LEDs for general lighting are just around the corner. LEDs have many advantages in general lighting systems, such as longer life and higher efficiency. However, LED technology faces some challenges. One of the challenges is how to produce high quality white light. White LEDs consist of a blue LED and a phosphor that moves the light output to other wavelengths of the spectrum. Many white LEDs do not produce a High Color Rendering Index (CRI), which is a measure of the ability of a light source to reproduce color.
By mixing two or more colors of LED light, a higher quality white light system can be obtained. In these multicolor systems, the light output of each color source drifts with time and temperature. Light sensors and small form factor microcontrollers (MCUs) can be used to maintain a specific color and Correlated Color Temperature (CCT). In this article, we'll take a closer look at sensors, required MCU resources, and software.
There are many affordable small light sensors on the market that provide information to the MCU for processing. Typically, the sensor has some optional color filters for measuring red, green, blue or white light (no filter). The light sensor output interface can be connected to the MCU in a series of ways. The photo-voltage sensor is connected to an analog-to-digital converter (ADC) through an output voltage. The optical frequency sensor provides a variable frequency output, and the output frequency is proportional to the amount of light. The pulse outputs of these sensors can be accumulated in the MCU timer to determine the level of illumination. Optical to digital sensors typically have a serial digital interface, such as I2C. Each type of sensor interface has unique advantages and requires different MCU resources. The system block diagram shown in Figure 1 shows a variety of MCU peripherals that are useful in color-tunable LED lighting designs .
In a complete closed-loop color control system, the MCU must read the color components from the light sensor, calibrate the light sensor output, and obtain the desired color by adjusting the output of each LED driver . LEDs require a constant current driver to maintain consistent light output. This can be achieved using a variety of driver technologies, including linear and switch mode solutions. The final choice depends on factors such as efficiency requirements, input voltage range, and the number of LEDs used.
The drive output can be controlled using different methods. First, the MCU can generate an analog reference voltage through a digital-to-analog converter (DAC) or a digital potentiometer. The reference voltage allows the driver output to vary between zero and maximum current. The MCU can also provide a PWM signal that is used to modulate the output of the driver. The PWM signal can be used to enable/disable the driver itself or to control the switch that disconnects the LED from the driver output. If PWM control is used, the selected PWM frequency is high enough so that the human eye does not notice any flicker.
The designer must determine the level of control resolution required by the color control system to select the MCU with the appropriate peripherals. For a photo-voltage sensor, the measurement resolution of the ADC on the MCU is important. The optical frequency sensor requires an MCU time base that is incremented by an external clock. Optical to digital sensors require a corresponding serial communication interface peripheral.
4L Deep Fryer,Household Electric Deep Fryer,Extra Filter 4.5L Electric Deep Fryer,Timer Control Electric Deep Fryer
Shaoxing Haoda Electrical Appliance Co.,Ltd , http://www.hotplates.nl