JP4107600B2 - 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 backlight of a liquid crystal panel, 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 on a single liquid crystal panel is being used. 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 grounded (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 an inverter circuit and a transformer, and the other end side is connected to another transformer and driven (hereinafter referred to as a double-sided drive system).

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

  By the way, in the discharge lamp driving device, a state in which no current flows between the transformer and the discharge lamp (hereinafter referred to as an open state) may occur due to poor contact of the discharge lamp electrode with the connector. In such an abnormal state, a normal liquid crystal display operation cannot be obtained, and this must be detected. As means for that purpose, for example, Patent Literature 1 and Patent Literature 2 disclose a one-side drive type discharge lamp driving device including a non-lighting detection circuit for detecting an open state.

  The discharge lamp driving apparatus of Patent Documents 1 and 2 is a one-side drive system, and the other end side of the discharge lamp is grounded and becomes a low voltage. Therefore, a resistor is provided between the other end side of each discharge lamp and the ground, By detecting the current flowing through the resistor, it is possible to detect whether or not each discharge lamp is in an open state.

  However, in the case of a double-sided discharge lamp driving device, a transformer is connected to both ends of the discharge lamp, and both ends of the discharge lamp have a high voltage, so that a resistor is provided between the discharge lamp and ground. Such a circuit configuration cannot be taken.

In addition, in the configuration in which the current flowing through both ends of the discharge lamp that is at a high voltage is detected using a current transformer or the like, there arises a problem that the product is downsized and the cost is hindered.
Japanese Patent Laid-Open No. 6-267654 JP 2004-241136 A

  An object of the present invention is to provide a discharge lamp driving device and a liquid crystal display device capable of detecting that at least one of a plurality of provided discharge lamps is in an open state in a double-sided drive method.

  Another object of the present invention is to provide a discharge lamp driving device and a liquid crystal display device that can be miniaturized.

  Still 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 problems, a discharge lamp driving device according to the present invention includes an inverter circuit, first and second transformers, first and second ballast capacitors, and a plurality of first and second discharge lamps. An electric lamp connection terminal, first and second voltage detection elements, and a signal processing unit are included. The inverter circuit converts a DC voltage into an AC voltage and outputs it. The first and second transformers are supplied with AC voltage from the inverter circuit to the input winding and output AC voltage from the output winding.

  There are a plurality of first ballast capacitors, one of the electrodes being connected to the output winding of the first transformer, and the other electrode being connected to each of the plurality of first discharge lamp connection terminals provided. Has been. There are a plurality of second ballast capacitors, one of each electrode being connected to the output winding of the second transformer, and the other electrode being connected to each of the plurality of second discharge lamp connection terminals provided. Has been. Each of the plurality of discharge lamps can be connected to each of the first and second discharge lamp connection terminals.

  There are a plurality of first voltage detection elements, and one end of each electrode is connected to at least one of the first and second discharge lamp connection terminals. There are a plurality of second voltage detection elements, and one end of each electrode is connected to the other end of the electrode provided in the first voltage detection element, and the other end is led to the ground terminal.

  The signal processing unit generates a signal for detecting the open state of the discharge lamp from the voltage generated between the connection point of the first voltage detection element and the second voltage detection element and the ground terminal.

  The discharge lamp driving device according to the present invention described above constitutes a liquid crystal display device in combination with a plurality of discharge lamps and a liquid crystal plate. Each of the plurality of discharge lamps has one electrode connected to the first discharge lamp connection terminal and the other electrode connected to the second discharge lamp connection terminal. The liquid crystal plate is disposed in front of the discharge lamp.

  In the liquid crystal display device described above, each of the discharge lamps is supplied with an AC voltage supplied to one of the electrodes from the output winding of the first transformer, and supplied to the other of the electrodes from the output winding of the second transformer. Driven in parallel from both sides by AC voltage, lights up. 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 of the present invention, one end of the electrode of the first voltage detection element is connected to at least one of the first and second discharge lamp connection terminals. In the second voltage detection element, one end of the electrode is connected to the other end of the electrode provided in the first voltage detection element, and the other end of the electrode is led to the ground terminal.

