While LEDS are, in general, very robust, failures still happen due to electrical over stress. Mauro Ceresa, EMEA Field Application Engineer Manager at Cree, will cover all aspects related to electrical over stress, or when an LED fails due to being subjected to a voltage beyond its specification limits. He will explain why the failure occurs and how to prevent this from happening. The article will explain the fundamental aspects of a good PCB layout design and how this is linked to the longevity of an LED.
Solid state light technology has become an important player in the lighting industry thanks to the many performance advantages that LEDs offer. The performance enhancements of this rising star technology – its efficiency advantages in particular – have led to many new applications and the widespread adoption of LED.
Solid state light usage proliferation exposes LEDs to a range of new and harsh working conditions, and demonstrates that their theoretical “great longevity” could easily be compromised by various environmental factors. Chemical incompatibility is one of the first issues customers face, but luckily, in most cases, this problem tends to become apparent quite rapidly when caused by a fixture design fault.
The speed at which these faults become evident means that the industry is becoming increasingly conscious that the expected lifetime of LEDs could be seriously compromised if they are exposed to volatile substances incompatible with solid state light constructing materials. Unfortunately, not all threats to LEDs are evident enough so as to enable users to take the necessary steps to fix the issue before a massive field failure occurs.
The most critical threat comes from the same source that powers the LEDs, and is known as “Electrical Over Stress” (EOS). An EOS occurs every time the LED driving current or voltage exceeds the component maximum rated values. There are many different types of EOS – some are generated during the LED assembling or testing process, while others are produced by the power supply or come from the environment induced by the electromagnetic field.
An EOS is the most dangerous threat for solid state light technology because it uses the same path used to light up the LED. In addition, the damage it causes is often not immediate. In many cases, the LED may only cease to work days or even months after installation. These two characteristics of an EOS mean it can be incredibly difficult to prevent, and expensive to solve. The time lapse between the EOS occurring and the failure to detect the fault can be quite long and have serious repercussions as more luminaires may be produced and installed, thereby increasing the cost of warranty replacement.