剖析開關電源電磁攪擾發生原因
電磁兼容（ElectroMagneticCompatibility，簡稱EMC）是指電子設備或體系在其電磁環境能正常作業，且不對該環境中任何事物構成不能承受的電磁打擾的才能。它包含電磁攪擾（EMI）和電磁敏感（EMS）兩方面的內容。EMI是指電器產品向外宣布攪擾。EMS是指電器產品反抗電磁攪擾的才能。一臺具備杰出電磁兼容性的設備應既不受周圍電磁噪聲的影響，也不對周圍環境構成電磁攪擾。電磁攪擾的三個要素是攪擾源、耦合通道和敏感體。按捺開關電源發生的攪擾對確保電子體系的正常安穩運行具有十分重要的含義，電磁攪擾的按捺技能首要包含削弱攪擾的能量，阻隔和減弱噪聲耦合途徑及進步設備對電磁打擾的反抗才能等。本文剖析了開關電源電磁攪擾發生原因，介紹了開關電源電磁攪擾(rao)按捺(na)技能及規劃辦法。
1.開關電源電磁攪擾的發生
開關電源一般是將工頻交流電整流為直流電，然后經過開關管的操控使其變為高頻，再經過整流濾波電路輸出，得到安穩的直流電壓。工頻整流濾波運用大容量電容充、放電，開關管高頻通斷，輸出整流二極管的反向恢復等作業進程中發生了極高的di/dt和du/dt，構成了激烈的浪涌電流和尖峰電壓，它是開關電源電磁攪擾發生的最基本原因。別的，開關管的驅動波形，MOSFET漏源波形等都是接近矩形波形狀的周期波。因而，其頻率是MHz等級的，這些高頻信號對開關電源的基(ji)本信號，特別(bie)是(shi)操控電路的信號構成攪擾。
1.1輸入(ru)整流電路(lu)的諧波攪擾
開關電源輸入(ru)端一般選用橋(qiao)(qiao)式整(zheng)(zheng)流(liu)(liu)(liu)(liu)、電(dian)(dian)(dian)(dian)容(rong)濾(lv)波(bo)(bo)電(dian)(dian)(dian)(dian)路(lu)。整(zheng)(zheng)流(liu)(liu)(liu)(liu)橋(qiao)(qiao)只有在(zai)脈(mo)動電(dian)(dian)(dian)(dian)壓(ya)超(chao)過輸入(ru)濾(lv)波(bo)(bo)電(dian)(dian)(dian)(dian)容(rong)上的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)壓(ya)時(shi)才能導通，電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)才從市電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源(yuan)(yuan)輸入(ru)，并對濾(lv)波(bo)(bo)電(dian)(dian)(dian)(dian)容(rong)充電(dian)(dian)(dian)(dian)。一旦濾(lv)波(bo)(bo)電(dian)(dian)(dian)(dian)容(rong)上的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)壓(ya)高于市電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)(de)(de)(de)瞬時(shi)電(dian)(dian)(dian)(dian)壓(ya)，整(zheng)(zheng)流(liu)(liu)(liu)(liu)管便(bian)截止。所以(yi)，輸入(ru)電(dian)(dian)(dian)(dian)路(lu)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)是脈(mo)沖性(xing)質的(de)(de)(de)(de)(de)，并且有著(zhu)豐厚的(de)(de)(de)(de)(de)高效諧波(bo)(bo)電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)。這(zhe)是由于整(zheng)(zheng)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)(dian)路(lu)的(de)(de)(de)(de)(de)非(fei)線性(xing)特性(xing)，整(zheng)(zheng)流(liu)(liu)(liu)(liu)橋(qiao)(qiao)交流(liu)(liu)(liu)(liu)側的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)嚴(yan)峻(jun)失真。
