The Main Causes of White LED Chip Failure or Necrosis

Published: October 26, 2017 Source: Foreign Website Share:

White LEDs are voltage-sensitive components. During normal operation, the current is typically around 20 mA. However, in real-world use, this current can increase due to various factors. If no protection is in place, such an increase can eventually lead to damage or failure of the LED chip.

The main causes of LED chip failure include:

1. Sudden spikes in the supply voltage.
2. Short circuits caused by faulty components, damaged PCB traces, or other wiring issues, which can cause localized overvoltage on the LED path.
3. A single LED chip shorting out due to manufacturing defects, causing the voltage drop to shift to other LEDs in the circuit.
4. Excessive internal heat that degrades the performance and lifespan of the LED chip.
5. Moisture entering the lamp housing, which can create conductive paths and lead to electrical faults.
6. Improper anti-static measures during assembly, which may damage the LED chip internally without any visible signs, making it prone to failure even under normal operating conditions.

So, how can we protect the LED chip circuit effectively?

1. Use a Fuse (Tube)

Fuses are commonly used for circuit protection, but they have limitations. They are one-time-use devices with slow response times, making them unsuitable for modern LED lighting applications. In large-scale projects like city illumination, the protection system must be fast, reliable, and able to reset automatically once the fault is cleared. Fuses are not ideal for this purpose due to their low efficiency and inconvenient replacement.

2. Use a Transient Voltage Suppression Diode (TVS)

TVS diodes offer fast response times and high surge absorption capabilities, making them suitable for protecting sensitive electronics. However, in practice, finding a TVS device that matches the exact voltage requirements of an LED circuit is challenging. Also, while TVS can protect against overvoltage, it does not handle overcurrent situations, which are often the primary cause of LED failure. This makes them less effective in certain applications.

3. Use a Self-Recovery Fuse (PTC)

A PTC (Polymer Positive Temperature Coefficient) fuse is a smart solution. It operates as a low-resistance component under normal conditions, but when an overcurrent occurs, it heats up and increases its resistance, limiting the current flow and protecting the LED. Once the fault is resolved, it automatically resets. This makes it ideal for long-term, maintenance-free protection.

There are two common ways to implement PTC protection:

• Branch Protection: Each series branch of LEDs can be protected individually by adding a PTC at the start of each branch. This method ensures precise and reliable protection for each section of the LED array.
• Overall Protection: A single PTC can be placed at the front of the entire LED string, offering a simpler and more compact solution. While less precise, it works well for consumer-grade LED products and provides satisfactory results in real-world use.

In conclusion, understanding the root causes of LED failures is crucial for designing robust and long-lasting lighting systems. By choosing the right protection method—whether fuses, TVS, or PTC—engineers can significantly improve the reliability and performance of white LED lamps.

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