LED Drive Apparatus Luminance Control via Flux Feedback
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Solution Overview
Problem
Automotive LED applications, such as LED illuminated micro-display console systems and heads-up display (HUD) systems, face challenges in maintaining luminance control across an extended temperature range and achieving a wide dimming ratio suitable for varying ambient light conditions, with existing solutions relying primarily on LED current feedback mechanisms that are insufficient for high dynamic range environments.
Innovation Solution
A method for controlling luminance in a color LED array involves selectively charging and discharging an energy storage device to generate light flux, adjusting the charging rate to maintain a predetermined light flux magnitude, and adapting the light flux set-point based on the anode-to-cathode voltage drop across the LED as it ages, allowing for both continuous and discontinuous mode operations to achieve high dimming ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If LED current feedback mechanism is used for luminance control, then the control mechanism is simple, but the dimming ratio is limited and cannot achieve high dynamic range
Solution Approach 1:
The patent introduces a light flux sensor as an intermediary component that measures the actual light flux output and feeds it back to the control circuit. This mediator enables precise control of the LED array's luminance by comparing the measured light flux with the desired setpoint, allowing the system to achieve high dimming ratios (up to 1:4000) that were not possible with simple current feedback alone.
2Ease of operation
If LED current is decreased for dimming, then the control implementation is straightforward, but the luminance control precision deteriorates at low current levels
Solution Approach 1:
The patent implements a closed-loop feedback control system where the light flux sensor continuously measures the actual luminance output and the control circuit adjusts the LED current accordingly. This feedback mechanism maintains high luminance control precision across the entire dimming range, including low current levels, by compensating for non-linearities and variations in LED characteristics that would otherwise degrade precision.
3Stability of the object's composition
If continuous mode operation is used, then the luminance output is smooth, but the dimming ratio is limited compared to discontinuous mode
Solution Approach 1:
The patent implements a dynamic control system that can switch between continuous mode and discontinuous pulse mode based on the required dimming level. At higher luminance levels, continuous mode provides smooth output, while at lower luminance levels, the system transitions to discontinuous pulse mode where the LED is driven in short pulses with variable duty cycle, enabling dimming ratios up to 1:4000. The control circuit dynamically adjusts the operating mode to optimize both smoothness and dimming range.
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 luminance control across a wide dynamic range, achieving dimming ratios of up to 1:4000 in discontinuous mode and 1:32 in continuous mode, effectively addressing the limitations of existing technologies by using light flux feedback to manage current availability and bypass switching.
Implementation Method 1
discharging the energy storage device through the selected primary color LED to generate a light flux output
Data Source
AI summary
For controlling a level of luminance produced by a color light-emitting diode (LED) array, a method includes: for a predetermined flux bit-slice period, activating a color enable signal to select a primary color LED and to select a predetermined light flux magnitude set-point; selectively charging an energy storage device and discharging the energy storage device through the selected primary color LED to generate a light flux output during the flux bit-slice period; adjusting a rate of selectively charging the energy storage device to maintain a magnitude of the light flux output at the predetermined light flux magnitude set-point during the flux bit-slice period; and adjusting the predetermined light flux magnitude set-point over the life of the selected LED as the selected LED ages as a function of an anode-to-cathode voltage drop across the selected LED for a given magnitude of current flowing through the selected LED.