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Patent Issued for Method of Driving Light-Emitting Diodes by Controlling Maximum Amount of Light and Backlight Assembly for Performing the Method

August 27, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Hong, Hyun-Seok (Daejeon, KR); Lee, Yo-Han (Namyangju-si, KR); Shin, Dong-Lyoul (Suwon-si, KR); Lee, Seung-Je (Seongnam-si, KR), filed on October 27, 2009, was published online on August 12, 2014.

The assignee for this patent, patent number 8803788, is Samsung Display Co., Ltd. (KR).

Reporters obtained the following quote from the background information supplied by the inventors: "Example embodiments of the present invention generally relate to a method of driving light-emitting diodes (LEDs), a backlight assembly for performing the method, and a display apparatus having the backlight assembly. More particularly, example embodiments of the present invention relate to a method of driving LEDs used in a liquid crystal display (LCD), a backlight assembly for performing the method, and a display apparatus having the backlight assembly.

"Generally, a liquid crystal display (LCD) apparatus includes an LCD panel displaying an image using light, and a backlight assembly disposed below (or behind) the LCD panel to provide light to the LCD panel.

"The typical LCD panel includes a first substrate having a plurality of thin-film transistors (TFTs) and a plurality of pixel electrodes, a second substrate having a common electrode facing the first substrate, and a liquid crystal layer interposed between the first substrate and the second substrate.

"The typical backlight assembly includes a light source unit generating light to provide light to the LCD panel. The light source unit may use rod-shaped cold cathode fluorescent lamps (CCFLs) as a light source generating light. Nowadays, however, the light source unit typically uses LEDs having low power consumption and high color reproduction as the light source. Generally, there are a red diode generating red light, a green diode generating green light, and a blue diode generating blue light in the LED. The red, green, and blue light generated from the red, green, and blue LEDs are mixed with each other to form white light. Here, color coordinates of the white light are determined according to amounts of the red, green, and blue light. To maintain the color coordinates of the white light, a display apparatus should detect the amounts of the red, green, and blue light generated from the red, green, and blue LEDs, and should feedback-control the red, green, and blue LEDs according to the detected amount of each of the red, green, and blue light.

"When the LCD apparatus is exposed to a high temperature or a high humidity environment for a long time, however, transformation of the apparatus may be generated. In other words, an amount of light which a light sensor detects earlier at an equipped position becomes different from an amount of light which the light sensor detects when the apparatus is transformed due to being maintained in a high temperature or high humidity environment for a long time. The amount of light detected when the apparatus is transformed may not be accurate compared to that detected earlier. Thus, the red, green, and blue LEDs may be feedback-controlled using detected data that is inaccurate.

"Similarly, when the red, green, and blue LEDs are feedback-controlled using the inaccurate data, the amounts of red, green, and blue light generated from the red, green, and blue LEDs may be changed, so that a reduction of luminance may be generated."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "Example embodiments of the present invention provide a method of driving light-emitting diodes (LEDs) capable of maintaining white color coordinates and preventing luminance variation. Example embodiments of the present invention also provide a backlight assembly for performing the above-mentioned method. Example embodiments of the present invention further provide a display apparatus having the above-mentioned backlight assembly.

"According to one embodiment of the present invention, there is provided a method of driving LEDs. In the method, amounts of red, green, and blue light generated from a red LED, a green LED, and a blue LED, respectively, are detected. Then, whether or not an actual light amount ratio is substantially identical to a reference light amount ratio is determined by comparing the actual light amount ratio of the red, green, and blue light with the reference light amount ratio. Then, the red, green, and blue LEDs are controlled so that the actual light amount ratio becomes substantially identical to the reference light amount ratio when the actual light amount ratio is not identical to the reference light amount ratio.

"In an example embodiment of the present invention, the reference light amount ratio may be a ratio of amounts of light of the red, green, and blue light corresponding to reference white color coordinates. Moreover, the reference light amount ratio may be a sequence of A:B:C corresponding to the red, green, and blue light, respectively, wherein 4.95.ltoreq.A.ltoreq.5.05, 7.92.ltoreq.B.ltoreq.8.08, and 2.97.ltoreq.C.ltoreq.3.03. In an example embodiment of the present invention, in determining whether or not the actual light amount ratio is substantially identical to the reference light amount ratio, analog values of the amounts of the red, green, and blue light may be converted into digital conversion values of the amounts of the red, green, and blue light, respectively. Then, whether or not the actual light amount ratio is substantially identical to the reference light amount ratio is determined by comparing the actual light amount ratio of the digital conversion values of the amounts of the red, green, and blue light with the reference light amount ratio. In an example embodiment of the present invention, the digital conversion values of the amounts of the red, green, and blue light may be between a maximum value and a digital maximum conversion value. Here, the digital maximum conversion value may be between 1000 and 1023. In an example embodiment of the present invention, when the actual light amount ratio is not identical to the reference light amount ratio, at least one of the analog values of the amounts of the red, green, and blue light may have a value greater than the maximum of the reference analog value, so that at least one of the digital conversion values of the amounts of the red, green, and blue light may have the digital maximum conversion value. In an example embodiment of the present invention, in controlling the red, green, and blue LEDs, respectively, the digital conversion value of the amounts of red, green, and blue light may be reduced to have the same ratio, so that the digital conversion values of the amounts of the red, green, and blue light may have a value less than the maximum of the digital conversion value.

