Littelfuse Open LED Protectors
PLED 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.
PLED devices help protect the LED from surges induced by nearby lightning strikes and ESD events. In addition, PLEDs contain reverse current diodes that will protect the LED string if the power supply is connected with reverse polarity. PLED 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.
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