High-power white LED as a new type of green lighting technology, light conversion efficiency, low energy consumption, long life, no maintenance and other advantages, has been applied to a variety of lighting areas. LED long life is based on its safe working environment, in terms of LED lighting, there are two main threats affect its life: First, over-electric shock, that is, the LED applied to the current exceeds the LED technical data in the maximum rated current , Including overpressure caused by over-voltage shock; the other is overheating damage. These damage can be expressed as immediate failure of the device, may also occur in the over-current shock event after a long time before failure, shorten the LED working life.
LED lighting damage causes
LED lamps failure comes from the power supply and drive failure, the second is derived from the LED device itself failure. Often the LED drive power and drive damage comes from the input power of the over-impact (EOS) and the load side of the fault. The input power of the over-impact will often cause the drive circuit driver chip damage, as well as passive components such as capacitive breakdown damage. Short-circuit fault at the load side may cause the overcurrent drive of the drive circuit, which may cause short-circuit damage or over-temperature damage caused by short-circuit fault. LED device itself, the main failure of the following circumstances.
1. 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. LED lighting systems are required to meet the IEC 61000-4-2 standard "Electrostatic discharge mode" 8kV contact discharge, to prevent the system in the electrostatic discharge may lead to over-electric shock failure.
LED PN junction array performance will be reduced or damaged, as shown in Figure 2. ESD event discharge path caused by the internal failure of the LED chip, this failure may only be local functional damage, serious will lead to permanent damage to the LED.
2. Transient overcurrent events
Transient overcurrent events refer to the current flowing through the LED that exceeds the maximum rated current in the LED data sheet, which may be due to direct or high voltage generation, such as transient lightning, switching power State switch noise, power grid fluctuations and other over-voltage events caused by overcurrent. These events are transient and have a very short duration, and we usually call them spikes such as "current spikes" and "voltage spikes". The case of transient overcurrent events also includes the power supply to the LED, or the transient overcurrent during live plugging.
For automotive LED lighting, ISO7637-2 transient surge load surge impact is an important threat to its normal work.
The failure mode of the LED after an electric shock is not fixed, but it usually causes the welding line to be damaged, as shown in Fig. This damage is usually caused by a large transient overcurrent. In addition to causing the weld wire to burn, it may cause damage to other parts of the weld line, such as sealing material.
Common Causes and Protection of LED Lamp Damage
For nearly 80% of the energy are converted into heat LED lighting design, thermal management and fault overheating protection is a challenge. Theory and practice have proved that the performance and life of LED LED junction temperature is closely related with the LED. When the LED chip junction temperature rise 10 ℃, luminous flux will decay 1%, LED life will be reduced by 50%.
Power supply and drive circuit protection
As the LED power supply circuit is susceptible to electric shock and short circuit fault and damage, so in the drive circuit design to take full account of various failure state protection measures to improve the reliability of the circuit, thereby reducing the repair rate. Tyco Electronics' LVR Series PTC achieves overcurrent and short circuit protection for AC power supplies, and ROV for over-current shock and surge protection. POLYZEN series is used for DC power input port over-voltage over-current protection components, LED string in the surface of the series is to achieve the load over-current or fault protection.
Common Causes and Protection of LED Lamp Damage
PPTC overcurrent and overheat protection in LED lighting
Although many high-end LED driver devices gradually integrated over-current, overheating and other protection functions, but in many occasions, especially in overheating protection, still need discrete components as a collaborative protection program to make the lamp has a higher reliability and more Long life.