Short Detection Circuit for Electroluminescent Devices
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Solution Overview
Problem
Existing methods for detecting shorts in light-emitting diodes (LEDs) and organic light-emitting diodes (OLEDs) are sensitive to production tolerances and environmental temperatures, making them unreliable for identifying defects caused by contaminants during production.
Innovation Solution
The electroluminescent device employs a short detection circuit with a triggerable voltage determining unit and a triggering unit that measures the voltage drop across the light-emitting element after a time period without a driving current, utilizing the difference in discharge behavior between a pristine and defective element to detect shorts, independent of absolute voltage thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage monitoring is used to detect shorts in light-emitting elements, then short detection capability is provided, but the detection becomes sensitive to production tolerances and environmental temperature variations
Solution Approach 1:
The patent changes the detection parameter from absolute voltage level to voltage decay rate. Instead of monitoring whether voltage stays above a fixed threshold, the system measures how quickly voltage decays after current interruption. A pristine element shows slow decay due to capacitance, while a shorted element shows rapid decay. This parameter transformation eliminates sensitivity to production tolerances and temperature variations that affect absolute voltage levels.
Solution Approach 2:
The patent applies preliminary action by intentionally interrupting the driving current before measurement to create a controlled discharge scenario. The current source is switched off for a predetermined time period, allowing the capacitance to discharge naturally. This preliminary current interruption creates the conditions necessary to observe the voltage decay behavior that distinguishes pristine from shorted elements.
2Ease of operation
If absolute voltage threshold monitoring is used for short detection, then detection simplicity is maintained, but adaptability to different production bins and temperatures is reduced
Solution Approach 1:
The patent transforms the detection approach from monitoring absolute voltage (which varies with binning and temperature) to monitoring voltage decay rate (which is relatively consistent across different conditions). This parameter change maintains operational simplicity while dramatically improving adaptability to different production bins and environmental temperatures.
Solution Approach 2:
The patent implements periodic action by repeatedly interrupting the current and measuring voltage decay at regular intervals. This periodic measurement approach allows continuous monitoring of element health while maintaining simplicity in the detection methodology. The rhythmic on-off-current pattern creates consistent measurement opportunities that work across different operating conditions.
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 method allows for robust short detection that is less sensitive to production variations and environmental factors, enabling reliable identification of defects and integration with dimming technologies like PWM and AM dimming, while also providing protection against high temperatures at defect locations.
Implementation Method 1
for a prestine light-emitting element having a capacitance, the voltage across the light-emitting element drops only very slowly from its forward voltage after a connected current source is turned off, i.e., after the light-emitting element is not provided with a driving current any more. This is due to the capacitance, which is charged during normal operation of the light-emitting element and which is only very slowly discharged by leakage effects when the driving current is turned off.
Implementation Method 2
In contrast, the behaviour of the light-emitting element is very different in the case of a short occuring therein. Once the connected current source is turned off, the voltage across the light-emitting element drops very fast towards 0V, because the capacitance is rapidly discharged due to the presence of the short.
Data Source
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AI summary
The present invention relates to an electroluminescent device (20) with a light- emitting element (21) having a capacitance, a switchable current source (22) being connected to the light-emitting element for providing a driving current to the light-emitting element, and a short detection circuit (23) for detecting a short in the light-emitting element. The short detection circuit comprises a triggerable voltage determining unit (24) for determining, upon being triggered, a voltage across the light-emitting element, a triggering unit (25) for triggering the triggerable voltage determining unit to determine the voltage across the light- emitting element after a time period (At) during which the driving current is not provided to the light-emitting element, and a short detection unit (26) for detecting a short in the light- emitting element based on the determined voltage across the light-emitting element. Therewith, the detection can be less sensitive with respect to production tolerances and the like.