JP7401332B2 - liquid crystal display device - Google Patents

Description

The present invention relates to a liquid crystal display device.

U.S. Pat. No. 5,002,002 discloses a power converter that generates an output voltage supplied to a first LED string based on input power, and a power converter that turns on or off the first LED string based on a first duty cycle signal. a first channel switch that receives a first programmed current level signal and adjusts the current flowing through the first LED string based on the signal; generating the first programmed current level signal for the first LED string corresponding to one of a limited set; An LED driver is disclosed that includes a brightness controller that generates a first duty cycle signal for driving a first channel switch.

United States Published Patent Publication US2013/0127344

The LED driver of Patent Document 1 has a function of measuring the voltage applied to each LED and adjusting the drive voltage based on the measured voltage when the maximum displayable brightness setting is changed. Furthermore, it also has a function to adjust the duty cycle of PWM (Pulse Width Modulation) processing for controlling the value of the current flowing through the LED. When driving an LED using this driver, it is also possible to turn off the LED by zeroing out the duty cycle of the LED. However, in this case, the voltage applied to the LED cannot be measured, so the drive voltage cannot be adjusted. Conversely, if the set value of the duty cycle of each LED is always maintained above the minimum duty cycle, voltage adjustment can be performed at any time as needed. However, in this case, black floating occurs on the display screen and the display quality deteriorates.

As described above, the conventional technology has the problem of not being able to prevent black floating and adjust voltage at the same time.

An object of one embodiment of the present invention is to realize a liquid crystal display device that achieves both prevention of black floating and voltage adjustment.

In order to solve the above problems, a liquid crystal display device according to one embodiment of the present invention includes a liquid crystal display panel, a backlight having a plurality of light emitting diode elements, and a predetermined driving voltage applied to the plurality of light emitting diode elements. a power supply section for supplying a power source, and a power supply unit that has the highest applied voltage between an anode and a cathode of the light emitting diode elements when the same voltage is supplied to the plurality of light emitting diode elements among the plurality of light emitting diode elements. a measuring unit that measures a voltage across a detection resistor of the first light emitting diode element when the driving voltage is applied to the first light emitting diode element; The detection resistor of the first light emitting diode element is measured without comparing the voltage of the detection resistor with the voltage of the detection resistor measured from the other light emitting diode elements when the driving voltage is supplied. This configuration includes an adjustment section that adjusts the drive voltage supplied from the power supply section based only on the voltage of the power supply section.

According to one aspect of the present invention, it is possible to realize a liquid crystal display device that achieves both prevention of black floating and voltage adjustment.

1 is a block diagram showing the configuration of a liquid crystal display device according to Embodiment 1 of the present invention. 1 is a diagram showing the front side of a liquid crystal display panel according to Embodiment 1 of the present invention. FIG. 1 is a diagram showing the internal structure of a backlight according to Embodiment 1 of the present invention. 3 is a flowchart showing the flow of drive voltage adjustment processing executed by the liquid crystal display device according to Embodiment 1 of the present invention. 1 is a diagram showing a display area of a liquid crystal display panel according to Embodiment 1 of the present invention. FIG. It is a figure showing the composition of the backlight concerning Embodiment 2 of the present invention. FIG. 7 is a diagram showing a display area of a liquid crystal display panel according to Embodiment 2 of the present invention. FIG. 7 is a diagram showing a display area of a liquid crystal display panel according to Embodiment 3 of the present invention.

[Embodiment 1]
(Configuration of liquid crystal display device 1)
FIG. 1 is a block diagram showing the configuration of a liquid crystal display device 1 according to Embodiment 1 of the present invention. The liquid crystal display device 1 is a display device capable of displaying various images including still images and moving images, and is realized as, for example, a television device. As shown in FIG. 1, the liquid crystal display device 1 includes a liquid crystal display panel 11, a display control section 12, a backlight 21, a power supply section 31, a voltage adjustment section 32 (detection section, adjustment section), and a plurality of LEDs (Light Emission Diodes). ) A driver 33, a plurality of MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) 34, and a duty ratio setting section 35 (determination section, update section). The backlight 21 has a plurality of LEDs 22 (light emitting diode elements). The LED driver 33 includes a current control section 41 and a voltage measurement section 42 (measurement section).

