JP4049270B2 - Discharge lamp driving device and liquid crystal display device - Google Patents

Description

  The present invention relates to a discharge lamp driving device for driving a discharge lamp used as a liquid crystal backlight, and a liquid crystal display device.

  In recent years, with an increase in the screen of a liquid crystal panel, a circuit system for driving a plurality of backlight discharge lamps in parallel is being used for one liquid crystal panel. As a means for driving a plurality of discharge lamps in parallel, a system in which one end side of a plurality of discharge lamps is connected to an inverter circuit and a transformer and the other end side is connected to GND (hereinafter referred to as a one-side drive system). And a system in which one end side of a plurality of discharge lamps is connected to one inverter circuit and a transformer, and the other end side is connected to another inverter circuit and a transformer (hereinafter referred to as a double-sided drive system). There is.

  Of these two methods, the double-sided drive method can reduce the output voltage of the inverter circuit and use circuit components with a low withstand voltage, thereby reducing the cost accordingly.

  Of these two methods, the double-sided drive method can reduce the output voltage of the inverter circuit and use circuit components with a low withstand voltage, thereby reducing the cost accordingly.

  By the way, in the discharge lamp driving device, the discharge lamp may be in an open state due to poor contact of the electrode of the discharge lamp with the connector. In such an abnormal state, a normal liquid crystal display operation cannot be obtained, and this must be detected.

  As a means for detecting the open state of a discharge lamp in a one-side drive type discharge lamp driving device, for example, one described in Patent Document 1 is known. However, in the case of the double-sided drive method, the both ends of the discharge lamp have a high voltage, so the technique described in Patent Document 1 cannot be applied. That is, Patent Document 1 does not disclose means for detecting the open state of the discharge lamp in the double-sided drive method.

Moreover, since the discharge lamp driving device of Patent Document 1 is configured to individually detect whether or not the discharge lamp is in an open state by individually providing a current detection circuit for each of the plurality of discharge lamps. There is a problem that the number of parts increases and the cost increases.
Japanese Patent Laid-Open No. 6-267654

  An object of the present invention is to provide a discharge lamp driving device and a liquid crystal display device capable of reliably detecting whether or not a discharge lamp is in an open state in a system in which a plurality of discharge lamps are connected in parallel and driven from both sides. Is to provide.

  Another object of the present invention is to provide a discharge lamp driving device and a liquid crystal display device capable of reducing the cost.

  In order to solve the above-described problem, a discharge lamp driving device according to the present invention includes a first discharge lamp driving device, a second discharge lamp driving device, and a signal processing unit.

  The first discharge lamp driving device includes a first inverter circuit, first and second transformers, and first and second current detection circuits. The first inverter circuit converts a DC voltage into an AC voltage and outputs the AC voltage.

  In the first transformer, an AC voltage is supplied to the input winding from the first inverter circuit, an output winding is led to the first discharge lamp connection terminal, and the second transformer is also an input winding. An AC voltage is supplied to the line from the first inverter circuit, and an output winding is led to the second discharge lamp connection terminal. A plurality of discharge lamps can be connected to the first and second discharge lamp connection terminals.

  The first current detection circuit detects a current flowing through the output winding of the first transformer to generate a first current detection signal, and the second current detection circuit includes the second transformer. The second current detection signal is generated by detecting the current flowing through the output winding.

  Next, the second discharge lamp driving device includes a second inverter circuit, third and fourth transformers, and third and fourth current detection circuits. The second inverter circuit is a circuit that converts a DC voltage into an AC voltage and outputs the AC voltage.

  The third transformer has an input winding supplied with an AC voltage from the second inverter circuit, an output winding led to a third discharge lamp connection terminal, and the fourth transformer has an input winding. An AC voltage is supplied to the line from the second inverter circuit, and an output winding is led to a fourth discharge lamp connection terminal. A plurality of discharge lamps can be connected to the third and fourth discharge lamp connection terminals.

