隨著電(dian)子產(chan)品(pin)集(ji)成(cheng)度(du)、處理器速(su)度(du)、開(kai)關(guan)速(su)率和接口速(su)率的不(bu)斷(duan)提升，電(dian)子產(chan)品(pin)ESD/EMI/EMC問(wen)題(ti)日益突出(chu)，尤其是當手持電(dian)子設(she)備向(xiang)輕薄小(xiao)巧方向(xiang)發(fa)展而且產(chan)品(pin)功能不(bu)斷(duan)增(zeng)加時，它們的輸入/輸出(chu)端(duan)口也(ye)隨之增(zeng)多，導致靜電(dian)放電(dian)進入系統并干擾或損壞集(ji)成(cheng)電(dian)路(lu)，電(dian)路(lu)保護是最(zui)容易出(chu)現問(wen)題(ti)的部分，也(ye)是容易被(bei)忽略的問(wen)題(ti)。

       在通信(xin)、消費、軍工、航(hang)空航(hang)天等(deng)領域，ESD往往是引(yin)起電路失效的(de)罪(zui)魁禍首(shou)，而(er)過流過壓(ya)保護器件選擇、傳導輻射電磁干擾消除(chu)、EMC測試環境等(deng)問題成為工程師(shi)在設計時的(de)難點(dian)，這(zhe)些問題該怎么解決呢？

       一、電路保護從元器件選型開始

       電(dian)(dian)(dian)(dian)路保(bao)(bao)(bao)護元(yuan)(yuan)器(qi)件(jian)通常包括過壓保(bao)(bao)(bao)護器(qi)件(jian)和(he)(he)過流(liu)保(bao)(bao)(bao)護器(qi)件(jian)兩種(zhong)，工程師需要針對各種(zhong)元(yuan)(yuan)器(qi)件(jian)的特點和(he)(he)不同的應(ying)用(yong)類型進行選擇(ze)。電(dian)(dian)(dian)(dian)子(zi)產品中，印制電(dian)(dian)(dian)(dian)路板的密(mi)度不斷(duan)提高，半導體元(yuan)(yuan)件(jian)和(he)(he)集成(cheng)電(dian)(dian)(dian)(dian)路的工作(zuo)電(dian)(dian)(dian)(dian)壓不斷(duan)降低，生(sheng)產商就(jiu)運(yun)用(yong)表面貼裝技(ji)術(shu)(shu)、片式(shi)多層陶瓷技(ji)術(shu)(shu)、陣(zhen)列技(ji)術(shu)(shu)等新(xin)技(ji)術(shu)(shu)開發小尺寸(cun)、滿足小電(dian)(dian)(dian)(dian)壓大電(dian)(dian)(dian)(dian)流(liu)電(dian)(dian)(dian)(dian)路保(bao)(bao)(bao)護需求的產品；可以預見，未(wei)來電(dian)(dian)(dian)(dian)子(zi)電(dian)(dian)(dian)(dian)力技(ji)術(shu)(shu)不斷(duan)發展，國(guo)內外電(dian)(dian)(dian)(dian)路保(bao)(bao)(bao)護元(yuan)(yuan)器(qi)件(jian)生(sheng)產商將繼續大力研發新(xin)產品、新(xin)技(ji)術(shu)(shu)，為各個應(ying)用(yong)領域提供合(he)適的、安全的電(dian)(dian)(dian)(dian)路保(bao)(bao)(bao)護元(yuan)(yuan)器(qi)件(jian)。

        選(xuan)擇適當的電路(lu)保(bao)護(hu)器(qi)件是實現(xian)高效(xiao)、可靠(kao)電(dian)(dian)路保(bao)護(hu)設計的(de)(de)關(guan)鍵，涉及(ji)到電(dian)(dian)路保(bao)護(hu)器件的(de)(de)選型，我(wo)們就必(bi)(bi)須要知(zhi)道各電(dian)(dian)路保(bao)護(hu)器件的(de)(de)作(zuo)用。在選擇電(dian)(dian)路保(bao)護(hu)器件的(de)(de)時候我(wo)們要知(zhi)道保(bao)護(hu)電(dian)(dian)路不應干(gan)擾受(shou)保(bao)護(hu)電(dian)(dian)路的(de)(de)正(zheng)常行(xing)(xing)為，此外(wai)，還必(bi)(bi)須防止(zhi)任何(he)電(dian)(dian)壓瞬態造成整個(ge)系統的(de)(de)重復性或(huo)非重復性的(de)(de)不穩(wen)定行(xing)(xing)為，進行(xing)(xing)多次模擬測試，從而實現(xian)電(dian)(dian)路防護(hu)方案的(de)(de)可靠(kao)性和實用性。

