Automotive LED Lighting Circuit Temperature Compensation
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Solution Overview
Problem
Conventional automotive LED light sources face challenges in maintaining the required luminous flux over time due to temperature dependence, struggling to meet UN standards for lumen maintenance rate, especially as the temperature of the semiconductor light source increases.
Innovation Solution
A lighting circuit with a temperature-sensing element and a constant current driver that adjusts the driving current in a manner that reduces the temperature differential in the initial start period and subsequent stable period, ensuring improved luminous flux stability by suppressing the correction amount at the start time and increasing it in the stable period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If constant current control is used to stabilize the driving current to a target amount, then the luminance can be controlled according to the driving current, but the lumen maintenance rate becomes less than 80% in the stable period due to temperature increase
Solution Approach 1:
The patent applies preliminary action by pre-adjusting the driving current based on predicted temperature increase. Before the semiconductor light source reaches its steady-state temperature, the control device already reduces the driving current according to a predetermined relationship between temperature and current. This proactive adjustment prevents excessive temperature rise and maintains luminous flux within the required range, achieving a lumen maintenance rate of 80% or higher without requiring complex real-time temperature sensing or feedback loops.
Solution Approach 2:
The patent changes the driving current parameter dynamically based on temperature conditions. Instead of maintaining a constant driving current, the system adjusts the current level according to the temperature increase that occurs during operation. The control device modifies the driving current parameter to compensate for temperature-induced luminous flux degradation, thereby maintaining reliable performance throughout the operational period.
2Illumination intensity
If the driving current is increased to compensate for temperature rise, then the luminous flux can be maintained, but the temperature differential in the start period becomes too large causing instability
Solution Approach 1:
The patent applies dynamics by implementing time-varying current adjustment rather than a static correction. The control device differentiates between the start period and stable period, applying different current adjustment strategies to each. During the start period, minimal current adjustment is made to maintain stability, while during the stable period, larger current reductions are applied to compensate for temperature effects. This dynamic approach maintains luminous flux stability while accounting for temperature rise.
Solution Approach 2:
The patent uses periodic action by dividing the operational timeline into distinct periods (start period and stable period) and applying different control strategies to each. The control device identifies the transition between periods and adjusts the driving current accordingly. This periodic control approach ensures that current adjustments are applied at the appropriate times, maintaining both stability during startup and luminous flux compensation during steady-state operation.
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 approach enhances the lumen maintenance rate and provides improved stability and reliability of the semiconductor light source, particularly for red LEDs, which have significant temperature dependence, thereby meeting or exceeding UN standards for automotive lamps.
Implementation Method 1
a temperature-sensing element having an electrical state that changes according to a temperature T of a semiconductor light source
Implementation Method 2
semiconductor light sources such as light-emitting diodes (LEDs)
Data Source
AI summary
An automotive lamp includes a temperature-sensing element having an electrical state that changes according to the temperature T of a semiconductor light source, and a constant current driver that generates a driving current ILED that corresponds to the temperature T. The maximum value of the temperature differential of the driving current ILED in a first temperature range from a reference temperature T0 to a first temperature T1 (T1>T0) is smaller than the maximum value of the temperature differential of the driving current ILED in a second temperature range from the first temperature T1 to a second temperature T2 (T2>T1).