Vehicle LED Thermistor Current Control
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Solution Overview
Problem
Lighting devices for vehicles face challenges in maintaining optimal temperature and brightness of light emitting diodes (LEDs) in high temperature and high humidity environments, leading to potential overheating and reduced light output.
Innovation Solution
A light emitting device with a substrate, a light emitting element, a resistive element connected in series, and a thermistor with a positive temperature coefficient connected in parallel, where the thermistor's resistance value adjusts to control the current flowing through the LED, maintaining the junction temperature within a safe range and ensuring desired light output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a light emitting diode is used as a light source in high temperature and high humidity environment, then the lighting device can operate in extreme conditions, but the temperature of the light emitting diode may become excessively high leading to reduced light output
Solution Approach 1:
A thermistor with positive temperature coefficient is introduced as an intermediary component between the power source and the light emitting diode. This thermistor acts as a temperature-sensitive resistor that automatically adjusts the current flowing to the LED based on temperature conditions, preventing excessive temperature rise without requiring active control systems
Solution Approach 2:
The thermistor provides automatic feedback control by changing its resistance value in response to temperature changes. When the LED temperature rises, the thermistor's resistance increases, thereby reducing the current flowing through the LED and preventing further temperature increase. This creates a self-regulating system that maintains LED operation within safe temperature ranges
2Illumination intensity
If the resistance of the thermistor decreases to increase voltage to the light emitting diode for maintaining light output, then the light output is maintained, but the temperature of the light emitting diode further rises
Solution Approach 1:
The patent utilizes the temperature-dependent resistance parameter change of the thermistor to control LED operation. By selecting a thermistor with appropriate positive temperature coefficient characteristics, the system automatically adjusts current levels based on temperature, preventing the scenario where increased voltage leads to excessive temperature rise
3Reliability
If a parallel resistance circuit with thermistor is used to block current during overvoltage, then overvoltage protection is achieved, but the temperature control in high environmental temperature conditions is insufficient
Solution Approach 1:
The thermistor serves dual function as both an overvoltage protection component and a temperature control element. Its position in the circuit allows it to respond to both voltage spikes and temperature changes, providing comprehensive protection without requiring separate control systems
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 configuration effectively suppresses excessive temperature rise of the light emitting element, maintaining brightness and light flux even in high environmental temperatures, ensuring reliable operation in extreme conditions.
Implementation Method 1
a thermistor with a positive temperature coefficient, and is connected in parallel to the resistive element
Data Source
AI summary
A light emitting device for a vehicle includes a substrate; a light emitting element which is provided on the substrate; a resistive element which is provided on the substrate, and connected in series with the light emitting element; and a thermistor which is provided on the substrate. The thermistor has a positive temperature coefficient, and is connected in parallel with the resistive element.