而直流(liu)側的諧波(bo)次數是n倍。所(suo)以，整流(liu)電(dian)路直流(liu)側高頻(pin)諧波(bo)電(dian)流(liu)不只使電(dian)路發生(sheng)功率，增加電(dian)路的無功功率，并且高頻(pin)諧波(bo)會沿(yan)著傳(chuan)輸線路發生(sheng)傳(chuan)導攪擾和(he)輻射攪擾。
1.2開關電路(lu)發生的攪擾
開關電路在開關電源中起著關(guan)鍵的(de)(de)(de)效果，一(yi)起也(ye)是(shi)首要的(de)(de)(de)攪擾(rao)源之(zhi)一(yi)。開(kai)關(guan)管負載為(wei)高頻變壓(ya)器初(chu)級線(xian)圈(quan)，是(shi)感性負載。其在(zai)導(dao)通瞬(shun)間，初(chu)級線(xian)圈(quan)發生很大的(de)(de)(de)涌流，并在(zai)初(chu)級線(xian)圈(quan)的(de)(de)(de)兩頭出(chu)現較高的(de)(de)(de)浪涌尖(jian)峰電壓(ya);在(zai)斷開(kai)瞬(shun)間，由于初(chu)級線(xian)圈(quan)的(de)(de)(de)漏磁通，致(zhi)使(shi)一(yi)部分能量沒有(you)(you)從一(yi)次線(xian)圈(quan)傳輸到二次線(xian)圈(quan)，儲藏在(zai)電感中的(de)(de)(de)這部分能量將和集電極(ji)電路中的(de)(de)(de)電容、電阻構成帶有(you)(you)尖(jian)峰的(de)(de)(de)衰減震蕩(dang)，疊加在(zai)關(guan)斷電壓(ya)上，構成關(guan)斷電壓(ya)尖(jian)峰。假如尖(jian)峰有(you)(you)足夠(gou)高的(de)(de)(de)起伏，那么很有(you)(you)或許把(ba)開(kai)關(guan)管擊穿(chuan)。
1.3高頻變壓器發(fa)生的共模傳(chuan)導打擾(rao)
高頻變壓器是開關電源中(zhong)完成(cheng)能(neng)量儲(chu)存、阻(zu)隔、輸出、電(dian)(dian)(dian)(dian)(dian)壓改(gai)換的重(zhong)要部(bu)(bu)件，它的漏(lou)感和(he)散布電(dian)(dian)(dian)(dian)(dian)容(rong)對(dui)電(dian)(dian)(dian)(dian)(dian)路的電(dian)(dian)(dian)(dian)(dian)磁(ci)(ci)兼容(rong)功(gong)能(neng)發(fa)生(sheng)較(jiao)大(da)的影響。由于初(chu)級(ji)線(xian)圈(quan)有(you)漏(lou)磁(ci)(ci)通(tong)，致使(shi)一(yi)部(bu)(bu)分能(neng)量沒有(you)傳(chuan)輸到(dao)次級(ji)線(xian)圈(quan)，而是經過(guo)集電(dian)(dian)(dian)(dian)(dian)極電(dian)(dian)(dian)(dian)(dian)路中(zhong)的電(dian)(dian)(dian)(dian)(dian)容(rong)、電(dian)(dian)(dian)(dian)(dian)阻(zu)構(gou)(gou)(gou)(gou)成(cheng)帶有(you)尖峰的衰減振蕩，疊加在關斷電(dian)(dian)(dian)(dian)(dian)壓上(shang)，構(gou)(gou)(gou)(gou)成(cheng)關斷電(dian)(dian)(dian)(dian)(dian)壓尖峰，發(fa)生(sheng)與初(chu)級(ji)線(xian)圈(quan)接通(tong)時一(yi)樣(yang)的磁(ci)(ci)化沖擊(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)瞬變，這(zhe)個(ge)噪聲會傳(chuan)導到(dao)輸入、輸出端，構(gou)(gou)(gou)(gou)成(cheng)傳(chuan)導打(da)(da)擾，重(zhong)者有(you)或(huo)(huo)許(xu)擊(ji)(ji)穿開關管。別的，高(gao)頻變壓器(qi)初(chu)級(ji)線(xian)圈(quan)、開關管和(he)濾波電(dian)(dian)(dian)(dian)(dian)容(rong)構(gou)(gou)(gou)(gou)成(cheng)的高(gao)頻開關電(dian)(dian)(dian)(dian)(dian)流(liu)環路或(huo)(huo)許(xu)會發(fa)生(sheng)較(jiao)大(da)的空間輻射，構(gou)(gou)(gou)(gou)成(cheng)輻射打(da)(da)擾。
