), and a tertiary winding 13 serving as a base winding facing the high-frequency power supply circuit 5. The electromagnetic transformer T.

In order to light the two discharge lamps 1a, 1b, the low-voltage side electrodes of the two discharge lamps 1a, 1b are connected in series, and the low-voltage terminals of the secondary windings 12(1), 12(2) of the electromagnetic transformer T are grounded to each other. The high-voltage terminals of the secondary windings 12(1), 12(2) of the electromagnetic transformer T are connected to the high-voltage side electrodes of the discharge lamps 1a, 1b through the connection terminals CCFL-1, CCFL-2, respectively. Then, an electromagnetic transformer T is connected to the high-frequency power supply 5 so as to output voltages whose phases are reversed to each other to the high-voltage terminal sides of the secondary windings 12 ( 1 ), 12 ( 2 ).

Thus, in the discharge lamp lighting device of Embodiment 1, the high-frequency power supply 5 is connected to the primary winding 11 of the electromagnetic transformer T, and at the same time, a high voltage with mutually reversed phases is generated from the secondary winding 12(1) and the secondary winding 12(2). The waveforms are applied to the high-voltage-side electrodes of the two discharge lamps 1a and 1b to simultaneously light both the discharge lamps 1a and 1b. Here, the high-frequency power supply 5 has a pair of transistors 5a and 5b whose emitters are commonly grounded and whose collectors are respectively connected to the high-voltage terminals of the first and second secondary windings of the electromagnetic transformer. The electromagnetic transformer has a tertiary winding, and the tertiary winding is connected to the bases of the pair of transistors 5a, 5b. A bias voltage from a DC power supply terminal 5d is supplied between the bases and collectors of the pair of transistors 5a and 5b. Furthermore, the capacitor 5c for determining the oscillation frequency is connected between the collectors of the pair of transistors 5a and 5b together with the inductance component of the electromagnetic transformer T. The high-frequency power supply 5 is a so-called inverter circuit composed of an oscillator and an electromagnetic transformer T together.

When the discharge lamps 1a and 1b are turned on, as shown in FIG. 1 , high-frequency voltages whose phases are inverted from each other are applied to the high-voltage-side electrodes of the discharge lamps 1a and 1b. When unbalance occurs on the high-voltage side of the secondary windings 12(1) and 12(2) due to the dispersion of the parasitic capacitance of the load, since the magnetic circuit of the electromagnetic transformer T is shared, when the lamp current of one side fluctuates, the other side changes. One side also changes in the same manner, and as a result, the discharge lamps 1a and 1b can maintain substantially the same luminance.

Next, its operation will be described. The capacitance of the discharge lamps 1a, 1b themselves connected as loads to the secondary windings 12(1) and 12(2) of the electromagnetic transformer T and the parasitic capacitances generated in them will affect the high-frequency power supply. The frequency F of 5 is affected. For example, when the parasitic capacitance accompanying the discharge lamps 1a and 1b increases, F∝1/(LC) ^1/2 becomes F∝1/(LC) 1/2 , so the frequency of the high-frequency power supply 5 decreases. Here, L is the inductance in the electromagnetic transformer T, and C is the capacitance of the capacitor 5 c of the high-frequency power supply 5 . As a result, since the reactance due to the inductance L component in the electromagnetic transformer T also decreases, the high-frequency current output to the secondary windings 12 ( 1 ), 12 ( 2 ) of the electromagnetic transformer T increases. This increase in the high-frequency current serves to compensate the tube current of the discharge lamps 1a, 1b, which is reduced due to leakage of the high-frequency current through the parasitic capacitance.

That is, in this discharge lamp lighting device, a fluctuation of the lamp current due to parasitic capacitance occurs in the first cold cathode discharge lamp 1a connected to the first secondary winding 12(1) of the electromagnetic transformer T, causing the electromagnetic The voltage in the inductance component in the transformer T changes so as to drop, and a current that cancels this fluctuating state is supplied to the first secondary winding 12 ( 1 ) of the electromagnetic transformer T. Also on the second cold cathode discharge lamp 1b connected to the second secondary winding 12(2) of the electromagnetic transformer T, the fluctuation of the lamp current caused by the parasitic capacitance occurs. The current that cancels out this shifting state. However, since the electromagnetic transformer T shares the primary winding 11, it can supply averaged currents of approximately the same magnitude to the first and second secondary windings 12(1), 12(2). As a result, the first and second cold-cathode discharge lamps 1a, 1b are lit at the same luminance by substantially the same current, and unevenness in luminance can be eliminated.

Also, in FIG. 1 , although not shown in the figure, a plurality of combinations consisting of electromagnetic transformer T and two discharge lamps 1a, 1b connected to its secondary side are provided, and the plurality of sets of discharge lamps 1a, 1b are arranged in The common metal reflector is housed in the casing for the backlight device together with the above-mentioned discharge lamp lighting device.

Therefore, when the discharge lamp lighting device of this embodiment is used as a direct type backlight, uneven brightness does not occur on the screen, and uniform brightness illumination can be performed.

Example 2

Next, a discharge lamp lighting device according to Embodiment 2 of the present invention will be described with reference to FIG. 3 . In the discharge lamp lighting device of the second embodiment, the configuration of the electromagnetic transformer T is the same as that of the first embodiment. In addition, a U-shaped bent tube 10 is used as a discharge lamp, and each of the high-voltage-side terminals of the high-voltage high-frequency secondary windings 12(1) and 12(2) of the high-voltage high-frequency secondary windings 12(1) and 12(2) of which the phases of the electrodes at both ends and the output electromagnetic transformer T are reversed is mutually reversed. Connect separately.