  The third current detection circuit detects a current flowing through the output winding of the third transformer to generate a third current detection signal, and the fourth current detection circuit includes the fourth transformer. The fourth current detection signal is generated by detecting the current flowing through the output winding.

  The signal processing unit generates a signal for detecting an open state of the discharge lamp when the first to fourth current detection signals are supplied and a difference in magnitude of the supplied signals is a predetermined value or more.

  The discharge lamp driving device according to the present invention constitutes a liquid crystal display device in combination with a first discharge lamp group, a second discharge lamp group, and a liquid crystal plate.

  Each of the plurality of discharge lamps constituting the first discharge lamp group is arranged in alignment, one of the electrodes is connected to the first discharge lamp connection terminal, and the other of the electrodes is connected to the second discharge lamp connection terminal. Connected.

  Each of the plurality of discharge lamps constituting the second discharge lamp group is arranged in alignment, one of the electrodes is connected to the third discharge lamp connection terminal, and the other of the electrodes is connected to the fourth discharge lamp connection terminal. Connected. The liquid crystal plate is disposed in front of the first discharge lamp group and the second discharge lamp group.

  In the liquid crystal display device described above, each of the discharge lamps constituting the first and second discharge lamp groups is driven by the AC voltage supplied from the first to fourth transformers and is lit. Since the liquid crystal plate is disposed in front of the discharge lamp, the discharge lamp functions as a backlight of the liquid crystal plate.

  In the liquid crystal display device, when all the discharge lamps constituting the discharge lamp group are connected to the first to fourth discharge lamp connection terminals, the same output current flows through all the transformers.

  On the other hand, when at least one discharge lamp is in the open state with respect to the first to fourth discharge lamp connection terminals, the output current of the transformer that should have been connected to the discharge lamp connection terminal in the open state Decrease.

  This decrease in output current is detected by the first to fourth current detection circuits. The signal processing unit opens the discharge lamp when the first to fourth current detection signals are supplied from the first to fourth current detection circuits and the difference in magnitude of the supplied signals is equal to or greater than a predetermined value. Since the signal for detecting the state is generated, when any of the first to fourth current detection signals becomes small due to the open state, a signal for detecting the open state of the discharge lamp is generated. This point will be described more specifically for each state of the open state of the discharge lamp.

(1) In the first discharge lamp driving device, when one of the discharge lamps included in the first discharge lamp group is in an open state on the first transformer side, in this case, the first transformer The output current that flows in the output winding of the current decreases. On the other hand, on the second transformer side, if the other electrode is normally connected to the second discharge lamp connection terminal, the output current flowing through the output winding of the second transformer is open on one side. Due to the presence of leakage currents occurring in the discharge lamp in the state, it does not decrease so much.

  For this reason, a difference arises between the current flowing through the output windings of the first transformer and the output current flowing through the output windings of the second to fourth transformers.

  Therefore, the first current detection circuit detects the current flowing in the output winding of the first transformer to generate a first current detection signal, and the second current detection circuit generates the output winding of the second transformer. A current flowing through the line is detected to generate a second current detection signal.

  Then, the first current detection signal and the second current detection signal are supplied to the signal processing unit, and the signal processing unit calculates the difference between the first current detection signal and the second current detection signal and opens the discharge lamp. A signal for detecting the state is generated. There are various ways of using the signal for detecting the open state of the discharge lamp. For example, it is possible to limit the operation of the inverter circuit with a signal for detecting the open state of the discharge lamp, or to display such that the discharge lamp is in an open state.

  In the second discharge lamp driving device, if all of the discharge lamps included in the second discharge lamp group are normally connected, the output currents of the third and fourth transformers are also normal values. Therefore, the difference between the first current detection signal detected by the first current detection circuit and the third and fourth current detection signals detected by the third and fourth current detection circuits is obtained. A signal for detecting the open state of the discharge lamp may be generated.

