LED標(biāo)牌應(yīng)用混合顏色、節(jié)能和復(fù)雜性

　　標(biāo)牌是最具挑戰(zhàn)性的LED應(yīng)用之一。它包括一個(gè)大而多樣化的市場(chǎng)，包括單色信息標(biāo)志（例如進(jìn)出口標(biāo)志）和簡單的信息標(biāo)志；公共汽車和火車站的多色目的地標(biāo)志；公共汽車和火車內(nèi)顯示。RGB應(yīng)用程序包括體育場(chǎng)館的大屏幕和小顯示屏，以及使用數(shù)千個(gè)LED驅(qū)動(dòng)芯片的多媒體廣告牌。例如，靠近公路的一個(gè)大廣告牌大小的標(biāo)志可以集成125000個(gè)或更多的設(shè)備。

　　標(biāo)志的基本知識(shí)

　　大型LED標(biāo)志由模塊組成，包括LED、驅(qū)動(dòng)器、電源、控制單元、傳感器和某種源于LED測(cè)序數(shù)據(jù)的處理器。具有高刷新率的RGB標(biāo)志顯示通常需要每個(gè)模塊上的MCU來實(shí)現(xiàn)色彩校正。對(duì)于在現(xiàn)場(chǎng)部署LED標(biāo)志/顯示后，微控制器對(duì)于處理突發(fā)事件也是非常重要的。隨著時(shí)間的推移，LED改變顏色，有時(shí)會(huì)失敗。模塊也開始失敗。MCU存儲(chǔ)關(guān)于舊模塊的操作特性的信息。這允許對(duì)新模塊進(jìn)行正確的顏色校準(zhǔn)。圖1顯示了在體育場(chǎng)中可以找到的高端標(biāo)志顯示屏的主要組成部分。

　　Figure 1： Large signage displays use hundreds of thousands of LED drivers （Courtesy of STMicroelectronics）。

　　The components of most interest in this article have the following primary characteristics：

　　The LEDs themselves typically have drive currents in the 8 to 10 mA range. The higher current devices are used for outdoor applications and different colors require different drive currents， which creates a design complication that will be discussed later.

　　The driver market is probably the most significant and – except for simple signage applications – 16-bit chips tend to predominate. They become progressively more expensive as special features such as error detection， gain control， PWM， the ability to identify LED failure， thermal shutdown and other features are added. Another important reason for 16-bit dominance is that many controllers output data in bytes.

　　Control units can be purchased but many design teams choose to create their own controller using an FPGA.