JP2011082108A - Led failure detecting device, backlight device, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an LED failure detecting device that distinctly detects a short-circuit failure and open failure of each of a plurality of series-connected LEDs using a simple configuration, and to provide a backlight device including the same and a liquid-crystal display device. <P>SOLUTION: When a short-circuit failure or an open failure occurs in any one of the plurality of series-connected LEDs 111, 112-11n, the current measured by an ammeter 20 is different for each LED 111, 112-11n, in which the short-circuit failure or the open failure occurs, and also, different for each short-circuit failure and each open failure. Specifically, the resistance values of all the resistors 241, 341, 242, 342-24n, 34n are different from each other. A failure detection control section 30 distinctly detects short-circuit failure and open failure of each LED 111, 112-11n, according to the current measured by the ammeter 20. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an LED failure detection device that detects a failure of an LED (light emitting diode), and a backlight device and a liquid crystal display device including the LED failure detection device, and in particular, distinguishes between a short failure and an open failure of each of a plurality of LEDs connected in series. The present invention relates to a technique for detecting separately.

For example, in Patent Document 1, not only the presence / absence of an LED failure, but when the LED has failed, the failure is either a short failure in which both ends of the LED are short-circuited or an open failure in which the LED connection path is disconnected. An LED failure detection device that can identify whether there is an LED is disclosed.
Specifically, the LED failure detection device disclosed in Patent Document 1 includes a resistance element connected in parallel to the LED and a resistance element connected to the cathode of the LED, and determines the potential of the cathode of the LED. It is to detect. In such a configuration, the cathode potential of the LED varies depending on whether the LED is in a normal state, a short circuit failure state, or an open failure state. Faults and open faults can be detected separately.
By the way, the LED may be used in a backlight device that is mounted on a liquid crystal display device such as a liquid crystal television receiver and illuminates a liquid crystal panel from behind. Specifically, the backlight device may be configured by arranging a plurality of LEDs in a row in which a plurality of LEDs are connected in series in the vertical direction. Even in a configuration in which a plurality of LEDs are connected in series as described above, it is desirable that a short-circuit failure and an open failure of the LEDs can be distinguished and detected as described above.

JP 2008-98495 A

However, for example, in order to apply the configuration according to Patent Document 1 to a configuration in which a plurality of LEDs are connected in series and detect a short-circuit failure and an open failure for each LED, the cathode potential is set for each LED. It is necessary to monitor with a control circuit. Therefore, it is necessary to provide a large number of input ports of the control circuit corresponding to the number of LEDs to be detected, which causes a problem that the configuration becomes complicated and the cost is increased. In particular, with the recent increase in screen size of liquid crystal display devices, the size of the backlight device is also increasing, and the number of LEDs provided in the backlight device is also increasing. Therefore, the input port corresponding to the number of LEDs is increased. It is not preferable to provide.
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to distinguish and detect a short fault and an open fault of each of a plurality of LEDs connected in series with a simple configuration. An object of the present invention is to provide an LED failure detection device, a backlight device including the same, and a liquid crystal display device.

In order to achieve the above object, according to the present invention, a current measured when a short failure or an open failure occurs in any of a plurality of LEDs connected in series is measured for each LED in which the short failure or the open failure occurs. Current change measuring means configured to be different for each short fault and open fault, and detecting and detecting the short fault and the open fault of each LED according to the current measured by the current change measuring means. The LED failure detection device is configured to include an LED failure detection means.
According to the present invention, it is possible to distinguish and detect a short fault and an open fault of each of the LEDs connected in series with a simple configuration in which only the current measured by the current change measuring means is monitored.

As a specific configuration example of the present invention, the current change measuring means is provided corresponding to each of the LEDs, and outputs different currents when the LED is normal, short-circuit failure, and open failure. It is conceivable to include a changing means and a total current measuring means for measuring the total output current of each of the current changing means. Further, each of the current changing means is different from a current output when each of the LED short-circuit failure and open failure is different from the current output when the other current change means is short-circuiting and open failure of the LED. It is configured to output current. The LED failure detecting means includes a total of output currents measured by the total current measuring means, and a predetermined current output by each of the current changing means when the LED is short-circuited and when the LED is open. Accordingly, the LED is configured to distinguish and detect a short fault and an open fault of each LED.
According to such a configuration, it is possible to distinguish and detect a short fault and an open fault of each of the LEDs by a simple configuration using one total current measuring unit for the plurality of LEDs.
More specifically, each of the current changing means is configured not to output a current when the LED is normal. In this case, the LED failure detecting means includes a total of output currents measured by the total current measuring means and a predetermined current output when any of the current changing means is short-circuited or open-failed of the LED. It is possible to specify that a short circuit fault or an open fault has occurred in the LED on the condition that the
For example, when the current changing means is a Zener diode connected in parallel to the LED with a reverse polarity and the voltage drop across the LED is smaller than a predetermined first threshold voltage, a predetermined first voltage is used. The first comparator connected to the output side of the first comparator and the first comparator that does not output the first output voltage when the output voltage is equal to or higher than the first threshold voltage. And when the voltage drop across the LED is equal to or higher than a predetermined second threshold voltage, a second output voltage identical to the predetermined first output voltage is output, When the voltage is smaller than the second threshold voltage, the second comparator does not output the second output voltage, and is connected to the output side of the second comparator, and has a resistance value different from that of the first resistance element. And a second resistance element having It is. In this case, the first threshold voltage is equal to or lower than the normal voltage drop of the LED, and the second threshold voltage is larger than the normal voltage drop of the LED, and the voltage drop when the Zener diode is energized. In addition to the following values, all the first resistance elements and the second resistance elements are configured to have different resistance values, so that short-circuit faults and open faults of each of the LEDs are distinguished and detected. It becomes possible to do.
Further, when the current changing means is a Zener diode connected in parallel to the LED with a reverse polarity and the voltage drop across the LED is smaller than a predetermined first threshold voltage, a predetermined first voltage is set. The first comparator connected to the output side of the first comparator and the first comparator that does not output the first output voltage when the output voltage is equal to or higher than the first threshold voltage. And when the voltage drop across the LED is equal to or higher than a predetermined second threshold voltage, a second output voltage different from the predetermined first output voltage is output, When the voltage is smaller than the second threshold voltage, the second comparator does not output the second output voltage, and is connected to the output side of the second comparator, and has the same resistance value as the first resistance element. It is also another example that the second resistive element having And it is considered to. In this case, the first threshold voltage is equal to or lower than the normal voltage drop of the LED, and the second threshold voltage is larger than the normal voltage drop of the LED, and the voltage drop when the Zener diode is energized. In addition to the following values, the short-circuit failure and the open failure of each of the LEDs can be distinguished and detected by configuring the first resistance elements to have different resistance values.

