The failure of LED lamps is caused by the failure of power supply and drive, and the failure of LED components. Generally, the damage of LED power supply and drive comes from the over-current shock (EOS) of input power supply and the open circuit fault of load end. The over-current impact of the input power often causes the damage of the drive chip in the drive circuit and the breakdown damage of passive components such as capacitors; while the short-circuit fault at the load end may cause the over-current drive of the drive circuit, and the drive circuit may have the short-circuit damage or the overheating damage caused by the short-circuit fault.
Failure of LED components
Transient overcurrent event
Transient over-current event refers to the current flowing through the LED exceeds the maximum rated current in the technical data manual of the LED, which may be caused directly by large current or indirectly by high voltage, such as transient lightning stroke, transient switching noise of switching power supply, grid fluctuation and other over-current events.
These events are transient and last for a very short time. Usually we call them "spikes", such as "current spikes" and "voltage spikes". Transient overcurrent events are also caused when the LED is powered on or plugged in or unplugged.
For LED lighting in automobile, ISO7637-2's transient load throw shock is an important threat to its normal operation.
The failure mode of LED is not fixed, but it usually leads to the damage of welding wire. This damage is usually caused by a large transient over-current, which may cause damage to other parts close to the welding wire, such as sealing materials, in addition to burnout of the welding wire. At present, ESD damage is the most common transient overvoltage hazard in the manufacturing, transportation and application of high integrated semiconductor components, while LED lighting system needs to meet the "human body electrostatic discharge mode" 8Kv contact discharge of IEC61000-4-2 standard, in order to prevent the system from over-current impact failure that may be caused by electrostatic discharge.
The performance of LED PN junction array is degraded or damaged, and the internal failure of LED chip caused by ESD event discharge path may be only the partial function damage, which will also lead to permanent damage of LED.
Overheating damage
For the LED lighting design, which nearly 80% energy is converted into heat dissipation, thermal management and fault overheat protection is an important topic. Both theory and practice have proved that the performance and life of LED are closely related to the working temperature of LED PN junction. When the junction temperature of the LED chip increases by 10 ℃, the luminous flux will decrease by 1%, and the life of the LED will be reduced by 50%.
