Non-linear CCT Control for Multi-source LED Lighting
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Solution Overview
Problem
Existing LED lighting systems with multiple sources of different correlated color temperatures (CCT) face inaccuracies in CCT control due to linear relationships, leading to significant deviations during brightness adjustments, especially at higher CCT levels, as they fail to account for thermal effects and mutual interdependencies between LEDs.
Innovation Solution
A non-linear correlated color temperature control system that independently adjusts the duty cycle and amplitude of supply currents for each LED source, considering thermal effects, junction temperature, and mutual thermal interdependencies to achieve precise CCT control, using equations that account for the averaged luminous flux and CCT of individual sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If linear control methods are used to adjust brightness of multiple LED sources, then the control system is simple, but the CCT control accuracy deteriorates significantly especially at higher CCT levels
Solution Approach 1:
The patent transforms the control approach from linear to non-linear by introducing temperature-dependent parameters. The control system now accounts for junction temperature variations and their effect on LED spectral output, using non-linear relationships between drive current, temperature, and CCT to achieve accurate color temperature control across wide brightness ranges.
Solution Approach 2:
The patent implements feedback control by continuously monitoring junction temperature and using it to adjust drive currents. Temperature sensors provide real-time feedback about thermal conditions, which the control system uses to compensate for temperature-induced CCT shifts, thereby maintaining accurate color temperature control despite varying brightness levels.
2Illumination intensity
If brightness is adjusted by changing current amplitude or duty cycle in existing systems, then luminous flux control is achieved, but undesired CCT changes occur during brightness adjustment
Solution Approach 1:
The patent decouples luminous flux control from CCT control by introducing temperature as an additional control parameter. Instead of relying solely on current amplitude or duty cycle adjustments, the system now modifies drive currents based on measured junction temperatures to compensate for thermal effects, allowing independent control of brightness and color temperature.
Solution Approach 2:
The system uses temperature feedback to maintain CCT stability during brightness adjustments. By continuously monitoring junction temperature and adjusting drive currents accordingly, the system compensates for temperature-induced spectral shifts, ensuring that CCT remains stable even as luminous flux varies.
3Adaptability or versatility
If wide-range CCT control from 2000K to 5000K is implemented using multiple LED arrays, then CCT versatility is improved, but control accuracy deteriorates due to thermal interdependencies between LEDs
Solution Approach 1:
The patent accounts for thermal interdependencies by introducing temperature-coupled control parameters. The system recognizes that heat generated by one LED array affects the junction temperature and spectral output of other arrays, and compensates for these cross-thermal effects by adjusting drive currents based on measured temperature variations.
Solution Approach 2:
The system implements comprehensive temperature monitoring and feedback control to manage thermal interdependencies. By measuring junction temperatures of individual LED arrays and using this feedback to adjust their respective drive currents, the system compensates for thermal coupling effects, maintaining accurate CCT control across the wide 2000K-5000K range.
Data Source
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AI summary
A correlated colour temperature control system (1) for a LED lighting system (2) having at least two LED sources (3, 4) with different correlated colour temperatures. The LED lighting system (2) has a combined correlated colour temperature resulting from the combination of the different correlated colour temperatures of the at least two LED sources (3, 4), and a combined luminous flux resulting from the combination of the luminous fluxes of the at least two LED sources (3, 4), with each LED source being supplied with a supply current. The correlated colour temperature control system (1) comprises a controller (5) to independently control one or both of the duty cycle and amplitude of each supply current, the duty cycle or amplitude of each supply current being varied by the controller in a non-linear relationship with the duty cycle or amplitude of at least one other of the supply currents, to generate a desired combined correlated colour temperature for the LED lighting system (2) at a desired combined luminous flux for the LED lighting system (3, 4). An associated method is also provided.