In addition, as a specific example of the present invention, the current change measuring means is provided corresponding to each of the LEDs, and outputs a different current when the LED is normal and when a short circuit failure occurs. And second current changing means for changing the current flowing in the LED circuit in which the LEDs are connected in series when the LED is normal and when there is an open failure, and the output from each of the first current changing means It is also conceivable to include a total current measuring means for measuring the sum of the current and the current flowing on the LED circuit. Each of the first current changing means is configured to output a current different from the current output by the other first current changing means when the LED is short-circuited. Further, each of the second current changing means is configured to change the current flowing in the LED circuit to a current different from that of the other second current changing means when the LED has an open failure. The LED failure detection means includes a total of output currents measured by the total current measurement means, a predetermined current output by each of the first current change means when the LED is short-circuited, and the LED current A short circuit failure and an open failure of each of the LEDs are distinguished and detected according to a predetermined current flowing on the LED circuit that is changed by each of the second current changing means at the time of an open failure.
Even with such a configuration, it is possible to distinguish and detect a short fault and an open fault of each of the LEDs by a simple configuration using one total current measuring unit for the plurality of LEDs.
In this case, when the voltage drop across the LED is smaller than a predetermined first threshold voltage, the first current changing means outputs a predetermined first output voltage, and the first current changing means outputs the first output voltage. A first comparator that does not output the first output voltage and a first resistance element connected to the output side of the first comparator. Conceivable. Further, it is conceivable that the second current changing means includes a Zener diode connected in parallel to the LED in reverse polarity and a third resistance element connected in series to the Zener diode. The first threshold voltage is a value equal to or lower than the normal voltage drop of the LED, and the voltage drop when the Zener diode and the third resistance element are energized is lower than the normal voltage drop of the LED. It can be considered that the resistance values of all the first resistance elements are different and the resistance values of all the third resistance elements are different.
According to such a configuration, the second comparator can be omitted as compared with the above-described specific example using the first comparator and the second comparator, and the LED can be realized with a simpler configuration. Each short fault and open fault can be detected separately.

By the way, this invention can also be grasped | ascertained as invention of the backlight apparatus which has several LED connected in series which illuminates a liquid crystal panel from back. That is, the backlight device may be configured to include the LED failure detection device that distinguishes and detects short-circuit failure and open failure of each LED.
In addition, a liquid crystal panel for displaying an image, a backlight device having a plurality of LEDs connected in series to illuminate the liquid crystal panel from behind, and a short circuit failure and an open failure of each LED of the backlight device are detected separately. It can also be understood as an invention of a liquid crystal display device comprising the LED failure detection device.

  According to the present invention, it is possible to distinguish and detect a short fault and an open fault of each of the LEDs connected in series with a simple configuration in which only the current measured by the current change measuring means is monitored.

The block diagram for demonstrating the principal part of the liquid crystal display device X which concerns on embodiment of this invention. The schematic diagram for demonstrating schematic structure of the backlight apparatus 4 which concerns on embodiment of this invention. The circuit diagram for demonstrating schematic structure of the LED failure detection apparatus Y which concerns on 1st Embodiment of this invention. The circuit diagram for demonstrating operation | movement of the LED failure detection apparatus Y which concerns on 1st Embodiment of this invention. The circuit diagram for demonstrating the other example of the LED failure detection apparatus Y which concerns on 1st Embodiment of this invention. The circuit diagram for demonstrating schematic structure of the LED failure detection apparatus Z which concerns on 2nd Embodiment of this invention. The circuit diagram for demonstrating operation | movement of the LED failure detection apparatus Z which concerns on 2nd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
First, a schematic configuration of the liquid crystal display device X according to the embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 1, a liquid crystal display device X according to an embodiment of the present invention includes a display control unit 1, a liquid crystal panel 2, a liquid crystal drive unit 3, a backlight device 4, a backlight control unit 5, an LED failure detection device. A liquid crystal television receiver having Y (Z) or the like. The liquid crystal display device X is characterized by the structure of the LED failure detection device Y (Z), which will be described in detail later.
A configuration in which the backlight device 4 includes the LED failure detection device Y (Z) is also conceivable. In this case, the backlight device 4 corresponds to the backlight device according to the present invention. The liquid crystal display device according to the present invention is not limited to a liquid crystal television receiver, and a display device of a personal computer corresponds to the liquid crystal display device according to the present invention.

The display control unit 1 receives a video signal included in a television broadcast received by an antenna (not shown) or a video content input from an external input terminal (not shown), and performs vertical synchronization based on the video signal. Signals and horizontal sync signals are generated. The video signal, the vertical synchronization signal, and the horizontal synchronization signal are input from the display control unit 1 to the liquid crystal driving unit 3.
The liquid crystal panel 2 is formed of a liquid crystal layer and a scan electrode and a data electrode for applying a scan signal and a data signal to the liquid crystal layer. The liquid crystal panel 2 includes a plurality of liquid crystal elements whose transmittance varies depending on an applied voltage. This is an active matrix type liquid crystal panel.
The liquid crystal driving unit 3 uses the scanning electrode (gate electrode) and the data electrode (source electrode) of the liquid crystal panel 2 based on the image signal, the vertical synchronizing signal, and the horizontal synchronizing signal input from the display control unit 1. By driving it, an image is displayed on the liquid crystal panel 2.

