As a new type of green lighting technology, high-power white LEDs have the advantages of high light conversion efficiency, low energy consumption, long life, and no maintenance, and are gradually being applied to various lighting fields. The long life of LEDs is based on their safe working environment. For LED lighting, there are two main threats that affect its life: First, over-power shock, that is, the current applied to the LED exceeds the maximum rated current in the LED's technical data sheet. Including over-voltage caused by over-voltage shock; the other is overheating damage. These damages can be manifested as an immediate failure of the device, and may also occur after a long-term impact event of the overcurrent before failing, shortening the LED operating life.
Causes of damage to LED luminaires
The failure of LED luminaires originates from the failure of power supply and drive, and the second is the failure of LED devices themselves. Damage to the LED power supply and the driver is usually caused by the over-voltage (EOS) of the input power supply and the open-circuit fault at the load. The over-current impact of the input power source often results in the damage of the driver chip in the driver circuit and the breakdown of passive components such as capacitors. A short-circuit fault on the load side may cause overcurrent driving of the driver circuit, and the driver circuit may be short-circuited or overheated due to a short-circuit fault. The failure of the LED device itself mainly has the following situations.
1. Transient overcurrent events
A transient overcurrent event means that the current flowing through the LED exceeds the maximum rated current in the LED's technical data sheet. This may be due to direct current generation or indirect generation by high voltage, such as transient lightning strikes, switching power transients. Overcurrent caused by overvoltage events such as switching noise and power grid fluctuations. These events are transient and extremely short in duration. We usually call them spikes, such as "current spikes" and "voltage spikes." Events that cause transient overcurrent events also include LED power-on or transient over-current during hot swap.
For LED lighting in automobiles, the transient loading surge surge of ISO7637-2 is an important threat to its normal operation.
The failure mode after the LED is subjected to electric shock is not fixed, but it usually leads to the damage of the welding line, as shown in Figure 1. This damage is usually caused by a very large transient overcurrent. In addition to causing the weld line to blow, it can also cause damage to other parts near the weld line, such as sealing materials.
Figure 1: LED welding line blown and damaged.
2. Electrostatic discharge event
Electrostatic Discharge (ESD) damage is the most common transient overvoltage hazard in the manufacture, transportation, and application of highly integrated semiconductor devices, and LED lighting systems must meet the “Electrostatic Discharge Mode of the Human Body†of the IEC61000-4-2 standard. 8kV contact discharge to prevent the possibility of over-power shock failure when the system is electrostatically discharged.
LED PN junction array performance will appear to be reduced or damaged, as shown in Figure 2. The internal failure of the LED chip caused by the discharge path of the ESD event may only be a partial functional impairment, and in severe cases it may also lead to permanent damage of the LED.