(2) In the first discharge lamp driving device, when one of the discharge lamps included in the second discharge lamp group is in an open state on the second transformer side, in this case, the second transformer The output current that flows in the output winding of the current decreases. On the other hand, on the first transformer side, if one of the electrodes is normally connected to the first discharge lamp connection terminal, the output current flowing through the output winding of the first transformer does not decrease so much. .

  For this reason, a difference arises between the current flowing through the output winding of the first transformer and the output current flowing through the output winding of the second transformer.

  Therefore, also in this case, the first current detection signal and the second current detection signal are supplied to the signal processing unit, and the signal processing unit takes the difference between the first current detection signal and the second current detection signal, A signal for detecting the open state of the discharge lamp can be obtained.

(3) In the first discharge lamp driving device, when the discharge lamps included in the second discharge lamp group are in an open state (both sides open) on the first and second transformer sides. The ability to detect the open state is one important feature of the present invention. Assuming that only the first discharge lamp driving device (single type) is used, the output current flowing through the output windings of the first and second transformers decreases when both sides are open. Although it is not possible to obtain a signal for detecting the open state of the discharge lamp by taking the difference between the current detection signal and the second current detection signal, in the present invention, the signal processing unit includes the first and second current detection signals. In addition, third and fourth current detection signals are also supplied.

  Therefore, the first or second current detection signal detected by the first or second current detection circuit and the third or fourth current detection signal detected by the third and fourth current detection circuits. By taking the difference, a signal for detecting the open state of the discharge lamp can be generated.

  In addition, since the liquid crystal display device of the present invention is not configured to detect whether or not each of the plurality of discharge lamps is in an open state, the cost can be reduced.

  (4) Regarding the open state of the discharge lamp in the second discharge lamp driving device, the description of the operation in the first discharge lamp driving device described above applies as it is.

As described above, according to the present invention, the following effects can be obtained.
(A) To provide a discharge lamp driving device and a liquid crystal display device capable of reliably detecting whether or not a discharge lamp is open in a system in which a plurality of discharge lamps are connected in parallel and driven from both sides. That is.
(B) Since a plurality of discharge lamps can be lit in parallel with one inverter circuit, a low-cost discharge lamp driving device and a liquid crystal display device can be provided.

  Other features of the present invention and the operational effects thereof will be described in more detail by way of examples with reference to the accompanying drawings.

  FIG. 1 is an electric circuit diagram showing an embodiment of a discharge lamp lighting device incorporating a discharge lamp driving device according to the present invention. The discharge lamp lighting device shown in the figure is used for a backlight device such as a liquid crystal TV and a monitor, and is a double-sided drive system. The first discharge lamp drive device A1 and the second discharge lamp drive device A2 are used. And a first discharge lamp group 41, second discharge lamp groups 41 and 42, and a signal processing unit 30. In the figure, the circuit part excluding the discharge lamp groups 41 and 42 from the discharge lamp lighting device corresponds to the discharge lamp driving device according to the present invention, and these are the objects of transaction as devices different from the discharge lamp groups 41 and 42. It becomes.

  First, the first discharge lamp driving device A1 includes a first inverter circuit 11, first and second transformers T11 and T21, and first and second current detection circuits 311 and 321.

  The first inverter circuit 11 converts the DC power source Vin into an AC voltage and outputs it. The direct current power source Vin is generally obtained by converting a commercial alternating current power source into direct current and then converting it with a DC / DC converter.

  The first transformer T11 is supplied with the AC voltage from the first inverter circuit 11 to the input winding L11, and receives the first AC voltage V1 and the first current I1 from the output winding L12 on the high voltage side. Output. The first AC voltage V1 is an AC high voltage of about 800V, for example.

  The low-voltage side output terminal of the output winding L12 is connected to GND via diodes D11 and D12 and a resistor R1. The diodes D11 and D12 and the resistor R1 constitute a first current detection circuit 311.

  The second transformer T21 is supplied with an AC voltage from the first inverter circuit 11 to the input winding L21, and outputs a second AC voltage V2 from the output winding L22 on the high voltage side. The second AC voltage V2 has a phase difference of 180 degrees with respect to the first AC voltage V1. According to such a double-sided drive system, the output voltage of the inverter circuit can be reduced, and circuit components having a low withstand voltage can be used, so that the cost can be reduced accordingly.