       二、電路保護器件的選擇技巧

       面對ESD、過壓(ya)、浪涌(yong)、過熱等現(xian)象帶來(lai)的(de)(de)巨大危(wei)害性，最(zui)新的(de)(de)電(dian)(dian)路保(bao)(bao)護(hu)(hu)器(qi)(qi)件除(chu)了(le)(le)需(xu)(xu)要關注(zhu)伏安特性、保(bao)(bao)護(hu)(hu)級別等因素(su)(su)之外，還(huan)要考慮其他(ta)很多問題。比如電(dian)(dian)子(zi)設備越來(lai)越輕(qing)薄，為(wei)了(le)(le)符(fu)合尺寸的(de)(de)限制并在更小(xiao)(xiao)的(de)(de)占(zhan)位(wei)面積(ji)中提(ti)供電(dian)(dian)路保(bao)(bao)護(hu)(hu)，保(bao)(bao)護(hu)(hu)器(qi)(qi)件制造商需(xu)(xu)要開發出(chu)尺寸更小(xiao)(xiao)的(de)(de)元(yuan)器(qi)(qi)件，這就需(xu)(xu)要廠商不斷提(ti)高元(yuan)器(qi)(qi)件的(de)(de)能(neng)量密(mi)度，當(dang)電(dian)(dian)子(zi)設備接(jie)(jie)(jie)口(kou)(kou)速率不斷提(ti)升，為(wei)保(bao)(bao)證信號完(wan)整性就必須考慮保(bao)(bao)護(hu)(hu)器(qi)(qi)件電(dian)(dian)容的(de)(de)大小(xiao)(xiao)，保(bao)(bao)護(hu)(hu)方案必須緊(jin)隨接(jie)(jie)(jie)口(kou)(kou)發展(zhan)的(de)(de)趨勢，確(que)保(bao)(bao)接(jie)(jie)(jie)口(kou)(kou)的(de)(de)可靠性，同時還(huan)得(de)保(bao)(bao)證保(bao)(bao)護(hu)(hu)元(yuan)器(qi)(qi)件的(de)(de)耐(nai)沖擊次數、抗震、防潮(chao)等因素(su)(su)。

       三、過流、過壓保護器件的特性

       保護器件雖然種類繁(fan)多，從功能上講可(ke)以分為過(guo)流保(bao)(bao)(bao)護(hu)(hu)和過(guo)壓保(bao)(bao)(bao)護(hu)(hu)。最重要的過(guo)流保(bao)(bao)(bao)護(hu)(hu)器(qi)件(jian)是熔斷器(qi)，也叫保(bao)(bao)(bao)險絲。它一般(ban)串聯(lian)在電(dian)(dian)(dian)(dian)(dian)路(lu)中，要求其電(dian)(dian)(dian)(dian)(dian)阻(zu)要小(xiao)（功耗(hao)小(xiao)），當(dang)(dang)(dang)電(dian)(dian)(dian)(dian)(dian)路(lu)正(zheng)常工作(zuo)(zuo)時(shi)，它只(zhi)(zhi)相當(dang)(dang)(dang)于(yu)一根導(dao)線(xian)，能夠長時(shi)間穩定的導(dao)通(tong)電(dian)(dian)(dian)(dian)(dian)路(lu)，由于(yu)電(dian)(dian)(dian)(dian)(dian)源或外(wai)部干擾(rao)而發生電(dian)(dian)(dian)(dian)(dian)流波動時(shi)，也應能承受一定范圍的過(guo)載(zai)，只(zhi)(zhi)有當(dang)(dang)(dang)電(dian)(dian)(dian)(dian)(dian)路(lu)中出現較大的過(guo)載(zai)電(dian)(dian)(dian)(dian)(dian)流(故障或短路(lu))時(shi)，熔斷器(qi)才會動作(zuo)(zuo)，通(tong)過(guo)斷開電(dian)(dian)(dian)(dian)(dian)流來(lai)保(bao)(bao)(bao)護(hu)(hu)電(dian)(dian)(dian)(dian)(dian)路(lu)的安(an)全，以避免(mian)產品燒(shao)毀(hui)的危險。

