LED power protection scheme and common causes of damage
Release date: 2017-11-21 Source: Foreign station sharing: 
As a new green lighting technology, high-power white LED has advantages of high light conversion efficiency, low energy consumption, long life and no maintenance, and is gradually applied to various lighting fields. The long life of LED is based on its safe working environment. For LED lighting, there are two main threats that affect its life: one is over-current shock, that is, the current applied to the LED exceeds the maximum rated current in the LED technical data sheet. , including over-current shock caused by over-voltage; the other is overheating damage. These damages can be manifested as immediate failure of the device, or it can occur after a long time after an overcurrent shock event, shortening the working life of the LED.
LED lamp damage
LED lamp failure is caused by failure of power supply and drive, and secondly by failure of LED device itself. Often the damage to the LED drive power supply and drive comes from the over-current surge (EOS) of the input supply and the open-circuit fault at the load. The over-current shock of the input power source often causes damage to the driver chip in the driver circuit and breakdown damage of passive components such as capacitors. A short-circuit fault at the load end may cause over-current drive of the drive circuit, and the drive circuit may be damaged by short-circuit or short-circuit fault. There are several main reasons for the failure of the LED device itself.
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, while LED lighting systems must meet the "electrostatic discharge mode" of IEC61000-4-2. 8kV contact discharge to prevent over-current shock failure of the system during electrostatic discharge.
The performance of the LED PN junction array will be reduced or damaged, as shown in Figure 2. The internal failure of the LED chip caused by the ESD event discharge path may be only a partial function damage, and if it is serious, it may cause permanent damage to the LED.
2. Transient overcurrent event
A transient overcurrent event is when the current flowing through the LED exceeds the maximum rated current in the LED technical data sheet. This may be due to a large current directly generated or indirectly generated by a high voltage, such as a transient lightning strike or a switching power supply. Overcurrent caused by overvoltage events such as state switching noise and grid fluctuations. These events are transient and have a very short duration. Usually we call them spikes such as “current spikes†and “voltage spikesâ€. The transient overcurrent event also includes the LED being powered on or the transient overcurrent when plugged in.
For LED lighting in cars, the transient load dump surge of ISO7637-2 is an important threat to its normal operation.
The failure mode of an LED after an electrical shock is not fixed, but it usually causes damage to the weld 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 may also cause damage to other parts of the weld line, such as sealing material.
Common causes and protection schemes for LED lamp damage
Thermal management and fault overheat protection are a challenge for LED lighting designs where nearly 80% of energy is converted to heat. Both theory and practice have demonstrated that the performance and lifetime of LEDs are closely related to the operating temperature of the PN junction of the LED. When the junction temperature in the LED chip rises by 10 ° C, the luminous flux is attenuated by 1%, and the lifetime of the LED is reduced by 50%.
Power and drive circuit protection
Since the LED power supply driving circuit is easily damaged by over-current shock and short-circuit fault, the protection measures of various fault states should be fully considered in the design of the driving circuit to improve the reliability of the circuit and thereby reduce the repair rate. Tyco Electronics' LVR Series PTCs provide overcurrent and short circuit protection for AC power supplies, and ROVs are used for over-current shock and surge protection. The POLYZEN series is an over-voltage and over-current integrated protection component for the DC power input port. The surface mount series in the LED light string is used to protect the load from overcurrent or open circuit faults.
Common causes and protection schemes for LED lamp damage
Overcurrent and overheat protection of PPTC in LED lighting
Although many high-end LED driver devices are gradually integrated with protection functions such as overcurrent and overheating, in many cases, especially for overheat protection, discrete component solutions are still needed as a synergistic protection scheme to make lamps more reliable and more reliable. Long life.
Label: LED power protection scheme and common causes of damage
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