The Department of Energy (DOE) has announced the third LED driver reliability report based on long-term accelerated life testing. The US Department of Energy's Solid State Lighting (SSL) researchers believe that the latest results confirm the Accelerated Pressure Test (AST) method, which shows good performance under all kinds of harsh conditions. In addition, test results and measured failure factors can inform drive developers of strategies to further improve reliability.
As is well known, LED drivers, like the LED components themselves, are critical to optimal light quality. A suitable driver design eliminates flicker and provides uniform illumination. The drive is also the most likely component of an LED light or fixture. After realizing the importance of the drive, DOE began a long-term drive test project in 2017. The project involves single-channel and multi-channel drives for fixtures such as ceiling recesses.
The US Department of Energy has previously released two reports on the testing process and progress, and is now publishing a third test data report covering the results of a 6000-7500 hour product test run under AST conditions.
In fact, the industry does not have the time to test drives in normal operating environments for many years. Instead, the US Department of Energy and its contractor RTI International have tested the drive in what they call the 7575 environment - indoor humidity and temperature are maintained at 75 °C. This test involves two stages of drive testing, independent of the channel. The single-stage design is less expensive, but lacks a separate circuit that first converts the AC to DC and then regulates the current, and this single circuit is unique to a two-stage design.
The US Department of Energy report stated that all of the drives were tested in 1175 environments for 1,000 hours in 11 different drives. When the drive is in the environmental chamber, the LED load connected to the drive is in an outdoor environment, so the AST environment only affects the drive. The DOE does not link the runtime under AST conditions to the runtime in a normal environment. The first batch of units failed after 1250 hours of operation, although some units were still running. After testing 4800 hours, 64% of the devices failed. Still, considering the harshness of the test environment, these results are already very good.
The researchers found that most of the faults occurred in the first phase of the drive, especially power factor correction (PFC) and electromagnetic interference (EMI) suppression circuits. In both phases of the driver, the MOSFET also has a fault. In addition to specifying areas such as PFCs and MOSFETs that can improve driver design, the AST also shows that faults can often be predicted based on the performance of the monitored drive. For example, monitoring power factor and inrush current can detect early failures in advance. An increase in flicker also indicates an impending failure.
For a long time, DOE's SSL program has been conducting important testing and research in the SSL field, including application scenario product testing under the Gateway project and commercial product performance testing under the Caliper project.
