JP4949777B2 - Light emitting diode blinking control device, lighting device, and liquid crystal display device - Google Patents

Description

  The present invention relates to a light-emitting diode blinking control device and a lighting device.

  Unlike cold cathode fluorescent lamps, light emitting diodes (hereinafter referred to as LEDs) do not use mercury, are small in size and can be driven with low power, and in recent years their light emission efficiency has been remarkably improved. The conventional LED module has been mainly used in the shape of a shell, but the surface mount type is gradually increasing, and the LED module is downsized. Until now, LEDs have often been used for display of indicators and the like. However, as efficiency has been improved, they have been developed as illumination applications and are gradually becoming popular.

  In recent years, with the rapid spread of liquid crystal televisions and mobile phones and the miniaturization of personal computers, the performance of liquid crystal display devices has been promoted, and the requirement is satisfied by using LEDs as the light source of the backlight.

On the other hand, with respect to image display technology in liquid crystal, a technology for rapidly blinking a discharge lamp as in Patent Document 1 has been proposed in order to solve the problem of moving image blur that liquid crystal has in recent years. In this technique, any one discharge lamp provided in each light emitting region is lit for a quarter vertical period after a three-fourth vertical period from the writing timing of the liquid crystal display unit, and the remaining three-fourth vertical period Is to turn off. Patent Document 2 discloses a technique in which a lamp illuminates a liquid crystal panel with light in which a pulse component emitted once per frame of a video signal and a pulse component emitted at a frequency higher than the frame frequency are mixed. Is described. It has also been proposed here to use LEDs as lamps. Since LEDs have better high-speed blinking performance than cold cathode tubes, technical development as in Patent Document 2 is expected in the future.
JP-A-11-202285 JP 2006-18200 A

  As a technique for improving the moving image performance, in addition to blinking of the light source, there is a method for controlling the brightness of the light source for each area of the screen so as to save power and improve contrast. In this method, when a bright image and a dark image are mixed in a video display on one screen, the light source directly under the bright image is lit brightly, and the light source directly under the dark image is controlled to be dark so that the contrast is improved. To improve image quality. That is, in one backlight, a bright region and a dark region are created and the liquid crystal is illuminated.

  When dimming an LED, generally there are a method of changing and controlling a current value applied to the LED, and two methods of applying a constant current by pulse driving and performing dimming control by the duty ratio. It is done. In the former case, when dimming the light, it is necessary to pass a current smaller than the rated current of the LED. However, in the low current region of the LED, the sensitivity of the current-voltage characteristic of the LED itself is high and it is difficult to perform control. For this reason, the latter method is often used in applications where the dimming range is regarded as important.

  However, when multiple LEDs are used in the same application, there is no problem in performing dimming collectively, but in order to dimm each LED independently, it is necessary to provide a mechanism for duty modulation for each LED. Therefore, there is a problem that the circuit itself becomes a large-scale one.

  On the other hand, when a backlight is formed with red, blue and green LED light sources suitable for a liquid crystal display device, it is necessary to adopt a configuration in which the light sources are arranged on the back surface of the liquid crystal panel. The method of placing a light source on the side of the screen and illuminating the liquid crystal through the light guide plate is known as the edge-light method, but in this method it is difficult to obtain the amount of light, so a large screen liquid crystal like a large TV is irradiated. Not suitable for backlighting. For this reason, as a backlight for illuminating a large liquid crystal of 20 inches or more, it is necessary to dispose the LED directly on the back surface of the liquid crystal surface. However, since the LED is a point light source, if the distance between the LED and the liquid crystal panel is too close, uneven brightness of light and darkness occurs on the display screen. In order to solve this problem, there are two methods: a method of reducing the difference between light and dark by increasing the distance between the LED light sources arranged on the liquid crystal surface and the back surface, and a method of increasing the number of LEDs and arranging them uniformly on the back surface of the liquid crystal panel. Used in combination. Generally, about 200 to 300 LEDs are required for a screen of about 32 inches.

  Furthermore, in order to take measures against moving image blur on the video screen displayed by the liquid crystal, a configuration in which the LED emits light with a pulse component as in the configuration of Patent Document 2 is necessary. Therefore, it is necessary to blink several hundreds of LEDs at high speed as described above.

