[Yankun Fu, a process development engineer at Cree, has written an article characterizing LED failures that occur due to electrical overstress. Part 1 is now up on our sister site EDN. -- Ed.]
Like any semiconductor component, all LEDs are susceptible to electrical overstress (EOS). Although EOS is by far the leading cause of LED failures regardless of the manufacturer, to date there has been no data to characterize EOS failures or determine the specific conditions that cause EOS failures. We tested more than a dozen commercially available LEDs from multiple manufacturers to identify the conditions that cause EOS failure in mid-power, high-power and chip-on-board (COB) LEDs. This article identifies the transient conditions that are benign to LED components and those that can induce EOS and catastrophic failure and suggests some ways to minimize the potential for EOS.
What is EOS?
EOS is the exposure of an LED to current or voltage beyond its maximum specifications. EOS failures result from excessive localized heat generated by the current or voltage transient that accompanies the EOS event. Like all semiconductor devices, LEDs have a limited ability to survive overstress, which we refer to as the maximum withstand power.
EOS differs from electrostatic discharge (ESD), the rapid transfer of static charge between a non-operating part and an object at a different electrical potential. EOS events have a duration that ranges from milliseconds to seconds, which is longer than ESD events that typically range from picoseconds to nanoseconds.
EOS can be a single event or an ongoing periodic or non-periodic event. Following are some typical causes of EOS:
- A driver that produces a current spike
- Constantly driving the LED over its maximum rated current
- A power surge from the main AC power input, such as a lightning strike
- Hot-plugging an LED into an energized power supply
Read the rest of the story at EDN.
— Keith Dawson 
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