Led Design Guide Page 30 LED Design Guide

LED Lighting Design Guide 2015 Littelfuse LED Lighting Design Guide www.littelfuse.com A series of tests were performed by Littelfuse to demonstrate the differences in overcurrent protection provided by fusible resistors and fuses. Overload and surge immunity tests were run on a 22ohm, 240V, 2W fusible resistor of the type sometimes used in retrofit LED bulb assemblies. The first test involved emulating a soft overload condition using 1.65A of constant current for the fusible resistor, equivalent to 60W minimum fusing power of that device. In a comparison test, Littelfuse TR5 and TE5 fuses were subjected to 3.2A and 4A of constant current. A step current test was conducted where the current was gradually increased by 0.165A every 5 minutes starting from 0.33A (at 2W rated power). Table 9 presents the results of these two sets of overcurrent tests. Fusing Resistor Fuse #382 1.6A Fuse #392 1.6A Overcurrent Gradual 0.33A-0.825A Constant 1.65A Constant 3.2A Constant 4A Constant 3.2A Constant 4A Constant 3.2A Constant 4A Fusing Time 16 min. 5 sec. 0.8 sec. 0.4 sec. 7 sec. 1.7 sec. 8.9 sec. 2.9 sec. During Fusing Smoke Glowing Fire Spark Explode After Fusing Discoloration Crack Rupture Risk of Fire YES NO Table 9. Overcurrent testing results for a fusible resistor and two different fuses made by Littelfuse. Potential Problems with Alternative LED Lamp Overcurrent Protection Technologies (continued) 30

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