FIG. 2 is a diagram showing the front side of the liquid crystal display panel 11 according to Embodiment 1 of the present invention. As shown in this figure, the liquid crystal display panel 11 has a display area 13 arranged on the front surface thereof. The display area 13 corresponds to a so-called display screen, and is an area on the liquid crystal display panel 11 where images are displayed. The display control unit 12 controls video display in the display area 13 of the liquid crystal display device 1. That is, the display control unit 12 displays a predetermined image on the display area 13 of the liquid crystal display panel 11.

FIG. 3 is a diagram showing the internal structure of the backlight 21 according to Embodiment 1 of the present invention. The backlight 21 is arranged on the back side of the liquid crystal display panel 11 and irradiates the back side of the liquid crystal display device 1 with light necessary for displaying an image. As shown in FIG. 3, the plurality of LEDs 22 are arranged in a region 23 within the backlight 21. Region 23 faces display region 13 when backlight 21 is arranged behind liquid crystal display panel 11 . The plurality of LEDs 22 are arranged in an array within the region 23. In the example of FIG. 3, the total number of LEDs 22 arranged in the area 23 is 32 in 4 rows and 8 columns. The LED 22 is a light emitting element that emits light necessary for displaying an image in the display area 13. In FIG. 1, only four LEDs 22 are illustrated for convenience.

LED 22 has an anode and a cathode. When a voltage is supplied to the LED 22, a voltage is applied between the anode and cathode of the LED 22. Among the plurality of LEDs 22, the LED 22A (first light emitting diode element) is the LED 22 with the largest applied voltage between the anode and cathode of the LED 22 when the same voltage is supplied to the plurality of LEDs 22. That is, among the plurality of LEDs 22, the LED 22A is also the one through which the smallest current flows when the same voltage is supplied to the plurality of LEDs 22. The LED 22 is an element that emits light whose intensity corresponds to the current flowing through the LED 22. In that sense, the LED 22A is the LED 22 with the lowest luminous efficiency among the plurality of LEDs 22. In FIG. 3, LED 22A is located at the lower right corner of area 23.

The power supply unit 31 uniformly supplies each LED 22 with a predetermined drive voltage for driving the plurality of LEDs 22 . As shown in FIG. 1, the anode of each LED 22 is connected to a wiring through which a driving voltage output from a power supply section 31 flows. The voltage adjustment section 32 adjusts the drive voltage supplied from the power supply section 31 to the plurality of LEDs 22 . Details of this adjustment will be described later.

A plurality of LED drivers 33 drive corresponding LEDs 22 . In this embodiment, one LED 22 is configured to drive two LEDs 22 individually. Therefore, although not shown in detail, the liquid crystal display device 1 includes 14 LED drivers 33. In FIG. 1, only two LEDs 22 corresponding to four LEDs 22 are illustrated for convenience. The LED driver 33A is an LED driver 33 for driving the LED 22A among the plurality of LED drivers 33.

The MOSFET 34 is a switching element for turning on or off the current flowing through the LED 22 when a driving voltage is supplied to the corresponding LED 22. MOSFET 34 has a gate, a source, and a drain. The gate of MOSFET 34 is connected to current control unit 41, the source of MOSFET 34 is connected to the cathode of LED 22, and the drain of MOSFET 34 is connected to voltage measurement unit 42 and grounded. Hereinafter, the MOSFET 34 connected to the current control section 41A will be referred to as MOSFET 34A.

The current control unit 41 controls the current flowing through the LED 22 when a driving voltage is supplied to the corresponding LED 22 by PWM processing. The current control unit 41 performs PWM processing by outputting a PWM signal to the MOSFET 34 corresponding to the LED 22. The PWM signal is a signal that defines a period during which the MOSFET 34 is turned on or off within one period of the PWM signal. During the off period when the PWM signal is low, MOSFET 34 is turned off, so that no current flows through LED 22. During the on period when the PWM signal is high, the MOSFET 34 is turned on, allowing current to flow through the LED 22.

