Burnout of LED lamp stems from the failure
The burnout of LED lamp stems from the failure of power supply and drive, and the failure of LED device itself.
The damage of the LED power supply and driver comes from the overcurrent impact (EOS) of the input power supply and the breakdown of the load end. Over-voltage impulse of input power often causes the damage of driving chip in driving circuit and the breakdown damage of passive components such as capacitors. Short-circuit fault at load end may cause overcurrent drive of driving circuit, which may cause short-circuit damage or overheating damage caused by short-circuit fault.
The failure of the LED device itself is mainly as follows:
(1) Transient overcurrent events
Transient overcurrent event refers to the current flowing through the LED exceeding the maximum rated current in the LED technical data manual. This may be due to the direct generation of high current or indirect generation of high voltage, such as transient lightning stroke, transient switching noise of switching power supply, power grid fluctuation and other overvoltage events. These events are transient and last for a very short time. Usually we call them spikes, such as "current spikes" and "voltage spikes". The transient overcurrent events also include the transient overcurrent when the LED is switched on or plugged in and out.
For LED lighting in automobiles, the transient load-throwing surge of ISO7637-2 is an important threat to its normal operation.
The failure mode of the LED after electric shock is not fixed, but usually leads to the damage of the welding line, as shown in Figure 1. This damage is usually caused by a large transient overcurrent. In addition to causing burnout of the welding line, it may also cause damage to other parts close to the welding line, such as sealing materials.
(2) ESD events
Electrostatic discharge (ESD) damage is one of the most common transient overvoltage hazards in the manufacture, transportation and application of highly integrated semiconductor devices. The LED lighting system must meet the IEC61000-4-2 standard of "human body electrostatic discharge" 8kV contact discharge, in order to prevent the system from overvoltage shock failure when electrostatic discharge occurs.
The performance of the LED PN junction array will be degraded or damaged, as shown in Figure 2. The internal failure of the LED chip caused by the discharge path of ESD event may be only partial function damage, and even permanent damage of the LED will occur if the failure is serious.
For LED lighting designs where nearly 80% of energy is converted to heat, thermal management and fault overheating protection are challenges. Both theory and practice have proved that the performance and lifetime of LED are closely related to the working temperature of the PN junction of LED. When the junction temperature of the LED chip increases by 10 C, the luminous flux decreases by 1%, and the lifetime of the LED chip decreases by 50%.