Tuesday, May 20
RadTech 2025 Detroit Michigan. https://radtech.org/radtech25/
Using In-situ TJ Measurement to Improve Lifetime Projections and Reduce UV-LED Product Cost and Size
UV LED products must operate for a specified lifetime while maintaining a minimum power output. To ensure these specifications are met, product designers typically rely on datasheet values for thermal resistance and calculate the nominal operating junction temperature (TJ) of the LED. LM-80 projections corresponding to this temperature are then used to estimate performance over the specified lifetime.
However, this industry-standard approach faces several challenges: 1) the product’s solder attachment may differ from the one used to calculate the datasheet’s thermal resistance (Rth), 2) the solder point temperature measurement may be inaccurate, and 3) in-situ thermocouple attachment may be difficult or impossible. These challenges increase the uncertainty in estimating the operating TJ.
To address this uncertainty, designers often build in safety margins by enlarging heatsinks, adding more LEDs to reduce drive currents, or lowering the product’s lifetime or power claims. While effective, these mitigation strategies are costly—they increase product size and cost, and they reduce the product’s competitiveness in the market.
This paper presents a measurement system and technique that offers a superior alternative: accurately measure the operating TJ in-situ, under real operating conditions, and optimize the product design using real data rather than estimates.