The backlight device 4 is disposed on the back surface of the liquid crystal panel 2 and illuminates the liquid crystal panel 2 from behind. FIG. 2 is a schematic diagram showing an example of the structure of the backlight device 4.
As shown in FIG. 2, the backlight device 4 includes a plurality of LED groups L <b> 1 to L <b> 12 arranged in parallel corresponding to a plurality of display areas in the vertical direction of the liquid crystal panel 2. Each of the LED groups L1 to L12 includes a plurality of LEDs 11 (111, 112,... 11n) arranged in parallel in the horizontal direction of the liquid crystal panel 2. In response to a control instruction from the backlight control unit 5, the backlight device 4 blinks a large number of the LEDs 11 in units of the LED groups L1 to L12.
Here, in each of the LED groups L1 to L12, the plurality of LEDs 11 are electrically connected in series (see FIG. 3). Each of the display areas corresponding to the LED groups L1 to L12 is an area including a plurality of lines of display pixels of the liquid crystal panel 2. Of course, the number of the LED groups L <b> 1 to L <b> 12 is not limited to this, and the design may be appropriately changed according to the size of the liquid crystal panel 2.

The LED failure detection device Y (Z) detects a short-circuit failure and an open failure of each of the plurality of LEDs 11 provided in each of the LED groups L1 to L12 provided in the backlight device 4. It is. The LED 11 short-circuit failure is a failure in which both ends of the LED 11 are short-circuited, and the open failure is a failure in which the connection path of the LED 11 is disconnected.
Hereinafter, the LED failure detection device Y according to the first embodiment of the present invention will be described first with reference to FIGS. 3 to 5, and then the LED failure according to the second embodiment of the present invention with reference to FIGS. 6 and 7. The detection device Z will be described.

(First embodiment)
As shown in FIG. 3, the LED failure detection device Y includes a resistor 10, an ammeter 20, current changing circuits A1, A2,... An provided for each of the LED groups L1 to L12, and the LED group. A failure detection control unit 30 common to L1 to L12 is provided. Of course, the failure detection control unit 30 may be provided corresponding to each of the LED groups L1 to L12.
The current change circuits A1, A2,... An are provided corresponding to each of the plurality of LEDs 11 (111, 112,... 11n) connected in series, and when the LEDs 11 are normal, short-circuited, and open-failed Each outputs a different current. Here, the current changing circuits A1, A2,... An are examples of current changing means. As shown in FIG. 3, the same reference numerals are given to the same components in the current change circuits A1, A2,.

The resistor 10 is connected in series to the previous stage of the current change circuit A1, and limits the current flowing through the LED 11.
The ammeter 20 is an example of a total current measuring unit that measures the sum of output currents from the current change circuits A1, A2,. Specifically, output terminals of operational amplifiers 23 and 33 (described later) provided in the current change circuits A1, A2,... An are connected in parallel, so that these output currents are added together and input to the ammeter 20. ing. The current measured by each of the ammeters 20 (hereinafter referred to as “measured total current”) is input to the failure detection control unit 30.
The failure detection control unit 30 includes control devices such as an MPU, a RAM, and a ROM, and according to the measured total current input from the ammeter 20 by executing a predetermined control program by the MPU. Then, processing for specifying the presence / absence of each of the LEDs 11 and the content of the failure is executed. Here, the failure detection control unit 30 for detecting the short failure and the open failure of each of the LEDs 11 corresponds to the LED failure detection means. The failure detection control unit 30 may also serve as a main control unit of the liquid crystal display device X. In this case, the main control unit corresponds to an LED failure detection unit.

Next, the configuration of the current change circuits A1, A2,.
As shown in FIG. 3, the current change circuits A1, A2,... An are connected in parallel to each of the LEDs 11 in reverse polarity, and the Zener diode 12 has a voltage drop when energized is larger than a voltage drop when the LED 11 is normal. And two operational amplifiers 23 (an example of a first comparator) connected to the anode and the cathode of the LED 11, an operational amplifier 33 (an example of a second comparator), and the − of the operational amplifier 23 from the anode side of the LED 11. Voltage dividing resistors 21 and 22 for adjusting the voltage input to the terminal, voltage dividing resistors 31 and 32 for adjusting the voltage input from the anode side of the LED 11 to the + terminal of the operational amplifier 33, and Resistors 241, 242,... 24n (an example of a first resistance element) connected to the output side of the operational amplifier 23 to adjust the output current, and the operational amplifier 3 Resistance adjusting of connected output current on the output side 341, 342, ... and a 34n (an example of a second resistive element).
The Zener diode 12 has a Zener voltage (breakdown voltage) set so as to be de-energized when the LED 11 is normal or short-circuited and energized when the LED 11 is open-failed. At this time, the voltage drop when the Zener diode 12 is energized is equal to or higher than a second threshold voltage that is a determination index of the operational amplifier 33 described later.

The operational amplifier 23 outputs a DC voltage of 5V (an example of a predetermined first output voltage) when the voltage drop across the LED 11 is smaller than a predetermined first threshold voltage, When the threshold voltage is 1 or more, a DC voltage of 5 V is not output.
Here, the first threshold voltage is a value that is determined in advance to determine whether or not a short circuit failure has occurred in the LED 11, and is a value that is equal to or less than the voltage drop of the LED 11 when it is normal. The operational amplifier 23 outputs a DC voltage of 5V when the LED 11 is short-circuited, and does not output a DC voltage of 5V when the LED 11 is not short-circuited.
The first threshold voltage is determined by dividing the voltage applied to the anode side of the LED 11 by the voltage dividing resistors 21 and 22 and inputting the divided voltage to the negative terminal of the operational amplifier 23. That is, the first threshold voltage is determined by the voltage applied to the anode side of the LED 11 and the resistance values of the voltage dividing resistors 21 and 22.