The backlight 21 is a backlight having a so-called local dimming function. The current control unit 41 can control the current value flowing through the LED 22 according to the drive voltage and duty ratio by changing the duty ratio (the ratio of the on period in one cycle) of the PWM signal. That is, a current can be passed through the LED 22 according to the drive voltage and the length of the on period of the PWM signal. Thereby, since the emission intensity of each LED 22 can be changed individually, the brightness of any part of the backlight 21 can be changed individually.

The duty ratio setting unit 35 sets the duty ratio of the PWM signal output to the LED 22 individually for each LED 22 . Specifically, the duty ratio setting unit 35 sets, for each LED driver 33, each duty ratio corresponding to the two LEDs 22 driven by the LED driver 33. The current control unit 41 outputs a PWM signal having an on-period of length according to the set duty ratio to the corresponding MOSFET 34. As a result, a current whose magnitude corresponds to the set duty ratio flows through the LED 22, so that the LED 22 emits light whose intensity corresponds to the set duty ratio.

The voltage measurement unit 42 measures the current flowing through the corresponding LED 22 based on the voltage of the detection resistor. The detection resistor is a voltage detection resistor connected in series to the cathode side of the LED 22. The voltage measuring unit 42 measures the voltage (voltage drop) that occurs in the voltage detection resistor when the driving voltage is supplied to the LED 22 . The voltage measured in this way corresponds to the voltage of the detection resistor. The voltage of the detection resistor is used to adjust the drive voltage of the LED 22A, and is used to adjust the duty ratio of the PWM signal output from the current control unit 41 of the LEDs 22 other than the LED 22A. In order to improve the quality of images displayed on the liquid crystal display panel 11, the liquid crystal display device 1 needs to improve the in-plane uniformity of the light emitted from the backlight 21 as much as possible. On the other hand, since characteristics of the LEDs 22 vary during manufacture, when the same driving voltage is supplied to each LED 22, variations occur in the voltage applied between the anode and the cathode. As a result, if only the same drive voltage is supplied to each LED 22, the current flowing through each LED 22 will vary, resulting in variation in the light emission intensity of each LED 22. In order to reduce this variation, the LED driver 33 adjusts the set value of the duty ratio corresponding to the LED 22 according to the measured voltage of the detection resistor.

Hereinafter, the voltage measuring section 42 that measures the voltage of the detection resistor of the LED 22A will be referred to as a voltage measuring section 42A. The voltage measurement unit 42A adjusts the drive voltage according to the voltage of the detection resistor measured from the LED 22A. The LED driver 33 corresponding to the LED 22 other than LED 22A, which has higher luminous efficiency than the LED 22A, makes the current uniform by adjusting the duty ratio of the PWM signal to reduce excess current based on the voltage of the detection resistor of the LED 22A. Ensure sex. For example, the higher the voltage of the detection resistor measured from the corresponding LED 22 is than the voltage of the detection resistor measured from the LED 22A, the smaller the set value of the duty ratio of the LED 22 is, the smaller the current will be when averaged over time. Make it flow. Thereby, the magnitude of the current flowing through each LED 22 can be made uniform.

The liquid crystal display device 1 uses the voltage of the detection resistor measured from the LED 22A to control the drive voltage supplied to each LED 22. When changing the brightness of an image displayed on the liquid crystal display panel 11, the liquid crystal display device 1 adjusts the drive voltage based only on the voltage of the detection resistor of the LED 22A. For example, the drive voltage is adjusted when a user inputs an instruction to change brightness, or when the brightness of an image is automatically changed in response to a change in the intensity of external light. The liquid crystal display device 1 adjusts the driving voltage to a voltage according to the changed luminance and the voltage of the detection resistor of the LED 22A. Thereby, the current flowing through each LED 22 is uniformly adjusted to the intensity according to the changed luminance, so that the intensity of the light emitted from the backlight 21 can be uniformly changed.