  In addition, as described above, the brightness of the light source is controlled for each area of the screen, and in order to configure the backlight aiming at power saving and contrast improvement, for the LED for each block individually or divided by area, It is necessary to control the brightness. When dimming the brightness of an ordinary LED, there are a method of controlling the current flowing through the LED and a method of controlling the LED by blinking the pulse and controlling it according to the duty width of the pulse. In view of the ease of dimming control when the brightness is darkened, brightness control by changing the duty width by turning on an LED pulse is generally used. It can be used in a manner overlapping with the above-described method of turning on an LED for moving image blur.

  However, when considering a configuration in which hundreds of LEDs are blinked at high speed and the brightness is controlled in the screen area as described above in order to improve moving image blur, ON / OFF control for individual LEDs is performed. Need to do it. As a circuit for applying and not applying power to the LED, if a drive circuit corresponding to the quantity is connected to the LED for each block divided by individual LED or area, a very large and complicated circuit configuration is required. Necessary.

  An object of the present invention is to provide a light-emitting diode blinking control device and a lighting device that perform blinking control on each LED with a simplified configuration that does not require a drive circuit for each LED provided for a plurality of LEDs. It is in.

  The above object is a light emitting diode blinking control device for controlling blinking of the light emitting diode of a lighting device using a plurality of light emitting diodes as a light source, the switch for short-circuiting between the anode and the cathode of at least one of the light emitting diodes, And a light emitting diode blinking control device comprising a control circuit for controlling opening and closing of the switch. The apparatus may further include a switch for short-circuiting both ends of the series body of the plurality of light emitting diodes.

  The above object is also achieved by a plurality of light emitting diodes as a light source, a drive circuit for driving the light emitting diodes, a switch for short-circuiting between the anode and the cathode of the at least one light emitting diode, and a control for opening and closing the switch. This is achieved by a lighting device comprising a circuit. The apparatus may further include a switch for short-circuiting both ends of the series body of the plurality of light emitting diodes.

  The liquid crystal display device according to the present invention includes the illumination device and a liquid crystal panel illuminated by the illumination device and provided with a video information signal. Here, the control circuit may control opening / closing of the switch based on the video information signal so that a light / dark region of an image displayed on the liquid crystal panel corresponds to a light / dark region of light emission of the light emitting diode. it can.

  According to the present invention, it is possible to obtain a light-emitting diode blinking control device and a lighting device that perform blinking control on each LED with a simplified configuration that does not require a driving circuit for each LED provided for a plurality of LEDs. it can. When the present invention is applied to a backlight for liquid crystal display, it is possible to realize a countermeasure against moving image blurring of display video by liquid crystal and brightness control for each area of the screen. In addition, since the circuit portion for controlling the LED is simplified, the circuit board can be miniaturized, so that the effect can be increased in the miniaturization of a product housing such as a television.

  FIG. 1 is a diagram showing an embodiment of a lighting device according to the present invention. In the figure, 1, 2 and 3 are light emitting diodes (LEDs), 4 is a drive circuit for driving the LEDs, 5 is a current detection resistor for converting the current flowing through the LED into a voltage value, and 6 is a voltage value generated by the current detection resistor 5. Is a feedback path for feedback to the drive circuit, 7 is a switch for short-circuiting the LED 1, 8 is a switch for short-circuiting the LED 3, 9 is a switch for short-circuiting the LEDs 1, 2, 3 connected in series, and 10 is a switch 7 is a control signal for instructing opening / closing (open short circuit), 11 is a control signal for instructing open / short circuit of the switch 9, 12 is a control signal for instructing open / short circuit of the switch 8, and 13 is an open short circuit for the switches 7, 8, 9 Is a control circuit that outputs control signals 10 to 12 for instructing. Reference numeral 50 denotes an LED blinking control device, which includes the above-described switches 7 to 9 and the control circuit 13.

  Thus, this illuminating device includes a plurality of LEDs 1 to 3 connected in series as a light source, a drive circuit 4 for driving the LEDs 1 to 3, and switches 7 and 8 for short-circuiting the anodes and cathodes of the LEDs 1 and 3. And a switch 9 for short-circuiting both ends of the series body of LEDs 1 to 3, and a control circuit 13 for controlling opening and closing of the switches 7 to 9. The position of the switch with respect to each LED is not limited to the present embodiment, and at least one switch for short-circuiting both ends of the series body of a plurality of light-emitting diodes as appropriate according to the application target of the lighting device or the number and arrangement of the LEDs. A switch for short-circuiting between the anode and the cathode of the light emitting diode can be provided.