On the other hand, when the voltage drop across the LED 11 is equal to or higher than a predetermined second threshold voltage, the operational amplifier 33 has the same 5V DC voltage (second output voltage as the output voltage of the operational amplifier 23). In the case where the voltage is smaller than the second threshold voltage, a DC voltage of 5 V is not output.
Here, the second threshold voltage is a value determined in advance to determine whether or not an open failure has occurred in the LED 11, and is greater than a voltage drop of the LED 11 during normal operation. The value is less than the voltage drop during energization. The operational amplifier 33 outputs a DC voltage of 5 V when an open failure occurs in the LED 11, and does not output a DC voltage of 5 V when an open failure does not occur in the LED 11.
The second threshold voltage is determined by the voltage applied to the anode side of the LED 11 being divided by the voltage dividing resistors 31 and 32 and input to the + terminal of the operational amplifier 33. That is, the second threshold voltage is determined by the voltage applied to the anode side of the LED 11 and the resistance values of the voltage dividing resistors 31 and 32.

.., 24n connected to the output side of the operational amplifier 23 and the resistors 341, 342 connected to the output side of the operational amplifier 33 in each of the current change circuits A1, A2,. ,... Have a resistance value different from 34n.
Therefore, as for the output current of each of the current change circuits A1, A2,..., An, when no DC voltage is output from either the operational amplifier 23 or the operational amplifier 33, or when a DC voltage of 5 V is output from the operational amplifier 23, It will change according to each situation when a DC voltage of 5V is output from the operational amplifier 33.

Further, in the LED failure detection device Y, all the resistors 241, 341, 242, 342,... 24n, 34n connected to the output sides of the operational amplifiers 23, 33 of the current change circuits A1, A2,. Each has a different resistance value. For example, it is conceivable that the resistance value gradually increases or decreases in the order of the resistors 241, 341, 242, 342,.
As a result, when a DC voltage of 5 V is output from each of the operational amplifiers 23 and 33, the current input to the ammeter 20 is different for each of the current change circuits A1, A2,. That is, each of the current change circuits A1, A2,... An is respectively in the event of a short circuit failure and an open failure of the LED 11, and each of the other current change circuits A1, A2,. A current different from the current output to each is output.
Therefore, in the LED failure detection device Y, when a short failure or an open failure occurs in any of the plurality of LEDs 11 (111, 111,... 11n), the current measured by the ammeter 20 is the short circuit. It differs for each LED 11 in which a failure or an open failure has occurred, and for each short failure and open failure. Here, the current change circuits A1, A2,... An and the ammeter 20 when implementing such a configuration are examples of current change measurement means.

The failure detection control unit 30 outputs the measured total current measured by the ammeter 20 and each of the current change circuits A1, A2,. According to the predetermined current, the short-circuit failure and the open failure of each LED 11 are distinguished and detected.
More specifically, the current changing circuits A1, A2,... An each output when the LED 11 is short-circuited and when the LED 11 is short-circuited are the resistors 241, 242,. 34n is predetermined. Therefore, the failure detection control unit 30 determines that the current changing circuits A1, A2,... An each output current when the LED 11 is short-circuited and open, that is, the measurement sum measured by the ammeter 20. Correspondence information indicating a correspondence relationship between the current and each of the LED 11 short failure and open failure is stored.
Then, the failure detection control unit 30 determines the measured total current measured by the ammeter 20 according to the correspondence information and the measured total current measured by the ammeter 20, and the current change circuit A1. , A2,..., An are identified as having a short failure or an open failure in the LED 11 on condition that a predetermined current output at the time of a short failure or an open failure of the LED 11 matches. To do.

Hereinafter, the operation of the current change circuits A1, A2,... An will be described by taking the current change circuit A1 as an example with reference to FIG. 4A shows the operation when the LED 111 is normal, FIG. 4B shows the operation when the LED 111 is short-circuited, and FIG. 4C shows the operation when the LED 111 is open-failed.
Here, it is assumed that the anode input voltage V0 of the LED 111 is 30.0V, the normal voltage drop V2 of the LED 111 is 0.7V, and the voltage drop V2 when the Zener diode 12 is energized is 1.2V. Therefore, when the LED 111 is normal, the output voltage V1 from the cathode of the LED 111 is 29.3V, and when the Zener diode 12 is energized, the output voltage V1 is 28.8V.
The resistance values of the voltage dividing resistors 21 and 22 are 1Ω and 59Ω, and the resistance values of the voltage dividing resistors 31 and 32 are 1Ω and 29Ω. Therefore, Vin1 input to the + terminal of the operational amplifier 23 is 29.5V (30 × (59/60)) obtained by dividing 30V of the input voltage V0 by the voltage dividing resistors 21 and 22. Vin3 input to the − terminal of 33 is 29.0 V (30 × (29/30)) obtained by dividing 30 V of the input voltage V0 by the voltage dividing resistors 31 and 32. That is, the first threshold voltage is set to 0.5 V, which is 0.7 V or less, which is a voltage drop when the LED 11 is normal, and the second threshold voltage is a voltage drop when the LED 11 is normal. The voltage drop is set to 1.0 V, which is greater than 7 V and 1.2 V or less, which is a voltage drop when the Zener diode 12 is energized.
Furthermore, it is assumed that the resistance values of the resistors 241 and 341 connected to the output side of the operational amplifiers 23 and 33 are 1 kΩ and 2 kΩ, respectively. Therefore, in the current change circuit A1, when a short fault occurs in the LED 111 and the output voltage Vout1 of 5 V is output from the operational amplifier 23, a current of 5 V / 1 kΩ = 5 mA is output. On the other hand, when the output voltage Vout2 of 5V is output from the operational amplifier 33 due to an open failure in the LED 111, a current of 5V / 2 kΩ = 2.5 mA is output.

