Motor Vehicle LED Matrix Thermal Management via PWM Control
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Solution Overview
Problem
LED matrices with small emitting surfaces in motor vehicle lighting face overheating issues due to rapid temperature fluctuations during PWM control, risking damage to semiconductor junctions.
Innovation Solution
A lighting device with a matrix of electroluminescent semiconductor elements and a power management circuit that uses a high-frequency PWM control signal (≥300Hz) to control the state of switch elements, reducing temperature increases at the semiconductor junctions by time-shifting the power supply of elementary light sources and limiting mutual heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If PWM control is used to dim LED intensity, then light intensity gradation is achieved, but temperature fluctuations cause semiconductor junction damage
Solution Approach 1:
The patent applies periodic PWM control to alternately activate groups of LED pixels, creating duty cycles where only subsets of pixels are active at any given time. This periodic switching pattern allows active pixels to dissipate heat during inactive periods, preventing cumulative thermal damage while maintaining overall illumination through temporal multiplexing of pixel groups.
Solution Approach 2:
The LED matrix is divided into multiple groups or subsets of pixels that can be independently controlled. By segmenting the pixel array and activating different groups in alternating PWM cycles, the patent distributes the thermal load across spatial segments, ensuring that no single group experiences continuous overheating while collectively providing the desired light output.
2Temperature
If high PWM frequency is used to reduce temperature increase, then junction heating is limited, but control precision for light intensity gradation is reduced
Solution Approach 1:
The patent transitions from controlling light intensity through a single dimension (PWM duty cycle of individual pixels) to a multi-dimensional approach by introducing temporal grouping. Different pixel groups are activated in different time slots within each PWM cycle, allowing the system to achieve fine-grained intensity control through the combination of duty cycle modulation and spatial-temporal pixel selection, thereby maintaining precision while operating at higher PWM frequencies.
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
Prevents overheating of semiconductor junctions, extending the lifespan of expensive and technically challenging LED components while allowing for precise gradation of light intensity without damaging the junctions.
Implementation Method 1
A light-emitting diode, LED, is a semiconductor electronic component capable of emitting light when an electric current passes through it
Implementation Method 2
This functionality is known to be achieved by controlling an LED using a binary pulse width modulation (PWM) control signal. The operation of the LED is thus periodically alternated between a light-emitting state and an off state
Implementation Method 3
The temperature of an LED increases during the emitting phase. For LEDs with an emitting surface area of one to several square millimeters, their thermal time constant is of the order of 20 milliseconds or more. That is, during an 'emitting' phase of a PWM cycle at 200, 100 or 50 Hz, the temperature of the LED increases by less than 20°C, to cool down during the following 'off' phase
Data Source
Figure 1~2
AI summary
The invention relates to a light device for a motor vehicle, comprising a matrix light source having a matrix of elementary light sources with an electroluminescent semiconductor element. Each elementary light source has an emitting surface that is less than or equal to 0.2 mm2. The measures proposed by the invention allow such a matrix light source to be powered without any risk of damage due to overheating of the semiconductive junctions of the elementary light sources that make up the light source.