  The current applied by the drive circuit 4 flows to the current detection resistor 5 via the LEDs 1, 2, 3. The voltage value generated at both ends of the current detection resistor 5 is fed back to the drive circuit 4 through the feedback path 6. The drive circuit 4 supplies a stable current to the LEDs 1, 2, 3 by controlling the current applied to the LEDs 1, 2, 3 so that the voltage value fed back from the current detection resistor 5 becomes constant. As a result, a constant current flows through the LEDs 1, 2, 3, so that the light emission amount of each LED is stabilized.

  When dimming, switches 7, 8, and 9 are used. A switch 9 is used to darken all of the LEDs 1, 2 and 3. The switch 9 is connected so as to open-circuit between the anode of the LED 1 and the cathode of the LED 3. The switch 9 opens and closes by pulse driving according to the control signal 11 generated by the control circuit 13. When the switch 9 is opened, current flows through the LEDs 1, 2, and 3, so that the brightness of each LED is maintained. When the switch 9 is short-circuited, almost no current flows through the LEDs 1, 2, and 3, and current flows through the current detection resistor 5 via the switch 9, so that the LEDs 1, 2 and 3 are turned off. The drive circuit 4 continues to operate regardless of whether the switch 9 is opened or closed in order to control the current to be applied according to the voltage value generated in the current detection resistor 5.

  If the opening / closing speed of the switch 9 is operated at a frequency of 50 to 60 Hz or higher, blinking cannot be recognized by human eyes, and it is assumed that it is always lit. For this reason, it can be recognized as dimming of brightness according to the open / close duty ratio within one cycle in which the switch 9 is opened and closed.

Next, when it is desired to dimm only the LED 1, it can be realized by using the switch 7. By opening and closing the switch 7 in accordance with the control signal 10 generated by the control circuit 13, when the switch 7 is open, current flows through the LED 1, the LED 1 emits light, the switch 7 is short-circuited, and the anode and cathode of the LED 1 are short-circuited. In this case, almost no current flows through the LED 1 and the current flows through the switch 7, so that the LED 1 is turned off. Dimming according to the duty ratio of opening and closing can be obtained by pulse driving the opening and closing of the switch 7.
When it is desired to dimm only the LED 3, the dimming of the LED 3 can be achieved by opening and closing the switch 8 in accordance with the control signal 12 in the same manner as described above.

  Next, dimming control of all the LEDs 1, 2 and 3 to a darker side and only LED 1 to be darker than the other LEDs 2 and 3 can be realized by using the switch 7 and the switch 9 together. I can do it. By making the pulse frequency for opening and closing the switch 9 sufficiently higher than the pulse frequency for opening and closing the switch 7, a clearer effect can be obtained.

  2A and 2B are examples of signal waveforms of control signals given to the switches, and FIG. 2C is a diagram showing an example of the blinking state of LEDs. 2 in FIG. 2A is a signal waveform of the control signal 11, which is an ON / OFF pulse. Since the switch 9 performs an opening / closing operation in accordance with the control signal 11, the flashing of light emission / extinguishing of the LEDs 1, 2, 3 is also performed in the same cycle. Here, the control signal 10 is superimposed. 2 shows a signal waveform of the control signal 10, which is an ON / OFF pulse having a shorter cycle than the signal waveform of the control signal 11. For this reason, as shown by 16 in FIG. 2C, the LED 1 is turned on / off (flashing) by a waveform in which the signal waveform 14 and the signal waveform 15 overlap. As a result, it is possible to perform dimming control of the entire LEDs 1, 2, and 3, and to control only the LED 1 more darkly.

  FIG. 3 is a diagram showing an example of an embodiment of a liquid crystal display device provided with the illumination device according to the present invention. As shown in the figure, the present liquid crystal display device includes an LED panel 17 equipped with a plurality of LEDs 22 and an illumination device (backlight device) 41 having an LED blinking control device (not shown), an illumination device 41 and video information. A signal is given, and a liquid crystal panel 42 that displays video such as characters and images based on the video information signal, and light from the lighting device 41 provided between the lighting device 41 and the liquid crystal panel 42 are suitable for the liquid crystal panel 42. And an optical sheet 43 to be transmitted. Thereby, the light emitted by the LED 22 mounted on the LED panel 17 of the lighting device 41 is transmitted to the liquid crystal panel 42 through the optical sheet 43 and illuminates the liquid crystal panel 42, so that characters, images, and the like are displayed on the liquid crystal panel 42. The video is displayed visually.

