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Reasons for LED failure


As a new 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 used in various lighting fields. The long life of LED is based on its safe working environment. For LED lighting, there are two main threats affecting its life: one is over-electric shock, that is, the current applied to the LED exceeds the maximum rated current in the LED technical data sheet , including overvoltage shock caused by overvoltage; the other is overheating damage. These damages can be manifested as immediate failure of the device, or it may occur long after the overcurrent shock event, shortening the working life of the LED.

Causes of damage to LED lamps

The failure of LED lamps comes from the failure of the power supply and drive, and the failure of the LED device itself. Usually, the damage to the LED drive power supply and the drive comes from the over-voltage shock (EOS) of the input power supply and the open circuit fault at the load end. The overvoltage impact of the input power often causes damage to the drive chip in the drive circuit, and breakdown damage to passive components such as capacitors. A short circuit fault at the load end may cause an overcurrent drive of the drive circuit, and the drive circuit may be damaged by a short circuit or overheated due to a short circuit fault. The failure of the LED device itself mainly has the following situations.

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 "human body electrostatic discharge model" of the IEC61000-4-2 standard 8kV contact discharge to prevent the system from failure due to over-electrical shocks that may be caused by 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 discharge path of the ESD event may only cause partial functional damage, and if it is serious, it will also cause permanent damage to the LED.

2. Transient overcurrent event

A transient overcurrent event means that the current flowing through the LED exceeds the maximum rated current in the LED technical data sheet, which may be directly generated by a large current or indirectly generated by a high voltage, such as transient lightning strikes, switching power supply transients, etc. Overcurrent caused by overvoltage events such as state switching noise and grid fluctuations. These events are transient and have a very short duration. We usually call them spikes, such as "current spikes" and "voltage spikes." The conditions that cause transient overcurrent events also include LED power-on, or transient overcurrent during live plugging and unplugging.

The failure mode of the LED after being subjected to an electric shock is not fixed, but it usually leads to damage to the welding wire, as shown in Figure 1. This damage is usually caused by extremely large transient overcurrents. In addition to causing the welding wire to burn out, it may also cause damage to other parts close to the welding line, such as sealing materials.

Common causes of damage to LED lamps and protection solutions

For LED lighting designs where nearly 80% of energy is converted into heat, thermal management and fault overheating protection are a challenge. Both theory and practice have proved that the performance and life of LEDs are closely related to the operating temperature of the LED's PN junction. When the junction temperature in the LED chip rises by 10°C, the luminous flux will be attenuated by 1%, and the life of the LED will be reduced by 50%.

Protection of power supply and drive circuit

Since the LED power drive circuit is easily damaged by over-electric shock and short-circuit faults, the protection measures for various fault states should be fully considered in the design of the drive circuit to improve the reliability of the circuit and reduce the repair rate. Tyco Electronics' LVR series PTC can realize over-current and short-circuit protection of AC power supply, and ROV is used for over-electric shock and surge protection. The POLYZEN series are overvoltage and overcurrent comprehensive protection components for DC power input ports, and the surface mount series in LED light strings are used for load overcurrent or open circuit fault protection.

Common causes of damage to LED lamps and protection solutions

PPTC overcurrent and overheating protection in LED lighting; although many high-end LED drive devices have gradually integrated overcurrent, overheating and other protection functions, in many occasions, especially in terms of overheating protection, discrete component solutions are still required as a collaborative protection solution , so that the lamps have higher reliability and longer life.

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