LED Lifetime Test Equipment Using Forward Voltage Junction Temperature Control
Solution Overview
Problem
Conventional LED lifetime test methods yield inconsistent results due to uncontrollable junction temperatures caused by variations in current and heat-dissipation abilities, leading to differing lifetime estimates for the same type of LEDs across different test systems.
Innovation Solution
A lifetime test equipment comprising an oven, current sources, a voltage meter, a control module, and a processing module that gradually changes and sustains oven temperature, providing specific currents to LEDs while measuring forward voltages to calculate junction temperatures using a variation relationship equation, ensuring consistent decay tests at known junction temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional decay test methods are used with uncontrolled current and heat dissipation, then LED lifetime can be tested under normal operation conditions, but the junction temperature cannot be controlled leading to inconsistent test results
Solution Approach 1:
The patent implements feedback control by measuring the forward voltage of the LED and using it to calculate the junction temperature. The system continuously monitors the forward voltage and adjusts the applied current accordingly to maintain the junction temperature within a predetermined range, ensuring consistent and reliable test results across different test systems.
Solution Approach 2:
The patent replaces direct thermal measurement and control mechanisms with an electrical measurement approach. Instead of using complex thermal sensors and control systems to directly control junction temperature, the system uses forward voltage measurement and calculation to indirectly determine and control temperature, simplifying the system while improving consistency.
2Measurement precision
If different test temperatures and currents are used for decay tests, then more comprehensive lifetime data can be obtained, but the test results vary across different test systems
Solution Approach 1:
The patent changes the control parameter from fixed temperature and current settings to dynamic parameter adjustment based on forward voltage measurement. By continuously monitoring forward voltage and adjusting the applied current to maintain junction temperature within a specified range, the system achieves both accurate lifetime estimation and compatibility across different test systems.
Solution Approach 2:
The patent transforms the static test condition approach into a dynamic control system. Instead of using fixed temperature and current values, the system dynamically adjusts the applied current based on real-time forward voltage measurements to maintain junction temperature within the predetermined range, enabling consistent results across varying test environments.
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 allows for accurate and consistent estimation of LED lifetime by controlling junction temperatures, thereby standardizing lifetime test results across different systems.
Implementation Method 1
The oven has an oven temperature. The oven gradually changes the oven temperature during a first period and sustains the oven temperature at a predetermined oven temperature point during a second period
Implementation Method 2
The voltage meter measures a forward voltage of the LED. The processing module calculates the junction temperature of the LED according to the forward voltage of the LED and a variation relationship equation between the forward voltage of the LED and the oven temperature
Data Source
AI summary
A life test device comprises an oven, a current source, a voltage meter, a control module, and a process module. A light-emitting diode (LED) is disposed in the oven. The temperature of the oven is gradually changed in a first period and remains at a set temperature in a second period. The current source provides a first current and a second current to the LED. The voltage meter measures forward voltages of the LED. The control module controls the current source to output the first or second current to the LED and controls the voltage meter to measure the forward voltages of the LED. The process module calculates a junction temperature of the LED according to the forward voltages and a variation relationship formula between the forward voltages and the temperature of the oven.