  The low voltage side output terminal of the output winding L22 is grounded via diodes D21 and D22 and a resistor R2. The diodes D21 and D22 and the resistor R2 constitute a second current detection circuit 321.

  Although not shown, normally, a current detection signal based on an OR signal of the first current detection circuit 311 and the second current detection circuit 321 is supplied to the first inverter circuit 11 to perform feedback control. It is like that.

  The second discharge lamp driving device A2 basically has the same circuit configuration as the first discharge lamp driving device A1. That is, the second discharge lamp driving device A2 includes the second inverter circuit 12, the third and fourth transformers T12 and T22, and the third and fourth current detection circuits 312 and 322.

  First, the second inverter circuit 12 converts the DC power supply Vin into an AC voltage and outputs it. The third transformer T12 is supplied with an AC voltage from the second inverter circuit 12 to the input winding L31, and outputs a third AC voltage V3 from the output winding L32 on the high voltage side. The third AC voltage V3 is an AC high voltage of about 800V, for example.

  The low-voltage side output terminal of the output winding L32 is grounded via diodes D31 and D32 and a resistor R3. The diodes D31 and D32 and the resistor R3 constitute a third current detection circuit 312.

  The fourth transformer T22 is supplied with an AC voltage from the second inverter circuit 12 to the input winding L41, and outputs a fourth AC voltage V4 from the output winding L42 on the high voltage side. The fourth AC voltage V4 is also an AC high voltage of about 800V, for example. The fourth AC voltage V4 has a phase difference of 180 degrees with respect to the third AC voltage V3.

  The low-voltage side output terminal of the output winding L42 is grounded via diodes D41 and D42 and a resistor R4. The diodes D41 and D42 and the resistor R4 constitute a fourth current detection circuit 322.

  The first discharge lamp group 41 includes n discharge lamps 411 to 41n. Examples of the discharge lamps 411 to 41n that can be used include CCFLs such as cold cathode tubes and EEFLs. The discharge lamps 411 to 41n are connected in parallel to each other. Each of the discharge lamps 411 to 41n is arranged in alignment, one of the electrodes is connected to the first discharge lamp connection terminal P1, and the other of the electrodes is connected to the second discharge lamp connection terminal P2.

  The first connection terminal P1 and the second connection terminal P2 are individually connected to one end of the output winding L12 of the first transformer T11 and the output winding L22 of the second transformer T21 via the ballast circuits 331 and 341. Connected. Each of the ballast circuits 331 and 341 has n capacitors, and one end of each capacitor is individually connected to the first discharge lamp connection terminal P1, and the other end is commonly connected to the first transformer. The output winding L12 of T11 and one end of the output winding L22 of the second transformer T21 are connected.

  The second discharge lamp group 42 includes n discharge lamps 421 to 42n. The discharge lamps 421 to 42n are connected in parallel to each other. Each of the discharge lamps 421 to 42n is arranged in alignment, one of the electrodes is connected to the third discharge lamp connection terminal P3, and the other of the electrodes is connected to the fourth discharge lamp connection terminal P4. .

  The third connection terminal P3 and the fourth connection terminal P4 are individually connected to one end of the output winding L32 of the third transformer T12 and the output winding L42 of the fourth transformer T22 via the ballast circuits 332 and 342, respectively. Connected. Each of the ballast circuits 332 and 342 has n capacitors, and one end of each capacitor is individually connected to the third discharge lamp connection terminal P3 and the other end is commonly connected to the third transformer. The output winding L32 of T12 and one end of the output winding L42 of the fourth transformer T22 are connected.

  The ballast circuits (331, 341) and (332, 342) are necessary when the discharge lamps (421 to 42n) and (411 to 41n) are of the CCFL type, but are not necessary of the EEFL type. .

