Led Design Guide Page 31 LED Design Guide

2015 Littelfuse LED Lighting Design Guide www.littelfuse.com LED Lighting Design Guide Additional tests on fusible resistors were performed according to IEC 61000-4-5 and the Energy Star surge immunity test standards. Results are detailed below. IEC Surge Test Results: Figure 18. IEC 61000-4-5 testing on a fusible resistor. As shown in Figure 18 , the fusible resistor was not able to withstand 40 strikes required by IEC 61000-4-5 standard. High resistance fusible resistors dissipate excessive heat when subjected to surge current that is applied in minute intervals. Heat accumulates, which in turn raises resistor body temperature and resistance. As a result, the fusible resistor opens before the required 40 surges. Energy Star test results: Again, fusible resistors were not able to withstand seven strikes required by the Energy Star standard ( Figure 19 ). Littelfuse test results revealed that fusing resistors can catch fire, spark, and even explode under abnormal overcurrent conditions, hence rendering them unsafe. These components generate excessive heat in transient surge testing causing them to open before the required number of surges are applied, for both IEC and Energy Star test methods. In a retrofit LED bulb, once the fusible resistor opens, the bulb will be disconnected from the power source, thus resulting in the failure of EMC testing. Moreover, the bulb is rendered useless. Potential Problems with Alternative LED Lamp Overcurrent Protection Technologies (continued) 31

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