高功率LED驅(qū)動(dòng)器找到自己的利基

　　以高容量驅(qū)動(dòng)一系列高亮度LED需要精心設(shè)計(jì)，同時(shí)實(shí)現(xiàn)寬調(diào)光比，同時(shí)保持顏色譜。幸運(yùn)的是，有一些集成的驅(qū)動(dòng)程序包可以應(yīng)對(duì)挑戰(zhàn)。

　　背景

　　大功率LED的光輸出已經(jīng)達(dá)到了100流明/ W的關(guān)鍵里程碑，一些制造商在實(shí)驗(yàn)室中聲稱擁有120流明/瓦特。這意味著LED在能效方面已經(jīng)超過了CFL（80流明/瓦特）。不過，據(jù)預(yù)測(cè)，到2012年底，LED將達(dá)到150流明/ W輸出。此外，所有目前的重點(diǎn)是“綠色”，LED不包含任何危險(xiǎn)材料，如CFL，其中有有毒汞蒸汽管內(nèi)。

　　LED照明成本已經(jīng)下降的很快。個(gè)別白光二極管的成本，其中一些進(jìn)入LED燈泡，占成本的大部分，已經(jīng)從幾年前的大約5美元降到了過去十二個(gè)月不到1美元的價(jià)格。許多LED行業(yè)分析師預(yù)測(cè)，在未來12個(gè)月內(nèi)，LED燈泡替代白熾燈的價(jià)格將達(dá)到消費(fèi)者可以接受的水平。一些LED制造商已經(jīng)聲稱他們已經(jīng)設(shè)計(jì)了發(fā)光芯片，可以為L(zhǎng)ED燈泡供電，這種燈可以與美國(guó)家庭中常用的75瓦白熾燈泡媲美。這種類型的LED芯片通常需要12瓦的功率才能輸出這種光。

　　One key performance feature that an LED driver IC must have today is the ability to adequately dim LEDs. Since LEDs are driven with a constant current， where the DC current level is proportional to LED brightness， to vary the LED brightness， there are two methods of dimming the light by controlling the LED current. The first method is analog dimming， where the LED DC current level is reduced proportionally by reducing the constant LED current level. Reducing the LED current can result in a change in LED color or inaccurate control of the LED current. The second method is digital or pulse-width-modulation （PWM） dimming. PWM dimming switches the LED on and off at a frequency at， or above 100 Hz， which is not perceivable to the human eye. The PWM dimming duty cycle is proportional to LED brightness while the on-time LED current remains at the same level （as set by an LED driver IC）， maintaining constant LED color during high dimming ratios. This method of PWM dimming can be used with ratios as high as 10，000:1 in certain applications.