Also in the discharge lamp lighting device of the second embodiment, since the high-frequency power supply 5 is connected to the common primary winding 11 of the electromagnetic transformer T, a high-voltage waveform from the first secondary winding 12 (1) is generated, and a high-voltage waveform from the first secondary winding 12 (1) is generated. High-frequency voltage that reverses the phase of the second secondary winding 12(2). These high-frequency voltages are respectively applied to the two electrodes of the curved tube 10 to cause the curved tube 10 to discharge and light the lamp.

When this curved tube 10 is turned on, as shown in FIG. The high-voltage side of the primary winding 12(1), 12(2) will produce unbalance, and because the magnetic circuit of the electromagnetic transformer T is shared, as explained in Embodiment 1, when the lamp current of one side fluctuates, the other side Since it also changes in the same way, the brightness on both sides of the curved tube 10 can be maintained to be the same. Therefore, even when the discharge lamp lighting device of this embodiment is used as a direct backlight, uneven brightness does not occur on the screen, and uniform brightness illumination can be performed.

Furthermore, the structure of connecting the output electrodes on the power supply circuit side of the curved tube discharge lamp 10 is preferably the structure shown in FIG. 4 . In this FIG. 4 , 21 is a substrate housed in the frame of the power supply device of the discharge lamp lighting device, and pads 22 ( 1 ) and 22 ( 2 ) are provided on the high-voltage high-frequency output portion of the substrate 21 . . On the other hand, lead wires 23 ( 1 ), 23 ( 2 ) drawn from both electrodes of the curved tube discharge lamp 10 are drawn in the same direction. And, when the curved tube discharge lamp 10 is connected to the power supply device, the two lead wires 23 ( 1 ), 23 ( 2 ) of the curved tube discharge lamp 10 are respectively connected to the pads 22 ( 1 ) of the frame body 21 by soldering. , Each connection of 22(2) is made in a state of not utilizing the wire harness.

Thereby, compared with the connection structure using the wire harness 24 shown in FIG. 5, the transmission efficiency of electric power can be improved. That is, since there are no parasitic capacitances between the wiring harness 24 and the reflector or housing included in the backlight device, there is no flow of leakage current from the wiring harness 24 through these parasitic capacitances. Therefore, the difference in the lighting current value between the electrodes of the discharge lamp 10 due to the difference in the parasitic capacitance around the wire harness can be suppressed, and unevenness in brightness can be prevented. In addition, it is also possible to reduce the cost by reducing the number of components such as the wire harness 24, the housing 25, the connector 26, and the insulating tube 27.

3 and 4, although not shown in the figure, a plurality of combinations of electromagnetic transformers T and curved discharge lamps 10 connected to the secondary side are provided, and the plurality of sets of discharge lamps 10 are arranged. The common metal reflector is housed in a case for a backlight device together with the above-mentioned discharge lamp lighting device, and is used as a direct type backlight device.

The present invention is not limited to the embodiments described above, and various modifications are possible.

For example, the transistors 5a and 5b constituting the high-frequency power supply 5 shown in FIG. 2 may be MOS transistors instead of bipolar transistors. In this case, the electrodes of the bipolar transistor, that is, the emitter, the collector, and the base, mean to be the source, the drain, and the gate of the MOS transistor, respectively.

In addition, the curved tube discharge lamp 10 shown in Fig. 3 and Fig. 4 does not necessarily need to have a U-shape.

In addition, the present invention is not limited to a direct type backlight device, but can also be applied to a so-called edge type backlight device in which a light source is arranged on the side of a light guide plate.

Claims (5)

1. A discharge lamp lighting device, characterized in that, It has: an electromagnetic transformer with a common primary winding and at least the first and second secondary windings; a first cold cathode discharge tube with an electrode connected to the high-voltage terminal of the first secondary winding of the electromagnetic transformer; an electrode connected to the high voltage terminal of the first secondary winding of the electromagnetic transformer; The other electrode of the first cold cathode discharge tube is connected, and the other electrode is connected to the second cold cathode discharge tube of the high voltage terminal of the second secondary winding of the electromagnetic transformer; and the second cold cathode discharge tube connected to the primary winding of the electromagnetic transformer high frequency power supply circuit, The low-voltage terminals of the first and second secondary windings of the electromagnetic transformer are respectively grounded, and voltages with phase inversion are applied to the high-voltage terminals of the first and second secondary windings of the electromagnetic transformer respectively. 2. The discharge lamp lighting device as claimed in claim 1, wherein the high-frequency power supply circuit has emitters that are commonly grounded, and the collectors are respectively connected to the high voltage of the first and second secondary windings of the electromagnetic transformer. A pair of transistors connected by terminals, the electromagnetic transformer has a tertiary winding, and the tertiary winding is connected to the bases of the pair of transistor elements. 3. A discharge lamp lighting device, characterized in that: It has: an electromagnetic transformer with a common primary winding and at least the first and second secondary windings; one electrode is connected to the high-voltage terminal of the first secondary winding of the electromagnetic transformer, and the other electrode is connected to the first secondary winding of the electromagnetic transformer. 2 a curved cold cathode discharge lamp connected to the high voltage terminal of the secondary winding; and a high frequency power supply circuit connected to the primary winding of said electromagnetic transformer, The low-voltage terminals of the first and second secondary windings of the electromagnetic transformer are respectively grounded, and voltages with phase reversal are applied to the high-voltage terminals of the first and second secondary windings of the electromagnetic transformer. 4. A discharge lamp lighting device, characterized in that the high-frequency power supply circuit is formed on a substrate provided with a high-voltage high-frequency output pad, and is connected to the electrode lead-out wire of the curved cold-cathode discharge lamp . 5. A backlight device, characterized in that it comprises the discharge lamp lighting device according to any one of claims 1 to 4 characterized by arranging a plurality of said cold cathode discharge lamps on a common reflector .

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