LED String Vulnerability



In any case, the failure of an LED string is often a costly maintenance issue in outdoor applications. Using LED protectors can help prevent this costly inconvenience.

Littelfuse Prode设备在哪里通常使用,他们做了什么?

Littelfuse PLED open-LED protection devices are often incorporated into the circuit designs of high-power LEDs in such applications as roadway lights and outdoor LED advertising display signs.

镀devices are connected in parallel with each LED in a series string. If one LED should fail open-circuit then the PLED connected to it will turn on and carry the current that would have gone through the failed LED. This keeps the rest of the string operating, so that only a single LED goes dark instead of the whole string.

In the off state, a PLED draws only a few microamps so it does not affect the circuit. When triggered it carries the full current of the string with a voltage drop of about 1.3 volts.


镀devices are typically connected across each LED in a string, but units are available to connect across two or even three LEDs. This reduces the cost of protection but causes more than one LED to go dark if one fails.

Littelfuse Prope设备如何与其他电路保护技术进行比较?

  • A PLED provides open LED protection; an SCR does as well, but a zener does not, as string current will overload it and shorten its life.
  • A PLED provides reverse polarity protection, while an SCR and a zener do not.
  • PLED和齐纳均提供ESD /防雷,但SCR没有。
特征 可控硅 齐纳二极管
LED开路保护 是的 是的
反极性保护 是的
ESD / Lightning / EFT保护 是的 是的
响应时间 ~100ns ~5µs -
Major disadvantages

Large device size

Typically requires a resistive voltage divider network to set the trigger voltage

Variation of triggering voltage versus temperature is quite large





以下是通常涉及为LED应用选择Littelfuse PLED设备的步骤:

  1. 定义Vf(正向电压),如果(正向电流),and the connection scheme of the LEDs.
  2. 定义LED串中的LED数,并了解电源的恒流源值和合规电压。
  3. 确定PLED设备适合VF,IF和PLED保护率,如下:
    1. PLED开关电流必须小于恒定电流源值
    2. 镀电电压必须小于电源合规电压。
    3. 每个PLED选择要保护字符串中的LED(1,2或3)。PLED6,触发6伏,保护一个LED;触发器在9伏特的PLED9可以与一对LED一起使用;并且PLED13可以使用三(注意,一个LED的失败分别导致两三个或三个外出)。
  4. 确定PLED设备的包装以适合照明环境。
  5. Define the ambient temperature of the PLED environment and provide adequate heat sinking if required.
  6. 通过使用受保护的LED旋转来对PLED进行测试。
  7. Review steps 2 and 3 to see if there is any issue.

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