詳解電容在電源中所起到的作用
2019/7/1 12:46:11??????點擊：
作為無源(yuan)元件之一的電容，其作用不外(wai)乎以下幾種：
1、應用于電源電路(lu)，實現旁路(lu)、去藕、濾波和儲能方面(mian)電容的作用，下面(mian)分類詳述之：
1)濾(lv)波
濾波是電(dian)(dian)(dian)容(rong)(rong)(rong)的(de)作用中很重要的(de)一(yi)部分(fen)。幾乎所有的(de)電(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)路(lu)中都會用到(dao)。從理論上(即假(jia)設電(dian)(dian)(dian)容(rong)(rong)(rong)為(wei)純(chun)電(dian)(dian)(dian)容(rong)(rong)(rong))說，電(dian)(dian)(dian)容(rong)(rong)(rong)越(yue)(yue)(yue)大(da)(da)，阻抗(kang)越(yue)(yue)(yue)小，通過(guo)(guo)的(de)頻(pin)(pin)(pin)率(lv)(lv)也越(yue)(yue)(yue)高(gao)。但(dan)實際上超過(guo)(guo)1uF的(de)電(dian)(dian)(dian)容(rong)(rong)(rong)大(da)(da)多為(wei)電(dian)(dian)(dian)解(jie)電(dian)(dian)(dian)容(rong)(rong)(rong)，有很大(da)(da)的(de)電(dian)(dian)(dian)感成份，所以頻(pin)(pin)(pin)率(lv)(lv)高(gao)后反而(er)阻抗(kang)會增大(da)(da)。有時會看(kan)到(dao)有一(yi)個(ge)電(dian)(dian)(dian)容(rong)(rong)(rong)量較大(da)(da)電(dian)(dian)(dian)解(jie)電(dian)(dian)(dian)容(rong)(rong)(rong)并聯了一(yi)個(ge)小電(dian)(dian)(dian)容(rong)(rong)(rong)，這時大(da)(da)電(dian)(dian)(dian)容(rong)(rong)(rong)通低(di)(di)頻(pin)(pin)(pin)，小電(dian)(dian)(dian)容(rong)(rong)(rong)通高(gao)頻(pin)(pin)(pin)。電(dian)(dian)(dian)容(rong)(rong)(rong)的(de)作用就是通高(gao)阻低(di)(di)，通高(gao)頻(pin)(pin)(pin)阻低(di)(di)頻(pin)(pin)(pin)。電(dian)(dian)(dian)容(rong)(rong)(rong)越(yue)(yue)(yue)大(da)(da)低(di)(di)頻(pin)(pin)(pin)越(yue)(yue)(yue)容(rong)(rong)(rong)易通過(guo)(guo)，電(dian)(dian)(dian)容(rong)(rong)(rong)越(yue)(yue)(yue)大(da)(da)高(gao)頻(pin)(pin)(pin)越(yue)(yue)(yue)容(rong)(rong)(rong)易通過(guo)(guo)。具(ju)體用在(zai)濾波中,大(da)(da)電(dian)(dian)(dian)容(rong)(rong)(rong)(1000uF)濾低(di)(di)頻(pin)(pin)(pin)，小電(dian)(dian)(dian)容(rong)(rong)(rong)(20pF)濾高(gao)頻(pin)(pin)(pin)。
曾有網友將濾波(bo)電(dian)(dian)容(rong) 比作“水塘”。由于電(dian)(dian)容(rong)的兩端電(dian)(dian)壓(ya)不會突變(bian)，由此可(ke)知，信號(hao)頻率(lv)越(yue)(yue)高則(ze)衰減越(yue)(yue)大，可(ke)很形象的說電(dian)(dian)容(rong)像個水塘，不會因幾滴水的加入或蒸發(fa)而(er)(er)引起水量(liang)的變(bian)化。 它把電(dian)(dian)壓(ya)的變(bian)動轉化為電(dian)(dian)流(liu)的變(bian)化，頻率(lv)越(yue)(yue)高，峰(feng)值電(dian)(dian)流(liu)就(jiu)越(yue)(yue)大，從而(er)(er)緩(huan)沖(chong)了電(dian)(dian)壓(ya)。濾波(bo)就(jiu)是充電(dian)(dian)，放電(dian)(dian)的過程。
2)旁(pang)路
