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The multicolor LED color of back light
by：ALLTOP
2020-12-11
1, the lead words
with the maturity of led technology, led have developed all sorts of color, also in a dramatic drop in cost. The output current is more than 300 ma LED driver circuit common inductive switch power supply and linear power supply drive way, useful also switch power supply and linear power driven joint way. Almost not to play in the linear power drive circuit and ripple, little interference on the circuit used in occasion of high electromagnetic compatibility requirements.
more mixed color color color LED backlight technology is a hotspot of current research. As early as in 2000, Japan has produced many chip type LED backlight products. Then, the company launched in many type of LED chip for high-performance LCD backlight. But the specific how to mix colors complementary, open literature now exist are few in number.
although the three colors red, green and blue leds produce a backlit wide color gamut, but red edge phenomenon exists. This paper USES white light-emitting diodes (leds) as the main light source, and then use orange light and blue light as complementary illuminant, get out of the game screen white color temperature in ( 6 500±100) K, u 'color coordinates in 0. 198±0. 01, v '0. 468±0. Standard densities within 01.
2, compensation circuit diagram
white light leds are in blue inspired $phosphor for white light, due to the LCD panel for shortwave component attenuation than the long wave components, so the white light LED light the screen after the color yellow, need both blu-ray, as well as red light.
in the case of a typical current 20 ma, room temperature orange lamp voltage is 2 v, blue lamp voltage is 3 v, white lamp voltage is 3 v.
3 kinds of lamp are 8 a string. Orange light in a typical work under the current situation of you just need to about 16 v, the linear constant current source driving circuit efficiency is less than 60%, due to the orange lamp is complementary, and therefore the largest loss of power is less than 1 w; White light and blue light of linear power efficiency more than 85%.
3 kinds of LED lights with linear constant current source driving all the way, each road set the sum current 200 ma, ensure each string of LED lights is the typical current 20 ma, as shown in figure 1. Each line of constant current source USES the same frequency PWM dimming signal independently, their frequency is fixed, SuiDiao brightness change with the different space time.
with FPGA as controller, dimming instructions according to the upper machine adjust the PWM duty cycle, so as to control the backlight brightness; Sample color sensor data, fine-tuning the orange light and blue light of the PWM duty cycle, ensure that the temperature change colour temperature is constant.
3, PWM dimming and complementary
3. 1 orange light and blue light complementary preparations before
figure 2 for the white light and the PWM dimming waveform figure of complementary color lights. Should guarantee the driver circuit to meet the following conditions:
( 1) Should be able to ensure that the LED constant current drive voltage required for the voltage output; ( 2) Drive circuit output current should have consistency on the conduction time, so that we can accomplish linear brightness adjustment; ( 3) In daytime mode, white light should gradually increases, and the complementary color of blue light and orange light should be according to the proportion of white light change gradually increased.
figure 2 white light and PWM dimming waveform figure of complementary color lights.
3. 2 in the SS - 230 flat-panel display system comprehensive analysis instrument on mix light figure 3 for SS -
230 photos of flat-panel display comprehensive analysis system. Experiment, and the white light from low light to high brightness, orange light and blue light also gradually increase in proportion, guarantee that the color temperature ( 6 500±30) K, color coordinates u '= 0. 198年,v′= 0。 468. Records from low to high brightness light brightness, white light, orange light and blue light dimming PWM waveform of the lasting period of high level data, records a total of 40 sets of data.
figure 3 SS - 230 flat-panel display comprehensive analysis system.
3. 3 data fitting
according to the record of 40 sets of data, can be concluded that under the condition of different brightness of three kinds of lamp dimming PWM high level of time. Fitting out under the three light dimmer high level time and the relationship between the brightness, as shown in figure 4.
in figure 3 three continuous curve expression is as follows: figure 3,
4 brightness and three kinds of lamp dimming series relationship.
type ( 1) L is brightness, W, O and B are white light, orange light and blue light PWM waveform high level time series, dimming cycle is 500 mu s, high level time series is ( 7FFF) 16 = ( 32, 767) Level 10.
3. Closed-loop control
4 color according to get fitting curve, the backlight and constant temperature and do the fitting curve of backlight under the condition of temperature, within the range of brightness adjustment can be standard white light source. But to ensure that the backlight LED constant temperature is impossible, as the LED temperature change, white light, orange light and blue light attenuation is not the same, color temperature drift phenomenon.
record color sensor in 200 that move light cycle, namely 100 ms, red, green and blue three color components of the output pulse number, these data as the brightness of the three color component values.
when the temperature changes, according to the color of sensors measure the red, green and blue three color brightness data, fine-tuning the orange light and blue light of the PWM waveform high level time, make the red, green and blue three color brightness ratio is constant, the temperature remains constant.
