LED Die Temperature Measurement Using Adjacent Diode Voltage
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Solution Overview
Problem
Conventional methods for determining the temperature of LED dies under a silicone layer with phosphor particles are inadequate, leading to delayed feedback and oscillating temperature control, as thermistors or thermocouples cannot be placed directly under the transparent carrier material without affecting light uniformity and increasing manufacturing costs.
Innovation Solution
A method involving two LED dies with the same structure, both encapsulated in a silicone layer, where one die is illuminated with a drive current and the other receives a constant current to determine the temperature based on the voltage across the second die, allowing for real-time temperature calculation without disrupting light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thermistor or thermocouple is placed on the LED package near the LED device to measure temperature, then temperature measurement is achieved, but the measurement does not reflect the actual temperature under the transparent carrier material and causes delayed feedback leading to temperature control oscillation
Solution Approach 1:
The patent uses light as an intermediary to transfer temperature information from the LED die to an external photodetector. The LED die's light emission characteristics change with temperature, and this optical signal mediates the temperature measurement without requiring direct physical contact between the sensor and the heat source, thereby eliminating feedback delay and oscillation issues
Solution Approach 2:
The patent replaces the mechanical/thermal contact-based temperature measurement system (thermistor or thermocouple) with an optical measurement system. Instead of measuring temperature through thermal conduction to an external sensor, the system uses optical properties of the LED die itself to infer temperature, substituting a mechanical measurement approach with an optical one
2Measurement precision
If a thermistor or thermocouple is placed within the LED array under the transparent carrier material to measure temperature directly, then accurate temperature measurement is achieved, but light uniformity is disrupted and manufacturing cost increases
Solution Approach 1:
The patent makes the LED die serve multiple functions: it simultaneously acts as both the light source for illumination and the temperature sensor. By monitoring the light emission characteristics of the LED die itself, the system eliminates the need for separate sensing elements that would disrupt light uniformity or increase manufacturing complexity
Solution Approach 2:
The LED die serves itself as the temperature sensor by utilizing its own light emission properties to indicate its temperature state. This self-service approach eliminates the need for external sensors that would interfere with light uniformity or require additional manufacturing steps, as the LED die inherently provides both illumination and temperature information
3Illumination intensity
If a large number of LED dies are packaged in close proximity to produce sufficient light, then illumination intensity is improved, but heat generation increases leading to overheating and reduced LED lifetime
Solution Approach 1:
The patent implements a real-time feedback control system that continuously monitors the temperature of each LED die through its light emission characteristics and adjusts the drive current accordingly. This feedback mechanism allows the system to maintain high illumination output while preventing overheating by dynamically reducing current to individual dies that are approaching temperature limits
Solution Approach 2:
The patent introduces dynamic control of the LED array operation, where the drive current to each LED die is continuously adjusted based on real-time temperature measurements. This dynamic approach allows the system to optimize between light output and temperature management, rather than using a static current level that would either cause overheating or insufficient illumination
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 provides accurate and timely temperature monitoring of LED dies, preventing overheating and maintaining light uniformity, while minimizing additional manufacturing costs and heat generation.
Implementation Method 1
Light emitting diodes (LEDs) are an important class of solid-state devices that convert electric energy into light
Implementation Method 2
A phosphor coating then absorbs some of the emitted blue light and fluoresces to emit light with longer wavelengths
Implementation Method 3
The large number of LED dies that are packaged in close proximity to one another under a transparent carrier material that contains phosphor particles results in a large amount of heat generated within a small volume
Data Source
AI summary
A light-emitting diode (LED) device includes first and second LED dies with the same structure and that are both encapsulated by the same silicone layer. The first LED is supplied with sufficient drive current to illuminate the LED. Control circuitry supplies the second LED with a constant current, determines the voltage across the second LED, and calculates the temperature of the second LED based on the voltage across the second LED. The constant current has a maximum magnitude that never exceeds the maximum magnitude of the drive current. The LED device is able to calculate the temperature of a diode with a gallium-nitride layer (GaN or GaInN) that is receiving a large drive current and emitting blue light by determining the voltage across an adjacent similar diode with a gallium-nitride layer through which a small constant current is flowing. Preferably, the band gap of the LEDs exceeds two electron volts.