  The signal processing unit 30 is supplied with the first to fourth current detection signals S1 to S4 from the first to fourth current detection circuits 311 to 322, and the difference in magnitude between the signals S1 to S4 is greater than or equal to a predetermined value. At some point, a signal S0 for detecting the open state of the discharge lamp is generated. The signal processing unit 30 can be configured by a microcomputer, or can be configured by an IC, an electronic component, or the like.

  The discharge lamp lighting device shown in FIG. 1 is combined with a liquid crystal plate to constitute a liquid crystal display device. FIG. 2 is a partial cross-sectional view of a liquid crystal display device incorporating the discharge lamp lighting device shown in FIG. In the illustrated liquid crystal display device, the discharge lamps (411 to 41n) and (421 to 42n) are arranged on one surface of the back plate 5 with a space therebetween, and the discharge lamps (411 to 41n) and (421 to 42n). The liquid crystal plate 6 is disposed on the front surface. The liquid crystal plate 6 is attached to rising portions 51 and 52 that are raised around the back plate 5. A substrate 7 on which a discharge lamp lighting device having the circuit configuration shown in FIG. 1 is mounted is attached to the other surface of the back plate 5.

  Next, the operation of the discharge lamp lighting device and the liquid crystal display device shown in FIGS. In these figures, in the first discharge lamp group 41, the first AC voltage V1 is applied to one of the electrodes, and the second AC voltage V2 is applied to the other of the electrodes. Output currents I1 and I2 flow, and the discharge lamps 411 to 41n are driven in parallel to light up.

  In the second discharge lamp group 42, the third AC voltage V3 is applied to one of the electrodes, and the fourth AC voltage V4 is applied to the other electrode, and the third and fourth output currents I3 and I4 are applied. Flows, and the discharge lamps 421 to 42n are driven in parallel to light up. Since the liquid crystal plate 6 is disposed in front of the first discharge lamp group 41 and the second discharge lamp group 42, the discharge lamp groups 41 and 42 function as a backlight of the liquid crystal plate 6 (see FIG. 2). .

  Next, the operation when the discharge lamp is open will be described for each open state with reference to FIGS. 3 and 4.

(1) In the first discharge lamp driving device A1, when one of the discharge lamps included in the first discharge lamp group 41 is in an open state on the first transformer T11 side, this open state is It is shown in FIG. As shown in FIG. 3, when one of the electrodes to be connected to the first discharge lamp connection terminal P1 of the discharge lamp 41n among the discharge lamps 411 to 41n is in an open state, the first transformer The output current I1 flowing through the output winding L12 of T11 decreases.

  On the other hand, assuming that the other electrode of the discharge lamp 41n is normally connected to the second discharge lamp connection terminal P2 connected to the output winding L22 of the second transformer T21, the second transformer The output current I2 flowing through the output winding L22 of T21 does not decrease so much due to the presence of leakage current due to the ground parasitic capacitance of the discharge lamp 41n.

  For this reason, a difference occurs between the output current I1 flowing through the output winding L12 of the first transformer T11 and the output current I2 flowing through the output winding L22 of the second transformer T21.

  Therefore, in the present invention, the first current detection circuit 311 detects the output current I1 flowing through the output winding L12 of the first transformer T11 to generate the first current detection signal S1, and the second current The detection circuit 321 detects the output current I2 flowing through the output winding L22 of the second transformer T21, and generates a second current detection signal S2.

  Then, the first current detection signal S1 and the second current detection signal S2 are supplied to the signal processing unit 30, and the signal processing unit 30 calculates the difference between the first current detection signal S1 and the second current detection signal S2. Then, a signal S0 for detecting the open state of the discharge lamp is generated. There are various uses of the signal S0 for detecting the open state of the generated discharge lamp. For example, the operation of the first inverter circuit 11 and the second inverter circuit 12 is limited by the signal S0 for detecting the open state of the discharge lamp, or the display indicating that the discharge lamp is in the open state is limited. Possible use.

