JP2013143554A - Abnormality detection device for light emitting device and abnormality detection method for light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an abnormality detection device for light emitting device and an abnormality detection method for light emitting device that can reduce misdetection of abnormality of a light emitting device.SOLUTION: Once detecting a channel of an error voltage such that a detection voltage determined by a current flowing to an LED 20 of each channel is lower than an abnormality detection voltage in a normal current state, a CPU 10 increases the current of the channel whose error voltage is detected, and forcibly decreases the duty ratio of a pulse width of the channel whose error voltage is detected to create a current increase state. With respect to the channel whose error voltage is detected, the CPU 10 disables the channel whose error voltage is detected again to be used when detecting the error voltage again in the current increase state, and puts the channel back into the normal current state when not detecting the error voltage again.

Description

  The present invention relates to an abnormality detection device for a light emitting device that detects an abnormality of a light emitting device such as a backlight, and an abnormality detection method for the light emitting device.

  Some display devices such as a liquid crystal display use a light emitting device such as a backlight. The backlight is configured using, for example, a plurality of light emitting diodes (hereinafter referred to as “LEDs”). A plurality of LEDs used for the backlight are distributed to a plurality of areas, and the open and short of the LEDs are monitored for each area. Open is an abnormality in which the resistance value of the LED becomes extremely large due to destruction of the LED and becomes almost disconnected, and short is an abnormality in which the resistance value of the LED becomes extremely small and becomes almost conductive. .

  However, when the drive current for driving the LED is small, the detection voltage is also small, so that it is difficult to detect the voltage with high accuracy. When using a voltage detection resistor to detect a voltage, increasing the resistance value of the voltage detection resistor can increase the detection voltage and increase the detection accuracy, but is consumed by the voltage detection resistor. Electric power increases and power consumption loss increases.

  In general, when a large current flows in an LED, the luminance efficiency deteriorates and the amount of heat generation increases. In addition, when a voltage corresponding to the current flowing through the voltage detection resistor is detected, a voltage fluctuation due to noise may be erroneously detected as an abnormality of the LED.

  As a prior art, there is a light emitting element driving device described in Patent Document 1. This light emitting element drive device measures the voltage between the terminals of each LED with the drive transistor driving each of the plurality of LEDs turned on, detects the abnormality of each LED based on the measured voltage between the terminals, When an error is detected, the occurrence of an LED abnormality is displayed on the external display device.

JP 2011-198913 A

  However, since the conventional technique described in Patent Document 1 also detects an abnormality of each LED based on the measured voltage between terminals, voltage fluctuation due to noise may be erroneously detected as an abnormality of the LED.

  An object of the present invention is to provide a light-emitting device abnormality detection device and a light-emitting device abnormality detection method that can reduce erroneous detection of abnormality of the light-emitting device.

The present invention includes a current control unit that controls a current flowing through the light emitting device;
A voltage detection unit for detecting a voltage between both terminals of the resistance element connected in series to the light emitting device;
When the voltage detected by the voltage detector becomes less than a predetermined abnormality detection voltage, the current flowing through the light emitting device controlled by the current control unit is increased by a predetermined current value, and the current flowing through the light emitting device is determined as a predetermined current. An abnormality detecting unit for determining that the light emitting device is abnormal when the voltage detected by the voltage detecting unit in a state where the voltage detecting unit is increased by a value is still less than a predetermined abnormality detecting voltage. An anomaly detection device.

In the present invention, the current control unit controls a current flowing in the light emitting device by a pulse width modulation method,
When the abnormality detection unit increases the current flowing through the light emitting device by a predetermined current value, the duty ratio of the pulse width modulation method controlled by the current control unit is reduced to a predetermined limit duty ratio. It is characterized by making it.