旁(pang)(pang)路電(dian)(dian)容是(shi)為本地(di)器(qi)件提供能(neng)(neng)量(liang)的(de)儲能(neng)(neng)器(qi)件，它能(neng)(neng)使(shi)穩(wen)壓器(qi)的(de)輸(shu)出均(jun)勻化(hua)，降低負(fu)載需(xu)求。就像(xiang)小型(xing)可充電(dian)(dian)電(dian)(dian)池一樣，旁(pang)(pang)路電(dian)(dian)容能(neng)(neng)夠被充電(dian)(dian)，并向(xiang)器(qi)件進(jin)行(xing)放 電(dian)(dian)。為盡量(liang)減少阻抗(kang)，旁(pang)(pang)路電(dian)(dian)容要盡量(liang)靠近負(fu)載器(qi)件的(de)供電(dian)(dian)電(dian)(dian)源管腳(jiao)和地(di)管腳(jiao)。這能(neng)(neng)夠很好地(di)防(fang)止輸(shu)入值過大而導(dao)致的(de)地(di)電(dian)(dian)位抬高和噪聲。地(di)彈是(shi)地(di)連接處在(zai)通過大 電(dian)(dian)流毛刺時(shi)的(de)電(dian)(dian)壓降。
3)去藕
去(qu)(qu)藕(ou)，又稱(cheng)解藕(ou)。從電(dian)(dian)(dian)(dian)(dian)路來(lai)說，總是(shi)(shi)(shi)(shi)(shi)可(ke)以區(qu)分為驅(qu)動(dong)(dong)(dong)的(de)(de)(de)(de)(de)源和(he)被驅(qu)動(dong)(dong)(dong)的(de)(de)(de)(de)(de)負載。如果負載電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)比(bi)較(jiao)(jiao)大，驅(qu)動(dong)(dong)(dong)電(dian)(dian)(dian)(dian)(dian)路要把電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)充電(dian)(dian)(dian)(dian)(dian)、放電(dian)(dian)(dian)(dian)(dian)，才能完成信(xin)(xin)號的(de)(de)(de)(de)(de)跳變(bian)，在上 升(sheng)沿比(bi)較(jiao)(jiao)陡(dou)峭的(de)(de)(de)(de)(de)時候(hou)，電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)比(bi)較(jiao)(jiao)大，這(zhe)(zhe)樣驅(qu)動(dong)(dong)(dong)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)就(jiu)(jiu)(jiu)會吸收很大的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，由于(yu)電(dian)(dian)(dian)(dian)(dian)路中(zhong)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)感，電(dian)(dian)(dian)(dian)(dian)阻(特(te)別(bie)是(shi)(shi)(shi)(shi)(shi)芯片管腳上的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)感，會產生(sheng)反彈)，這(zhe)(zhe)種電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)相對 于(yu)正(zheng)常情況來(lai)說實際(ji)上就(jiu)(jiu)(jiu)是(shi)(shi)(shi)(shi)(shi)一(yi)(yi)(yi)種噪聲(sheng)，會影響前級的(de)(de)(de)(de)(de)正(zheng)常工作。這(zhe)(zhe)就(jiu)(jiu)(jiu)是(shi)(shi)(shi)(shi)(shi)耦(ou)合(he)。去(qu)(qu)藕(ou)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)就(jiu)(jiu)(jiu)是(shi)(shi)(shi)(shi)(shi)起到一(yi)(yi)(yi)個電(dian)(dian)(dian)(dian)(dian)池的(de)(de)(de)(de)(de)作用(yong)，滿(man)足驅(qu)動(dong)(dong)(dong)電(dian)(dian)(dian)(dian)(dian)路電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)(de)變(bian)化，避免相互間(jian)的(de)(de)(de)(de)(de)耦(ou)合(he)干(gan)(gan)擾(rao)(rao)。