As described above, the voltage applied to the LED 22A (ie, the voltage between the anode and the cathode) is the maximum voltage among the voltages applied to all the LEDs 22 included in the backlight 21. Therefore, by adjusting the drive voltage according to the voltage of the detection resistor of the LED 22A, it is guaranteed that a drive voltage of a strength necessary for causing a sufficiently strong current to flow through the LED 22A is supplied. The LEDs 22 other than LED 22A have higher luminous efficiency than the LED 22A, so if a drive voltage adjusted according to the voltage of the detection resistor of the LED 22A is supplied, a sufficiently strong current can flow through them like the LED 22. . Therefore, it is possible to ensure uniformity of the current flowing through each LED 22 after voltage adjustment.

(Adjustment of driving voltage)
FIG. 4 is a flowchart showing the flow of the drive voltage adjustment process executed by the liquid crystal display device 1 according to the first embodiment of the present invention. Before step S1 in FIG. 4 is executed, the video display on the liquid crystal display panel 11 is muted. That is, each LED 22 including the LED 22A is turned off, and a black image is displayed in the display area 13 of the liquid crystal display panel 11. Under this situation, the duty ratio setting unit 35 determines whether or not the occurrence of an event for which the drive voltage should be adjusted has been detected (step S1). The duty ratio setting unit 35 detects, for example, an instruction to change the display brightness input by the user to the liquid crystal display device 1 as the occurrence of an event for which the drive voltage should be adjusted. If NO in step S1, the liquid crystal display device 1 ends the process of FIG. 4 without adjusting the drive voltage.

On the other hand, if YES in step S1, the duty ratio setting unit 35 determines whether the set value of the duty ratio of the LED 22A is less than the minimum duty ratio (step S2). If YES in step S2, the duty ratio setting unit 35 updates the set value of the duty ratio of the LED 22A to the minimum duty ratio (step S3). Thereby, the voltage measurement unit 42A outputs a PWM signal having an on period according to the updated minimum duty ratio to the MOSFET 34A. As a result, a current corresponding to the minimum duty ratio flows through the LED 22A, so that the LED 22A emits light with an intensity corresponding to the minimum duty ratio.

Note that in step S3, the duty ratio setting unit 35 does not update the duty ratio settings for the other LEDs 22 other than the LED 22A. Moreover, in the case of NO in step S2, the duty ratio setting unit 35 does not change the set value of the duty ratio of the LED 22A. Therefore, the LED 22A continues to emit light at an intensity corresponding to the set duty ratio.

After the LED 22A emits light, the voltage measurement unit 42A measures the voltage of the detection resistor of the LED 22A (step S4). The voltage measurement unit 42A outputs the measured voltage of the detection resistor of the LED 22A to the voltage adjustment unit 32. The voltage adjustment unit 32 adjusts the drive voltage based only on the voltage of the detection resistor of the LED 22A, without comparing the input voltage of the detection resistor with the voltage of the detection resistor measured from other LEDs 22 other than the LED 22A. (Step S5). Thereby, the power supply unit 31 outputs the adjusted drive voltage to each LED 22. As a result, each current flowing through each LED 22 is changed to each current according to the adjusted drive voltage and the duty ratio corresponding to each LED 22. Thereby, the intensity of the light emitted from the backlight 21 can be uniformly adjusted within the irradiation surface, so the brightness of the image can be accurately changed to a new brightness.

FIG. 5 is a diagram showing the display area 13 of the liquid crystal display panel 11 according to Embodiment 1 of the present invention. In this embodiment, it is assumed that the duty ratio setting unit 35 detects the occurrence of an event for which the drive voltage should be adjusted while all the LEDs 22 arranged in the region 23 are turned off. In this case, the duty ratio setting unit 35 updates only the duty ratio setting value corresponding to the LED 22A to the minimum duty ratio. This lights up the LED 22A, making it possible to measure the voltage across the detection resistor of the LED 22A. Therefore, the voltage measuring section 42A measures the voltage of the detection resistor of the LED 22A, and notifies the voltage adjusting section 32 of the voltage. The voltage adjustment unit 32 adjusts the drive voltage based only on the notified voltage of the detection resistor. On the other hand, the duty ratio setting unit 35 maintains the duty ratios of all the LEDs 22 arranged within the region 23 at a value less than the minimum duty ratio. As a result, each LED 22 arranged within the area 23 continues to be turned off. Therefore, as shown in FIG. 8, when adjusting the drive voltage, only the lower right corner position 14 corresponding to the LED 22A in the display area 13 lights up, and black display is maintained in the entire remaining range other than the position 14.