Further, the present invention is used in the light emitting device configured by connecting a plurality of light emitting diodes in series for each of a plurality of channels,
The current control unit controls the current for each channel,
The voltage detection unit detects, for each channel, a voltage between both terminals of a resistance element connected in series to the light emitting diode for each channel,
The abnormality detection unit is a channel in which the voltage detected by the voltage detection unit is less than the predetermined abnormality detection voltage when the voltage detected by the voltage detection unit in any channel is less than the predetermined abnormality detection voltage. The voltage detected by the voltage detector is still predetermined in a state where the current flowing through the channel controlled by the current controller is increased by a predetermined current value and the current flowing through the channel is increased by the predetermined current value. When the voltage is less than the abnormality detection voltage, the channel is determined to be abnormal, and the voltage detected by the voltage detection unit in a state where the current flowing through the channel is increased by a predetermined current value is equal to or higher than the predetermined abnormality detection voltage. In some cases, it is determined that the channel is not abnormal.

  In the present invention, when the abnormality detection unit determines that there is no abnormality, the abnormality detection unit determines that the abnormality is not abnormal, and causes the current flowing through the channel to return to the current value before being increased by a current value determined in advance by the current control unit. And

  According to the present invention, when the abnormality detection unit determines that there is an abnormality, the current control unit stops the current flowing through the channel determined to be abnormal.

Further, the present invention is executed by an abnormality detection device including a current control unit that controls a current flowing through the light emitting device and a voltage detection unit that detects a voltage between both terminals of a resistance element connected in series to the light emitting device. An abnormality detection method for a light emitting device,
A current increasing step for increasing the current flowing through the light emitting device controlled by the current control unit by a predetermined current value when the voltage detected by the voltage detection unit is less than the predetermined abnormality detection voltage;
An abnormality that determines that the light emitting device is abnormal when the voltage detected by the voltage detector is still less than the predetermined abnormality detection voltage with the current flowing through the light emitting device increased by a predetermined current value in the current increasing step A method for detecting an abnormality of the light emitting device.

  According to the present invention, the current control unit controls the current flowing through the light emitting device. A voltage detection part detects the voltage between the both terminals of the resistive element connected in series with a light-emitting device. The abnormality detection unit increases the current flowing through the light emitting device controlled by the current control unit by a predetermined current value when the voltage detected by the voltage detection unit is less than the predetermined abnormality detection voltage, and the light emitting device When the voltage detected by the voltage detection unit is still less than the predetermined abnormality detection voltage in a state where the current flowing in is increased by a predetermined current value, it is determined that the light emitting device is abnormal. Therefore, the abnormality detection device of the light emitting device can reduce erroneous detection of abnormality of the light emitting device.

  According to the invention, the current control unit controls the current flowing through the light emitting device by a pulse width modulation method. The abnormality detection unit is configured to set a predetermined duty ratio of a pulse width of a pulse width modulation method controlled by the current control unit when the current flowing through the light emitting device is increased by a predetermined current value. To lower. Therefore, the abnormality detection device of the light emitting device can suppress an increase in the amount of heat generated by the light emitting diode due to an increase in current.

  According to the invention, the abnormality detection device for a light emitting device is used in the light emitting device configured by connecting a plurality of light emitting diodes in series for each of a plurality of channels. The current control unit controls the current for each channel. The voltage detection unit detects a voltage between both terminals of a resistance element connected in series to the light emitting diode for each channel. When the voltage detected by the voltage detection unit in any channel is less than the predetermined abnormality detection voltage, the voltage detected by the voltage detection unit is less than the predetermined abnormality detection voltage. The voltage detected by the voltage detector is still increased in a state where the current flowing through the channel controlled by the current controller is increased by a predetermined current value and the current flowing through the channel is increased by the predetermined current value. When the voltage is less than a predetermined abnormality detection voltage, the channel is determined to be abnormal, and the voltage detected by the voltage detection unit in a state where the current flowing through the channel is increased by a predetermined current value is a predetermined abnormality detection voltage. When it is above, it is determined that the channel is not abnormal. Therefore, the abnormality detection device of the light emitting device can detect abnormality of the light emitting diode of the backlight for each channel.

  According to the present invention, when the abnormality detection unit determines that there is no abnormality, the abnormality detection unit determines that there is no abnormality and causes the current flowing through the channel to return to the current value before being increased by the current value determined by the current control unit. Therefore, the abnormality detection device for the light emitting device can prevent erroneous detection of voltage fluctuation due to noise as abnormal.