在開關電源的調頻變壓器初次級之間存在著散布電容。用一個設備電容（設備對地的散布電容）來與整個開關電源等效，就(jiu)(jiu)構(gou)(gou)成了攪(jiao)擾(rao)通道(dao)。共模攪(jiao)擾(rao)經(jing)(jing)過(guo)變(bian)壓(ya)器(qi)的(de)耦(ou)合電(dian)容(rong)(rong)，經(jing)(jing)過(guo)設(she)備電(dian)容(rong)(rong)再回來大地，就(jiu)(jiu)得到(dao)一個(ge)由變(bian)壓(ya)器(qi)耦(ou)合電(dian)容(rong)(rong)與設(she)備電(dian)容(rong)(rong)構(gou)(gou)成的(de)分(fen)壓(ya)器(qi)。脈沖變(bian)壓(ya)器(qi)初級線圈(quan)、開關管(guan)和濾波電(dian)容(rong)(rong)構(gou)(gou)成的(de)高頻(pin)開關電(dian)流(liu)環路或許(xu)會發生較(jiao)大的(de)空間輻射(she)，構(gou)(gou)成輻射(she)打擾(rao)。
1.4散布及寄生參數引起的開關電源噪聲
開關電源的散布參數是大都攪擾的內涵因素，開關電源和散熱器之間的散布電容、變壓器初次級之間的散布電容、原副邊的漏感都是噪聲源。共模攪擾便是經過變壓器初、次級之間的散布電容以及開關電源與散熱器之間的散布電容傳輸的。其中變壓器繞組的散布電容與高頻變壓器繞組結構、制作工藝有關。開關電源與散(san)熱器之間的(de)(de)散(san)布(bu)電容與開關(guan)(guan)(guan)管的(de)(de)結構以及開關(guan)(guan)(guan)管的(de)(de)安裝(zhuang)方(fang)法有關(guan)(guan)(guan)。選用帶有屏蔽的(de)(de)絕緣襯墊能夠減小開關(guan)(guan)(guan)管與散(san)熱器之間的(de)(de)散(san)布(bu)電容。
在高頻作業下的元件都有高頻寄生特性，對其作業狀況發生影響。高頻作業時導線變成了發射線、電容變成了電感、電感變成了電容、電阻變成了共振電路，當頻率過高時各元件的頻率特性發生了相當大的改變。為了確保開關電源在高頻作業時的安穩性，規劃開關電源時要充分考慮元件在高頻作業時的特性，挑選運用高頻特性比較好的元件。別的，在高頻時，導線寄生電感的感抗顯著增加，由于電感的不可控性，最終使其變成一根發射線，也就成為了開關電源中的輻射攪擾源。
2.按捺電磁攪擾的辦法
開關電源存在著(zhu)共模攪擾(rao)和(he)差模攪擾(rao)兩(liang)種電(dian)磁(ci)攪擾(rao)方式。依據前面(mian)剖(pou)析的(de)電(dian)磁(ci)攪擾(rao)源，結合它們的(de)耦合途徑，能夠從EMI濾波器、吸(xi)收(shou)電(dian)路、接(jie)地(di)和(he)屏(ping)蔽等幾個方面(mian)來按(an)捺攪擾(rao)，把電(dian)磁(ci)攪擾(rao)衰減到答應極限之內。
2.1交流(liu)輸入EMI濾波器
濾波是一種按捺傳導攪擾的辦法，在電源輸入端接上濾波器能夠按捺來自電網的噪聲對電源本身的侵害，也能夠按捺由開關電源發生(sheng)并(bing)向(xiang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)網反應的(de)(de)(de)(de)攪(jiao)(jiao)擾(rao)。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)濾(lv)波(bo)器作為(wei)按捺電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)線(xian)(xian)(xian)(xian)傳導(dao)攪(jiao)(jiao)擾(rao)的(de)(de)(de)(de)重要單元，在(zai)(zai)(zai)(zai)設備(bei)或(huo)體(ti)系的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)磁(ci)(ci)兼容(rong)(rong)規劃中(zhong)具有極(ji)其重要的(de)(de)(de)(de)效(xiao)果。