將(jiang)旁(pang)(pang)路電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)和(he)去(qu)(qu)藕(ou)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)結合(he)起來(lai)將(jiang)更容(rong)(rong)(rong)(rong)易理解。旁(pang)(pang)路電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)實際(ji)也是(shi)(shi)(shi)(shi)(shi)去(qu)(qu)藕(ou)合(he)的(de)(de)(de)(de)(de)，只是(shi)(shi)(shi)(shi)(shi)旁(pang)(pang)路電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)一(yi)(yi)(yi)般(ban)(ban)是(shi)(shi)(shi)(shi)(shi)指(zhi)高頻(pin)(pin)旁(pang)(pang)路，也就(jiu)(jiu)(jiu)是(shi)(shi)(shi)(shi)(shi)給高頻(pin)(pin)的(de)(de)(de)(de)(de)開關(guan)噪聲(sheng)提高一(yi)(yi)(yi)條低(di)阻抗泄防(fang) 途徑。高頻(pin)(pin)旁(pang)(pang)路電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)一(yi)(yi)(yi)般(ban)(ban)比(bi)較(jiao)(jiao)小(xiao)，根據(ju)諧振頻(pin)(pin)率一(yi)(yi)(yi)般(ban)(ban)是(shi)(shi)(shi)(shi)(shi)0.1u，0.01u等，而去(qu)(qu)耦(ou)合(he)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)一(yi)(yi)(yi)般(ban)(ban)比(bi)較(jiao)(jiao)大，是(shi)(shi)(shi)(shi)(shi)10uF或者更大，依據(ju)電(dian)(dian)(dian)(dian)(dian)路中(zhong)分布參數，以及驅(qu)動(dong)(dong)(dong) 電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)(de)變(bian)化大小(xiao)來(lai)確(que)定。旁(pang)(pang)路是(shi)(shi)(shi)(shi)(shi)把輸入信(xin)(xin)號中(zhong)的(de)(de)(de)(de)(de)干(gan)(gan)擾(rao)(rao)作為濾除對象，而去(qu)(qu)耦(ou)是(shi)(shi)(shi)(shi)(shi)把輸出信(xin)(xin)號的(de)(de)(de)(de)(de)干(gan)(gan)擾(rao)(rao)作為濾除對象，防(fang)止(zhi)干(gan)(gan)擾(rao)(rao)信(xin)(xin)號返(fan)回電(dian)(dian)(dian)(dian)(dian)源。這(zhe)(zhe)應該是(shi)(shi)(shi)(shi)(shi)他(ta)們的(de)(de)(de)(de)(de)本質區(qu)別(bie)。
4)儲能
儲(chu)能型電(dian)(dian)容(rong)器(qi)通(tong)(tong)過整流器(qi)收集(ji)電(dian)(dian)荷(he)，并(bing)將存儲(chu)的(de)能量通(tong)(tong)過變換器(qi)引線傳(chuan)送至電(dian)(dian)源(yuan)的(de)輸出端(duan)。電(dian)(dian)壓額定值為(wei)40～450VDC、電(dian)(dian)容(rong)值在220～150 000uF之間的(de)鋁電(dian)(dian)解電(dian)(dian)容(rong)器(qi)(如EPCOS公司(si)的(de) B43504或B43505)是較(jiao)為(wei)常用(yong)的(de)。根據不(bu)同的(de)電(dian)(dian)源(yuan)要求，器(qi)件有時會(hui)采用(yong)串聯、并(bing)聯或其(qi)組合的(de)形式， 對于(yu)功率級超過10KW的(de)電(dian)(dian)源(yuan)，通(tong)(tong)常采用(yong)體(ti)積較(jiao)大的(de)罐形螺(luo)旋端(duan)子電(dian)(dian)容(rong)器(qi)。