Specifically, in the current change circuit A1, the voltage drop V2 (0.7 V) occurs in the LED 111 when the LED 111 is normal, as shown in FIG. Therefore, 29.3 V which is the output voltage V1 is input as Vin of the + terminal of the operational amplifier 23 and Vin4 of the − terminal of the operational amplifier 33, respectively.
In this case, the operational amplifier 23 determines that Vin2 (29.3 V) at the + terminal is equal to or lower than Vin1 (29.5 V) at the − terminal and does not output Vout1 (Vout1 = 0 V). Also, the operational amplifier 33 determines that Vin3 (29.0 V) at the + terminal is equal to or lower than Vin4 (29.3 V) at the − terminal and does not output Vout2 (Vout2 = 0 V).
Therefore, the current change circuit A1 is configured not to output a current when the LED 111 is normal. That is, when the LEDs 11 corresponding to all the current change circuits A1, A2,... An are normal, the measured total current measured by the ammeter 20 is zero.

Next, as shown in FIG. 4B, in the current change circuit A1, when the LED 111 is short-circuited, the LED 111 becomes conductive, so the voltage drop V2 becomes 0V (V0 = V1 = 30). .0V). Therefore, 30.0 V, which is the output voltage V1, is input as Vin at the positive terminal of the operational amplifier 23 and Vin4 at the negative terminal of the operational amplifier 33, respectively.
In this case, the operational amplifier 23 determines that Vin2 (30.0 V) at the + terminal is higher than Vin1 (29.5 V) at the − terminal, and outputs Vout1 (Vout1 = 5 V). On the other hand, the operational amplifier 33 determines that Vin3 (29.0 V) at the + terminal is equal to or lower than Vin4 (30.0 V) at the − terminal and does not output Vout2 (Vout2 = 0 V).
Accordingly, the current changing circuit A1 is configured to output a current (5 mA = 5 V / 1 kΩ) corresponding to the output voltage Vout1 (5 V) and the resistance value (1 kΩ) of the resistor 241 when the LED 111 is short-circuited. Has been. That is, when the LED 11 corresponding to one of the current change circuits A1, A2,... An is short-circuited, different currents are generated depending on the current change circuits A1, A2,. The ammeter 20 measures the total measurement current.

Further, as shown in FIG. 4C, in the current change circuit A1, when the LED 111 is in an open failure, the circuit of the LED 111 is cut off and the Zener diode 12 is energized. Since a voltage drop of .2V occurs, the voltage drop V2 across the LED 111 is 1.2V. Therefore, 28.8V, which is the output voltage V1, is input as Vin of the + terminal of the operational amplifier 23 and Vin4 of the − terminal of the operational amplifier 33, respectively.
In this case, the operational amplifier 23 determines that Vin2 (28.8V) at the + terminal is equal to or lower than Vin1 (29.5V) at the − terminal and does not output Vout1 (Vout1 = 0V). On the other hand, the operational amplifier 33 determines that Vin3 (29.0V) at the positive terminal is higher than Vin4 (28.8V) at the negative terminal, and outputs Vout2 (Vout2 = 5V).
Therefore, the current changing circuit A1 outputs a current (2.5 mA = 5 V / 2 kΩ) corresponding to the output voltage Vout2 (5 V) and the resistance value (2 kΩ) of the resistor 341 when the LED 111 is open. It is configured. That is, even when an open failure occurs in the LED 11 corresponding to any one of the current change circuits A1, A2,... An, different currents are generated depending on the current change circuits A1, A2,. Is measured by the ammeter 20 as the measured total current.
In particular, in the LED failure detection device Y, since the resistance values of all the resistors 241, 341, 242, 342,... 24n, 34n are different, any one of the plurality of LEDs 11 connected in series is The measured total current measured by the ammeter 20 at the time of an open failure is all different depending on the current change circuits A1, A2,... An corresponding to the LED 11 in which the short failure or the open failure has occurred.

Then, the failure detection control unit 30 distinguishes and detects a short-circuit failure and an open failure of each of the LEDs 11 according to the measured total current measured by the ammeter 20.
Specifically, the failure detection control unit 30 determines that a short-circuit failure has occurred in the LED 111 corresponding to the current change circuit A1 when the measured total current measured by the ammeter 20 is 5 mA. If the measured total current is 2.5 mA, it is determined that an open failure of the LED 111 corresponding to the current change circuit A1 has occurred. Further, the failure detection control unit 30 determines that all the LEDs 11 are normal when the measured total current is zero. The failure detection control unit 30 similarly applies the current change circuits A2, A3,... An when the LED 11 corresponding to the other current change circuits A2, A3,. The occurrence of a short fault or an open fault and the location of the fault are detected according to the measured total current output by the ammeter 20 when the short fault or the open fault occurs.

  As described above, in the LED failure detection device Y, the measured total current measured by one ammeter 20 is different for each LED 11 in which a short failure or an open failure has occurred, and the short failure and the open failure. Therefore, it is possible to distinguish and detect a short fault and an open fault of each of the plurality of LEDs 11 with a simple configuration in which only the measured total current measured by the ammeter 20 is monitored.

Here, since the resistance values of all of the resistors 241, 242,... 24n and the resistors 341, 342,... 34n are different, the current change circuits A1, A2 at the time of short-circuit failure and open failure of the LEDs 11 respectively. ,..., Taking as an example the case where the output current from An is varied.
On the other hand, as shown in FIG. 5, in the LED failure detection device Y, when each of the operational amplifiers 33 has a voltage drop across the LED 11 equal to or higher than a predetermined second threshold voltage, Another embodiment can be considered to output a DC voltage of 6V different from the output voltage of 5V. At this time, it is conceivable that a resistor 241 having the same resistance value as that of the output side of the operational amplifier 23 is also connected to the output side of the operational amplifier 33. However, even in this case, in order to identify the LED 11 in which a short circuit failure or an open failure has occurred, the resistor 241 is set so that the currents output from the operational amplifiers 23 and 33 of the current change circuits A1, A2,. , 242,... 24n must have different resistance values (that is, resistance values of the resistors 341, 342,... 34n).
Even when the LED failure detection device Y is configured in this way, it is output when a short failure or an open failure of the LED 11 corresponding to each of the current change circuits A1, A2,. Since the currents are different, it is possible to distinguish and detect a short fault or an open fault of each of the LEDs 11 corresponding to the current change circuits A1, A2,. In such a configuration, the type of resistance value to be used may be small, so that a configuration with excellent productivity can be realized.
Of course, each of the operational amplifiers 23 outputs a DC voltage of 6V different from 5V which is the output voltage of the operational amplifier 33 when the voltage drop across the LED 11 is smaller than a predetermined first threshold voltage. It is also conceivable that