  In the second discharge lamp driving device A2, if all of the discharge lamps 421 to 42n included in the second discharge lamp group 42 are normally connected, the third and fourth transformers T12, The output current of T22 is also at a normal value. Therefore, the first current detection signal S1 detected by the first current detection circuit 311 and the third or fourth current detection signal S3, S4 detected by the third and fourth current detection circuits 312, 322. And a signal S0 for detecting the open state of the discharge lamp may be generated. Moreover, as will be described in detail later, according to this method, it is possible to obtain an excellent effect of being able to detect both-side open.

(2) In the first discharge lamp driving device A1, when one of the discharge lamps included in the first discharge lamp group 41 is in the open state on the second transformer T21 side, the circuit in this open state The operation can be inferred from FIG. 3 and will be described briefly. First, the output current I2 flowing through the output winding L22 of the second transformer T21 decreases. On the other hand, on the first transformer T11 side, assuming that one of the electrodes is normally connected to the first discharge lamp connection terminal P1, the output current flowing in the output winding L12 of the first transformer T11. I1 does not decrease so much.

  For this reason, a difference occurs between the current I1 flowing through the output winding L12 of the first transformer T11 and the output current I2 flowing through the output winding L22 of the second transformer T21.

  Accordingly, also in this case, the first current detection signal S1 and the second current detection signal S2 are supplied to the signal processing unit 30, and the signal processing unit 30 outputs the first current detection signal S1 and the second current detection signal. The difference S2 can be taken to obtain a signal S0 for detecting the open state of the discharge lamp.

  When detecting not only the one-side open state but also the both-side open state, the third or fourth current detection detected by the second current detection signal S2 and the third and fourth current detection circuits 312, 322. As described above, the difference between the signals S3 and S4 should be taken.

(3) In the first discharge lamp driving device A1, one of the discharge lamps included in the first discharge lamp group 41 is open on both sides of the first transformer T11 and the second transformer T21. Case FIG. 4 shows this open state. And it is a big feature of the present invention that this state can be detected. In this case, since the output currents I1 and I2 flowing through the output windings L12 and L22 of the first and second transformers T11 and T21 both decrease, the first current detection signal S1 and the second current detection signal S2 The signal S0 for detecting the open state of the discharge lamp cannot be obtained by taking the difference, but the signal processing unit 30 includes not only the first and second current detection signals S1 and S2, but also the third and fourth Current detection signals S3 and S4 are also supplied.

  Accordingly, the first or second current detection signal S1, S2 detected by the first or second current detection circuit 311 or 321 and the third or fourth current detection circuit 312 or 322 detected by the third or fourth current detection circuit 312 or 322. By taking the difference from the fourth current detection signals S3 and S4, a signal S0 for detecting the open state of the discharge lamp can be generated.

  (4) About the open state in 2nd discharge lamp drive device A2, the operation | movement description in 1st discharge lamp drive device A1 demonstrated with reference to FIG.3 and FIG.4 is applied as it is.

  Since the liquid crystal display device of the present invention is not configured to individually detect whether or not each of the plurality of discharge lamps 411 to 41n is in an open state, the cost is low.

  As described above, the signal to be compared with the first current detection signal S1 is the third current detection signal S3 or the fourth current detection signal S4, that is, the signal combination of “Takigake”. preferable. Similarly, the signal compared with the second current detection signal S2 is preferably the third current detection signal S3 or the fourth current detection signal S4. When comparing the first current detection signal S1 and the second current detection signal S2, it is difficult to detect a double-sided open state in which one and the other of the electrodes such as discharge are in an open state (see FIG. 4). On the other hand, in the case of “taskaki”, the open state on both sides can be detected. This point will be described more specifically with reference to FIGS.

  FIG. 5 is a block diagram showing a specific configuration of the signal processing unit. In the figure, the signal processing unit includes comparison circuits 301 and 302 and a determination circuit 303. The comparison circuit 301 is supplied with the first and third current detection signals S1 and S3, and generates a first difference signal S301 corresponding to the difference between the supplied signals.

