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Image of Littelfuse PLED Devices

One solution is to place a PLED device across each of the LEDs in a string. While the LED is functioning normally, the PLED is completely dormant. However, when a bond wire fails, the full compliance voltage of the constant current source immediately appears across the failed LED. This triggers the PLED device into action. The PLED will turn on, bypassing all of the string current around the defective LED, keeping the remaining LEDs illuminated. Replacing the defective LED and restarting the string current will reset the PLED device. In many applications, the failure of a single LED may not be critical or even noticeable, saving a potentially expensive service call for repair or replacement. Notice that the PLED on-state voltage is less than the voltage of an LED. This means the power dissipation of an active PLED is actually lower than the power dissipation of a healthy LED. Therefore, after an LED fails open, the temperature of the fixture will go down, helping to avoid further failures in the system.

PTM Published on: 2011-10-31