2、應用于信號(hao)電路，主要完成耦合、振(zhen)蕩/同步及(ji)時間(jian)常數(shu)的作(zuo)用：
1)耦(ou)合(he)
舉個例子來講，晶(jing)體管放大器發(fa)射極有(you)一個自給偏壓電(dian)(dian)阻(zu)，它(ta)同(tong)時又(you)使(shi)信號產生(sheng)(sheng)壓降反饋到輸(shu)入端(duan)形成了(le)輸(shu)入輸(shu)出信號耦合，這個電(dian)(dian)阻(zu)就是產生(sheng)(sheng)了(le)耦合的(de)元(yuan)件，如果在(zai)這個電(dian)(dian)阻(zu)兩端(duan)并聯一個電(dian)(dian)容(rong)，由于適當(dang)容(rong)量的(de)電(dian)(dian)容(rong)器對(dui)交(jiao)流(liu)信號較小的(de)阻(zu)抗,這樣就減小了(le)電(dian)(dian)阻(zu)產生(sheng)(sheng)的(de)耦合效應，故(gu)稱(cheng)此電(dian)(dian)容(rong)為去耦電(dian)(dian)容(rong)。
2)振蕩/同步(bu)
包括RC、LC振(zhen)蕩(dang)器及晶體的負載電(dian)容都屬于這一范疇。
3)時間常數(shu)
這就是常(chang)見的(de)(de) R、C 串(chuan)聯(lian)構成(cheng)的(de)(de)積分電(dian)路。當輸(shu)入信號(hao)電(dian)壓加在輸(shu)入端時，電(dian)容(C)上(shang)(shang)的(de)(de)電(dian)壓逐漸(jian)上(shang)(shang)升(sheng)。而其充電(dian)電(dian)流則隨著電(dian)壓的(de)(de)上(shang)(shang)升(sheng)而減小。電(dian)流通過電(dian)阻(zu)(R)、電(dian)容(C)的(de)(de)特性通過下面的(de)(de)公式描述：
i = (V/R)e-(t/CR)
我們知道(dao)了電容的作用(yong)以后下面來談談電容在使用(yong)中的注(zhu)意事項
A. 什(shen)么(me)是好電容。
1.電(dian)容容量越(yue)大越(yue)好。
很多人(ren)在(zai)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)的(de)(de)(de)替換中往(wang)往(wang)愛用大容(rong)(rong)(rong)量(liang)(liang)(liang)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)。我們知道(dao)雖然電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)越(yue)(yue)大，為IC提(ti)供(gong)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流補償(chang)的(de)(de)(de)能力(li)越(yue)(yue)強。且不說(shuo)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)容(rong)(rong)(rong)量(liang)(liang)(liang)的(de)(de)(de)增(zeng)大帶來的(de)(de)(de)體積(ji)變大，增(zeng)加成本的(de)(de)(de)同時(shi)還影響空(kong)氣流動和散熱。關(guan)鍵在(zai)于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)上存在(zai)寄(ji)生(sheng)電(dian)(dian)(dian)(dian)(dian)(dian)感，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)放電(dian)(dian)(dian)(dian)(dian)(dian)回(hui)路(lu)會在(zai)某個頻(pin)(pin)(pin)點(dian)上發(fa)生(sheng)諧振(zhen)(zhen)。在(zai)諧振(zhen)(zhen)點(dian)，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)的(de)(de)(de)阻抗(kang)(kang)小(xiao)。因此放電(dian)(dian)(dian)(dian)(dian)(dian)回(hui)路(lu)的(de)(de)(de)阻抗(kang)(kang)最(zui)小(xiao)，補充能量(liang)(liang)(liang)的(de)(de)(de)效果也(ye)(ye)最(zui)好(hao)。