  According to the present invention, when the abnormality detection unit determines that there is an abnormality, the current control unit stops the current flowing through the channel that has been determined to be abnormal. Therefore, the abnormality detection device of the light emitting device can reduce the power consumption in the channel where the abnormality is detected to zero.

  According to the invention, the abnormality detection device including the current control unit that controls the current flowing through the light emitting device and the voltage detection unit that detects the voltage between both terminals of the resistance element connected in series to the light emitting device emits light. In executing the apparatus abnormality detection method, in the current increasing step, when the voltage detected by the voltage detection unit becomes less than a predetermined abnormality detection voltage, a current flowing through the light emitting device controlled by the current control unit is determined in advance. Increase by the current value. In the abnormality determination step, when the voltage detected by the voltage detector is still less than the predetermined abnormality detection voltage in a state where the current flowing through the light emitting device is increased by a predetermined current value in the current increasing step, the light emitting device Judged to be abnormal. Therefore, the abnormality detection method for the light emitting device can reduce erroneous detection of abnormality of the light emitting device.

It is a block diagram which shows the structure of the liquid crystal display 1 which is one Embodiment of this invention. 3 is a circuit diagram showing the configuration of an LED control device 17 for one channel. FIG. It is a figure which shows the change of the detection voltage by noise. It is a flowchart which shows the process sequence of an abnormality detection process.

  FIG. 1 is a block diagram showing a configuration of a liquid crystal display 1 according to an embodiment of the present invention. The liquid crystal display 1 includes a central processing unit (hereinafter referred to as “CPU”) 10, a read only memory (hereinafter referred to as “ROM”) 11, and a random access memory (hereinafter referred to as “RAM”). ) 12, a liquid crystal display (hereinafter referred to as “LCD”) panel 13, an LCD panel controller 14 and a backlight 15.

  The CPU 10 serving as the abnormality detection unit controls the LCD panel controller 14 and the backlight 15 by executing a program stored in the ROM 11. The ROM 11 is configured by a nonvolatile rewritable semiconductor memory such as a flash memory, for example. The ROM 11 stores a program executed by the CPU 10 and information for initial setting. The RAM 12 is constituted by a rewritable semiconductor memory such as a static random access memory (hereinafter referred to as “SRAM”). The RAM 12 stores information necessary for the CPU 10 to execute the program.

  The LCD panel 13 is constituted by a liquid crystal panel, for example. The LCD panel 13 displays the image information received from the LCD panel controller 14 as an image. The LCD panel controller 14 controls the LCD panel 13. The CPU 10 converts video input received from a device that outputs a video signal, for example, a video playback device, into image information and sends the image information to the LCD panel controller 14. The LCD panel controller 14 sends image information received from the CPU 10 to the LCD panel 13 to display it as an image.

  The backlight 15 includes a light emitting diode (hereinafter referred to as “LED”) device 16, an LED control device 17, and a power supply unit 18. The backlight 15 is provided on the back side of the LCD panel 13 and illuminates the LCD panel 13 from the back side.

  The LED device 16 is divided into a plurality of areas 19, for example, a total of 192 areas 19 composed of 12 vertically and 16 horizontally. Each area 19 includes a plurality of LEDs 20 connected in series, for example, six LEDs 20. One LED is composed of six LEDs 20 included in one area. Accordingly, 192 channels are formed in the LED device 16.

  The LED control device 17 that is a current control unit is a driver that controls the LED device 16. The LED control device 17 performs control of current flowing through each channel and brightness control by a pulse width modulation (hereinafter referred to as “PWM”) method for each channel according to an instruction from the CPU 10. The frequency of PWM is 1560 Hz, for example.

  The LED control device 17 includes a current register for instructing the target current value of the amount of electricity that the CPU 10 causes the LED control device 17 to flow to each channel. The initial value of the target current value for each channel is stored in the ROM 11, and the CPU 10 uses the initial value of the target current value stored in the ROM 11 as the current of the LED control device 17 in the initial setting process immediately after the power is turned on. Set to register. The LED control device 17 controls the current flowing through each channel so that the target current value set in the current register is obtained.

  In addition, the LED control device 17 includes an error register for notifying the CPU 10 of the channel in which the error voltage is detected. The error voltage is a voltage lower than an abnormality detection voltage described later.

