RGB LED Color Mixing
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Introduction of RGB LED color mixing control using linear dimming with Avago’s color management controller
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RGB LED Color Mixing
- 6. Evaluation Results Where subscript ‘m’ represents the measured values and subscript ‘s’, the reference set point. The du’v’ are computed and listed in Table 1.
- 7. DLP Application With The HDJD-J823 Color Controller
Notas do Editor
- Welcome to this module application of RGB LED color mixing control. We will introduce RGB LED color mixing control using linear dimming with Avago Technologies’ color management controllers, ADJD-J823 and HDJD-J822.
- Here is the list of terminologies we will use in this training module.
- PWM dimming is typically the preferred dimming method, as the wavelength does not shift during dimming. The RGB mixing application is easier to control with PWM. Linear dimming is limited in RGB LED applications due to the wavelength shift caused by changes to the LED current during linear dimming. The shift in wavelength makes precise color control difficult to achieve. However, the use of Avago’s color controller, ADJD-J823 or HDJD-J822, can provide precise color control. The LED backlight driver board is a typically application who has three similar channels. The Red channel is discussed and shown in this page. The key components involved with the linear dimming are the low pass filter and the AS1104 LED driver. The low pass filter is a simple RC filter design. The main purpose is to generate an average analog voltage, VLINR, which is proportional to the PWMR duty cycle. This analog voltage together with the RSET resistor will set the LED current. The ON input of the AS1104 LED driver is connected to the ENR output of the field sequencer block.
- The figure is the LED backlight driver board for control evaluation. A fixed voltage VP and RSET programmed the peak LED current. The PWM signal is connected to the ON input of the AS1104 LED driver. The voltage VP is set to the maximum of the VLINR, VLING and VLINB voltages. These output low pass filter voltages are obtained during linear dimming without field sequencing at 9000K white. This setting allows comparable luminance for the control PWM dimming.
- The right figure shows the graphical result of the linear dimming with field sequencing. The centre of the Blue squares represent the set point, while the centre of the Red diamonds represent the color achieved by the LED backlight screen. The lowest performance is 0.006 for Red. The software provided with the HDJD-JD04 kit is used to perform an initial calibration, and set the color points for measurement. The Yxy measurements were obtained for the various color set points and converted to Yu’v’ and du’v’ is calculated. The formula’s used are above. Where subscript ‘m’ represents the measured values and subscript ‘s’, the reference set point. The du’v’ are computed and listed in Table 1.
- The figure shows the over-simplified system block diagram of a DLP projector application. This diagram illustrates the LED light source and its color management system. The light from the Red, Green and Blue LEDs is gathered and thoroughly mixed by the mixing block. A small window opening allows a color sensor to sense the mixed light. The converted analog voltages, VLINR, VLING and VLINB, are derived from the HDJD-J823 PWM outputs: PWMR, PWMG and PWMB respectively. The HDJD-J823 will adjust these analog voltages so that a white reference light is obtained from the R, G, and B LEDs. The sequenced R, G, B light is sensed by the HDJD-S722 color sensor. The output of the color sensor is passed through a low pass filter which provides optical feedback to the HDJD-J823. The ENABLE signals, ENR, ENG and ENB from the DLP formatter memory activate one at a time. The LED light colors can be sequenced at equal times. The time spanning through one ENR, ENG and ENB is set at the RGB frame period.
- The ADJD-J823 is a CMOS mixed-signal IC with integrated RGB photosensors designed to be the optical feedback device of an RGB LED-based backlighting system. A typical system consists of an array of red, green and blue (RGB) LEDs, LED drivers and the ADJD-J823. The device samples the light output from the RGB LED array, processes the color information and adjusts the light output from the RGB LEDs until the target color is achieved. To achieve this, the device integrates an RGB photosensor array, an analog-to-digital converter front-end, a color data processing logic core and a high-resolution 12-bit PWM output generator.
- The HDJD-J822 is a CMOS mixed-signal IC designed to be the optical feedback controller of an LED-based lighting system. A typical system consists of an array of red, green and blue LEDs, LED drivers, a tri-color photosensor that samples the light output, and the HDJD-J822. The IC interfaces directly to the photosensor, processes the color information and adjusts the light output from the LEDs until the desired color is achieved. To achieve this, the IC integrates a high-accuracy 10-bit analog-to-digital converter front-end, a color data processing logic core, and a high-resolution 12-bit PWM output generator.
- Thank you for taking the time to view this presentation on the RGB LED color mixing controllers . If you would like to learn more or go on to purchase some of these devices, you can either click on the link embedded in this presentation, or simple call our sales hotline. For more technical information you can either visit the Avago site – link shown – or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility.