LED Failure Detection via Analog Max Value Detector
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Solution Overview
Problem
Diagnosing individual light emitting diodes (LEDs) in a matrix configuration is challenging due to variations in forward voltage caused by supply current, temperature, and material parameters, making it difficult to distinguish between functional and defective LEDs, especially in automotive headlight applications where high circuitry outlay is required.
Innovation Solution
A method involving a circuit apparatus that applies a constant current to LEDs via a supply terminal, using switching elements controlled by a microcontroller to set the luminous state of LEDs, and an analog maximum value detector to observe the voltage signal at the supply terminal, allowing for the detection of failed LEDs with reduced circuitry outlay by analyzing the maximum value signal without needing to know the exact time of its occurrence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the total voltage across the entire light emitting diode matrix is measured, then the circuitry outlay is reduced, but the measurement precision decreases due to small percentage changes being within the measurement accuracy range
Solution Approach 1:
The patent segments the light emitting diode matrix into individual rows or columns, each equipped with its own switching element. This allows the total voltage to be measured in segments rather than as a single large value, thereby improving measurement precision while keeping circuitry outlay low. Each segment's voltage contribution can be individually analyzed to detect failures.
Solution Approach 2:
The patent employs periodic switching of individual rows or columns of LEDs, where each segment is switched on and off in sequence. By measuring the voltage signal during these periodic intervals, the system can detect the influence of individual LED groups on the total voltage, enabling precise failure detection with minimal circuitry.
2Measurement precision
If individual light emitting diodes are diagnosed by corresponding interconnection with a diagnosis circuit, then the measurement precision is improved, but the circuitry outlay increases excessively
Solution Approach 1:
The patent makes the switching elements serve dual functions: they control the luminous state of individual LED rows or columns during normal operation and simultaneously enable diagnosis mode by allowing selective voltage measurement. This multi-functionality eliminates the need for separate diagnosis circuitry, reducing circuitry outlay while maintaining high measurement precision.
Solution Approach 2:
The existing control circuitry for switching LEDs is utilized to perform both lighting control and failure diagnosis functions. The system uses its own switching elements and voltage measurement capabilities to detect failures, rather than requiring external or dedicated diagnosis equipment, thereby minimizing additional circuitry requirements.
3Measurement precision
If fast analog-to-digital conversion is implemented to capture voltage signal changes, then the measurement precision is improved, but the device complexity and cost increase
Solution Approach 1:
By switching individual LED rows or columns periodically and measuring voltage during these intervals, the system creates distinct voltage signal patterns that can be detected with standard conversion speeds. The periodic nature of the switching allows sufficient time for analog-to-digital conversion without requiring ultra-fast converters, thus reducing device complexity while maintaining adequate measurement precision.
Data Source
AI summary
A method for detecting a failure of at least one light emitting diode in a light emitting diode arrangement to which a supply current is applied by a constant-current source via a supply terminal and in which a respective luminous state of the light emitting diodes is set individually or in groups by means of a respective switching element by respective short-circuiting is disclosed, wherein a voltage signal of a chain voltage dropped across the light emitting diodes and dependent on the respective switching state of the switching elements is tapped off by a circuit apparatus at the supply terminal. The voltage signal is fed to an analog maximum value detector of the circuit apparatus, the maximum value detector is operated for a predetermined measurement duration and a maximum value signal of the voltage signal is provided at an output of the maximum value detector after the measurement duration.