  The power supply unit 18 applies a voltage to each channel. The voltage applied to each channel is a voltage based on a voltage of 37.5 V, but is variable for each channel according to an instruction from the CPU 10. Further, the power supply unit 18 can stop the voltage supply in units of channels in accordance with an instruction from the CPU 10.

  FIG. 2 is a circuit diagram showing the configuration of the LED control device 17 for one channel. The LED control device 17 includes a transistor Tr1, a transistor Tr2, a resistor Rs, a differential amplifier Amp, and a voltage detection unit 21 for each channel. The transistors Tr1 and Tr2 are P-type field effect transistors, but may be configured by N-type field effect transistors.

  The six LEDs 20, the transistors Tr1 and Tr2, and the resistor Rs are connected in series in this order between the power supply unit 18 and the ground. Specifically, the anode of the first LED 20 is connected to the power supply unit 18, and the cathode of the first LED 20 is connected to the anode of the second LED 20. The second to sixth LEDs 20 are connected to the cathode of the preceding LED 20 and the anode of the next LED 20. The cathode of the sixth LED 20 is connected to the drain of the transistor Tr1, the source of the transistor Tr1 is connected to the drain of the transistor Tr2, the source of the transistor Tr2 is connected to one end of the resistor Rs, and the other end of the resistor Rs. Is connected to ground. The resistor Rs is a resistor element.

  A PWM signal that indicates the pulse width of the duty ratio that is instructed by the CPU 10 is input to the gate of the transistor Tr1. The duty ratio is a ratio of the pulse width that is turned on in one period of the PWM signal, and is expressed as a percentage. When the PWM signal is on, that is, when it is at a high level, the transistor Tr1 becomes conductive, and when the PWM signal is off, that is, when it is low, the transistor Tr1 is disconnected. Therefore, the CPU 10 can change the time during which the LED is lit in one cycle by changing the pulse width.

  The output terminal of the differential amplifier Amp is connected to the gate of the transistor Tr2. A target current value signal indicating a target current value specified by the CPU 10 is input to the non-inverting input terminal of the differential amplifier Amp, and one end of the resistor Rs is input to the inverting input terminal of the differential amplifier Amp. . The transistor Tr2 and the differential amplifier Amp are controlled so that the current value of the current flowing through the LED 20 matches the target current value. The voltage detector 21 detects the voltage between both terminals of the resistor Rs, and notifies the CPU 10 of the detected voltage.

  FIG. 3 is a diagram illustrating changes in the detection voltage due to noise. Since the detection voltage that can be detected by the resistor Rs is larger when the current flowing through the resistor Rs is larger, the influence of noise is less. Conversely, when the current flowing through the resistor Rs is small, the detection voltage becomes small, and when affected by noise or the like, voltage fluctuation due to noise is likely to be erroneously detected as an abnormality of the LED 20.

  FIG. 3A is a diagram illustrating a change in the detection voltage due to noise in a normal current state. The normal current state is, for example, a state where a current of 56 mA is passed through the LED 20. In the normal current state, when the resistance value of the resistor Rs is 0.2Ω, the detection voltage detected by the voltage detection unit 21 is 0.2Ω × 56 mA = 11.2 mV. In the normal current state, there is a moment when the detection voltage becomes less than the abnormality detection voltage due to the noise shown in FIG. 3, and the CPU 10 can erroneously detect that the detection voltage is less than the abnormality detection voltage as an abnormality of the LED 20. There is sex. The abnormality detection voltage is 5 mV, for example.

  In the case of an abnormality in which the LED 20 is open, the detection voltage is 0 V, and the detection voltage is constantly less than the abnormality detection voltage. However, in the case of voltage fluctuation due to noise, the detection voltage returns to 11.2 mV when the influence of noise disappears.

  FIG. 3B is a diagram illustrating a change in the detection voltage due to noise in a current increasing state. The current increase state is, for example, a state where a current of 120 mA is passed through the LED 20. That is, the current increase state is a state in which the current value 56 mA in the normal current state is increased by a predetermined current value, for example, a current value 64 mA. In the current increase state, the detection voltage detected by the voltage detection unit 21 is 0.2Ω × 120 mA = 24.0 mV. In the current increase state, depending on the noise shown in FIG. 3, the detection voltage does not become less than the abnormality detection voltage, and is not easily affected by the noise.

