LED String Failure Detection via Inductor Voltage Imbalance
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Solution Overview
Problem
Existing LED lighting systems struggle to detect failures, such as single LED shorts or disconnections, especially in automotive applications where multiple LED strings with equal total forward voltages are connected in parallel, making it difficult to measure significant voltage changes.
Innovation Solution
The system includes an LED lighting circuit with parallel LED strings connected in series with individual inductors, allowing for failure detection by measuring voltage differences between these inductors, which can detect both single LED shorts and entire string disconnections without requiring additional contacts or reference voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LED modules are monitored using traditional methods (multimeters, clamp meters, thermal cameras), then some failure modes can be detected, but the monitoring process is time-consuming, requires manual intervention, and cannot detect all failure modes (particularly intermittent failures)
Solution Approach 1:
The LED module incorporates self-diagnostic capability through integrated current sources that automatically test diode strings without external intervention. The control circuit performs built-in resistance measurements and communicates results via I2C interface, enabling the system to monitor its own health status continuously without requiring manual inspection or specialized equipment.
Solution Approach 2:
The patent replaces manual mechanical inspection methods (physical measurement with multimeters, clamp meters, thermal cameras) with an electronic automated monitoring system. The system uses integrated current sources and control circuits to electronically measure resistance values and detect failures, substituting human-operated mechanical tools with automated electronic diagnostics.
2Device complexity
If LED modules use simple resistance monitoring, then the detection system remains simple, but intermittent failures and nuanced failure modes cannot be distinguished from normal operation
Solution Approach 1:
The monitoring system is segmented into distinct functional components: multiple current sources for different test conditions, separate measurement circuits for resistance values, communication interfaces for data transmission, and control logic for coordinating operations. This modular segmentation allows the system to achieve high measurement precision through specialized subsystems while managing overall complexity through organized functional separation.
Solution Approach 2:
The system employs multiple current sources that apply different current parameters to the LED diode strings during testing. By varying the current magnitude and characteristics, the system can detect different failure modes that would be indistinguishable under single-condition operation. The control circuit measures resistance values under multiple parameter conditions to accurately distinguish failures from normal variations.
3Reliability
If comprehensive monitoring of all LED modules is implemented, then all failures can be detected, but the communication bandwidth requirements and system resource usage increase significantly
Solution Approach 1:
The I2C communication interface serves multiple functions: it transmits resistance measurement data from all LED modules, receives test commands from the controller, and coordinates operation across the entire LED array. This universal communication protocol eliminates the need for separate dedicated communication channels for each module, reducing overall bandwidth requirements while maintaining comprehensive monitoring coverage.
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 effectively detects LED failures by measuring voltage imbalances between inductors, enabling timely shutdown of affected parts of the lighting system and preventing further damage.
Implementation Method 1
A LED module includes a first current source coupled to a first string of diodes, a second current source coupled to a second string of diodes, a control circuit coupled to the current sources and the diodes, and an interface circuit coupled to the control circuit. The control circuit can cause the interface circuit to transmit a first resistance value associated with the first string of diodes and a second resistance value associated with the second string of diodes.
Data Source
Figure 1
Figure 2
Figure 3~4B
AI summary
An LED lighting system, an automotive lighting system and a method of detecting failure in an LED lighting system are described herein. An LED lighting system includes an LED lighting circuit and a failure detection circuit. The LED lighting circuit includes a first string of a first plurality of LEDs electrically coupled in series with a first inductor and a second string of a second plurality of LEDs electrically coupled in series with a second inductor. The first and second strings each have an equal total forward voltage. The failure detection circuit is configured to detect a failure in the LED lighting circuit based on detection of a voltage difference between the first inductor and the second inductor.