(Main effects)
As described above, the liquid crystal display device 1 adjusts the drive voltage supplied from the power supply unit 31 to each LED 22 based only on the voltage of the detection resistor measured from the LED 22A. Thereby, the voltage can be adjusted while the LED 22 of the LED 22A remains off, so that it is possible to suppress black floating in the area 23 due to light emission from the LEDs 22 other than the LED 22A. Therefore, prevention of black floating in the region 23 and voltage adjustment can be achieved at the same time.

When the liquid crystal display device 1 detects the occurrence of an event that requires voltage adjustment, it lights up the LED 22A, so that the voltage across the detection resistor can be measured from the LED 22A. Thereby, voltage adjustment can be performed reliably. Further, since it is not necessary to light up the LEDs 22 other than the LED 22A, it is possible to prevent black floating in the area 23. Furthermore, since the LED 22 is turned on at the minimum brightness to adjust the voltage, the conspicuousness of the lighting of the LED 22A in the area 23 can be minimized. Furthermore, since the LED 22A disposed at the end of the area 23 corresponding to the display area 13 is turned on when adjusting the voltage, the conspicuousness of the lighting of the LED 22A can be suppressed.

(Modified example)
The LED 22A may be placed anywhere in the region 23 other than the lower right corner. For example, the LED 22A may be placed at any position at the end of the region 23. Alternatively, the LED 22A may be placed at a position other than the end of the region 23. Before manufacturing the backlight 21, the manufacturer of the backlight 21 specifies in advance the LED 22A with the highest voltage VF among all the LEDs 22 to be incorporated into the backlight 21. Then, when manufacturing the backlight 21, the LED 22A is placed at a desired position in the region 23. The manufacturer of the liquid crystal display device 1 stores information indicating the arrangement position of the LED 22 in the area 23 in an arbitrary storage area in the liquid crystal display device 1 . The duty ratio setting unit 35 specifies the LED 22A based on this information at the time of voltage adjustment, and updates the set value of the duty ratio corresponding to the LED 22A to the minimum duty ratio. Thereby, regardless of where the LED 22A is placed, the liquid crystal display device 1 controls the drive voltage based only on the voltage of the detection resistor measured from the LED 22A when performing voltage adjustment. Therefore, since the driving voltage can be controlled while each LED 22 other than the LED 22A is turned off, it is possible to prevent black floating and adjust the voltage at the same time.

The duty ratio setting unit 35 may set the duty ratio setting value corresponding to the LED 22A to an arbitrary duty ratio greater than or equal to the minimum duty ratio when adjusting the voltage. Even when a duty ratio larger than the minimum duty ratio is set for the LED 22, since the LED 22A naturally lights up, the drive voltage can be reliably adjusted based on the voltage of the detection resistor measured from the LED 22.

[Embodiment 2]
FIG. 6 is a diagram showing the configuration of a backlight 21 according to Embodiment 2 of the present invention. The configuration of the liquid crystal display device 1 according to this embodiment is basically the same as the configuration of the liquid crystal display device 1 shown in FIG. However, in this embodiment, the liquid crystal display device 1 includes a backlight 21 having the configuration shown in FIG. In the backlight 21 according to the present embodiment, unlike the first embodiment, the LED 22A is not arranged inside the region 23. That is, as shown in FIG. 6, the LED 22A is arranged outside the area 23.

Before manufacturing the backlight 21, the manufacturer of the backlight 21 specifies in advance the LED 22A with the highest voltage VF among all the LEDs 22 to be incorporated into the backlight 21. Then, when manufacturing the backlight 21, the LED 22A is placed outside the area 23, and all the LEDs 22 other than the LED 22A are placed inside the area 23. Even when the LED 22 is turned on, the light from the LED 22A is not irradiated onto the display area 13 of the liquid crystal display panel 11, so the user of the liquid crystal display device 1 does not visually recognize the light from the LED 22A.

