文章主要(yao)是討(tao)論和分析開關(guan)電(dian)(dian)源(yuan)印制板(ban)布線(xian)原則(ze)、開關(guan)電(dian)(dian)源(yuan)印制板(ban)銅皮走(zou)線(xian)的(de)一些(xie)事項(xiang)、開關(guan)電(dian)(dian)源(yuan)印制板(ban)大電(dian)(dian)流走(zou)線(xian)的(de)處(chu)理以及反激電(dian)(dian)源(yuan)反射電(dian)(dian)壓的(de)一個確定(ding)因(yin)素等方面，解決鋁基板(ban)在(zai)開關(guan)電(dian)(dian)源(yuan)中的(de)應(ying)用(yong)、多層印制板(ban)在(zai)開關(guan)電(dian)(dian)源(yuan)電(dian)(dian)路中的(de)應(ying)用(yong)的(de)一些(xie)大家關(guan)注(zhu)的(de)問(wen)題。

　　一、引言

　　開(kai)關(guan)電(dian)(dian)(dian)(dian)源是(shi)一種電(dian)(dian)(dian)(dian)壓(ya)轉(zhuan)(zhuan)換電(dian)(dian)(dian)(dian)路(lu)(lu)，主要的(de)工(gong)作內容是(shi)升(sheng)壓(ya)和降壓(ya)，廣(guang)泛應(ying)用于現代電(dian)(dian)(dian)(dian)子產品。因為開(kai)關(guan)三極管總是(shi)工(gong)作在(zai)(zai)(zai) “開(kai)” 和“關(guan)” 的(de)狀態，所以叫(jiao)開(kai)關(guan)電(dian)(dian)(dian)(dian)源。開(kai)關(guan)電(dian)(dian)(dian)(dian)源實質就是(shi)一個振(zhen)蕩(dang)電(dian)(dian)(dian)(dian)路(lu)(lu)，這(zhe)種轉(zhuan)(zhuan)換電(dian)(dian)(dian)(dian)能(neng)的(de)方式(shi)，不僅應(ying)用在(zai)(zai)(zai)電(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)路(lu)(lu)，在(zai)(zai)(zai)其它的(de)電(dian)(dian)(dian)(dian)路(lu)(lu)應(ying)用也(ye)很普遍(bian)，如液晶顯示器的(de)背光電(dian)(dian)(dian)(dian)路(lu)(lu)、日光燈等。開(kai)關(guan)電(dian)(dian)(dian)(dian)源與變(bian)壓(ya)器相比(bi)具有(you)效率高、穩(wen)性好、體(ti)積(ji)小等優點，缺點是(shi)功率相對較小，而且(qie)會(hui)對電(dian)(dian)(dian)(dian)路(lu)(lu)產生高頻(pin)干擾，變(bian)壓(ya)器反饋式(shi)振(zhen)蕩(dang)電(dian)(dian)(dian)(dian)路(lu)(lu)，能(neng)產生有(you)規律的(de)脈沖電(dian)(dian)(dian)(dian)流或電(dian)(dian)(dian)(dian)壓(ya)的(de)電(dian)(dian)(dian)(dian)路(lu)(lu)叫(jiao)振(zhen)蕩(dang)電(dian)(dian)(dian)(dian)路(lu)(lu)，變(bian)壓(ya)器反饋式(shi)振(zhen)蕩(dang)電(dian)(dian)(dian)(dian)路(lu)(lu)就是(shi)能(neng)滿足這(zhe)種條(tiao)件(jian)的(de)電(dian)(dian)(dian)(dian)路(lu)(lu)。