"According to another embodiment of the present invention, a backlight assembly includes a light source unit and a light source controller. The light source unit includes red, green, and blue LEDs generating red, green, and blue light, respectively. The light source controller detects respective amounts of the red, green, and blue light, to compare the actual light amount ratio of the red, green, and blue light with the reference light amount ratio. The light source controller controls the red, green, and blue LEDs, respectively, so that an actual light amount ratio becomes substantially identical to a reference light amount ratio when the actual light amount ratio is not identical to the reference light amount ratio.

"In an example embodiment of the present invention, the light source controller may include a red light sensor, a green light sensor, a blue light sensor, and a controller element. The red, green, and blue light sensors may respectively detect amounts of red, green, and blue light generated from the red, green, and blue LEDs, respectively. The controller element may control the red, green, and blue LEDs, respectively, so that the actual light amount ratio becomes substantially identical to the reference light amount ratio, when the actual light amount ratio is not identical to the reference light amount ratio, by comparing the actual light amount ratio of the red, green, and blue light with the reference light amount ratio. In an example embodiment of the present invention, the light source controller may include a red sensing amplification part, a green sensing amplification part, and a blue sensing amplification part. The red sensing amplification part may amplify an analog value of the amount of red light output from the red light sensor to provide the amplified analog value to the controller element. The green sensing amplification part may amplify an analog value of the amount of green light output from the green light sensor to provide the amplified analog value to the controller element. The blue sensing amplification part may amplify an analog value of the amount of blue light output from the blue light sensor to provide the amplified analog value to the controller element. In an example embodiment of the present invention, each of the red, green, and blue sensing amplification parts may amplify the analog values of the amounts of the red, green, and blue light, respectively, to have the same ratio. In an example embodiment of the present invention, each of the red, green, and blue sensing amplification part may include an operational amplifier, a first resistor, and a second resistor. The operational amplifier may include a first input terminal connected to each of the red, green, and blue light sensors and an output terminal connected to the controller element. The first resistor may be connected between a second input terminal of the operational amplifier and a ground terminal. The second resistor may be connected between a second input terminal of the operational amplifier and the output terminal of the operational amplifier. In an example embodiment of the present invention, the controller element may convert analog values of the amounts of the red, green, and blue light respectively input from the red, green, and blue sensing amplification parts into digital conversion values. The controller element may compare the actual light amount ratio of the digital conversion values of the amounts of the red, green, and blue light with the reference light amount ratio to determine whether or not the actual light amount ratio is substantially identical to the reference light amount ratio. In an example embodiment of the present invention, the digital conversion values of the amounts of the red, green, and blue light may be between a zero value and a digital maximum conversion value. In an example embodiment of the present invention, when the actual light amount ratio is not identical to the reference light amount ratio, at least one of the analog values of the amount of the red, green, and blue light may have a value greater than the maximum of the reference analog values corresponding to the maximum of the digital conversion values, so that at least one of the digital conversion values of the amounts of the red, green, and blue light may have the digital maximum conversion value. In an example embodiment of the present invention, the controller element may control the red, green, and blue sensing amplification parts, respectively, to reduce the analog values of the amounts of the red, green, and blue light respectively output from the red, green, and blue light sensors to have the same ratio, so that the analog values become less than the maximum of the reference analog values, when at least one of the digital conversion values of the amounts of the red, green, and blue light has the digital maximum conversion value. In an example embodiment of the present invention, the backlight assembly may further include a light amount ratio memory which stores the reference light amount ratio to provide the light source controller with the stored reference light amount ratio.

"According to still another embodiment of the present invention, a display apparatus includes a display panel and a backlight assembly. The display panel displays an image using light. The backlight assembly is disposed below the display panel to generate light. The backlight assembly includes a light source unit and a light source controller. The light source unit includes red, green, and blue LEDs respectively generating red, green, and blue light. The light source controller detects the red, green, and blue light, respectively, to compare the actual light amount ratio of the red, green, and blue light. When the actual light amount ratio is not identical to the reference light amount ratio, the light source controller controls the red, green, and blue LEDs, respectively, so that the actual light amount ratio becomes substantially identical to the reference light amount ratio.

"In an example embodiment of the present invention, the backlight assembly may further include an optical member disposed between the light source unit and the display panel. The light source controller may be disposed at an edge of a lower surface of the optical member facing the light source unit.

"According to a method of driving an LED in accordance with an embodiment, a backlight assembly for performing the method, and a display apparatus having the backlight assembly, an actual ratio of red, green, and blue light generated from red, green, and blue LEDs is compared with a reference light amount ratio already stored to be maintained to be substantially identical to the reference light amount ratio, so that embodiments of the present invention may prevent luminance from decreasing or white color coordinates from being changed by warping of the LCD apparatus due to external conditions such as temperature or humidity."

For more information, see this patent: Hong, Hyun-Seok; Lee, Yo-Han; Shin, Dong-Lyoul; Lee, Seung-Je. Method of Driving Light-Emitting Diodes by Controlling Maximum Amount of Light and Backlight Assembly for Performing the Method. U.S. Patent Number 8803788, filed October 27, 2009, and published online on August 12, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8803788.PN.&OS=PN/8803788RS=PN/8803788

Keywords for this news article include: Electronics, Light-emitting Diode, Samsung Display Co. Ltd.

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Source: Electronics Newsweekly


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