降壓調(diào)節(jié)器使驅(qū)動(dòng)高亮度LED容易

　　“垃圾輸入，垃圾輸出”不只是適用于計(jì)算機(jī)編程。LED產(chǎn)生的光的質(zhì)量直接關(guān)系到驅(qū)動(dòng)器的電壓和電流的質(zhì)量，這使得驅(qū)動(dòng)電路和發(fā)射器一樣重要。對(duì)于低亮度LED，線性調(diào)節(jié)器通常可以完成這項(xiàng)工作。高亮度應(yīng)用提出更嚴(yán)格的性能規(guī)格，促使工程師選擇更先進(jìn)的解決方案，如開(kāi)關(guān)穩(wěn)壓器，開(kāi)關(guān)電容轉(zhuǎn)換器或反激式轉(zhuǎn)換器。在這個(gè)組中，降壓開(kāi)關(guān)降壓開(kāi)關(guān)通常是首選，因?yàn)樗鼈兒?jiǎn)單、高效且易于穩(wěn)定。當(dāng)適當(dāng)?shù)刂付ê驮O(shè)計(jì)成一個(gè)系統(tǒng)時(shí)，降壓調(diào)節(jié)器可以提供令人印象深刻的成本/效益性能。

　　LED是直接帶隙半導(dǎo)體，其輸出隨電壓的變化而非線性變化（圖1）。閾值電壓，或正向電壓（VF），從設(shè)備到設(shè)備的任何類(lèi)型的LED略有不同。即使是單個(gè)設(shè)備，VF也會(huì)隨溫度和年齡的變化而漂移。相反，作為驅(qū)動(dòng)電流函數(shù)的輸出對(duì)于任何設(shè)備都是線性的，所以用恒流源驅(qū)動(dòng)led提供最佳性能。

　　Figure 1： LED current varies nonlinearly with respect to voltage. （Courtesy： RECOM）

　　Drive circuitry is often an afterthought， especially for lighting designers. Focusing on the illumination aspects of the design and leaving the power aspects for the end may compromise performance and manufacturability.

　　“［Designers］ want to make their fixture look a certain way and generate a certain amount of light，” says Alex Craig， application systems engineer for lighting， Fairchild Semiconductor. “As a result， they might put six LEDs in parallel， but six LEDs in parallel are likely not as efficient as six LEDs in series.” Smart engineers take a holistic design approach by developing an efficient lighting configuration that lends itself to common power topologies.