  According to this configuration, when at least one of the plurality of discharge lamps is in an open state, a voltage that can be substantially regarded as an open voltage is generated at the discharge lamp connection terminal in the open state. A voltage value different from the voltage appearing at the discharge lamp connection terminal in the state is shown. For this reason, the voltage generated between the connection point of the first voltage detection element and the second voltage detection element and the ground terminal changes.

  The signal processing unit detects the open state of the discharge lamp from the voltage generated between the connection point of the first voltage detection element and the second voltage detection element and the ground terminal, and detects the open state of the discharge lamp. A signal can be generated.

  There are various uses of the signal for detecting the open state of the generated discharge lamp. For example, it is possible to limit the operation of the inverter circuit by a signal for detecting the open state of the discharge lamp or to keep the display of the open state.

  In addition, since the liquid crystal display device of the present invention detects a voltage rather than a current, it can be configured using the first and second voltage detection elements made up of capacitors and the like, and the product can be reduced in size and cost. Can be achieved.

As described above, according to the present invention, the following effects can be obtained.
(A) It is possible to provide a discharge lamp driving device and a liquid crystal display device capable of detecting that at least one of a plurality of discharge lamps in an open state is in an open state.
(B) A discharge lamp driving device and a liquid crystal display device that can be miniaturized can be provided.
(C) It is possible to provide a discharge lamp driving device and a liquid crystal display device capable of reducing the cost.

  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. This discharge lamp lighting device is used for a backlight device such as a liquid crystal TV and a monitor, for example. The illustrated discharge lamp lighting device is a double-sided drive method (floating method), and includes a master device 31, a slave device 32, first and second ballast capacitors C11 to C1n, C21 to C2n, and a first device. Voltage detection elements Cc1 to Ccn, Ce1 to Cen, second voltage detection elements Cd1 to Cdn, Cf1 to Cfn, signal processing unit 30, first and second substrates 310 and 320, and discharge lamps 21 to 2n Including. A circuit portion obtained by removing the discharge lamps 21 to 2n from the discharge lamp lighting device corresponds to the discharge lamp driving device according to the present invention, and these are subject to transaction as a device different from the discharge lamps 21 to 2n.

  Master device 31 includes an inverter circuit 11 and a first transformer T11. The 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 includes an input winding L11 and an output winding L12. The input winding L11 is supplied with an AC voltage from the inverter circuit 11. The output winding L12 is grounded at the low voltage side output terminal, and outputs the first AC voltage V1 from the high voltage side output terminal. The first AC voltage V1 is an AC high voltage of about 800V, for example.

  The slave device 32 includes a second transformer T21. The second transformer T21 includes an input winding L21 and an output winding L22. An AC voltage is supplied from the inverter circuit 11 to the input winding L21. The output winding L22 is grounded at the low voltage side output terminal, and outputs the second AC voltage V2 from the high voltage side output terminal.

  The second AC voltage V2 is, for example, an AC high voltage of about 800 V, and 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 voltages of the transformers T11 and T21 can be reduced, and circuit components with a low withstand voltage can be used, so that the cost can be reduced accordingly.

  Although not shown, the current flowing between the low-voltage side output terminal of the output winding L12 and the ground and the current flowing between the low-voltage side output terminal of the output winding L22 and the ground are detected and fed back to the inverter circuit 11. It is preferable to perform constant current control.

  In each of the first ballast capacitors C11 to C1n, one of the electrodes is connected in common and led to the output winding L12 of the first transformer T11, and the other electrode is connected to the first discharge lamp connection terminals P11 to P1n. Are individually connected to each. The first discharge lamp connection terminals P11 to P1n are for connection to one of the electrodes of the discharge lamps 21 to 2n.

  In each of the second ballast capacitors C21 to C2n, one of the electrodes is connected in common and led to the output winding L22 of the second transformer T21, and the other electrode is connected to the second discharge lamp connection terminals P21 to P2n. Are individually connected to each. The second discharge lamp connection terminals P21 to P2n are for connecting to the other electrodes of the discharge lamps 21 to 2n.

  The capacitance values of the ballast capacitors C11 to C1n and C21 to C2n are basically selected to be substantially equal, but it is preferable that they are slightly different according to variations in the tube current of each discharge lamp.

  In FIG. 1, one end of the electrode of the first voltage detection element Cc1 is connected to the first discharge lamp connection terminal P11. In the second voltage detection element Cd1, one end of the electrode is connected to the other end of the electrode provided in the first voltage detection element Cc1, and the other end of the electrode is led to the ground terminal. The ground terminal is a terminal connected to the ground (GND).

