A new DOE report, Accelerated Stress Testing Results on Single-Channel and Multichannel Drivers – the third in a series on light-emitting diode (LED) driver robustness – summarizes the findings of extensive accelerated stress testing (AST) of LED drivers. The findings confirm the effectiveness of AST methods to research driver failure mechanisms and provide an indication of specific methods that can improve the reliability of LED drivers.
Drivers are a crucial component of solid-state lighting (SSL), because they convert incoming electricity into a form compatible with LEDs. The most common failure sites in SSL devices are the capacitors and transistors in electronic drivers. Although our understanding of other SSL failure mechanisms has increased greatly over the past five years, there’s still a lot of uncertainty about the failure mechanisms of LED drivers, because they come in so many different varieties. AST is a way to study failure mechanisms by operating under extreme conditions – in this case, a high-temperature, high-humidity environment of 75˚C and 75% relative humidity (or “7575” environment) was used.
The 11 drivers tested in the latest study were two-stage LED drivers that could be used to operate troffers, the most common type of office lighting, and similar fixtures. LED drivers that convert incoming electricity in two stages operate in the following manner: Stage 1 converts the alternating-current (AC) energy into direct-current (DC) energy and provides power factor correction and electromagnetic interference suppression, while Stage 2 converts the intermediate DC energy into a form suited to drive the LED efficiently.
Of the 11 drivers tested in the latest study, seven (64%) failed in less than 4,800 hours, with failure times ranging from 1,250 hours to 4,554 hours. Some of the drivers in the earlier tests are still operating near full capabilities after 6,000 hours to 7,500 hours in the 7575 environment. All of the drivers studied under these test conditions survived for at least 1,000 hours, demonstrating the generally robust performance of SSL drivers.
The research also demonstrates that measuring and tracking certain electrical properties of SSL drivers, such as power factor, at different dimming levels can provide insights into their remaining useful life long before failure occurs. This information is useful for predicting the health of SSL drivers, and for future research aimed at reducing the impact of electronics failure on SSL device reliability.
In addition, the findings confirm the effectiveness of AST as the primary method to research driver failure mechanisms, the impact of drivers on the reliability of SSL systems, and the energy consumed by the driver over its useful life. The findings also provide an indication of several specific methods that can improve the reliability of SSL drivers. Improving the performance of these devices, through new designs or improved part selection, should provide additional gains in the robustness of SSL drivers.