LED Series Fault Detection via Voltage Ratio Monitoring
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing circuits for detecting short circuits in LED chains are unreliable due to variations in temperature and aging effects, and are limited in detecting failures in chains with a large number of LEDs, often leading to false positives or missed detections.
Innovation Solution
A circuit with a voltage divider and evaluation unit that assesses the voltage ratio across the LED chain, using a pre-defined ratio to determine the presence of defective LEDs, and a digital potentiometer to adjust for production tolerances, allowing for more robust and accurate fault detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If voltage monitoring is used to detect short circuits in LED chains, then fault detection capability is improved, but reliability deteriorates due to temperature and aging variations causing false positives
Solution Approach 1:
The patent changes the detection parameter from absolute voltage levels to voltage ratios. By monitoring the ratio between the voltage at the intermediate node and the supply voltage, the system becomes insensitive to temperature and aging variations that affect absolute voltages, thereby improving detection reliability while maintaining fault detection capability
Solution Approach 2:
The patent introduces an intermediate evaluation that compares the actual voltage ratio against a predetermined reference ratio. This intermediary comparison mechanism filters out false positives caused by environmental variations, resolving the contradiction between detection sensitivity and reliability
2Difficulty of detecting and measuring
If voltage divider is used to monitor LED chain voltage, then fault detection is enabled, but manufacturing precision deteriorates due to tolerance variations in resistor values
Solution Approach 1:
The patent incorporates a feedback mechanism where the actual voltage ratio measured during operation is compared against a reference ratio stored in memory. This feedback approach compensates for manufacturing tolerances in the voltage divider resistors, enabling reliable fault detection without requiring high manufacturing precision
Solution Approach 2:
The reference ratio is predetermined and stored before operation begins. This preliminary action allows the system to account for manufacturing variations upfront, compensating for resistor tolerance variations during normal operation and maintaining detection accuracy
3Difficulty of detecting and measuring
If traditional fault detection methods are used in LED chains with many LEDs, then detection coverage is improved, but false alarms increase due to cumulative voltage variations
Solution Approach 1:
The patent transitions from monitoring absolute voltage drops across the entire LED chain to monitoring the ratio of voltages at different points. This parameter change eliminates the cumulative effect of voltage variations across multiple LEDs, maintaining detection coverage while reducing false alarms caused by tolerance stacking
Data Source
AI summary
A device can be used for detecting failures in an illumination device having a plurality of light emitting diodes connected in series. A first circuit node, a second circuit node, and a third circuit node interface the illumination device such that a voltage supplying the plurality of light emitting diodes is applied between the first and the second circuit node and a first fraction of the supply voltage drop is provided between the third and the second circuit node. An evaluation unit is coupled to the first circuit node, the second circuit node, and the third circuit node and configured to assess whether a voltage present at the third circuit node is within a pre-defined range of tolerance about a nominal value that is defined as a second fraction of the supply voltage present between the first and the second circuit node.