  The comparison circuit 302 is supplied with the second and fourth current detection signals S2 and S4, and generates a second difference signal S302 corresponding to the difference between the supplied signals. When at least one of the first difference signal S301 and the second difference signal S302 is equal to or greater than a predetermined value, the comparison circuit 302 determines that one of the discharge lamps is in a one-side open state, A signal S0 for detecting the open state is generated.

  For example, as shown in FIG. 3, when one of the electrodes of the discharge lamp 41n is in an open state, the first difference signal S301 is equal to or greater than a predetermined value, so that the determination circuit 303 is in a one-side open state. A signal S0 for determining and detecting the open state of the discharge lamp is generated.

  Also, as shown in FIG. 4, when one of the electrodes of the discharge lamp 41n and the other are both in an open state, the first difference signal S301 and the second difference signal S302 are equal to or greater than a predetermined value. Therefore, the determination circuit 303 determines that both sides of the discharge lamp are open, and generates a signal S0 for detecting the open state of the discharge lamp.

  FIG. 6 is a block diagram showing a specific configuration of the signal processing unit. In the figure, the comparison circuit 303 is supplied with first and fourth current detection signals S1 and S4, and generates a first difference signal S303 corresponding to the difference between the supplied signals.

  The comparison circuit 304 is supplied with the second and third current detection signals S2 and S3, and generates a second difference signal S304 corresponding to the difference between the supplied signals. When at least one of the first difference signal S303 and the second difference signal S304 is equal to or greater than a predetermined value, the comparison circuit 304 determines that one of the discharge lamps is open and opens the discharge lamp. A signal S0 for detecting the state is generated.

  FIG. 7 is a block diagram showing a specific configuration of the signal processing unit. In the figure, the signal processing unit includes a maximum value circuit 305 and a determination circuit 303. The maximum value circuit 305 selects the maximum signal among the first to fourth current detection signals S1 to S4 and generates the reference signal S305.

  The determination circuit 303 compares the reference signal S305 and each of the first to fourth current detection signals S1 to S4, and detects the open state of the discharge lamp when the difference in signal magnitude is equal to or greater than a predetermined value. A signal S0 to be generated is generated. For example, as shown in FIG. 3, when one of the electrodes of the discharge lamp 41n is in an open state, the determination circuit 303 detects that the first current detection signal S1 is small and determines the open state of the discharge lamp. Signal S0 to detect.

  In addition, when one of the electrodes of the discharge lamp 41n and the other are in an open state as shown in FIG. 3, the determination circuit 303 indicates that the first and second current detection signals S1 and S2 are small. A signal S0 for detecting and detecting the open state of the discharge lamp is generated.

  8 is an electric circuit diagram showing another embodiment of a discharge lamp lighting device using the discharge lamp driving device according to the present invention, and FIG. 9 is a block diagram of a signal processing unit used in the discharge lamp lighting device of FIG. It is. In the figure, the same components as those shown in FIGS. 1 to 7 are denoted by the same reference numerals, and redundant description is omitted.

  The illustrated discharge lamp driving device includes m discharge lamp driving devices A1 to Am, a signal processing unit 30, and discharge lamp groups 41 to 4m. Each of the first to mth discharge lamp driving devices A1 to Am outputs first to second m current detection signals (S1 to S2m). The signal processing unit 30 generates a signal S0 for detecting the open state of the discharge lamp from these current detection signals.

  In FIG. 9, a maximum value circuit 305 selects a maximum signal from the first to second m current detection signals S1 to S2m, and generates a reference signal S305. The determination circuit 303 compares the reference signal S305 and each of the first to second m current detection signals S1 to S2m, and detects the open state of the discharge lamp when the difference in signal magnitude is equal to or greater than a predetermined value. A signal S0 to be generated is generated.

  The discharge lamp driving device shown in FIG. 8 has substantially the same configuration as that of the discharge lamp driving device shown in FIGS.

  Although the contents of the present invention have been specifically described above with reference to the preferred embodiments, it is obvious that those skilled in the art can take various modifications based on the basic technical idea and teachings of the present invention. It is.