  If the detection voltage is less than the abnormality detection voltage in the current increase state shown in FIG. 3B, it is possible that the LED 20 is open. In this case, the CPU 10 turns off the channel. When the detected voltage is equal to or higher than the abnormality detection voltage in the current increase state shown in FIG. 3B, the CPU 10 determines that there is no abnormality. That is, the CPU 10 determines that the detection voltage becomes less than the abnormality detection voltage in the normal current state due to the influence of noise, and returns the current flowing through the LED 20 to 56 mA in the normal current state.

  In other words, when the abnormal voltage is detected in the normal current state, the CPU 10 increases the current for a certain time, for example, 1 second, and performs the detection abnormality confirmation process. The abnormal voltage is an error voltage lower than the abnormality detection voltage. The detection abnormality confirmation process is a process for confirming the presence or absence of abnormality of the LED 20 based on the presence or absence of an abnormal voltage in an increased current state.

  In the detection abnormality confirmation process, the CPU 10 suppresses the amount of heat generated by the LED 20 that increases as the current increases by forcibly lowering the duty ratio to a predetermined duty ratio, for example, a duty ratio of 10%. Moreover, reducing the duty ratio to a predetermined limit duty ratio can also suppress an increase in luminance due to an increase in current.

  FIG. 4 is a flowchart showing a processing procedure of the abnormality detection processing. When the power source of the liquid crystal display 1 is turned on and becomes operable, the CPU 10 proceeds to step A1.

  In step A1, the CPU 10 performs a normal operation. Specifically, the CPU 10 outputs a target current value signal for setting the target current value of the current flowing through each channel to the current value set in the current register. The current value set in the current register is 56 mA, which is a current value in a normal current state, for example. That is, the CPU 10 sets the current flowing through each channel as the current value in the normal current state. When the LED control device 17 detects a channel whose detection voltage is less than the abnormality detection voltage during normal operation, the LED control device 17 sets an error in the error register of the channel whose detection voltage is less than the abnormality detection voltage.

  In step A2, the CPU 10 determines whether an error voltage is detected. If there is a channel for which an error is set in the error register, the CPU 10 determines that an error voltage has been detected, and proceeds to step A3. If there is no channel for which an error is set in the error register, the CPU 10 detects the error voltage. It is determined that there is not, and the process returns to Step A1. Steps A2 and A3 are current increase steps.

  In step A3, the CPU 10 increases the current of the channel that detected the error voltage. Specifically, the CPU 10 outputs a target current value signal for setting the target voltage value to 120 mA, which is the current value in the current increasing state, to the channel where the error voltage is detected.

  In step A4, the CPU 10 forcibly decreases the duty ratio of the pulse width of the channel in which the error voltage is detected. Specifically, the CPU 10 outputs a PWM signal for setting the duty ratio of the pulse width to 10% to the channel where the error voltage is detected.

  In step A5, the CPU 10 performs an error voltage detection process. In the error voltage detection process, the LED control device 17 detects whether or not the detected voltage is less than the abnormality detection voltage for the channel in which the error voltage is detected in step A2, and detects the channel whose detection voltage is less than the abnormality detection voltage. Set an error in the error register.

  In step A6, the CPU 10 determines whether an error voltage is detected. When the error voltage is detected again for the channel for which the error voltage has been detected in step A2, the CPU 10 determines that the error voltage has been detected, and proceeds to step A7. When the error voltage is not detected again for the channel for which the error voltage has been detected in step A2, the CPU 10 determines that the error voltage has not been detected, cancels the predetermined limit duty ratio, and returns to step A1. Steps A5 and A6 are abnormality determination steps.

  In step A7, the CPU 10 sets the channel in which the error voltage is detected again to be unusable, and returns to step A1. In step A7, when there is a channel that has not detected the error voltage again other than the channel that has detected the error voltage again, the predetermined duty ratio is canceled for the channel that has not detected the error voltage again, and step A1. Return to.

