LEDs are fragile solid-state devices. An LED is essentially a diode, structured as a P-N junction that emits light when forward-biased. One of the major causes of an electrical open circuit in an LED is thermomechanical stress on the wire bonds. Other causes of LED open circuits are electrostatic discharge (ESD) events or surges induced by nearby lightning events. These threats are especially high in outdoor applications. Devices such as MOVs, fuses, and TVS diodes are essential for a circuit protection strategy because they can prevent transients and surges from damaging delicate LEDs. However, none of these traditional circuit protection devices can prevent an entire string of LEDs from going out if a single LED fails.
An open LED protector can be connected in parallel with each LED in a string; it will shunt current around an open-failed LED to keep the rest of the string lit. When the LED fails, it becomes open-circuit, and the open LED protector goes into conduction, limiting its voltage drop to about 1.3V and keeping the rest of the string operating.