(Second Embodiment)
Hereinafter, the LED failure detection device Z according to the second embodiment of the present invention will be described with reference to FIGS. 6 and 7.
As shown in FIG. 6, the LED failure detection device Z includes a resistor 10, an ammeter 20, current changing circuits B1, B2,... Bn (first currents) provided corresponding to the LED groups L1 to L12. An example of changing means), current changing circuits C1, C2,... Cn (an example of second current changing means) and a failure detection control unit 30 common to the LED groups L1 to L12.
The current change circuits B1, B2,... Bn are provided corresponding to each of the plurality of LEDs 11 (111, 112,... 11n) connected in series, and differ at least when the LED 11 is normal and when a short circuit failure occurs. Output current.
The current changing circuits C1, C2,... Cn are provided corresponding to each of the plurality of LEDs 11 (111, 112,... 11n) connected in series, and at least when the LED 11 is normal and when an open failure occurs. The current flowing on the LED circuit in which the LEDs 11 are connected in series is changed. Here, the current change times B1, B2,... Bn and the current change circuits C1, C2,... Cn are examples of the current change measuring means.

The ammeter 20 is an example of a total current measuring means for measuring the sum of the output current from each of the current changing times B1, B2,... Bn and the current flowing on the LED circuit.
Specifically, output terminals of the operational amplifiers 241, 242,... 24n provided in the current change circuits B1, B2,... Bn are connected in parallel, and each of the output terminals and the LED circuit are connected in parallel. Thus, these output currents are added together and input to the ammeter 20.
As in the first embodiment, the failure detection control unit 30 determines whether or not each of the LEDs 11 has a failure according to the current measured by the ammeter 20 (hereinafter referred to as “measured total current”) and the failure of the LED 11. Execute processing to identify the contents.

Next, the configuration of the current change circuits B1, B2,... Bn and the current change circuits C1, C2,.
As shown in FIG. 6, the current changing circuits B1, B2,... Bn include an operational amplifier 23 (an example of a first comparator) connected to the anode and cathode of the LED 11, and the operational amplifier from the anode side of the LED 11. 23, voltage dividing resistors 21 and 22 for adjusting the voltage input to the negative terminal thereof, and resistors 241, 242,..., 24n connected to the output side of the operational amplifier 23 for adjusting the output current (of the first resistance element) Example). Here, all the resistors 241, 242,... 24n have different resistance values. Thus, the current changing circuits B1, B2,... Bn output a current different from the current output by the other current changing circuits B1, B2,. .
Since the operations of the current change circuits B1, B2,... Bn are the same as those described in the first embodiment, a detailed description is omitted here, that is, no current is output when the LED 11 is normal. When the LED 11 is short-circuited, a different current is output for each of the current change circuits B1, B2,.

Further, the current change circuits C1, C2,... Cn include a Zener diode 12 connected in parallel to the LED 11 in reverse polarity, and resistors 131, 132,... 13n (third resistor) connected in series to the Zener diode 12. An example of an element). Here, all of the resistors 131, 132,... 13n have different resistance values. Thus, the current changing circuits C1, C2,... Cn change the current flowing on the LED circuit when the LED 11 is open to a different current from the other current changing circuits C1, C2,. Further, the voltage drop caused by the Zener diode 12 and the resistors 131, 132,... 13n is larger than the voltage drop of the LED 11 when it is normal.
In the LED failure detection device Z configured in this manner, the ammeter 20 measures the short-circuit failure or the open failure in any of the plurality of LEDs 11 (111, 112,... 11n). The measured total current differs for each LED 11 in which the short failure or open failure has occurred, and for each short failure and open failure.

Then, the failure detection control unit 30 includes the measured total current measured by the ammeter 20, a predetermined current output when each of the current change circuits B 1, B 2,. A short circuit failure and an open failure of each LED 11 are distinguished and detected according to a predetermined current flowing on the LED circuit that is changed by each of the current changing circuits C1, C2,... Cn at the time of the open failure of the LED 11. To do.
Specifically, the currents output by the current change circuits B1, B2,... Bn when the LED 11 is short-circuited and when the LED 11 is short-circuited are predetermined by the resistors 241, 242,. The current flowing on the LED circuit, which is changed by each of the current changing circuits C1, C2,... Cn at the time of the open failure of the LED 11 by each of the current changing circuits B1, B2,. 132,... 13n.
Therefore, the failure detection control unit 30 is therefore configured such that the failure detection control unit 30 adds the current output from each of the current change circuits B1, B2,... Bn and the current flowing on the LED circuit, that is, the ammeter. Corresponding information indicating the correspondence between the measured total current measured by 20 and the short failure and open failure of each LED 11 is stored.
Then, the failure detection control unit 30 distinguishes and detects a short failure or an open failure of each of the LEDs 11 according to the correspondence information and the measured total current measured by the ammeter 20.