FIG. 7 is a diagram showing the display area 13 of the liquid crystal display panel 11 according to the second embodiment of the present invention. In this embodiment, the duty ratio setting unit 35 always sets the minimum duty ratio to the LED 22A. Thereby, regardless of whether the liquid crystal display panel 11 is displaying an image or not, the LED 22A continues to be lit at the minimum brightness. In this embodiment, it is assumed that the duty ratio setting unit 35 detects the occurrence of an event for which the drive voltage should be adjusted while all the LEDs 22 arranged in the region 23 are turned off. At this time, since the LED 22A is lit, it is possible to measure the voltage across the detection resistor of the LED 22A. Therefore, the voltage measuring section 42A measures the voltage of the detection resistor of the LED 22A, and notifies the voltage adjusting section 32 of the voltage. The voltage adjustment unit 32 adjusts the drive voltage based only on the notified voltage of the detection resistor. On the other hand, the duty ratio setting unit 35 maintains the duty ratios of all the LEDs 22 arranged within the region 23 at a value less than the minimum duty ratio. As a result, each LED 22 arranged within the area 23 continues to be turned off, so that black display is maintained in the entire range of the display area 13, as shown in FIG.

(Main effects)
In this embodiment, since the LED 22A is always lit at the minimum brightness, the drive voltage can be reliably adjusted based on the voltage of the detection resistor measured from the LED 22A. At this time, since the LED 22A is arranged outside the region 23, the light emitted from the LED 22A is not noticeable. Furthermore, since each LED 22 arranged in the area 23 is turned off, it is also possible to prevent black floating during voltage adjustment. Therefore, in this embodiment as well, it is possible to realize a liquid crystal display device 1 that can both prevent black floating and adjust drive voltage.

(Modified example)
In this embodiment, the duty ratio setting unit 35 may always set the duty ratio of the LED 22A to be less than the minimum duty ratio, except at the timing of voltage adjustment. In this example, when the duty ratio setting unit 35 detects the occurrence of an event for which the drive voltage should be adjusted, the duty ratio setting unit 35 updates the duty ratio setting value for the LED 22A to the minimum duty ratio or more. As a result, the LED 22A lights up, making it possible to measure the voltage across the detection resistor of the LED 22A. Therefore, the voltage measuring section 42A measures the voltage of the detection resistor of the LED 22A, and notifies the voltage adjusting section 32 of the voltage. The voltage adjustment unit 32 adjusts the drive voltage based only on the notified voltage of the detection resistor. On the other hand, the duty ratio setting unit 35 maintains the duty ratios of all the LEDs 22 arranged within the region 23 at a value less than the minimum duty ratio. As a result, each LED 22 arranged within the area 23 continues to be turned off, so that black display is maintained in the entire range of the display area 13, as shown in FIG. Further, after adjusting the drive voltage, the duty ratio setting unit 35 updates the duty ratio setting value for the LED 22A to the minimum duty ratio. As a result, the LED 22A continues to be turned off until the next voltage adjustment timing.

In this example as well, as in the second embodiment, it is possible to realize a liquid crystal display device 1 that can prevent the occurrence of black floating and adjust the drive voltage at the same time. Furthermore, in this example, since the LED 22A is always turned off except at the timing of voltage adjustment, power consumption can be reduced compared to the second embodiment.

[Embodiment 3]
FIG. 8 is a diagram showing the display area 13 of the liquid crystal display panel 11 according to Embodiment 3 of the present invention. The configuration of the liquid crystal display device 1 according to this embodiment is the same as the configuration of the liquid crystal display device 1 according to the second embodiment. That is, the LED 22A with the highest applied voltage is arranged inside the region 23 of the backlight 21 (lower right corner).