　　開(kai)關電源(yuan)分為，隔(ge)離(li)與非隔(ge)離(li)兩(liang)種形(xing)式(shi)，在(zai)(zai)這(zhe)里主要(yao)談一談隔(ge)離(li)式(shi)開(kai)關電源(yuan)的拓撲形(xing)式(shi)，在(zai)(zai)下文中，非特別(bie)說明，均(jun)指(zhi)(zhi)隔(ge)離(li)電源(yuan)。隔(ge)離(li)電源(yuan)按照結構形(xing)式(shi)不(bu)同，可(ke)分為兩(liang)大類：正(zheng)激(ji)式(shi)和反激(ji)式(shi)。反激(ji)式(shi)指(zhi)(zhi)在(zai)(zai)變(bian)壓(ya)器原(yuan)邊(bian)(bian)導通時副(fu)邊(bian)(bian)截(jie)止(zhi)，變(bian)壓(ya)器儲能(neng)(neng)。原(yuan)邊(bian)(bian)截(jie)止(zhi)時，副(fu)邊(bian)(bian)導通，能(neng)(neng)量釋放到(dao)(dao)負載的工作狀態，一般常(chang)(chang)規反激(ji)式(shi)電源(yuan)單(dan)管多，雙管的不(bu)常(chang)(chang)見(jian)。正(zheng)激(ji)式(shi)指(zhi)(zhi)在(zai)(zai)變(bian)壓(ya)器原(yuan)邊(bian)(bian)導通同時副(fu)邊(bian)(bian)感應出對應電壓(ya)輸出到(dao)(dao)負載，能(neng)(neng)量通過變(bian)壓(ya)器直(zhi)接傳遞。按規格又(you)可(ke)分為常(chang)(chang)規正(zheng)激(ji)，包(bao)括單(dan)管正(zheng)激(ji)，雙管正(zheng) 激(ji)。半(ban)橋(qiao)(qiao)、橋(qiao)(qiao)式(shi)電路(lu)都(dou)屬于(yu)正(zheng)激(ji)電路(lu)。

　　正激(ji)和(he)反(fan)激(ji)電(dian)(dian)路(lu)(lu)各(ge)有其(qi)特點，在設計電(dian)(dian)路(lu)(lu)的過程中(zhong)為達到最優性(xing)價比，可以靈(ling)活運用。一(yi)般在小功(gong)(gong)率(lv)場合可選用反(fan)激(ji)式。稍微大(da)一(yi)些可采(cai)(cai)用單管正激(ji)電(dian)(dian)路(lu)(lu)，中(zhong)等功(gong)(gong)率(lv)可采(cai)(cai)用雙(shuang)管正激(ji)電(dian)(dian)路(lu)(lu)或(huo)半(ban)橋電(dian)(dian)路(lu)(lu)，低電(dian)(dian)壓(ya)時采(cai)(cai)用推(tui)挽電(dian)(dian)路(lu)(lu)，與半(ban)橋工作(zuo)狀態相同。大(da)功(gong)(gong)率(lv)輸出，一(yi)般采(cai)(cai)用橋式電(dian)(dian)路(lu)(lu)，低壓(ya)也(ye)可采(cai)(cai)用推(tui)挽電(dian)(dian)路(lu)(lu)。

　　反(fan)激式電(dian)源(yuan)因其結構簡單(dan)，省掉了一個和(he)變壓(ya)器體積大小差不(bu)多的(de)電(dian)感，而在中小功(gong)(gong)率電(dian)源(yuan)中得到廣泛的(de)應(ying)用(yong)。在有些介(jie)紹中講到反(fan)激式電(dian)源(yuan)功(gong)(gong)率只能做到幾(ji)十瓦，輸出(chu)功(gong)(gong)率超過100瓦就(jiu)沒(mei)有優(you)勢(shi)，實現起來有難度。本人(ren)認為一般情況下是這樣的(de)，但(dan)也不(bu)能一概而論，PI公司的(de)TOP芯片(pian)就(jiu)可做到300瓦，有文章介(jie)紹反(fan)激電(dian)源(yuan)可做到上(shang)千瓦，但(dan)沒(mei)見過實物。輸出(chu)功(gong)(gong)率大小與輸出(chu)電(dian)壓(ya)高低(di)有關。

