LED’s magazine’s April 2020 issue features the article Simpler LED Junction Temperature Measurement, written by Vektrex CTO Jeff Hulett. The article discusses how the SpikeSafe SMU solves a critical problem for luminaire manufacturers – how to make in-situ junction temperature measurements.

Luminaire makers struggle with junction temperature measurement because the available methods are not possible to implement with complete luminaire assemblies or they require expensive, exotic equipment that is difficult to use. These challenges have led to measurement compromises – such as estimating junction temperature using an average thermal resistance – that often produce inaccurate results.

The semiconductor industry recognized this need and produced two testing standards that described a non-invasive measurement method, called the Electrical Test Method (ETM). The standards, JESD51-51 and JESD51-14 have been available for more than a decade, but adoption has been limited to large manufacturers that can afford the investment in specialized equipment and expert personnel to interpret the results.

In the article Hulett describes how the low-cost SpikeSafe SMU can be used is used to make accurate in-situ junction temperature measurements of a commercial can light using the ETM. The SMU’s built-in dual current sources and high-speed digitizer easily meet the electrical requirements of the ETM – fast current transitions and low-noise voltage sampling. Vektrex’s Control Panel software application performs the critical Vf projections needed to calculate the final junction temperature.

The resulting in-situ ensemble Tj measurement provided validation that the article’s luminaire and its heat-flow elements – LED attachment, circuit boards, and heat sink, were all operating correctly. In-fact, the results showed the Tj was quite low.

This low Tj result illustrates the main advantage of simpler ETM measurements using the SpikeSafe SMU: luminaire designs can be optimized to improve performance and reduce cost. Without accurate Tj data, designers are forced to overdesign critical heat flow structures such as heat sinks. This is analogous to the situation that existed before modern CAD tools were available – mechanical structures were routinely overdesigned. Using the SMU, designers can refine designs and reduce product cost, ultimately delivering more value to the end customer.

Contact Vektrex to learn more about how to use the SMU to make in-situ Tj measurements.