Hereinafter, the operations of the current change circuits B1, B2,... Bn and the current change circuits C1, C2,... Cn will be described by taking the current change circuits B1, C1 as an example, with reference to FIG. 7A shows the operation when the LED 111 is normal, FIG. 7B shows the operation when the LED 111 is short-circuited, and FIG. 7C shows the operation when the LED 111 is open-failed.
Here, the anode input voltage V0 of the LED 111 is 30.0 V, the normal voltage drop V21 of the LED 111 is 0.7 V, the voltage drop V23 when the Zener diode 12 is energized is 1.2 V, and the resistance 131 It is assumed that the voltage drop V24 during energization is 0.8V. Therefore, when the LED 111 is normal, the output voltage V1 from the cathode of the LED 111 is 29.3V, and when the Zener diode 12 and the resistor 131 are energized, the output voltage V1 is 28.0V.
The resistance values of the voltage dividing resistors 21 and 22 are 1Ω and 59Ω. Therefore, Vin1 input to the + terminal of the operational amplifier 23 is 29.5V (30 × (59/60)) obtained by dividing 30V of the input voltage V0 by the voltage dividing resistors 21 and 22. That is, the first threshold voltage is set to 0.5 V, which is 0.7 V or less, which is a voltage drop when the LED 11 is normal.
Furthermore, it is assumed that the resistance value of the resistor 241 connected to the output side of the operational amplifier 23 is 1 kΩ. Therefore, when the output voltage Vout1 of 5V is output from the operational amplifier 23, the current change circuit B1 outputs a current of 5V / 1 kΩ = 5 mA. As described above, since the resistors 241, 242,... 24n of the current change circuits B1, B2,... Bn have different resistance values, the current change circuits B1, B2,. The currents that are output when a short circuit failure occurs are all different.

Specifically, in the current change circuit B1, as shown in FIG. 7A, when the LED 111 is normal, the voltage drop V2 across the LED 111 becomes the voltage drop V21 (0.7V). An output voltage V1 of 29.3V is input as Vin2 of the + terminal of the operational amplifier 23.
In this case, the operational amplifier 23 determines that Vin2 (29.3 V) at the + terminal is equal to or lower than Vin1 (29.5 V) at the − terminal and does not output Vout1 (Vout1 = 0 V). That is, the current change circuit B1 is configured not to output a current when the LED 111 is normal.
On the other hand, in the current change circuit C1, the Zener diode 12 and the resistor 131 are not energized when the LED 111 is normal. Therefore, when all the LEDs 11 are normal, the current I flowing on the LED circuit in which the plurality of LEDs 11 are connected in series is expressed by the following equation, where R1 is the resistance value of the resistor 10 and n is the number of the LEDs 11. The current I is expressed by (1) and measured by the ammeter 20.
I = (V0−n · V21) / R1 (1)

Next, as shown in FIG. 7B, in the current change circuit B1, when the LED 111 is short-circuited, the LED 111 becomes conductive, so that the voltage drop V2 across the LED 111 is a voltage drop V22 (0V). (V0 = V1 = 30.0V). Therefore, 30.0V which is the output voltage V1 is input as Vin2 of the + terminal of the operational amplifier 23, and the operational amplifier 23 has Vin2 (30.0V) of the + terminal from Vin1 (29.5V) of the-terminal. Vout1 is output (Vout1 = 5V). As a result, a current of 5 mA (5 V / 1 kΩ) is output from the current change circuit B1.
On the other hand, in the current change circuit C1, when the LED 111 is short-circuited, the Zener diode 12 and the resistor 131 are not energized. Therefore, when a short circuit failure occurs in any of the LEDs 11, the current I flowing on the LED circuit is expressed by the following equation (2), where R1 is the resistance value of the resistor 10 and n is the number of the LEDs 11. expressed.
I = (V0− (n−1) · V21) / R1 (2)
Therefore, the sum of the current I and the current (5 mA) output from the current change circuit B1 is measured by the ammeter 20 as the measured total current. In this case, the measured total current varies depending on which of the current changing circuits B1, B2,.

Further, as shown in FIG. 7C, in the current change circuit B1, when the LED 111 is open, the circuit of the LED 111 is cut off and the Zener diode 12 and the resistor 131 are energized. As a result, the voltage drop V2 across the LED 111 becomes 2.0 V, which is the sum of the voltage drop V22 (1.2 V) and the voltage drop V23 (0.8 V). Therefore, 28.0V which is the output voltage V1 is input as Vin2 of the + terminal of the operational amplifier 23, and the operational amplifier 23 has Vin2 (28.0V) of the + terminal equal to or lower than Vin1 (29.5V) of the − terminal. Therefore, Vout1 is not output (Vout1 = 0V).
On the other hand, in the current change circuit C1, the Zener diode 12 and the resistor 131 are energized when the LED 111 is short-circuited. Therefore, if a short circuit failure occurs in any of the LEDs 11, the current I flowing on the LED circuit is R1, the resistances 131, 132,. When the number of is represented by n, it is expressed by the following equation (3), and the current I is measured by the ammeter 20 as the measured total current.
I = (V0− (n−1) · V21−V22) / (R1 + R13) (3)
Accordingly, the current flowing on the LED circuit in which the LEDs 11 are connected in series, that is, the measured total current measured by the ammeter 20 changes in accordance with the resistance value R13 of the resistor 131.

Then, the failure detection control unit 30 distinguishes and detects a short-circuit failure and an open failure of each of the LEDs 11 according to the measured total current measured by the ammeter 20.
Specifically, the failure detection control unit 30 determines that the measured total current measured by the ammeter 20 matches the total of the current I and the current output from the current change circuit B1 shown in the equation (2). In this case, it is specified that a short circuit failure has occurred in the LED 111 corresponding to the current change circuit B1. If the measured total current matches the current I when the resistance value of the resistor 131 is substituted for the resistance value R13 of the equation (3), the LED 111 corresponding to the current change circuit B1 is opened. Identifies that a failure has occurred. Further, the failure detection control unit 30 determines that all the LEDs 11 are normal when the measured total current matches the current I shown in the equation (1).
As described above, also in the LED failure detection device Z, the current measured by one ammeter 20 is different for each LED 11 in which a short failure or an open failure has occurred, and is different for each short failure and open failure. Therefore, with a simple configuration in which only the total current measured by the ammeter 20 is monitored, it is possible to distinguish and detect a short fault and an open fault of each of the plurality of LEDs 11.

