**The Principle of LED Color Temperature and Brightness Adjustment**
LED color temperature refers to the perception of light as warm or cool, which is determined by the ratio of red and blue light. Increasing the amount of red light makes the color appear warmer, while increasing blue light makes it cooler. To adjust brightness, the current flowing through the LED is changed—higher current results in brighter light, and lower current makes it dimmer. This current regulation is typically achieved using PWM (Pulse Width Modulation), a technique that controls the power delivered to the LED by varying the width of the electrical pulses. The pulse width is often controlled by adjusting the values of resistors and capacitors in the circuit. A larger RC time constant leads to a longer pulse width, resulting in higher brightness.
In a dimmable color LED ceiling lamp, there are usually two independent channels: one for warm white (around 3000K) and another for cool white (around 7000K). Each channel can be adjusted separately. By setting different brightness levels on each channel, you can control both the overall brightness and the color temperature. For example, if the warm white channel is at 10% brightness and the cool white channel is at 40%, the combined color temperature may be around 5000K, offering a balanced mix of warm and cool tones. This method allows for true dimming with adjustable color temperature, providing greater flexibility in lighting environments.
**A New Method for LED Color Temperature Adjustment**
Traditional methods of adjusting LED color temperature involve using two separate dimming power supplies to drive high and low color temperature LED arrays. The color temperature is adjusted by changing the current ratios between the two LEDs. However, this approach only allows for color temperature adjustment, not linear dimming. To address these limitations, a new method has been proposed that uses a single dimming power supply. With minimal additional components, this method enables both color temperature and brightness control without interference, reducing costs and improving system reliability. It also offers greater flexibility in lighting control and is more energy-efficient.
**Conventional Methods of LED Color Temperature Adjustment**
One common method involves using two white LED arrays—one for warm white (around 3000K) and one for cool white (around 7000K). These arrays are arranged alternately to ensure even mixing of the two colors. By adjusting the driving current ratio between the two arrays, the overall color temperature of the lamp can be controlled. This is typically done using two PWM signals, each controlling the current for a separate LED array. The brightness of each color can be adjusted independently, allowing for a wide range of color temperatures.
**Problems with the Conventional Method**
Despite its effectiveness, the conventional method has several drawbacks. One major issue is that it is difficult to achieve smooth brightness adjustment without affecting the color temperature. Most LED drivers have only one dimming pin, which limits the ability to independently control both brightness and color temperature. Additionally, using two power supplies reduces efficiency, especially at lower power levels. As shown in Figure 2, the efficiency of an AC-DC LED driver drops significantly when the input power is low. This leads to increased power loss and heat generation, which can reduce the lifespan and reliability of the system. Moreover, higher power consumption diminishes the energy-saving benefits of LEDs.
**The New Method of LED Color Temperature Adjustment**
The new method simplifies the process by using a single dimming power supply and a few additional components. This approach eliminates the need for two separate power sources, reducing hardware complexity and improving efficiency. It also ensures that brightness and color temperature adjustments do not interfere with each other, allowing for more precise and flexible lighting control. This innovation is particularly useful in applications where both dimming and color temperature adjustment are required, such as in smart lighting systems and commercial lighting environments.
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