  Similarly, one end of the electrodes of the first voltage detection elements Cc2 to Ccn is connected to the first discharge lamp connection terminals P12 to P1n, and one end of the electrode of the second voltage detection elements Cd2 to Cdn is the first one. The other ends of the electrodes provided in the voltage detection elements Cc2 to Ccn are connected, and the other end of the electrode is led to the ground terminal. In the embodiment, the first and second voltage detection elements Cc1 to Ccn, Cd1 to Cdn, Ce1 to Cen, and Cf1 to Cfn are capacitors, but may be configured by resistors, inductors, and the like.

  The first voltage detection elements Cc1 to Ccn are connected to the first discharge lamp connection terminals P11 to P1n, that is, the point connected to the electrode not commonly connected among the electrodes of the ballast capacitors C11 to C1n is the voltage detection. Is essential. This is because if the first voltage detection elements Cc1 to Ccn are connected to the commonly connected electrodes of the ballast capacitors C11 to C1n, the first voltage detection elements Cc1 to Ccn are output windings of the first transformer T11. This is because the voltage appearing on the line L12 is detected, and the voltage change in the open state cannot be captured.

  The relationship between the second discharge lamp connection terminals P21 to P2n and the first voltage detection elements Ce1 to Cen and the relationship between the first voltage detection elements Ce1 to Cen and the second voltage detection elements Cf1 to Cfn are as follows: The relationship between the first discharge lamp connection terminals P11 to P1n and the first voltage detection elements Cc1 to Ccn, and the relationship between the first voltage detection elements Cc1 to Ccn and the second voltage detection elements Cd1 to Cdn. The details are omitted.

  The signal processing unit 30 includes voltages V31 to V3n generated at connection points between the first voltage detection elements Cc1 to Ccn and the second voltage detection elements Cd1 to Cdn, and the first voltage detection elements Ce1 to Cen and the second voltage detection elements Cd1 to Cdn. Voltages V41 to V4n generated at connection points with the voltage detection elements Cf1 to Cfn are supplied, and a signal S0 for detecting the open state of the discharge lamps 21 to 2n is generated using these signals. The signal processing unit 30 may be configured by software, or may be configured by an IC, an electronic component, or the like.

  The discharge lamps 21 to 2n are, for example, CCFL types such as cold cathode discharge lamps. Each of the discharge lamps 21 to 2n is arranged in alignment so that the longitudinal directions thereof coincide. The discharge lamps 21 to 2n are provided with electrodes at both ends in the longitudinal direction.

  One of the electrodes of the discharge lamps 21 to 2n is led to the other of the electrodes of the first ballast capacitors C11 to C1n via the first discharge lamp connection terminals P11 to P1n. The other of the electrodes of the discharge lamps 21 to 2n is led to the other of the electrodes of the second ballast capacitors C21 to C2n via the second discharge lamp connection terminals P21 to P2n.

  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 FIG. 2, the discharge lamps 21 to 2n are arranged on the one surface of the back plate 5 so as to be spaced apart from each other. A liquid crystal plate 6 is disposed in front of the discharge lamps 21 to 2n. The liquid crystal plate 6 is attached to rising portions 51 and 52 that are raised around the back plate 5. The first and second substrates 310 and 320 having the circuit configuration shown in FIG. 1 are attached to the other surface of the back plate 5.

  Next, the operation of the liquid crystal display device shown in FIG. 2 will be described. When all the discharge lamps 21 to 2n are in a normal connection state (when not in an open state), the discharge lamps 21 to 2n are applied with the first AC voltage V1 on one of the electrodes and the second on the other electrode. The AC voltage V2 is applied and lights up. Since the liquid crystal plate 6 is disposed in front of the discharge lamps 21 to 2n, the discharge lamps 21 to 2n function as backlights of the liquid crystal plate 6.

Next, the operation in the open state will be described with reference to FIG. FIG. 3 shows an example in which the discharge lamp 21 is in an open state with the first discharge lamp connection terminal P11 and the discharge lamp 22 is in an open state with the second discharge lamp connection terminal P22. Is shown.
First, the case where the discharge lamp 21 is in an open state with the first discharge lamp connection terminal P11 will be described.