In this embodiment, it is assumed that the occurrence of an event for which the drive voltage should be adjusted is detected while all the LEDs 22 are turned off. In response to this detection, as shown in FIG. 8, the display control unit 12 sets a predetermined OSD ( On Screen Display) Display image 15. The OSD image 15 is an image for displaying a menu regarding settings of the liquid crystal display device 1, for example. Since the LED 22A is arranged at the lower right corner of the area 23, the OSD image 15 is displayed in a range including the lower right corner of the display area 13. In order to display the OSD image 15, it is necessary to cause each LED 22 corresponding to the display range of the OSD image 15 to emit light. Therefore, when displaying the OSD image 15, the duty ratio setting unit 35 updates the duty ratio setting value of each LED 22 corresponding to the display range of the OSD image 15 to a value corresponding to the brightness of the displayed OSD image 15. do. As a result, a current according to the set duty ratio flows through the plurality of LEDs 22 including the LED 22A, so that these LEDs 22 are turned on.

Since the LED 22A is lit when the OSD image 15 is displayed, it is possible to measure the voltage across the detection resistor of the LED 22A. Therefore, the voltage measuring section 42A measures the voltage of the detection resistor of the LED 22A, and notifies the voltage adjusting section 32 of the voltage. The voltage adjustment unit 32 adjusts the drive voltage based only on the notified voltage of the detection resistor. On the other hand, the duty ratio setting unit 35 maintains the duty ratio of each LED 22 that does not correspond to the display range of the OSD image 15 at a value less than the minimum duty ratio. As a result, each of the remaining LEDs 22 is turned off, so that black display is maintained in the display area 13 other than the display range of the OSD image 15, as shown in FIG.

As described above, in this embodiment, in order to light up the LED 22A corresponding to the OSD image 15 by displaying the OSD image 15, it is necessary to reliably adjust the drive voltage based on the voltage of the detection resistor measured from the LED 22A. I can do it. At this time, since the OSD image 15 is displayed at a position overlapping the LED 22A, the light emitted from the LED 22A is not hidden behind the OSD image 15 and is not noticeable. Furthermore, since each LED 22 corresponding to a region other than the display range of the OSD image 15 in the area 23 is turned off, occurrence of black floating during voltage adjustment can be prevented.

In this embodiment, the LED 22A may be placed at any position other than the lower right corner inside the area 23. For example, the LED 22A may be arranged at the center, upper part, lower part, etc. of the region 23. Before manufacturing the backlight 21, the manufacturer of the backlight 21 specifies in advance the LED 22A with the highest voltage VF among all the LEDs 22 to be incorporated into the backlight 21. Then, when manufacturing the backlight 21, the LED 22A is arranged at a desired position in the region 23. The manufacturer of the liquid crystal display device 1 stores information indicating the arrangement position of the LED 22 in the area 23 in an arbitrary storage area within the liquid crystal display device 1. At the time of voltage adjustment, the display control unit 12 determines the display range of the OSD image 15 in the display area 13 based on this information, and displays the OSD image 15 in the determined display range. As a result, no matter where the LED 22A is placed within the area 23, the OSD image 15 is displayed in the display range corresponding to the LED 22A, so it is possible to adjust the drive voltage without making the LED 22A stand out. can.

(Modified example)
When adjusting the voltage, the display control unit 12 displays any information (text, image, etc.) other than the OSD image 15 in the display area 13 of the liquid crystal display panel 11, including the position opposite the area 23. Good too. Even when information other than the OSD image 15 is displayed, the LED 22A corresponding to the display range of the information is still lit. Therefore, the voltage can be adjusted while displaying black (turning off the LED 22) outside the display range of the OSD image 15 in the area 23.

〔summary〕
A liquid crystal display device according to aspect 1 of the present invention includes: a liquid crystal display panel; a backlight having a plurality of light emitting diode elements; a power supply unit supplying a predetermined drive voltage to the plurality of light emitting diode elements; Among the light emitting diode elements, when the same voltage is supplied to the plurality of light emitting diode elements, the first light emitting diode element with the highest applied voltage between the anode and the cathode of the light emitting diode element is selected. a measuring unit that measures the voltage of the detection resistor of the first light emitting diode element when is applied to the first light emitting diode element; Based only on the measured voltage of the detection resistor of the first light emitting diode element, without comparing the voltage of the detection resistor measured from the other light emitting diode elements when voltage is supplied, the power source The configuration includes an adjustment section that adjusts the drive voltage supplied from the drive section.

