LED Junction Temperature Estimation via Heatsink Proxy
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Solution Overview
Problem
Existing LED lighting systems face challenges in efficiently estimating the junction temperature of multiple LEDs without separate temperature sensors, especially in applications where processing power is limited, such as in arrays or RGBW setups, due to the complexity of directly measuring the junction temperature of each LED.
Innovation Solution
The system employs a controller with a processor and memory unit that estimates the junction temperature of one string of LEDs and uses this to calculate the heatsink temperature, which is then used to estimate the junction temperature of other strings, eliminating the need for separate temperature-measuring components and allowing for indirect estimation across multiple LEDs sharing a heatsink.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct temperature measurement is used for each LED string, then measurement precision is improved, but device complexity increases due to requiring separate temperature sensors for each LED
Solution Approach 1:
The patent uses the electrical characteristics (I-V curve) of the LED as a copy or proxy for temperature measurement. Instead of directly measuring temperature with sensors, the system measures voltage at different currents and uses the known relationship between LED electrical characteristics and temperature to infer junction temperature. This eliminates the need for separate temperature sensors while maintaining measurement capability.
Solution Approach 2:
The patent replaces the mechanical/physical temperature sensing system with an electrical measurement system. By measuring the voltage across the LED at specified currents and using the diode equation relationship, the system substitutes direct thermal measurement with electrical characteristic analysis, thereby eliminating the need for separate temperature sensors.
2Device complexity
If sensor-less sensing techniques are used to estimate junction temperature from electrical characteristics, then device complexity is reduced, but processing power requirements increase
Solution Approach 1:
The patent performs temperature estimation as a preliminary action before full LED operation. By estimating the junction temperature using simplified calculations based on voltage measurements at two current levels, the system prepares temperature data in advance, reducing the need for complex real-time processing during normal operation.
Solution Approach 2:
The patent uses a simplified version of the temperature estimation technique that measures voltage at only two specific current levels rather than performing complete I-V curve analysis. This partial measurement approach provides sufficient temperature estimation accuracy for most applications while significantly reducing the computational burden on the processor.
3Measurement precision
If junction temperature is directly measured for all LED strings, then measurement precision is improved, but loss of time increases due to the time required to measure each LED individually
Solution Approach 1:
The patent merges the temperature measurement process with the normal LED operation by using the same current paths and electrical connections. The voltage measurements taken during PWM dimming or normal operation serve dual purposes: controlling LED brightness and estimating junction temperature simultaneously, thereby eliminating separate measurement time.
Solution Approach 2:
The controller is designed to perform multiple functions using the same measurement infrastructure. The electrical characteristics measurements used for temperature estimation can also inform LED performance monitoring, efficiency calculations, and operational optimization, making the measurement system universally applicable across multiple functions rather than dedicated solely to temperature measurement.
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 reduces processing power requirements and allows for accurate temperature estimation of multiple LEDs without direct measurement, enabling efficient control of LED lighting systems, particularly in applications with multiple colors where temperature variations are significant.
Implementation Method 1
the peak wavelength and perceived colour of an LED depends on the operating temperature. Furthermore the luminous intensity of an LED can vary with temperature
Implementation Method 2
a plurality of strings of LEDs each having a junction and being mounted on the heatsink
Data Source
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AI summary
An LED lighting system is disclosed comprising: a heatsink; a plurality of strings of LEDs each string comprising one or more LEDs each having a junction and being mounted on the heatsink, and a controller comprising a memory unit and a processor and being configured to supply a current to each of the strings of LEDs; The processor comprises: a first temperature estimation subunit configured to generate an estimate of a temperature of the junction of a one of strings of LEDs; a heatsink temperature estimation subunit configured to estimate a temperature of the heatsink unit from the first estimate; and a second temperature estimation subunit configured to provide an estimate of a temperature of the junction of a second string of LEDs, from the estimated temperature of the heatsink. A controller for and method of operating a plurality of LEDs are also disclosed.