LED Forward Voltage Virtual Sensor for Thermal Control
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Solution Overview
Problem
Lighting systems with arrays of LEDs face challenges in active thermal control due to temperature sensitivity, where existing methods using NTC thermistors are complex, costly, and prone to inaccuracies, especially with varying forward voltage activation levels across LEDs, making it difficult to accurately measure junction temperatures and manage thermal conditions.
Innovation Solution
A virtual temperature-sensor system that utilizes the forward voltage across the LED array as a proxy for temperature, converting it to a detectable level by a microcontroller to adjust the electrical current and alleviate thermal conditions, thereby maintaining luminance and prolonging LED life without the need for additional thermal measurement devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If NTC thermistor is attached to or embedded within the PCB to measure temperature, then temperature measurement capability is provided, but device complexity and cost increase due to additional electrical connections and instrumentation
Solution Approach 1:
The LED array itself serves as the temperature sensor by utilizing its inherent forward voltage-temperature relationship. The LEDs measure their own junction temperature through forward voltage measurement, eliminating the need for separate NTC thermistors and associated instrumentation, thereby reducing device complexity while maintaining temperature measurement capability
Solution Approach 2:
Instead of using physical temperature sensors (NTC thermistors), the system creates a virtual temperature sensor by measuring the forward voltage of the LEDs and converting it to temperature readings through calibration curves. This virtual copy of temperature measurement functionality eliminates the need for physical sensing components
2Measurement precision
If NTC thermistor is used to measure PCB temperature, then temperature data is obtained, but measurement accuracy deteriorates because PCB temperature does not represent LED junction temperature
Solution Approach 1:
The LED array measures its own junction temperature directly through forward voltage measurement, eliminating the information loss that occurs when measuring PCB temperature instead. Each LED's forward voltage directly reflects its junction temperature, providing accurate thermal information without relying on thermal conduction from the junction to the PCB
3Adaptability or versatility
If LEDs with varying forward voltage activation levels are used, then manufacturing flexibility is improved, but temperature measurement reliability deteriorates due to large temperature variance across the LED array
Solution Approach 1:
The system divides the LED array into multiple segments or groups, measuring the forward voltage of individual LEDs or small groups rather than treating the entire array as a single measurement unit. This segmentation allows accurate temperature measurement even when individual LEDs have different forward voltage characteristics
Solution Approach 2:
The system applies different measurement or calibration approaches to different regions or individual LEDs within the array, accounting for local variations in forward voltage. Each LED or group can be characterized independently, maintaining measurement reliability despite manufacturing variances
4Device complexity
If forward voltage is used as virtual temperature sensor, then device complexity is reduced, but measurement precision must be maintained through accurate voltage-to-temperature conversion
Solution Approach 1:
The system performs preliminary calibration during manufacturing or initial operation, establishing accurate forward voltage-to-temperature conversion curves for each LED or LED group. These pre-established calibration data enable precise temperature measurement during operation without requiring complex real-time calculations
Solution Approach 2:
The system replaces physical temperature sensing mechanisms (NTC thermistors, thermocouples) with an electrical measurement approach, using forward voltage measurement and mathematical conversion to determine temperature. This substitution simplifies the physical system while maintaining measurement capability through electrical characteristics
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 simplifies thermal management, reduces complexity and cost, and provides more accurate temperature representation, effectively maintaining LED luminance and extending their useful life by dynamically adjusting electrical current based on measured forward voltage thresholds.
Implementation Method 1
converting the forward voltage to a level that is detectable by an MCU of the lighting system
Implementation Method 2
due to LEDs having an inherent relationship between forward voltage and junction temperature
Implementation Method 3
reduce an amount of an electrical current provided to the array of LEDs to decrease the forward voltage and alleviate a thermal condition
Data Source
AI summary
This document describes systems and techniques that use a virtual temperature-sensor for active thermal-control of a lighting system having an array of LEDs. The system and techniques use a forward voltage across the array of LEDs as the virtual temperature-sensor, converting the forward voltage to a level that is detectable by an MCU of the lighting system. In response to determining that the forward voltage exceeds a threshold, the lighting system may reduce an amount of an electrical current provided to the array of LEDs to decrease the forward voltage and alleviate a thermal condition that may be detrimental to the array of LEDs, thereby maintaining luminance capabilities of the array of LEDs and prolonging life of the array of LEDs.