1: Display control unit 2: Liquid crystal panel 3: Liquid crystal drive unit 4: Backlight device 5: Backlight control unit 10: Resistor 11 (111, 111,... 11n): LED (light emitting diode)
12: Zener diodes 131, 132,... 13n: resistance (an example of a third resistance element)
21, 22, 31, 32: voltage dividing resistors 241, 242,..., 24 n: resistors (an example of a first resistor element)
341, 342,... 34n: resistance (an example of a second resistance element)
20: Ammeter (an example of total current measuring means)
30: Failure detection control unit (an example of LED failure detection means)
A1, A2,... An: current change circuit (an example of current change means)
B1, B2,... Bn: current changing circuit (an example of first current changing means)
C1, C2,... Cn: current changing circuit (an example of second current changing means)
L1 to L12: LED group X: Liquid crystal display device Y, Z: LED failure detection device

Claims (9)

The current measured when a short-circuit failure or an open failure occurs in any of a plurality of LEDs connected in series differs depending on the LED in which the short-circuit failure or open failure occurs, and for each short-circuit failure and open failure. Current change measuring means configured differently;
LED failure detection means for distinguishing and detecting a short fault and an open fault of each of the LEDs according to the current measured by the current change measurement means;
An LED failure detection device comprising: The current change measuring means is provided corresponding to each LED, and current changing means for outputting different currents when the LED is normal, short-circuit failure, open failure, and outputs of each of the current change means A total current measuring means for measuring the total current,
Each of the current changing means has a predetermined current different from a current output when the LED short-circuit failure and an open failure, respectively, and when the other current change means outputs a short-circuit failure and an open failure of the LED, respectively. Output,
The LED failure detecting means responds to the sum of the output currents measured by the total current measuring means, and the predetermined currents output by the current changing means when the LED is short-circuited and when the LED is short-circuited, respectively. The LED failure detection device according to claim 1, wherein a short-circuit failure and an open failure of each LED are distinguished and detected. Each of the current changing means does not output a current when the LED is normal,
The total of output currents measured by the total current measuring means by the LED fault detecting means coincides with a predetermined current that is output when any of the current changing means is short or open of the LED. 3. The LED failure detection device according to claim 2, wherein the LED failure detection device identifies that a short failure or an open failure has occurred in the LED on the condition that The current changing means is
A Zener diode connected in parallel to the LED in reverse polarity;
When the voltage drop across the LED is smaller than a predetermined first threshold voltage, a predetermined first output voltage is output, and when the voltage drop is equal to or higher than the first threshold voltage, the first voltage is output. A first comparator that does not output the output voltage, a first resistance element connected to the output side of the first comparator,
When the voltage drop across the LED is greater than or equal to a predetermined second threshold voltage, a second output voltage that is the same as the predetermined first output voltage is output, and the second threshold voltage is output. A second comparator that does not output the second output voltage if it is smaller than the voltage, and a second comparator connected to the output side of the second comparator and having a resistance value different from that of the first resistor element. A resistance element;
With
The first threshold voltage is a value less than or equal to the normal voltage drop of the LED, and the second threshold voltage is greater than the normal voltage drop of the LED and a value less than or equal to the voltage drop when the Zener diode is energized. The LED failure detection device according to claim 2, wherein all of the first resistance elements and the second resistance elements have different resistance values. The current changing means is
A Zener diode connected in parallel to the LED in reverse polarity;
When the voltage drop across the LED is smaller than a predetermined first threshold voltage, a predetermined first output voltage is output, and when the voltage drop is equal to or higher than the first threshold voltage, the first voltage is output. A first comparator that does not output the output voltage, a first resistance element connected to the output side of the first comparator,
When the voltage drop across the LED is equal to or higher than a predetermined second threshold voltage, a second output voltage different from the predetermined first output voltage is output, and the second threshold voltage is output. If smaller, a second comparator that does not output the second output voltage and a second comparator connected to the output side of the second comparator and having the same resistance value as the first resistor element A resistance element;
With
The first threshold voltage is a value less than or equal to the normal voltage drop of the LED, and the second threshold voltage is greater than the normal voltage drop of the LED and a value less than or equal to the voltage drop when the Zener diode is energized. The LED failure detection device according to claim 2, wherein all of the first resistance elements have different resistance values. The current change measuring means is provided corresponding to each of the LEDs, and a first current changing means for outputting different currents when the LED is normal and when a short fault occurs, and when the LED is normal, an open fault A second current changing means for changing a current flowing on the LED circuit in which the LEDs are connected in series at each time, an output current from each of the first current changing means and a current flowing on the LED circuit; A total current measuring means for measuring the total,
Each of the first current changing means outputs a current different from the current output when the other first current changing means outputs a short circuit failure of the LED when the LED short circuit failure occurs;
Each of the second current changing means changes the current flowing on the LED circuit to a current different from that of the other second current changing means when the LED has an open failure;
The LED failure detection means includes a total of output currents measured by the total current measurement means, a predetermined current output when each of the first current change means is a short circuit failure of the LED, and an open failure of the LED. The short circuit failure and the open failure of each of the LEDs are distinguished and detected according to a predetermined current flowing on the LED circuit that is sometimes changed by each of the second current changing means. The LED failure detection device described. When the voltage drop across the LED is smaller than a predetermined first threshold voltage, the first current changing means outputs a predetermined first output voltage, and the first threshold voltage In the case of the above, a first comparator that does not output the first output voltage, and a first resistance element connected to the output side of the first comparator,
The second current changing means comprises a Zener diode connected in parallel to the LED in reverse polarity, and a third resistance element connected in series to the Zener diode;
The first threshold voltage is equal to or less than the normal voltage drop of the LED, and the voltage drop when the Zener diode and the third resistance element are energized is larger than the normal voltage drop of the LED. The LED failure detection apparatus according to claim 6, wherein all of the first resistance elements have different resistance values and all of the third resistance elements have different resistance values. A backlight device having a plurality of LEDs connected in series for illuminating a liquid crystal panel from behind,
A backlight device comprising the LED failure detection device according to claim 1, wherein a short failure and an open failure of each LED are distinguished and detected. A liquid crystal panel for displaying an image, a backlight device having a plurality of LEDs connected in series for illuminating the liquid crystal panel from behind, and a short circuit failure and an open failure of each LED of the backlight device are detected separately. A liquid crystal display device comprising the LED failure detection device according to any one of 1 to 7.

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