  To set a channel to be unusable, for example, the supply of voltage to the channel by the power supply unit 18 is stopped, the duty ratio of the channel is set to 0%, or the target current value is set to 0 mV. Can be realized. Channels set to be unusable are excluded from control targets as unusable in steps A1 to A6.

  The liquid crystal display 1 of the above-described embodiment can correctly detect the malfunction of the LED 20 without being affected by noise, and can reduce erroneous detection of abnormality of the LED 20.

  In the above-described embodiment, an abnormality that causes the LED 20 to open is detected by detecting the voltage between both terminals of the resistor Rs. However, an abnormality that causes the LED 20 to be shorted flows through the LED 20 even if the LED 20 is short-circuited. Since the current value of the current does not change, it cannot be detected in the above-described embodiment.

  An abnormality that causes the LED 20 to be short-circuited can be detected by detecting the voltage drop of the six LEDs 20 included in each channel. That is, when the voltage drop voltage caused by the six LEDs 20 becomes less than the voltage drop voltage caused by the normal six LEDs 20 and continues, it indicates that one of the LEDs 20 is short-circuited. It can be detected.

  In the above-described embodiment, the backlight 15 is described as an example of the light-emitting device, but is not limited to the backlight 15. The light emitting device may be any device that emits light, and may be an illumination device such as a light bulb or a fluorescent lamp.

  Thus, the LED control device 17 controls the current flowing through the light emitting device. The voltage detector 21 detects a voltage between both terminals of the resistor Rs connected in series to the light emitting device. Then, when the voltage detected by the voltage detection unit 21 is less than the predetermined abnormality detection voltage, the CPU 10 increases the current flowing through the light emitting device controlled by the LED control device 17 by a predetermined current value, and the light emitting device When the voltage detected by the voltage detection unit 21 is still less than the predetermined abnormality detection voltage in a state where the current flowing in is increased by a predetermined current value, it is determined that the light emitting device is abnormal. Therefore, the abnormality detection device of the light emitting device can reduce erroneous detection of abnormality of the light emitting device.

  Further, the LED control device 17 controls a current flowing through the light emitting device by a pulse width modulation method. When the current flowing through the light emitting device is increased by a predetermined current value, the CPU 10 reduces the pulse width duty ratio of the pulse width modulation method controlled by the LED control device 17 to a predetermined limit duty ratio. . Therefore, the abnormality detection device of the light emitting device can suppress an increase in the amount of heat generated by the light emitting diode due to an increase in current.

  Furthermore, the abnormality detection device of the light emitting device is used for the light emitting device configured by connecting a plurality of LEDs 20 in series for each of a plurality of channels. The LED control device 17 controls the current for each channel. The voltage detector 21 detects the voltage between both terminals of the resistor Rs connected in series to the LED 20 for each channel for each channel. Then, when the voltage detected by the voltage detection unit 21 in any channel is less than the predetermined abnormality detection voltage, the CPU 10 detects that the voltage detected by the voltage detection unit 21 is less than the predetermined abnormality detection voltage. For the channel, the voltage detected by the voltage detector 21 in a state where the current flowing through the channel controlled by the LED control device 17 is increased by a predetermined current value and the current flowing through the channel is increased by the predetermined current value. When the voltage is still below the predetermined abnormality detection voltage, the channel is determined to be abnormal, and the voltage detected by the voltage detection unit 21 in a state where the current flowing through the channel is increased by a predetermined current value is predetermined abnormality. When it is equal to or higher than the detection voltage, it is determined that the channel is not abnormal. Therefore, the abnormality detection device of the light emitting device can detect abnormality of the LED 20 of the backlight for each channel.

  Further, when it is determined that there is no abnormality, the CPU 10 determines that there is no abnormality, and causes the LED control device 17 to return the current flowing through the channel to the current value before being increased by a predetermined current value. Therefore, the abnormality detection device for the light emitting device can prevent erroneous detection of voltage fluctuation due to noise as abnormal.

  Further, when the CPU 10 determines that there is an abnormality, the LED control device 17 stops the current flowing in the channel that has been determined to be abnormal. Therefore, the abnormality detection device of the light emitting device can reduce the power consumption in the channel where the abnormality is detected to zero.

