驅動發光二極管：Cap還是Cap

　　高亮度發光二極管今天可以使用，其正向電流比它們的前輩大100倍以上。這些新設備不僅高亮度，而且高功率。單芯片與耗散5 W和多芯片模塊與超過25瓦的功率現已。高效率和低功耗的要求決定了新一代高亮度（HB）、高功率（HP）發光二極管的開關電源，因為電壓調節器和限流電阻不再合適。高亮度，高功率LED需要一個恒流源，以充分利用其不斷增長的發光效率和充滿活力，純顏色。這種新型開關恒流源的拓撲結構是基本降壓變換器。使用降壓轉換器的最有說服力的論點是將這種簡單的DC/DC轉換器轉換成恒流源。這篇文章將解釋如何選擇，或可能排除的輸出電容器時，設計一個降壓穩壓器恒流驅動的HB發光二極管。

　　Controlled current

　　The buck regulator is uniquely suited to be a constant current driver because the output inductor is in series with the load. Regardless of whether a buck regulator is used as a voltage source or a current source， selection of the inductor forms the cornerstone of the system design. With an inductor in series with the output， the average inductor current is always equal to the average output current， and the buck converter naturally maintains control of the AC-current ripple. By definition， the LED driver is a constant load system; hence a large amount of output capacitance is not necessary to maintain VO during load transients.