4, 'theory of
in the SS - 230 flat-panel display system on the comprehensive analysis instruments, from low to high brightness brightness changes measured 40 points, adjust PWM pulse high level of the three kinds of light time, get a standard white light source. Then USES the linear fitting brightness under different conditions are obtained by 3 kinds of lamp of PWM waveform in proportion to the duration of high level relationships, according to the relationship between the dimming can ensure that the entire brightness range back light source is the standard pigments. According to the output of red, green and blue color sensor 3 color channel data, fine-tuning the orange light and blue light of PWM high level time, maintain the red, green and blue three color channel data connection between the proportion of color temperature constant. Using the above way to get out of the screen white color temperature at ( 6 500±100) K, u 'color coordinates in 0. 198±0. 01, v '0. 468±0. Standard densities within 01.
with the maturity of led technology, led have developed all sorts of color, also in a dramatic drop in cost. The output current is more than 300 ma LED driver circuit common inductive switch power supply and linear power supply drive way, useful also switch power supply and linear power driven joint way. Almost not to play in the linear power drive circuit and ripple, little interference on the circuit used in occasion of high electromagnetic compatibility requirements.
more mixed color color color LED backlight technology is a hotspot of current research. As early as in 2000, Japan has produced many chip type LED backlight products. Then, the company launched in many type of LED chip for high-performance LCD backlight. But the specific how to mix colors complementary, open literature now exist are few in number.
although the three colors red, green and blue leds produce a backlit wide color gamut, but red edge phenomenon exists. This paper USES white light-emitting diodes (leds) as the main light source, and then use orange light and blue light as complementary illuminant, get out of the game screen white color temperature in ( 6 500±100) K, u 'color coordinates in 0. 198±0. 01, v '0. 468±0. Standard densities within 01.
2, compensation circuit diagram
white light leds are in blue inspired $phosphor for white light, due to the LCD panel for shortwave component attenuation than the long wave components, so the white light LED light the screen after the color yellow, need both blu-ray, as well as red light.
in the case of a typical current 20 ma, room temperature orange lamp voltage is 2 v, blue lamp voltage is 3 v, white lamp voltage is 3 v.
3 kinds of lamp are 8 a string. Orange light in a typical work under the current situation of you just need to about 16 v, the linear constant current source driving circuit efficiency is less than 60%, due to the orange lamp is complementary, and therefore the largest loss of power is less than 1 w; White light and blue light of linear power efficiency more than 85%.
3 kinds of LED lights with linear constant current source driving all the way, each road set the sum current 200 ma, ensure each string of LED lights is the typical current 20 ma, as shown in figure 1. Each line of constant current source USES the same frequency PWM dimming signal independently, their frequency is fixed, SuiDiao brightness change with the different space time.
with FPGA as controller, dimming instructions according to the upper machine adjust the PWM duty cycle, so as to control the backlight brightness; Sample color sensor data, fine-tuning the orange light and blue light of the PWM duty cycle, ensure that the temperature change colour temperature is constant.
3, PWM dimming and complementary
3. 1 orange light and blue light complementary preparations before
figure 2 for the white light and the PWM dimming waveform figure of complementary color lights. Should guarantee the driver circuit to meet the following conditions:
( 1) Should be able to ensure that the LED constant current drive voltage required for the voltage output; ( 2) Drive circuit output current should have consistency on the conduction time, so that we can accomplish linear brightness adjustment; ( 3) In daytime mode, white light should gradually increases, and the complementary color of blue light and orange light should be according to the proportion of white light change gradually increased.
figure 2 white light and PWM dimming waveform figure of complementary color lights.
3. 2 in the SS - 230 flat-panel display system comprehensive analysis instrument on mix light figure 3 for SS -
230 photos of flat-panel display comprehensive analysis system. Experiment, and the white light from low light to high brightness, orange light and blue light also gradually increase in proportion, guarantee that the color temperature ( 6 500±30) K, color coordinates u '= 0. 198年,v′= 0。 468. Records from low to high brightness light brightness, white light, orange light and blue light dimming PWM waveform of the lasting period of high level data, records a total of 40 sets of data.
figure 3 SS - 230 flat-panel display comprehensive analysis system.
3. 3 data fitting
according to the record of 40 sets of data, can be concluded that under the condition of different brightness of three kinds of lamp dimming PWM high level of time. Fitting out under the three light dimmer high level time and the relationship between the brightness, as shown in figure 4.
in figure 3 three continuous curve expression is as follows: figure 3,
4 brightness and three kinds of lamp dimming series relationship.
type ( 1) L is brightness, W, O and B are white light, orange light and blue light PWM waveform high level time series, dimming cycle is 500 mu s, high level time series is ( 7FFF) 16 = ( 32, 767) Level 10.
3. Closed-loop control
4 color according to get fitting curve, the backlight and constant temperature and do the fitting curve of backlight under the condition of temperature, within the range of brightness adjustment can be standard white light source. But to ensure that the backlight LED constant temperature is impossible, as the LED temperature change, white light, orange light and blue light attenuation is not the same, color temperature drift phenomenon.
record color sensor in 200 that move light cycle, namely 100 ms, red, green and blue three color components of the output pulse number, these data as the brightness of the three color component values.
when the temperature changes, according to the color of sensors measure the red, green and blue three color brightness data, fine-tuning the orange light and blue light of the PWM waveform high level time, make the red, green and blue three color brightness ratio is constant, the temperature remains constant.
4, 'theory of
in the SS - 230 flat-panel display system on the comprehensive analysis instruments, from low to high brightness brightness changes measured 40 points, adjust PWM pulse high level of the three kinds of light time, get a standard white light source. Then USES the linear fitting brightness under different conditions are obtained by 3 kinds of lamp of PWM waveform in proportion to the duration of high level relationships, according to the relationship between the dimming can ensure that the entire brightness range back light source is the standard pigments. According to the output of red, green and blue color sensor 3 color channel data, fine-tuning the orange light and blue light of PWM high level time, maintain the red, green and blue three color channel data connection between the proportion of color temperature constant. Using the above way to get out of the screen white color temperature at ( 6 500±100) K, u 'color coordinates in 0. 198±0. 01, v '0. 468±0. Standard densities within 01.
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