　　反激(ji)電源(yuan)變(bian)壓器漏感是一個非常關鍵(jian)的(de)參數，由于反激(ji)電源(yuan)需要變(bian)壓器儲存(cun)能量，要 使(shi)變(bian)壓器鐵芯得到充分利用(yong)，一般都要在磁(ci)(ci)路中(zhong)(zhong)開氣隙，其目的(de)是改變(bian)鐵芯磁(ci)(ci)滯回(hui)線(xian)的(de)斜(xie)率，使(shi)變(bian)壓器能夠承受大的(de)脈沖電流沖擊(ji)，而不至于鐵芯進入飽和非線(xian)形(xing)狀 態，磁(ci)(ci)路中(zhong)(zhong)氣隙處于高磁(ci)(ci)阻狀態，在磁(ci)(ci)路中(zhong)(zhong)產(chan)生漏磁(ci)(ci)遠大于完全(quan)閉合(he)磁(ci)(ci)路。

　　脈沖(chong)電(dian)(dian)(dian)(dian)壓(ya)(ya)連(lian)線(xian)盡(jin)(jin)可能短，其中(zhong)輸(shu)(shu)入(ru)開(kai)關(guan)管到(dao)變(bian)(bian)壓(ya)(ya)器連(lian)線(xian)，輸(shu)(shu)出(chu)變(bian)(bian)壓(ya)(ya)器到(dao)整流管連(lian)接線(xian)。脈沖(chong)電(dian)(dian)(dian)(dian)流環路盡(jin)(jin)可能小(xiao)如輸(shu)(shu)入(ru)濾波電(dian)(dian)(dian)(dian)容(rong)正到(dao)變(bian)(bian)壓(ya)(ya)器到(dao)開(kai)關(guan)管返回電(dian)(dian)(dian)(dian)容(rong)負(fu)。輸(shu)(shu)出(chu)部分變(bian)(bian)壓(ya)(ya)器出(chu)端(duan)到(dao)整流管到(dao)輸(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)感到(dao)輸(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)容(rong)返回變(bian)(bian)壓(ya)(ya)器電(dian)(dian)(dian)(dian)路中(zhong)X電(dian)(dian)(dian)(dian)容(rong)要(yao)盡(jin)(jin)量接 近開(kai)關(guan)電(dian)(dian)(dian)(dian)源輸(shu)(shu)入(ru)端(duan)，輸(shu)(shu)入(ru)線(xian)應(ying)(ying)(ying)避免與(yu)其他(ta)電(dian)(dian)(dian)(dian)路平行，應(ying)(ying)(ying)避開(kai)。Y電(dian)(dian)(dian)(dian)容(rong)應(ying)(ying)(ying)放(fang)置(zhi)在(zai)機殼接地端(duan)子或FG連(lian)接端(duan)。共摸電(dian)(dian)(dian)(dian)感應(ying)(ying)(ying)與(yu)變(bian)(bian)壓(ya)(ya)器保持(chi)一定距離，以避免磁偶合。

　　輸(shu)出(chu)電(dian)容(rong)一般可采用(yong)(yong)兩只(zhi)一只(zhi)靠近整(zheng)流管另(ling)一只(zhi)應(ying)靠近輸(shu)出(chu)端子，可影響(xiang)電(dian)源輸(shu)出(chu)紋波(bo)指(zhi)標，兩只(zhi)小容(rong)量電(dian)容(rong)并聯(lian)效果應(ying)優于用(yong)(yong)一只(zhi)大(da)(da)容(rong)量電(dian)容(rong)。發熱器件要和電(dian)解 電(dian)容(rong)保持(chi)一定距離，以(yi)延長整(zheng)機(ji)壽(shou)命(ming)，電(dian)解電(dian)容(rong)是開關電(dian)源壽(shou)命(ming)的瓶勁，如變壓器、功率管、大(da)(da)功率電(dian)阻要和電(dian)解保持(chi)距離，電(dian)解之間也(ye)須留(liu)出(chu)散熱空間，條件允許可將其放置在進風(feng)口。