  As described above, one end of the electrode of the first voltage detection element Cc1 is connected to the first discharge lamp connection terminal P11, and one end of the electrode of the second voltage detection element Cd1 is the first voltage detection. The other end of the electrode provided in the element Cc1 is connected, and the other end of the electrode is led to the ground terminal.

  For this reason, when the discharge lamp 21 is in an open state with the first discharge lamp connection terminal P11, the voltage generated at the first discharge lamp connection terminal P11 rises to a value that can be substantially regarded as an open voltage, In response to this, the voltage V31 generated at the connection point between the first voltage detection element Cc1 and the second voltage detection element Cd1 also changes. The same applies to the case where the first discharge lamp connection terminals P12 to P1n and the discharge lamps 22 to 2n are opened.

Next, the case where the discharge lamp 22 is in an open state with the second discharge lamp connection terminal P22 will be described. One end of the electrode of the first voltage detection element Ce2 is connected to the second discharge lamp connection terminal P22, and one end of the electrode of the second voltage detection element Cf2 is provided in the first voltage detection element Ce2. The other end of the electrode is connected to the ground terminal.

  For this reason, when the discharge lamp 22 is in an open state with the discharge lamp connection terminal P22, the voltage generated at the second discharge lamp connection terminal P22 rises to a value that can be substantially regarded as an open-circuit voltage. Thus, the voltage V42 generated at the connection point between the first voltage detection element Ce2 and the second voltage detection element Cf2 also changes. The same applies when the second discharge lamp connection terminals P21, P23 to P2n and the discharge lamps 21, 23 to 2n are opened.

  The signal processing unit 30 is supplied with signals corresponding to the voltages V31 to V3n, V41 to V4n, and detects from these signals that any of the discharge lamps 21 to 2n is abnormal and detects an open state. The signal S0 is output.

  Specifically, for example, when all the discharge lamp connection terminals P11 to P1n and P21 to P2n are in a normal connection state (when not in an open state), voltages generated at the discharge lamp connection terminals P11 to P1n and P21 to P2n For example, the peak voltage is about 0.8 kV.

  On the other hand, for example, when the discharge lamp connection terminal P11 is in an open state and is in a floating state, the voltage generated at the first discharge lamp connection terminal P11 is substantially up to a voltage value that can be regarded as an open voltage. The voltage V31 greatly increases (for example, peak voltage 1.8 kV), and the voltage V31 generated at the connection point between the first voltage detection element Cc1 and the second voltage detection element Cd1 also increases significantly. The signal processing unit 30 captures the change in voltage and generates a signal S0. The same can be said when the discharge lamp connection terminals P12 to P1n and P21 to P2n are opened.

  There are various uses of the signal S0 for detecting the open state of the generated discharge lamp. For example, use of limiting the operation of the inverter circuit 11 or keeping the display in an open state is conceivable.

  In addition, since the liquid crystal display device of the present invention detects a voltage rather than a current, it can be configured using the first and second voltage detection elements made up of capacitors and the like, and the product can be reduced in size and cost. Can be achieved.

  The ballast capacitor or the capacitor constituting the voltage detection element may be a chip component or the like, but may be formed on the substrate using the dielectric constant of the substrate. Specific examples thereof are shown in FIGS. 4 is a plan view of the substrate used in the discharge lamp driving device shown in FIG. 1, FIG. 5 is a bottom view of the substrate shown in FIG. 4, and FIG. 6 is a cross-sectional view taken along line 6-6 in FIG. 7 is a cross-sectional view taken along line 7-7 in FIG.

  4 to 7, in the first substrate 310, the one surface side 311 and the other surface side 312 are opposed to each other. On the one surface side 311, for example, the inverter circuit 11, the first transformer T <b> 11, and the like are mounted on the component mounting portion A. The pattern 61 is one of the electrodes provided in the first ballast capacitors C11 to C1n, and the patterns 81 to 8n are the other ends of the electrodes provided in the first voltage detection elements Cc1 to Ccn.

  A pattern group 7 is provided on the other surface 312. The pattern group 7 includes patterns 71, 72,. In the patterns 71 to 7n, the other of the electrodes provided in the first ballast capacitors C11 to C1n and one end of the electrodes provided in the first voltage detection elements Cc1 to Ccn are integrally formed.