        在(zai)(zai)熔斷(duan)器(qi)分斷(duan)電(dian)(dian)路(lu)(lu)(lu)的(de)(de)(de)過程(cheng)中,由于(yu)電(dian)(dian)路(lu)(lu)(lu)電(dian)(dian)壓(ya)的(de)(de)(de)存在(zai)(zai),在(zai)(zai)熔體斷(duan)開的(de)(de)(de)瞬間(jian)會發(fa)生電(dian)(dian)弧(hu),高質(zhi)量的(de)(de)(de)熔斷(duan)器(qi)應該(gai)盡量避(bi)免這(zhe)種(zhong)飛(fei)弧(hu);在(zai)(zai)分斷(duan)電(dian)(dian)路(lu)(lu)(lu)后,熔斷(duan)器(qi)應能(neng)耐受(shou)加(jia)在(zai)(zai)兩(liang)端的(de)(de)(de)電(dian)(dian)路(lu)(lu)(lu)電(dian)(dian)壓(ya).熔斷(duan)器(qi)受(shou)脈(mo)沖損傷會逐步(bu)降低承受(shou)脈(mo)沖的(de)(de)(de)能(neng)力,選用時(shi)需(xu)要考慮必要的(de)(de)(de)安(an)全(quan)余(yu)量;這(zhe)個安(an)全(quan)余(yu)量是指(zhi)熔斷(duan)器(qi)的(de)(de)(de)總熔斷(duan)(動作(zuo))時(shi)間(jian)，它是預飛(fei)弧(hu)時(shi)間(jian)和飛(fei)弧(hu)時(shi)間(jian)之和。

       所以在選擇(ze)的(de)(de)時(shi)(shi)候(hou)需要留意它(ta)的(de)(de)熔(rong)(rong)(rong)(rong)斷特性(xing)和額定電流這個基本條(tiao)件(jian)；另外安(an)裝時(shi)(shi)要考慮熔(rong)(rong)(rong)(rong)斷器周(zhou)邊的(de)(de)環境(jing)(jing)，熔(rong)(rong)(rong)(rong)斷器只有達到本身的(de)(de)熔(rong)(rong)(rong)(rong)化熱(re)能值的(de)(de)時(shi)(shi)候(hou)才會熔(rong)(rong)(rong)(rong)斷，如果(guo)是在環境(jing)(jing)較冷的(de)(de)狀(zhuang)況下，它(ta)的(de)(de)熔(rong)(rong)(rong)(rong)斷時(shi)(shi)間會變化，這是使用時(shi)(shi)必須留意的(de)(de)。

       四、EMC測試要點

       電磁兼容性（EMC）是指設備或系統在電磁環境中性能不降級的狀態。EMC，一方面要求系統內沒有嚴重的干擾源即設備在正常運行過程中對所在環境產生的電磁干擾不能超過一定的限值，另一方面要求設備或系統自身有較好的抗電磁干擾性即器具對所在環境中存在的電磁干擾具有一定程度的抗擾度，即電磁敏感性。
       EMC包括EMI(電(dian)磁(ci)干擾(rao))及(ji)EMS(電(dian)磁(ci)耐受性)兩部(bu)份(fen)：

       1）EMI電磁干(gan)擾，乃為機(ji)器本身在(zai)執行(xing)應有功能的過程中(zhong)所產生不利于其它系統的電磁噪(zao)聲。

 ;      2）EMS乃指(zhi)機器在執行應有(you)功能的過程(cheng)中不受(shou)周(zhou)圍(wei)電磁環境影響的能力(li)。

       五、如何消除電磁干擾？

       電(dian)(dian)(dian)磁(ci)(ci)干(gan)(gan)擾，是指電(dian)(dian)(dian)子設備自身(shen)工(gong)作過程中，產(chan)生的(de)電(dian)(dian)(dian)磁(ci)(ci)波，對(dui)外發射，從而對(dui)設備其(qi)它部(bu)分或外部(bu)其(qi)它設備造(zao)成干(gan)(gan)擾。系統要發生電(dian)(dian)(dian)磁(ci)(ci)兼(jian)容性問題(ti)即電(dian)(dian)(dian)磁(ci)(ci)干(gan)(gan)擾,必(bi)須具備三(san)個因(yin)素,就(jiu)是電(dian)(dian)(dian)磁(ci)(ci)干(gan)(gan)擾源(yuan)、耦合途徑、敏(min)感設備。所以,在解(jie)決電(dian)(dian)(dian)磁(ci)(ci)干(gan)(gan)擾問題(ti)時,要從這三(san)個因(yin)素人手,對(dui)癥下(xia)藥,消除(chu)其(qi)中某一(yi)個因(yin)素,就(jiu)能(neng)解(jie)決電(dian)(dian)(dian)磁(ci)(ci)兼(jian)容問題(ti)。常用(yong)的(de)有效(xiao)的(de)方法有:接(jie)地技(ji)術、屏蔽技(ji)術、濾波技(ji)術。