　　二、印制板布線的一些原則

　　印制(zhi)板(ban)設計(ji)時(shi)，要考(kao)慮到干(gan)擾(rao)(rao)對(dui)系統的(de)(de)(de)影響，將(jiang)電(dian)(dian)(dian)路(lu)(lu)的(de)(de)(de)模擬(ni)(ni)部(bu)分和(he)數字(zi)部(bu)分的(de)(de)(de)電(dian)(dian)(dian)路(lu)(lu)嚴格分開，對(dui)核心電(dian)(dian)(dian)路(lu)(lu)重點防(fang)護(hu)，將(jiang)系統地(di)線環(huan)繞，并布線盡可能粗，電(dian)(dian)(dian)源(yuan)(yuan)增加濾波電(dian)(dian)(dian)路(lu)(lu)，采用DC-DC隔(ge)離(li)，信(xin)號采用光電(dian)(dian)(dian)隔(ge)離(li)，設計(ji)隔(ge)離(li)電(dian)(dian)(dian)源(yuan)(yuan)，分析容(rong)易產(chan)生干(gan)擾(rao)(rao)的(de)(de)(de)部(bu)分（如(ru)時(shi)鐘電(dian)(dian)(dian)路(lu)(lu)、通訊電(dian)(dian)(dian)路(lu)(lu)等）和(he)容(rong)易被干(gan)擾(rao)(rao)的(de)(de)(de)部(bu)分（如(ru)模擬(ni)(ni)采樣電(dian)(dian)(dian)路(lu)(lu)等），對(dui)這兩(liang)種類(lei)型的(de)(de)(de)電(dian)(dian)(dian)路(lu)(lu)分別(bie)采取措(cuo)施(shi)(shi)。對(dui)于(yu)干(gan)擾(rao)(rao)元件(jian)采取抑(yi)制(zhi)措(cuo)施(shi)(shi)，對(dui)敏感元件(jian)采取隔(ge)離(li)和(he)保(bao)護(hu)措(cuo)施(shi)(shi)，并且將(jiang)它(ta)們在(zai)空(kong)(kong)間和(he)電(dian)(dian)(dian)氣(qi)上拉開距離(li)。在(zai)板(ban)級設計(ji)時(shi)，還要注意元器件(jian)放置(zhi)要遠離(li)印制(zhi)板(ban)邊(bian)沿，這對(dui)防(fang)護(hu)空(kong)(kong)氣(qi)放電(dian)(dian)(dian)是有利的(de)(de)(de)。樣電(dian)(dian)(dian)路(lu)(lu)的(de)(de)(de)原理圖設計(ji)參見圖1。

　　圖1 樣電路的原理圖設計(ji)原理圖

　　線(xian)間距(ju)(ju)(ju)：隨著印制(zhi)線(xian)路板(ban)(ban)制(zhi)造(zao)工(gong)藝的不(bu)斷完(wan)善和(he)提高(gao)，一般(ban)加工(gong)廠制(zhi)造(zao)出線(xian)間距(ju)(ju)(ju)等于甚至小于0.1mm已經(jing)不(bu)存在(zai)什么問題，完(wan)全(quan)能(neng)夠滿足大(da)多(duo)數應(ying)用(yong)場合(he)。考慮 到開關電源所(suo)采(cai)用(yong)的元器件(jian)及生(sheng)(sheng)產工(gong)藝，一般(ban)雙面(mian)板(ban)(ban)最小線(xian)間距(ju)(ju)(ju)設為0.3mm，單面(mian)板(ban)(ban)最小線(xian)間距(ju)(ju)(ju)設為0.5mm，焊(han)盤(pan)(pan)與(yu)焊(han)盤(pan)(pan)、焊(han)盤(pan)(pan)與(yu)過(guo)孔(kong)或過(guo)孔(kong)與(yu)過(guo)孔(kong)，最小 間距(ju)(ju)(ju)設為0.5mm，可避免在(zai)焊(han)接操作過(guo)程中出現(xian)“橋(qiao)接”現(xian)象。，這樣大(da)多(duo)數制(zhi)板(ban)(ban)廠都(dou)能(neng)夠很(hen)輕松滿足生(sheng)(sheng)產要求，并可以把成(cheng)品率控制(zhi)得非常高(gao)，亦可實現(xian)合(he)理 的布線(xian)密度及有一個較經(jing)濟(ji)的成(cheng)本。