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)進線(xian)(xian)(xian)(xian)端(duan)一般選(xuan)用(yong)(yong)如圖(tu)1所(suo)示(shi)的(de)(de)(de)(de)EMI濾(lv)波(bo)器電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。該電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)能(neng)夠有效(xiao)地(di)按捺交流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)輸入端(duan)的(de)(de)(de)(de)低頻差模(mo)打(da)擾(rao)和高頻段共(gong)模(mo)打(da)擾(rao)。在(zai)(zai)(zai)(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)中(zhong)，跨接(jie)在(zai)(zai)(zai)(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)兩(liang)頭的(de)(de)(de)(de)差模(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)Cx1、Cx2（亦(yi)稱X電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)）用(yong)(yong)于(yu)濾(lv)除差模(mo)攪(jiao)(jiao)擾(rao)信號(hao)，一般選(xuan)用(yong)(yong)陶瓷電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)器或(huo)聚脂(zhi)薄(bo)膜電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)器，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)值一般取(qu)(qu)0.1~0.47F。而(er)中(zhong)心連線(xian)(xian)(xian)(xian)接(jie)地(di)的(de)(de)(de)(de)共(gong)模(mo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)Cy1和Cy2（亦(yi)稱Y電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)）則用(yong)(yong)來短路(lu)(lu)共(gong)模(mo)噪聲電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)，取(qu)(qu)值規模(mo)一般為(wei)C1=C2#2200pF。按捺電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)L1、L2一般取(qu)(qu)100~130H，共(gong)模(mo)扼流(liu)圈(quan)(quan)L是(shi)由兩(liang)股等同并(bing)且按同方(fang)(fang)向(xiang)繞制在(zai)(zai)(zai)(zai)一個(ge)磁(ci)(ci)芯(xin)上的(de)(de)(de)(de)線(xian)(xian)(xian)(xian)圈(quan)(quan)組成(cheng)，一般要求其電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)量L#15~25mH。當負載電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)渡過共(gong)模(mo)扼流(liu)圈(quan)(quan)時，串聯在(zai)(zai)(zai)(zai)火線(xian)(xian)(xian)(xian)上的(de)(de)(de)(de)線(xian)(xian)(xian)(xian)圈(quan)(quan)所(suo)發生(sheng)的(de)(de)(de)(de)磁(ci)(ci)力線(xian)(xian)(xian)(xian)和串聯在(zai)(zai)(zai)(zai)零線(xian)(xian)(xian)(xian)上線(xian)(xian)(xian)(xian)圈(quan)(quan)所(suo)發生(sheng)的(de)(de)(de)(de)磁(ci)(ci)力線(xian)(xian)(xian)(xian)方(fang)(fang)向(xiang)相(xiang)反，它(ta)們在(zai)(zai)(zai)(zai)磁(ci)(ci)芯(xin)中(zhong)彼此抵(di)消。