但當頻(pin)(pin)(pin)率(lv)超過(guo)諧振(zhen)(zhen)點(dian)時(shi)，放電(dian)(dian)(dian)(dian)(dian)(dian)回(hui)路(lu)的(de)(de)(de)阻抗(kang)(kang)開(kai)(kai)始增(zeng)加，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)提(ti)供(gong)電(dian)(dian)(dian)(dian)(dian)(dian)流能力(li)便開(kai)(kai)始下降。電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)的(de)(de)(de)容(rong)(rong)(rong)值越(yue)(yue)大，諧振(zhen)(zhen)頻(pin)(pin)(pin)率(lv)越(yue)(yue)低，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)能有效補償(chang)電(dian)(dian)(dian)(dian)(dian)(dian)流的(de)(de)(de)頻(pin)(pin)(pin)率(lv)范(fan)圍也(ye)(ye)越(yue)(yue)小(xiao)。從(cong)保(bao)證電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)提(ti)供(gong)高頻(pin)(pin)(pin)電(dian)(dian)(dian)(dian)(dian)(dian)流的(de)(de)(de)能力(li)的(de)(de)(de)角度來說(shuo)，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)越(yue)(yue)大越(yue)(yue)好(hao)的(de)(de)(de)觀點(dian)是錯誤的(de)(de)(de)，一般的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)設計中都有一個參考值的(de)(de)(de)。
2.同樣容(rong)量的(de)電(dian)容(rong)，并聯越多(duo)的(de)小電(dian)容(rong)越好
耐(nai)壓(ya)(ya)值(zhi)、耐(nai)溫值(zhi)、容(rong)值(zhi)、ESR(等效電阻)等是(shi)(shi)電容(rong)的(de)(de)幾個重要參(can)數，對(dui)于ESR自然是(shi)(shi)越(yue)低(di)越(yue)好(hao)。ESR與(yu)電容(rong)的(de)(de)容(rong)量(liang)、頻率、電壓(ya)(ya)、溫度等都有關(guan)系。當電壓(ya)(ya)固定時候(hou)，容(rong)量(liang)越(yue)大，ESR越(yue)低(di)。在板卡(ka)設計中采用(yong)多(duo)個小(xiao)(xiao)電容(rong)并連多(duo)是(shi)(shi)出(chu)與(yu)PCB空間(jian)的(de)(de)限制，這(zhe)樣有的(de)(de)人就認為，越(yue)多(duo)的(de)(de)并聯小(xiao)(xiao)電阻，ESR越(yue)低(di)，效果(guo)越(yue)好(hao)。理論上是(shi)(shi)如此，但是(shi)(shi)要考慮到電容(rong)接腳焊點的(de)(de)阻抗，采用(yong)多(duo)個小(xiao)(xiao)電容(rong)并聯，效果(guo)并不一(yi)定突出(chu)。
3.ESR越低(di)，效果越好。
結(jie)合我們上(shang)面的(de)(de)(de)提高(gao)的(de)(de)(de)供電(dian)(dian)(dian)電(dian)(dian)(dian)路(lu)(lu)來(lai)說(shuo)(shuo)，對(dui)于輸(shu)(shu)入(ru)電(dian)(dian)(dian)容(rong)來(lai)說(shuo)(shuo)，輸(shu)(shu)入(ru)電(dian)(dian)(dian)容(rong)的(de)(de)(de)容(rong)量(liang)要(yao)(yao)(yao)大一點。相對(dui)容(rong)量(liang)的(de)(de)(de)要(yao)(yao)(yao)求，對(dui)ESR的(de)(de)(de)要(yao)(yao)(yao)求可以(yi)適當的(de)(de)(de)降低。因為(wei)輸(shu)(shu)入(ru)電(dian)(dian)(dian)容(rong)主(zhu)要(yao)(yao)(yao)是耐壓，其次(ci)是吸收MOSFET的(de)(de)(de)開(kai)關脈沖。對(dui)于輸(shu)(shu)出(chu)電(dian)(dian)(dian)容(rong)來(lai)說(shuo)(shuo)，耐壓的(de)(de)(de)要(yao)(yao)(yao)求和容(rong)量(liang)可以(yi)適當的(de)(de)(de)降低一點。