In the figure, when the electrode area of the first voltage detection element is S1, the thickness of the first substrate 310 is d1, the electric conductivity of vacuum is ε ₀ , and the relative dielectric constant of the first substrate 310 is ε _r , The electrostatic capacitance of one voltage detection element Cc1 to Ccn is
Cc1 to Ccn = (ε ₀ ε _r S1) / d1
It becomes.

Similarly, when the electrode area of the first ballast capacitor is S2, the capacitance of the first ballast capacitors C11 to C1n is
C11 to C1n = (ε ₀ ε _r S2) / d1
It becomes.

  The second substrate 320 has a configuration similar to that of the first substrate 310. Specifically, the second transformer T21 is mounted on the component mounting portion A, and the pattern 61 is one of the electrodes provided in the second ballast capacitors C21 to C2n. The patterns 81 to 8n are the other ends of the electrodes provided in the first voltage detection elements Ce1 to Cen. The patterns 71 to 7n are the other electrode provided in the second ballast capacitors C21 to C2n and one end of the electrode provided to the first voltage detection elements Ce1 to Cen.

  In the illustrated embodiment, the first voltage detection elements Cc1 to Ccn and the ballast capacitors C11 to C1n are formed on the same substrate 310, so that the cost and size can be reduced. The same applies to the substrate 320.

  Furthermore, since the other end of the electrode provided in the first ballast capacitor and one end of the electrode provided in the first voltage detection element are made common to form patterns 71 to 7n, the cost and size can be reduced. Can do.

  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 a figure explaining the case where the open state of a discharge lamp arises in the discharge lamp lighting device shown in FIG. It is a top view of the board | substrate used for the discharge lamp drive device shown in FIG. It is a bottom view of the board | substrate shown in FIG. FIG. 6 is a cross-sectional view taken along line 6-6 in FIG. FIG. 7 is a cross-sectional view taken along line 7-7 in FIG.

Explanation of symbols

11 Inverter circuit T11, T21 1st, 2nd transformer Cc1-Ccn, Ce1-Cen 1st voltage detection element Cd1-Cdn, Cf1-Cfn 2nd voltage detection element 30 Signal processing part 21-2n Discharge lamp

Claims (2)

An inverter circuit; first and second transformers; first and second ballast capacitors; a plurality of first and second discharge lamp connection terminals; first and second voltage detection elements; and signal processing. And a discharge lamp driving device including a substrate ,
The inverter circuit is a circuit that converts a DC voltage into an AC voltage and outputs the AC voltage,
The first and second transformers are supplied with AC voltage from the inverter circuit to the input winding, and output AC voltage from the output winding,
A plurality of the first ballast capacitors, one of the electrodes being connected to the output winding of the first transformer, and the other of the electrodes being provided with a plurality of the first discharge lamp connection terminals Connected to each of the
A plurality of the second ballast capacitors, one of the electrodes being connected to the output winding of the second transformer, and the other of the electrodes being provided with the second discharge lamp connection terminal. Connected to each of the
Each of the first and second discharge lamp connection terminals can be connected to a plurality of discharge lamps,
The first voltage detection element is a capacitor, and a plurality of electrodes, and one end of each electrode is connected to at least one of the first and second discharge lamp connection terminals,
The second voltage detection element is a capacitor, and there are a plurality of electrodes. One end of each electrode is connected to the other end of the electrode provided in the first voltage detection element, and the other end is a ground terminal. Led to
The signal processing unit includes a connection point of the first voltage detecting element and the second voltage detecting device, a voltage generated between the ground terminal, generates a signal for detecting the open state of the discharge lamp ,
The other end of the electrode provided in the first voltage detection element is provided on one surface of the substrate,
One end of the electrode provided in the first voltage detection element is provided on the other surface of the substrate.
Discharge lamp driving device. A liquid crystal display device including a discharge lamp driving device, a plurality of discharge lamps, and a liquid crystal plate,
The discharge lamp driving device is the one described in claim 1 ,
Each of the plurality of discharge lamps has one electrode connected to the first discharge lamp connection terminal and the other electrode connected to the second discharge lamp connection terminal.
The liquid crystal plate is disposed in front of the discharge lamp;
Liquid crystal display device.

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