Packaging and AC powering of LED array

Abstract

High power LEDs for lighting application can be implemented with dies. Multiple LEDs are usually connected in series to sustain high power supply voltage like AC 110V due to low LED forward voltage. AC-DC converter is often required for LED arrays working under an AC power supply. But the AC-DC converter brings power consumption overhead and degrades the overall system efficiency as much as 15%. In this work, a high power ceramic COB (Chip On Board) LED array packaging technology capable of working under AC 110V is developed. A total of 40 LEDs are used in the ceramic COB LEDs array to allow it work directly under AC 110V power supply. A special powering method is designed and dedicated to the COB LED array. The special powering method ensures both high light output and high LEDs array reliability especially under supply voltage variations. The measured COB LEDs current vs. AC supply voltage variation is shown in Fig.1 An extremely high driving efficiency (>98%) at the max power and a high power factor are achieved due to the elimination of the AC-DC converter. The electrical efficiency over LEDs forward current is plotted in Fig.2. The structure and top view of COB LED packaging is shown in Fig.3 and Fig.4. The COB package dimension is 68mm by 28mm. With 150mA LEDs forward current, the measured total power is 20W. The max LEDs forward current for this design is 700mA and the max power is 95W. The cross section of the PCB design is shown in Fig.5. Since AC-DC converter reliability is becoming the bottleneck of the high power LED lighting system, the presented ceramic COB LEDs array package with the special powering circuit reliability is enhanced due to the elimination of AC-DC converter. The system reliability is performed and shown in Fig.6. There is no performance degradation of both the ceramic COB LED and control circuit for 1000 hours. Long term reliability test of the system is still under testing and will be presented.