因而(er)，即使在(zai)(zai)(zai)(zai)大負載電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)(de)(de)情況下，磁(ci)(ci)芯(xin)也不會飽滿。而(er)關(guan)于(yu)共(gong)模(mo)攪(jiao)(jiao)擾(rao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)，兩(liang)個(ge)線(xian)(xian)(xian)(xian)圈(quan)(quan)發生(sheng)的(de)(de)(de)(de)磁(ci)(ci)場是(shi)同方(fang)(fang)向(xiang)的(de)(de)(de)(de)，會出現(xian)較(jiao)大電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)，然(ran)后起到衰(shuai)減共(gong)模(mo)攪(jiao)(jiao)擾(rao)信號(hao)的(de)(de)(de)(de)效(xiao)果。
2.2運用吸收電路
開關電源發生EMI的首要原因是電壓和電流的急劇改變，因而需求盡或許地下降電路中電壓和電流的改變率（du/dt和di/dt）。采取吸收電路能夠按捺EMI，其基本原理便是在開關關斷時為其供給旁路，吸收積蓄在寄生散布參數中的能量，然后按捺攪擾的發生。能夠在開關管兩頭并聯如圖2（a）所示的RC吸收電路，開關管或二極管在注冊和關斷進程中，管中發生的反向尖峰電流和尖峰電壓，能夠經過緩沖的辦法予以克服。緩沖吸收電路能夠削減尖峰電壓的起伏和削減電壓波形的改變率，這關于半導體器材運用的安全性非常有好處。與此一起，緩沖吸收電路還下降了射頻輻射的頻譜成份，有益于下降射頻輻射的能量。箝位電路首要用來避免半導體器材和電容器被擊穿的風險。兼顧箝位電路維護效果和開關電源的(de)效率要求，TVS管(guan)的(de)擊穿電(dian)(dian)壓(ya)(ya)挑選(xuan)為初級繞組(zu)感(gan)應電(dian)(dian)壓(ya)(ya)的(de)1.5倍。當TVS上的(de)電(dian)(dian)壓(ya)(ya)超過必定起伏時(shi)(shi)，器材迅(xun)速導(dao)通(tong)，然后將浪涌(yong)能量(liang)泄放掉，并(bing)將浪涌(yong)電(dian)(dian)壓(ya)(ya)的(de)幅值約束在必定的(de)起伏。在開(kai)關管(guan)漏極和輸(shu)出二(er)極管(guan)的(de)正極引線上可串聯帶可飽(bao)滿(man)磁芯(xin)線圈(quan)或微晶磁珠，材質一般為鈷，當經過正常電(dian)(dian)流時(shi)(shi)磁芯(xin)飽(bao)滿(man)，電(dian)(dian)感(gan)量(liang)非常小。一旦電(dian)(dian)流要反(fan)向流過時(shi)(shi)，它將發(fa)生非常大(da)的(de)反(fan)電(dian)(dian)勢，這樣就能有(you)效地按捺二(er)極管(guan)的(de)反(fan)向浪涌(yong)電(dian)(dian)流。
2.3屏蔽辦法
按捺輻射噪聲的有效辦法便是屏蔽。能夠用導電功能杰出的資料對電場進行屏蔽，用磁導率高的資料對磁場進行屏蔽。為了避免變壓器的磁場走漏，使變壓器初次級耦合杰出，能夠運用閉合磁環構成磁屏蔽，如罐型磁芯的漏磁通就顯著比E型的小很多。開關電源的連接線，電源線都應該運用具有屏蔽層的導線，盡量避免外部攪擾耦合到電路中。或許運用磁珠、磁環等EMC元件，濾除電源及信號線的高頻攪擾。可是，要注意信號頻率不能遭到EMC元件的攪擾，也便是信號頻率要在濾波器的通帶之內。整個開關電源的外殼也需求有杰出的屏蔽特性，接縫處要契合EMC規則的屏蔽要求。經過上述辦法確保開關電源既不受外部(bu)電(dian)磁(ci)環境的攪擾(rao)(rao)也不會(hui)對外部(bu)電(dian)子設備發生攪擾(rao)(rao)。