It is an electric circuit diagram which shows one Example of the discharge lamp lighting device incorporating the discharge lamp drive device which concerns on this invention. It is a fragmentary sectional view of the liquid crystal display device incorporating the discharge lamp lighting device shown in FIG. It is an electric circuit diagram for demonstrating operation | movement when a discharge lamp is in an open state. It is another electric circuit diagram for demonstrating operation | movement when a discharge lamp is in an open state. It is a block diagram which shows the specific structure of a signal processing part. It is a block diagram which shows the specific structure of a signal processing part. It is a block diagram which shows the specific structure of a signal processing part. It is an electric circuit diagram which shows another Example of the discharge lamp drive device which concerns on this invention. It is a block diagram of the signal processing part used for the discharge lamp drive device of FIG.

Explanation of symbols

30 Signal processor 11 First inverter circuit 12 Second inverter circuit 41, 42 Discharge lamp group S1 to S4 First to fourth current detection signals S0 A signal for detecting the open state of the discharge lamp

Claims (2)

A discharge lamp driving device including a first discharge lamp driving device, a second discharge lamp driving device, and a signal processing unit,
The first discharge lamp driving device includes a first inverter circuit, first and second transformers, and first and second current detection circuits,
The first inverter circuit is a circuit that converts a DC voltage into an AC voltage and outputs the AC voltage,
In the first transformer, an AC voltage is supplied to the input winding from the first inverter circuit, and the output winding is led to the first discharge lamp connection terminal.
In the second transformer, an AC voltage is supplied to the input winding from the first inverter circuit, and the output winding is led to the second discharge lamp connection terminal.
A plurality of discharge lamps can be connected to the first and second discharge lamp connection terminals,
The first current detection circuit detects a current flowing through the output winding of the first transformer, and generates a first current detection signal.
The second current detection circuit detects a current flowing through the output winding of the second transformer, and generates a second current detection signal;
The second discharge lamp driving device includes a second inverter circuit, third and fourth transformers, and third and fourth current detection circuits,
The second inverter circuit is a circuit that converts a DC voltage into an AC voltage and outputs the AC voltage,
In the third transformer, an AC voltage is supplied to the input winding from the second inverter circuit, and an output winding is led to the third discharge lamp connection terminal.
In the fourth transformer, an AC voltage is supplied to the input winding from the second inverter circuit, and an output winding is led to the fourth discharge lamp connection terminal.
A plurality of discharge lamps can be connected to the third and fourth discharge lamp connection terminals,
The third current detection circuit detects a current flowing through the output winding of the third transformer, and generates a third current detection signal.
The fourth current detection circuit detects a current flowing through the output winding of the fourth transformer, and generates a fourth current detection signal;
The signal processing unit
The first to fourth current detection signals are supplied;
Generating a first difference signal corresponding to a difference between one of the third current detection signal and the fourth current detection signal and the first current detection signal;
Generating a second difference corresponding to a difference between the other of the third current detection signal and the fourth current detection signal and the second current detection signal;
Based on the first difference signal and the second difference signal, a signal for detecting an open state of the discharge lamp is generated.
Discharge lamp driving device. A liquid crystal display device including a discharge lamp driving device, a first discharge lamp group, a second discharge lamp group, and a liquid crystal plate,
The discharge lamp driving device is the one described in claim 1 ,
Each of the plurality of discharge lamps constituting the first discharge lamp group is arranged in alignment, one of the electrodes is connected to the first discharge lamp connection terminal, and the other of the electrodes is the second discharge lamp. Connected to the connection terminal,
Each of the plurality of discharge lamps constituting the second discharge lamp group is arranged in alignment, one of the electrodes is connected to the third discharge lamp connection terminal, and the other of the electrodes is the fourth discharge lamp. Connected to the connection terminal,
The liquid crystal plate is disposed in front of the first discharge lamp group and the second discharge lamp group.
Liquid crystal display device.

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