In the liquid crystal display device according to the second aspect of the present invention, in the first aspect, the value of the current flowing through the first light emitting diode element when the driving voltage is supplied is set to a duty ratio corresponding to the first light emitting diode element. a current control unit that controls by PWM processing based on a set value of the ratio; a detection unit that detects the occurrence of an event that should control the drive voltage; and a current control unit that detects the occurrence of an event that should control the drive voltage; and an updating unit that updates the set value to a duty ratio equal to or higher than the minimum duty ratio when it is determined that the set value is less than the minimum duty ratio. It may be a configuration in which it is provided.

In the liquid crystal display device according to a third aspect of the present invention, in the second aspect, the updating section may update the set value to the minimum duty ratio.

In the liquid crystal display device according to aspect 4 of the present invention, in any one of aspects 1 to 3, the first light emitting diode element is located at an end portion of the backlight in an area corresponding to the display area of the liquid crystal display panel. It may be arranged in a configuration where the

In the liquid crystal display device according to aspect 5 of the present invention, in any one of aspects 1 to 3, the first light emitting diode element is arranged outside an area of the backlight that corresponds to a display area of the liquid crystal display panel. It may be configured as follows.

In the liquid crystal display device according to aspect 6 of the present invention, in any one of aspects 1 to 3, the first light emitting diode element is arranged inside an area of the backlight that corresponds to a display area of the liquid crystal display panel. The display device may further include a display control unit that displays predetermined information in a range including a position facing the first light emitting diode element in the display area.

[Additional notes]
The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. are also included within the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

1 Liquid crystal display device 11 Liquid crystal display panel 12 Display control unit 13 Display area 14 Position 15 OSD image 21 Backlight 22, 22A LED
23 Area 31 Power supply section 32 Total 32 Voltage adjustment section 33, 33A LED driver 34, 34A MOSFET
35 Duty ratio setting section 41, 41A Current control section 42, 42A Voltage measurement section

Claims (6)

LCD display panel;
a backlight having a plurality of light emitting diode elements and having a local dimming function;
a power supply section that supplies a predetermined drive voltage to the plurality of light emitting diode elements;
An applied voltage applied between an anode and a cathode of the light emitting diode element when the same voltage is supplied to the plurality of light emitting diode elements among the plurality of light emitting diode elements when the driving voltage is supplied. a current control unit that controls the value of the current flowing through the first light emitting diode element with the largest value by PWM processing based on the set value of the duty ratio corresponding to the first light emitting diode element;
a detection unit that detects the occurrence of an event that should control the drive voltage , which is an instruction to change the display brightness of the liquid crystal display panel ;
a determination unit that determines whether the set value is less than a minimum duty ratio when the event is detected;
an updating unit that updates the set value to a duty ratio greater than or equal to the minimum duty ratio when it is determined that the set value is less than the minimum duty ratio;
A voltage of a detection resistor of the first light emitting diode element when the driving voltage is applied to the first light emitting diode element from the first light emitting diode element, which is driven with a duty ratio in which the set value has been updated. A measuring section to measure;
without comparing the measured voltage of the detection resistor of the first light emitting diode element with the voltage of the detection resistor measured from other light emitting diode elements other than the first light emitting diode element. and an adjustment section that adjusts the drive voltage supplied from the power supply section based only on the voltage of the detection resistor . The updating unit does not update the duty ratio setting value of the other light emitting diode element from the duty ratio setting value that was set before the event was detected. LCD display device. The first light emitting diode element is arranged inside a region of the backlight corresponding to a display region of the liquid crystal display panel,
The display device further includes a display control unit that displays OSD image information related to the instruction to change the display brightness in a range including a position facing the first light emitting diode element in the display area. The liquid crystal display device according to claim 1 or 2 . 3. The liquid crystal display device according to claim 1 , wherein the updating unit updates the set value to the minimum duty ratio. 3. The liquid crystal display device according to claim 1, wherein the first light emitting diode element is disposed at an end portion of the backlight in a region corresponding to a display region of the liquid crystal display panel. 3. The liquid crystal display device according to claim 1, wherein the first light emitting diode element is arranged outside an area of the backlight that corresponds to a display area of the liquid crystal display panel.

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