  FIG. 4 is a diagram showing an example of the illumination device 41 used in the liquid crystal display device shown in FIG. In FIG. 4, a portion surrounded by a broken line 17 is an LED panel arranged on the back surface of the liquid crystal panel. The LED panel 17 is configured by using a plurality of LED aggregates (series bodies) indicated by broken lines 18, 19, 20, and 21. The LED aggregates 18, 19, 20, and 21 are each configured by connecting individual LEDs 22 in series. Reference numerals 27, 28, 29, and 30 denote drive circuits for driving the LED aggregates 18, 19, 20, and 21 by current control. Reference numerals 23, 24, 25, and 26 denote current detection resistors that generate a feedback voltage necessary for the drive circuits 27 to 30 to perform current control.

  31, 32, 33, 34, 35, and 36 are switches for short-circuiting the LEDs, and opening and short-circuiting of the corresponding switches are controlled by a control signal 38 indicated by an arrow surrounded by a broken line. Reference numeral 37 denotes a control circuit that outputs a control signal 38 for controlling the open / short circuit of the switches 31, 32, 33, 34, 35, and 36. Reference numeral 39 denotes a video information signal. An LED blinking control device 55 includes the above-described switches 31 to 36 and a control circuit 37.

  The LED aggregates 18, 19, 20, and 21 configured by the LEDs 22 are turned on when power is applied by the drive circuits 27, 28, 29, and 30. The current flowing through the LED aggregates 18, 19, 20, and 21 is configured to flow to the ground via the current detection resistors 23, 24, 25, and 26. The voltages across the current detection resistors 23, 24, 25, and 26 are fed back to the drive circuits 27, 28, 29, and 30, and the drive circuits 27, 28, 29, and 30 control the current so that the feedback voltage becomes constant. Thus, the light quantity of the LED 22 can be stabilized.

  The switches 31, 32, 33, 34, 35, and 36 are described as an example of the switch connected to the LED 22. However, the number of the switches and the connection position, that is, the position where the switch is arranged in which LED is appropriately determined. It is determined and may be arbitrary. In addition, the switch can be constituted by a transistor such as a MOSFET or a photocoupler, but is not limited thereto.

  Since all the LEDs need to blink in order to eliminate the blur of the moving image, as shown by the switch 31, both ends of the LED assembly (series body) 21 are connected and sent from the control circuit 36. According to the control signal 38, blinking is performed by opening and closing the switch 31. Similarly, the LED aggregates (series bodies) 18, 19, and 20 are also provided with the same switches as the LED aggregate (series bodies) 21 described above, and the LED blinking control device 55 is configured for the entire screen. The LED can blink on the screen.

  Then in order to perform the brightness control for each area of the screen, it is necessary to set whether to control the advance which areas. In this figure, as an example, a region where the LED 22 that is opened and closed by the switch 32 is arranged is shown. The control circuit 37 sends a control signal 38 to the switch 32 by the information sent to the control circuit 37 from the video information signal 39, and controls the brightness of the LEDs connected by the switch 32 by the duty for opening and closing the switch 32. Is possible. As a result, it is possible to control the brightness of the region where the LEDs that are opened and closed by the switch 32 are arranged.

  At this time, even if the switch 32 is opened and closed, when the switch 32 is short-circuited, a current equivalent to the current flowing through the LED flows, so the voltage across the current detection resistor 26 does not change. For this reason, the brightness of LEDs other than between the switches 32 in the LED assembly 21 is maintained, and the brightness of only the LEDs between the switches 32 is controlled. For example, the control circuit 37 can control opening / closing of the switch based on the video information signal 39 so that the light / dark region of the image displayed on the liquid crystal panel 42 corresponds to the light / dark region of the light emission of the LED. By doing so, the LED immediately below the bright image is controlled to be lit brightly and the LED immediately below the dark image to be darkened. Therefore, the contrast of the image displayed on the liquid crystal panel 42 is improved to improve the image quality. be able to.

When it is necessary to further subdivide the region, it is possible to narrow the region by providing switches for individual LEDs as shown by the switches 34, 35, and 36 and opening and closing them. Further, for example, the connection position of the switch 33 provided between both ends of the series body of the plurality of LEDs is partially overlapped with the connection position of the switch 32 provided between both ends of the series body of another plurality of LEDs. This makes it possible to diversify the area setting.
In addition, when performing the cancellation of the moving image blur and the brightness control for each area of the screen at the same time, by performing the opening / closing control of other switches such as the switch 32 at a frequency sufficiently faster than the opening / closing frequency of the switch 31, It can be feasible.

