LED Forward Voltage Measurement for Aging Compensation
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Solution Overview
Problem
Existing methods for compensating for aging effects in LEDs during normal operation are either intrusive or ineffective, as they either disturb the operation mode or fail to accurately account for environmental influences like ambient temperature.
Innovation Solution
An electronic device with a measurement unit that applies a test current sequentially to each LED to determine its forward voltage, using a differential amplifier and ADC converter to dynamically adjust the driving algorithm and compensate for aging and environmental effects without disrupting normal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a test current is applied to determine LED forward voltage for aging compensation, then measurement precision is improved, but the operation mode may be disturbed
Solution Approach 1:
The patent applies periodic test current pulses at defined intervals (e.g., every 1000 frames or 30 seconds) rather than continuous measurement. This periodic action allows the system to obtain forward voltage measurements for aging compensation while limiting the duration and frequency of interruptions to normal display operation, thus resolving the contradiction between measurement precision and operation mode disturbance.
Solution Approach 2:
The system performs forward voltage measurements and determines aging compensation factors in advance during idle periods or between display updates. By preparing compensation data beforehand, the system ensures accurate aging compensation is ready when needed without disrupting the normal display operation mode at critical moments.
2Measurement precision
If stress pulses are applied to determine aging characteristics, then measurement precision is improved, but the LED aging is accelerated
Solution Approach 1:
The patent changes the parameters of the test current from high-amplitude stress pulses to low-amplitude measurement currents that closely resemble normal operating conditions. By adjusting the current magnitude to be within or near the normal display range, the system achieves sufficient measurement precision for aging characterization without applying the excessive stress that would accelerate LED degradation and reduce reliability.
Solution Approach 2:
The system uses multiple low-cost measurement points and statistical analysis of forward voltage variations over time to determine aging characteristics, replacing the need for expensive and aggressive stress testing. This approach accepts smaller individual measurement signals but compensates through multiple samples and analysis, achieving reliable aging data without the harmful effects of high-stress pulses.
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 allows for accurate compensation of LED performance deterioration due to aging and environmental factors, ensuring consistent performance over the LED's lifetime without accelerated aging or operational disturbance.
Implementation Method 1
a measurement unit comprising an internal current source connectable, one at a time, to each LED of the plurality of LEDs, the measurement unit being adapted for determining a separate forward voltage of each LED by imposing a test current of said internal current source to each LED
Implementation Method 2
The measuring unit may comprise a differential amplifier for measuring the forward voltage differentially
Implementation Method 3
The measurement unit may comprise a differential amplifier, a variable current source and an ADC converter, for determining a forward voltage of the LED
Implementation Method 4
an electronic device comprising one or more LEDs
Implementation Method 5
a plurality of techniques are known for compensating for aging effects. European patent application EP 2334144 describes a method of determining ageing characteristics of a LED whereby a current stress pulse is applied. The LED thereby is monitored to determine when the thermal heating induced by the current stress pulse has been dissipated
Implementation Method 6
The LED thereby is monitored to determine when the thermal heating induced by the current stress pulse has been dissipated to a desired level
Data Source
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Figure 3
AI summary
The present invention relates to an electronic device (100), the electronic device (100) comprising at least one LED (121), a driving unit (110) for applying a driving algorithm for driving the LED (121) during normal operation, and a measurement unit (130) for determining a forward voltage of the LED by imposing a test current to the LED, the measurement unit (130) being programmed for determining test current characteristics taking into account said driving algorithm.