脈沖在XLamp LED電流驅動：信息及注意事項

　　有可能在更高的水平上以連續脈沖模式操作LED，但也有可能對效率、色度和長期可靠性產生不利影響的權衡。

　　在這樣的應用支持團隊經常被問及是否是安全的操作我們的LED脈沖電流超過最大數據表評級。這個問題通常是在合理的產品需求范圍內提出的，如緊急車輛應用、特殊頻閃照明甚至脈沖調制等一般照明調光應用。

　　簡短的答案是“它取決于”多個變量影響LED的初始和長期性能和可靠性。這些包括熱電阻，脈沖持續時間，以及電流振幅，頻率和占空比。

　　一般來說，?Cree公司的XLamp LED產品組合是寬廣到足以容納照明大多數和脈沖電流的照明要求在這些組件數據表規格。產品如XLamp XM-L多安培最大電流規格。

　　However， to explore the limits of the possible， but not necessarily reasonable， we’ll review three types of overcurrent conditions：

　　Single-pulse events， e.g.， electrical overstress or EOS，

　　Repetitive pulsing， e.g. pulse-width modulation， and

　　Ripple effects.

　　Electrical overstress （EOS） is often associated with catastrophic failures such as an electrostatic discharge （ESD）， in-rush current， or other types of transient electrical surge.1 Designers of LED drivers should be sure to take all necessary precautions to protect the LEDs from EOS. The second type of over-current condition is often associated with applications in which the LEDs operate in a flashing mode such as emergency vehicle lights， strobe lights， or signaling beacons. High-frequency pulsing， i.e.， greater than 120 hertz， is often used to control the brightness of LEDs in dimming applications. Finally， ripple current is a repetitive， cyclical peak-to-peak variation in a direct-current waveform that may be derived from an insufficiently filtered alternating current source or switched-mode power supply.

　　Within specification boundaries， none of these conditions is cause for concern in regard to the long-term lumen maintenance or reliability of the LED. But any of these in an “over-current” situation， i.e.， beyond data-sheet specification， can decrease LED lifetime.