  Thus, in the present invention, in addition to the drive circuit for turning on the LEDs, a control circuit for controlling turning on and off of each LED is provided. Switch means for performing a short circuit is provided for each LED or for a plurality of LEDs connected in series, and this switch is controlled by the control circuit described above. Further, the driving means in the LED driving circuit is configured to control the current flowing through the LED. For this reason, even if one or more LEDs among the at least one LED connected to the drive circuit are short-circuited between the anode and the cathode by the switch means, the LEDs that are not short-circuited are not bright. There is no fluctuation. On the other hand, the LED short-circuited between the anode and the cathode is turned off because the current flowing through the LED is less than light emission because it is short-circuited by the switch means. Thereby, blinking control can be realized. In addition, since it is possible to control any short circuit depending on the connection position of the switch means, a drive circuit is not required for each LED, and a moving image blurring of a display image by liquid crystal and brightness control for each screen area are performed. Is possible.

  The present invention relates to a light-emitting diode blinking control device and a lighting device, and has industrial applicability.

It is a figure which shows one Example of the illuminating device which concerns on this invention. (A), (b) is an example of the signal waveform of the control signal given to each switch, (c) is a figure which shows the example of the blinking state of LED. It is a figure which shows an example of embodiment of the liquid crystal display device provided with the illuminating device which concerns on this invention. It is a figure which shows an example of the illuminating device used for the liquid crystal display device shown in FIG.

Explanation of symbols

1, 2, 3, 22 ... LED, 4, 27, 28, 29, 30 ... drive circuit, 5, 23, 24, 25 ... current detection resistor, 7, 8, 9, 31, 32, 33, 34, 35 , 36 ... switch, 10, 11, 12, 38 ... control signal, 13, 27, 28, 29, 30 ... drive circuit, 17 ... liquid crystal display device, 18, 19, 20, 21 ... LED assembly, 41 ... illumination Device 42 ... Liquid crystal panel 43 ... Optical sheet

Claims (6)

A light-emitting diode blinking control device for controlling blinking of the light-emitting diode of a lighting device using a plurality of light-emitting diodes as a light source, the switch for short-circuiting between an anode and a cathode of the at least one light-emitting diode, and the switch Another switch for short-circuiting both ends of a series body of a plurality of light-emitting diodes including the light-emitting diode to be short-circuited, and a control circuit that controls opening and closing of each switch for dimming the light-emitting diode , A light-emitting diode blinking control device characterized in that dimming according to the duty ratio of opening and closing can be obtained by pulse-driving the opening and closing of each switch by a control circuit . The signal waveform of the control signal output from the control circuit to the switch for short-circuiting the anode and cathode of the light-emitting diode short-circuits both ends of a series body of a plurality of light-emitting diodes including the light-emitting diode from the control circuit. 2. The light-emitting diode blinking control device according to claim 1, wherein the on / off pulse has a cycle shorter than a signal waveform of a control signal output to another switch . A plurality of light emitting diodes as light sources, a driving circuit for driving the light emitting diodes, a switch for short-circuiting between the anode and the cathode of the at least one light emitting diode, and a plurality of the light emitting diodes short-circuited by the switch Another switch for short-circuiting both ends of the series body of light emitting diodes, and a control circuit for controlling opening and closing of each switch for dimming the light emitting diode, and opening and closing of each switch by the control circuit An illuminating device characterized in that light control according to a duty ratio of opening and closing can be obtained by pulse driving . The signal waveform of the control signal output from the control circuit to the switch for short-circuiting the anode and cathode of the light-emitting diode short-circuits both ends of a series body of a plurality of light-emitting diodes including the light-emitting diode from the control circuit. 4. The lighting device according to claim 3, wherein the ON / OFF pulse has a cycle shorter than a signal waveform of a control signal output to another switch .   5. A liquid crystal display device comprising: the illumination device according to claim 3; and a liquid crystal panel illuminated by the illumination device and provided with a video information signal. The control circuit controls the opening and closing of the switch so that a light / dark region of an image displayed on the liquid crystal panel corresponds to a light / dark region of light emission of the light emitting diode based on the video information signal. The liquid crystal display device according to claim 5.

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