LED Driver Current Derating With Thermistor Brightness Control
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Solution Overview
Problem
Existing light-emitting element driving devices fail to effectively manage temperature-induced brightness reduction and heat generation in LED lighting systems, particularly in high-temperature environments, leading to decreased performance and reduced lifespan.
Innovation Solution
The implementation of a current setter and current adder system that adjusts the reference current based on ambient temperature using thermistors with negative coefficients, combined with a constant current source, to maintain optimal output current and brightness levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the output current is increased to maintain LED brightness, then the brightness is improved, but heat generation increases and lifespan decreases
Solution Approach 1:
The patent implements dynamic current adjustment by making the current setting resistor value changeable based on temperature conditions. The resistance value is dynamically modified in response to temperature changes, allowing the output current to be adjusted accordingly. This resolves the contradiction by enabling the system to maintain appropriate brightness while reducing heat generation through adaptive current control rather than fixed current operation.
2Temperature
If the output current is decreased to reduce heat generation, then temperature is reduced, but brightness decreases
Solution Approach 1:
The patent changes the resistance parameter of the current setting resistor based on temperature conditions. When temperature increases, the resistance value is modified to adjust the output current accordingly. This parameter change enables the system to reduce heat generation through lower current while maintaining brightness through compensatory resistance adjustment, effectively resolving the trade-off between temperature control and brightness maintenance.
3Temperature
If temperature-based derating is implemented to reduce heat generation, then temperature is controlled, but brightness regulation becomes complex
Solution Approach 1:
The patent employs a thermistor that automatically responds to temperature changes by changing its resistance value, which in turn adjusts the output current without requiring complex external control circuitry. The thermistor self-regulates the current based on temperature, enabling temperature-based derating while keeping the brightness regulation mechanism relatively simple. This resolves the contradiction by using a passive, self-regulating component rather than an active, complex control system.
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 solution effectively maintains LED brightness and reduces heat generation by dynamically adjusting the output current in response to temperature changes, thereby prolonging the lifespan of the LED lighting system.
Implementation Method 1
The current setter is connected to a setting resistor and a negative-coefficient thermistor that are externally connected to the light-emitting element driving device. The current setting resistor and the negative-coefficient thermistor are connected in parallel. The current setter yields current setting characteristics with a positive coefficient (such that, as the resistance value of the current setting resistor increases, the reference current increases). This permits the reference current to be decreased as the ambient temperature of the thermistor rises, and thus allows temperature-based derating of the output current.
Data Source
AI summary
A light-emitting element driving device (5) includes: a first external terminal (SET terminal) connectable to a first setting resistor (Rset); a second external terminal (SET_TH terminal) connectable to a first thermistor (TH1) with a negative coefficient arranged beside a light-emitting element light source (10); a current setter (2) that generates a setting current (Iset) based on the resistance value of the first setting resistor; a current adder (3) that generates an addition current (Iadd) with a negative coefficient to the resistance value of the first thermistor; and a current driver (1) that generates an output current (Iout) that passes through the light-emitting element light source connected between an application terminal for a supply voltage (Vin) and a ground terminal based on a reference current (Iref) which is the sum of the setting current and the addition current.