LED Color Temperature Control via Multi-Path Current Steering
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Solution Overview
Problem
Existing methods for controlling the color and color temperature of light emitted by LEDs suffer from significant power losses and require large components, making them inefficient and difficult to miniaturize, especially when dealing with multiple LED paths and temperature-sensitive phosphor-coated LEDs.
Innovation Solution
A system with multiple selectable paths for drive current flow, using primary and secondary light-emitting elements and control means to direct current, allowing for efficient color and color temperature control without substantial power losses, achieved through a series-parallel circuit configuration with transistors and smoothing mechanisms to minimize flicker and component size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If DC-to-DC converter with fly-back configuration is used to control LED current, then colour temperature control is achieved, but the number of parts per LED increases significantly
Solution Approach 1:
The patent combines multiple LED strings of different colors (red, green, blue) into a single parallel circuit configuration, sharing common current control circuitry. This merging approach allows color temperature control without requiring separate DC-to-DC converters for each LED string, thereby reducing the number of parts per LED while maintaining adaptability for CCT control.
Solution Approach 2:
The current control circuit is designed to universally control multiple LED strings with different forward voltage characteristics through a single control path. The circuit can adjust current distribution across red, green, and blue LED strings simultaneously, providing multi-functional color temperature control without requiring dedicated control circuits for each LED type.
2Adaptability or versatility
If high side switches are used as current limiting devices in multiple LED paths, then colour control is enabled, but power losses increase significantly
Solution Approach 1:
The patent replaces the traditional mechanical switching approach (high side switches acting as variable resistors) with a more efficient electronic current control mechanism. By using controlled current sources and PWM dimming techniques, the system achieves color control without the significant power losses associated with resistive switching, thereby reducing energy loss while maintaining color control capability.
3Adaptability or versatility
If shunting techniques are used to provide variable current flow through LEDs, then colour adjustment is possible, but large inductors are required which increase device size
Solution Approach 1:
The patent extracts the inductance function from the current control circuit by implementing current regulation through alternative means such as controlled current sources and PWM dimming. This eliminates the need for large inductors that would be required for shunting techniques, thereby reducing device volume while maintaining color adjustment capability through electronic control methods.
4Illumination intensity
If LEDs are driven at rated power to compensate for luminous flux decrease with temperature, then light output is maintained, but heat generation increases causing avalanche effect and permanent damage
Solution Approach 1:
The patent implements temperature feedback control mechanisms that monitor LED junction temperature and adjust drive current accordingly. By reducing current when temperature increases, the system maintains luminous flux within acceptable ranges while preventing excessive heat generation that would cause avalanche effects and permanent LED damage, thereby improving reliability.
Solution Approach 2:
The system uses PWM dimming techniques that periodically switch the LED on and off at high frequencies, effectively controlling average power delivery. This periodic action allows the LED to cool during off-periods while maintaining adequate luminous output during on-periods, preventing thermal accumulation and associated damage while maintaining illumination intensity.
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
This approach enables precise control of color temperature and color with minimal power loss and reduced component count, enhancing efficiency and allowing for miniaturization while maintaining low system costs and reducing the risk of overheating and damage to LEDs.
Implementation Method 1
an array of light-emitting elements such as light-emitting diodes (LEDs)
Implementation Method 2
semiconductor and organic light-emitting diodes (LEDs and OLEDs) have made these solid-state devices suitable for use in general illumination applications
Implementation Method 3
light sources that use a phosphor coating to produce visible light are typically very sensitive to changes in their junction temperature
Implementation Method 4
the excitation spectra of phosphors is typically configured such that the peak excitation wavelengths do not coincide with the center wavelength emitted by the LED
Implementation Method 5
a plurality of control means, wherein one or more control means is operatively positioned between the power source and each of the primary path and the one or more secondary paths, the control means for directing the current through one or more of the primary path and the one or more secondary paths
Data Source
AI summary
The present invention provides a method and apparatus for controlling the correlated colour temperature (CCT) or colour of light produced by an array of light-emitting elements by providing multiple selectable paths for the flow of drive current. The apparatus includes a primary path comprising primary light-emitting elements, and one or more secondary paths comprising secondary light-emitting elements that are used for compensation or correction of the colour of light emitted by the primary light-emitting elements. A plurality of control means, for example switches are used to direct current through particular paths. During operation, the drive current primarily flows through the primary light-emitting elements and is redirected, periodically for example, to a secondary path comprising light-emitting elements of a particular colour that is desired in addition to the colour produced by the primary light-emitting elements.