2.4變壓器的繞制
在規劃(hua)高頻變壓器(qi)時(shi)必須把漏(lou)(lou)感減(jian)到最小。由于漏(lou)(lou)感越大(da)，發生(sheng)的(de)(de)(de)尖峰電壓幅值越高，漏(lou)(lou)極箝位(wei)電路的(de)(de)(de)損耗就越大(da)，這必然導致電源效率下降。減(jian)小變壓器(qi)的(de)(de)(de)漏(lou)(lou)感一般(ban)選用削減(jian)原邊繞組的(de)(de)(de)匝數(shu)、增大(da)繞組的(de)(de)(de)寬度、減(jian)小各繞組之間(jian)的(de)(de)(de)絕緣(yuan)層等辦法。
變壓器首(shou)要的寄(ji)生參數為(wei)漏(lou)感(gan)、繞組間(jian)電(dian)(dian)容(rong)(rong)、交叉耦合(he)電(dian)(dian)容(rong)(rong)。變壓器繞組間(jian)的交叉耦合(he)電(dian)(dian)容(rong)(rong)為(wei)共模噪聲流過整個體系供給了通(tong)路。
在(zai)(zai)變壓器(qi)的繞制(zhi)進程中選用法拉第(di)屏蔽來(lai)減小交(jiao)叉耦(ou)合電(dian)容。法拉第(di)屏蔽簡單來(lai)說便(bian)是用銅箔(bo)或(huo)鋁箔(bo)包(bao)繞在(zai)(zai)原邊繞組(zu)和副邊繞組(zu)之(zhi)間(jian)，構成一(yi)個表面屏蔽層阻隔(ge)區，并接(jie)地(di)，其華夏邊繞組(zu)和副邊繞組(zu)交(jiao)織(zhi)繞制(zhi)，以(yi)減小交(jiao)叉耦(ou)合電(dian)容。在(zai)(zai)安裝規程上一(yi)般要求散熱器(qi)接(jie)地(di)，那么(me)開關管(guan)漏極與散熱器(qi)之(zhi)間(jian)的寄(ji)(ji)生電(dian)容就為共模噪(zao)聲供(gong)給了通路，能夠在(zai)(zai)漏極和散熱器(qi)之(zhi)間(jian)加一(yi)銅箔(bo)或(huo)鋁箔(bo)并接(jie)地(di)以(yi)減小此寄(ji)(ji)生電(dian)容。
2.5接(jie)地技能的使用
開關電源需求重(zhong)視地線的連(lian)接(jie)，地線承擔著參閱(yue)電(dian)平(ping)(ping)的重(zhong)擔，特別是操(cao)控電(dian)路的參閱(yue)地，如電(dian)流檢測電(dian)阻(zu)的地電(dian)平(ping)(ping)緩無阻(zu)隔輸出的分壓電(dian)阻(zu)的地電(dian)平(ping)(ping)。
（1）設備(bei)的信號接(jie)(jie)地(di)(di)。設備(bei)的信號接(jie)(jie)地(di)(di)，或許是以(yi)設備(bei)中(zhong)的一(yi)點(dian)或一(yi)塊金(jin)屬來(lai)作為信號的接(jie)(jie)地(di)(di)參(can)閱點(dian)，它(ta)為設備(bei)中(zhong)的所有信號供給了(le)一(yi)個(ge)公共(gong)參(can)閱電位。如浮地(di)(di)和混(hun)合接(jie)(jie)地(di)(di)，別的還(huan)有單點(dian)接(jie)(jie)地(di)(di)和多點(dian)接(jie)(jie)地(di)(di)。
（2）設備接(jie)(jie)大(da)地。在工程實踐中，除仔細(xi)考慮(lv)設備內(nei)部的(de)(de)信號(hao)接(jie)(jie)地外，一(yi)般還將(jiang)設備的(de)(de)信號(hao)地，機殼與大(da)地連在一(yi)起，以大(da)地作為設備的(de)(de)接(jie)(jie)地參(can)閱點。
操(cao)控信號的地(di)(di)電平衰減應盡(jin)或許(xu)的小，因而(er)，選用操(cao)控部(bu)分一點接地(di)(di)，然后將公(gong)共連接點再單點接至功率地(di)(di)。這(zhe)種接地(di)(di)方(fang)法能夠使噪聲(sheng)源和敏感電路(lu)別(bie)離。別(bie)的，地(di)(di)線盡(jin)量鋪寬，對空白區域可敷銅填滿，力求下降地(di)(di)電平差錯和EMI。
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