  Furthermore, the abnormality detection device including the LED control device 17 that controls the current flowing through the light emitting device and the voltage detection unit 21 that detects the voltage between both terminals of the resistor Rs connected in series to the light emitting device is an abnormality of the light emitting device. In executing the detection method, in steps A2 and A3, when the voltage detected by the voltage detection unit 21 becomes less than a predetermined abnormality detection voltage, a current flowing through the light emitting device controlled by the LED control device 17 is determined in advance. Increase by the current value. In steps A5 and A6, when the voltage detected by the voltage detection unit 21 in the state where the current flowing through the light emitting device in steps A2 and A3 is increased by a predetermined current value is still less than the predetermined abnormality detection voltage, It is determined that the light emitting device is abnormal. Therefore, the abnormality detection method for the light emitting device can reduce erroneous detection of abnormality of the light emitting device.

1 Liquid crystal display 10 CPU
11 ROM
12 RAM
13 LCD panel 14 LCD panel controller 15 Back panel 16 LED device 17 LED control device 18 Power supply unit 19 Area 20 LED

Claims (6)

A current control unit for controlling a current flowing in the light emitting device;
A voltage detection unit for detecting a voltage between both terminals of the resistance element connected in series to the light emitting device;
When the voltage detected by the voltage detector becomes less than a predetermined abnormality detection voltage, the current flowing through the light emitting device controlled by the current control unit is increased by a predetermined current value, and the current flowing through the light emitting device is determined as a predetermined current. An abnormality detecting unit for determining that the light emitting device is abnormal when the voltage detected by the voltage detecting unit in a state where the voltage detecting unit is increased by a value is still less than a predetermined abnormality detecting voltage. Anomaly detection device. The current control unit controls a current flowing through the light emitting device by a pulse width modulation method,
When the abnormality detecting unit increases the current flowing through the light emitting device by a predetermined current value, the duty ratio of the pulse width modulation method controlled by the current control unit is reduced to a predetermined limiting duty ratio. The abnormality detection device for a light-emitting device according to claim 1. Used in the light emitting device configured by connecting a plurality of light emitting diodes in series for each of a plurality of channels,
The current control unit controls the current for each channel,
The voltage detection unit detects, for each channel, a voltage between both terminals of a resistance element connected in series to the light emitting diode for each channel,
The abnormality detection unit is a channel in which the voltage detected by the voltage detection unit is less than the predetermined abnormality detection voltage when the voltage detected by the voltage detection unit in any channel is less than the predetermined abnormality detection voltage. The voltage detected by the voltage detector is still predetermined in a state where the current flowing through the channel controlled by the current controller is increased by a predetermined current value and the current flowing through the channel is increased by the predetermined current value. When the voltage is less than the abnormality detection voltage, the channel is determined to be abnormal, and the voltage detected by the voltage detection unit in a state where the current flowing through the channel is increased by a predetermined current value is equal to or higher than the predetermined abnormality detection voltage. 3. The light emitting device according to claim 1, wherein the channel is determined not to be abnormal at a certain time. Abnormality detection device.   4. The abnormality detecting unit, when determining that there is no abnormality, determines that the abnormality is not abnormal, and causes the current flowing through the channel to return to a current value before being increased by a predetermined current value by a current control unit. The abnormality detection apparatus of the light-emitting device described in 1.   5. The abnormality detection of the light emitting device according to claim 3, wherein when the abnormality detection unit determines that there is an abnormality, the current control unit stops the current flowing through the channel determined to be abnormal. apparatus. Abnormality detection of the light-emitting device executed by the abnormality detection device including a current control unit that controls a current flowing through the light-emitting device and a voltage detection unit that detects a voltage between both terminals of a resistance element connected in series to the light-emitting device A method,
A current increasing step for increasing the current flowing through the light emitting device controlled by the current control unit by a predetermined current value when the voltage detected by the voltage detection unit is less than the predetermined abnormality detection voltage;
An abnormality that determines that the light emitting device is abnormal when the voltage detected by the voltage detector is still less than the predetermined abnormality detection voltage with the current flowing through the light emitting device increased by a predetermined current value in the current increasing step A method for detecting abnormality of the light emitting device.