Application Note Heat Dissipation from NC4U13xx depending on Tj 1. Objective The light output of LEDs is reduced under the influence of heat generation. When LEDs are operated over the absolute maximum junction temperature (Tjmax), the performance is severely degraded. It is critical to design the heat dissipation not to exceed the Tjmax for NC4U13xx to achieve a high reliability and a high performance. This document provides the Tj evaluation results under three conditions by using different heat sinks. Please use the data as reference for NC4U13xx’s thermal design at your site. 2. Tj Calculation Tj can be obtained by the following formula: Tj = Ts + Rthj-s × PD Light Emitting Diode where, Tj: Junction Temperature [°C] Ts: Soldering Temperature [°C] Rthj-s: Thermal resistance between the LED die and the Ts measuring point [°C/W] * The Rthj-s of NC4U13xx is Typ:1.7 [°C/W] (Max:2.2 [°C/W] ) PD: Input Power [W] TS Point 3. Tj Measurement Result Figure 1 Ex.1 Copper Board + Heat Sink A IF(A) 0.3 0.5 0.7 TS (℃) 70 93 117 VF(V) 13.3 13.5 13.7 Ts Measuring Point Tj (℃) 77 104 133 Ex.2 Copper Board + Heat Sink B IF(A) 0.3 0.5 0.7 TS (℃) 53 67 79 VF(V) 13.4 13.7 14.0 Tj (℃) 60 79 96 Reverse Surface Front Side Figure 2 Copper Board Ex.3 Copper Board + Heat Sink C IF(A) 0.3 0.5 0.7 TS (℃) 51 64 77 VF(V) 13.4 13.7 14.0 Tj (℃) 58 76 94 HS-A HS-B HS-C Front Side HS-A HS-B HS-C Reverse Surface 4. Heat Dissipation Materials - Metal-based board; Copper, Dimension; 30mm×30mm×1.7mm Figure 3 Copper Board & Heat Sink - Heat Sink A: 30mm×30mm×h=20mm, Depth: 4mm, Fin; 64 pcs. (Dimension of Fin; 1mm×2mm, Structure; 8×8) - Heat Sink B: 50mm×38mm×h=25mm, Depth; 5mm, Fin; 8 pcs. (Dimension of Fin; 1mm×38mm, Structure; 1×8） - Heat Sink C: 54mm×54mm×h=35mm, Depth; 4mm, Fin; 64pcs. (Dimension of Fin: 0.8mm×9mm and Structure; 5×13) Note: Absolute Maximum Ratings Nichia specifies the absolute maximum ratings for NC4U13xx as IF=0.7A and Tjmax =130°C. We cannot assure the performance of the LEDs if they are used above the specified temperature and IF. Thank you very much for your cooperation. This sheet contains tentative information, we may change contents without notice. (SP-QR-C-1841A) Oct. 3, 2013