Autotransformer LED Driver with Color Temperature Shift
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Solution Overview
Problem
Existing illumination devices with LEDs are not easily dimmable and cannot adjust color temperature when dimming, which is a requirement for applications like bedside lamps or reading lamps where both features are desirable.
Innovation Solution
An illumination device using an autotransformer with two outputs, where one part of the LEDs is coupled to the first output and another part to the second output, allowing the ratio of output voltages to change automatically, thereby adjusting the color temperature of the light output when dimming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple ballast resistor approach is used to power LEDs from mains, then device complexity and cost are reduced, but dimming capability is lost
Solution Approach 1:
The LED illumination device is divided into multiple independent LED strings, each connected to a different output of the autotransformer. This segmentation allows independent control of each string's brightness by adjusting the autotransformer ratio, enabling dimming functionality while maintaining circuit simplicity.
Solution Approach 2:
The autotransformer ratio is made variable rather than fixed, allowing dynamic adjustment of the voltage distribution to different LED strings. This dynamic adjustment mechanism provides continuous dimming control without requiring complex electronic driver circuits.
2Illumination intensity
If dimming is implemented in LED illumination devices, then light output is reduced, but color temperature control is not automatically achieved
Solution Approach 1:
The autotransformer with multiple outputs serves multiple functions simultaneously: it provides voltage transformation for dimming control and enables color temperature adjustment by selectively adjusting the voltage ratio to different LED strings with different color temperatures. This multi-functionality resolves the contradiction between dimming and color temperature control.
Solution Approach 2:
By changing the autotransformer ratio parameter, the voltage distribution to different LED strings is altered, which simultaneously changes both the overall light output intensity and the color temperature of the combined light. This parameter change approach enables coordinated control of both illumination intensity and color temperature.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables simple and cost-effective dimming of LED illumination devices while shifting the light output to a lower color temperature, enhancing functionality for specific applications.
Implementation Method 1
an autotransformer with two outputs
Data Source
AI summary
An illumination device (1) comprises: mains input terminals (2, 3); a power source (30), having input terminals (31, 32) coupled to the mains input terminals and having three output terminals (33, 35, 34), one of said output terminals being a common output terminal (35). A first output (36) is defined by a first output terminal and said common output terminal; a second output (37) is defined by a second output terminal and said common output terminal. A first LED string (110) is connected to the first power source output in series with a first resistor (120). A second LED string (210) is connected to the second power source output in series with a second resistor (220). The power source is controllable to vary the voltage at the common output terminal within the range from the voltage at the first output terminal to the voltage at the second output terminal.