Vehicle LED PWM Diagnostic Mode via Variable Period
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Solution Overview
Problem
Existing lighting systems with semiconductor light sources operated using pulse-width modulation (PWM) face challenges in performing comprehensive diagnostics without restricting normal functionality or causing undesirable flickering effects, especially when switching on or during high-frequency operations.
Innovation Solution
Implementing a diagnostic mode that uses a longer period duration for the PWM signal during diagnostics, maintaining the same duty cycle as normal operation, and reducing the frequency to 50 Hz, allowing for a more extensive and detailed diagnosis without significant intensity fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a PWM signal with high frequency is used during normal operation, then the lighting device operates efficiently with controlled brightness, but the diagnosis of the semiconductor light source cannot be completed within one period
Solution Approach 1:
The patent applies dynamics by making the period duration of the PWM signal variable rather than fixed. During normal operation, a first period duration is used for efficient brightness control, while during diagnosis mode, a second, longer period duration is used to accommodate complete diagnosis within one period. This dynamic adjustment resolves the contradiction between operational efficiency and diagnostic completeness.
2Productivity
If the pulse duration is increased during diagnosis to complete the diagnosis within one period, then the diagnosis can be completed, but the duty cycle changes causing a lightning-like effect
Solution Approach 1:
The patent changes the period duration parameter during diagnosis mode while keeping the duty cycle constant. This allows the pulse duration to effectively increase (since pulse duration = duty cycle × period duration) without changing the duty cycle itself, thus completing the diagnosis within one period while avoiding the lightning-like effect that would result from duty cycle changes.
3Illumination intensity
If the duty cycle is increased during diagnosis to ensure visible light emission, then the semiconductor light source emits sufficient light for diagnosis, but the average power increases causing overheating
Solution Approach 1:
The patent uses periodic action by extending the period duration during diagnosis mode while maintaining the original duty cycle. This ensures the semiconductor light source emits visible light during the pulse phase for adequate diagnosis, while the extended off-phase within the longer period allows sufficient cooling, thus preventing overheating while maintaining visible light emission.
Data Source
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AI summary
The present invention relates to a method for operating a lighting device (10) of a motor vehicle. The lighting device (10) comprises at least one semiconductor light source (18), in particular a light-emitting diode, which is operated by means of a pulse-width modulated signal (I) with a predefinable duty cycle (d) between pulse duration (TE) and period duration (T). The semiconductor light source (18) undergoes a diagnostic procedure at predefinable times, wherein the semiconductor light source (18) is supplied with a pulse (TE0) of the pulse-width modulated signal (I) for the entire duration of the diagnostic procedure. During the diagnostic procedure, the semiconductor light source (18) is operated in a diagnostic mode (32) that differs from the normal operation (34) of the semiconductor light source (18), wherein during the diagnostic mode (32) the period duration (T0) of the pulse-width modulated signal (I) is selected to be greater than the period duration (T) during the normal operation (34).