ESR的(de)(de)(de)要(yao)(yao)(yao)求則高(gao)一點，因為(wei)這里要(yao)(yao)(yao)保(bao)證的(de)(de)(de)是足夠的(de)(de)(de)電(dian)(dian)(dian)流通過量(liang)。但(dan)這里要(yao)(yao)(yao)注意的(de)(de)(de)是ESR并不是越(yue)低越(yue)好，低ESR電(dian)(dian)(dian)容(rong)會引起(qi)開(kai)關電(dian)(dian)(dian)路(lu)(lu)振(zhen)蕩(dang)。而消振(zhen)電(dian)(dian)(dian)路(lu)(lu)復雜同時會導致成本(ben)(ben)的(de)(de)(de)增加。板卡設計中，這里一般有一個(ge)參(can)考值，此作為(wei)元(yuan)件選用參(can)數，避免消振(zhen)電(dian)(dian)(dian)路(lu)(lu)而導致成本(ben)(ben)的(de)(de)(de)增加。
4.好(hao)電容代(dai)表著高品質。
“唯電(dian)(dian)容(rong)(rong)論”曾(ceng)經盛極(ji)一(yi)(yi)(yi)(yi)時(shi)，一(yi)(yi)(yi)(yi)些(xie)廠商(shang)和媒體也刻意的(de)(de)(de)把這個事情做(zuo)成一(yi)(yi)(yi)(yi)個賣點。在板(ban)卡設計(ji)中(zhong)，電(dian)(dian)路設計(ji)水平是關鍵。和有的(de)(de)(de)廠商(shang)可以(yi)用(yong)兩相供電(dian)(dian)做(zuo)出(chu)比一(yi)(yi)(yi)(yi)些(xie)廠商(shang)采用(yong)四相供電(dian)(dian)更穩定(ding)(ding)的(de)(de)(de)產(chan)品(pin)一(yi)(yi)(yi)(yi)樣，一(yi)(yi)(yi)(yi)味(wei)的(de)(de)(de)采用(yong)高價電(dian)(dian)容(rong)(rong)，不(bu)一(yi)(yi)(yi)(yi)定(ding)(ding)能做(zuo)出(chu)好產(chan)品(pin)。衡量一(yi)(yi)(yi)(yi)個產(chan)品(pin)，一(yi)(yi)(yi)(yi)定(ding)(ding)要(yao)全方位多角度(du)的(de)(de)(de)去考慮，切不(bu)可把電(dian)(dian)容(rong)(rong)的(de)(de)(de)作用(yong)有意無意的(de)(de)(de)夸大。
B. 電容(rong)爆漿之面面談
爆(bao)漿(jiang)的種類：
分(fen)兩類，輸入(ru)電(dian)容爆漿和輸出電(dian)容爆漿。
對(dui)于輸入電(dian)(dian)(dian)(dian)容來說，就是(shi)我(wo)是(shi)說的C1，C1對(dui)由電(dian)(dian)(dian)(dian)源接收到的電(dian)(dian)(dian)(dian)流(liu)進行(xing)過(guo)(guo)濾。輸入電(dian)(dian)(dian)(dian)容爆漿和電(dian)(dian)(dian)(dian)源輸入電(dian)(dian)(dian)(dian)流(liu)的品質有關。過(guo)(guo)多的毛刺(ci)電(dian)(dian)(dian)(dian)壓，峰值電(dian)(dian)(dian)(dian)壓過(guo)(guo)高，電(dian)(dian)(dian)(dian)流(liu)不穩定(ding)等(deng)都使電(dian)(dian)(dian)(dian)容過(guo)(guo)于充放電(dian)(dian)(dian)(dian)過(guo)(guo)于頻繁，長(chang)時間處(chu)于這(zhe)類工作環境(jing)下的電(dian)(dian)(dian)(dian)容，內部溫度升(sheng)高很(hen)快。超(chao)過(guo)(guo)泄爆口的承受極限(xian)就會(hui)發生爆漿。
對于輸出電(dian)容來說，就(jiu)我說的(de)C2，對經電(dian)源模(mo)塊(kuai)調整后的(de)電(dian)流(liu)(liu)進行濾波。此處電(dian)流(liu)(liu)經過一(yi)次(ci)過濾，比較平穩，發(fa)生爆漿的(de)可能(neng)性相對來說小了不少。但如(ru)果(guo)(guo)環境(jing)溫度(du)過高，電(dian)容同樣容易發(fa)生爆漿。爆，報也。采用垃圾東(dong)西自然(ran)要爆，報應啊。欲(yu)知過去因者，見其現在果(guo)(guo);欲(yu)知未來果(guo)(guo)者，見其現在因。
電解電容爆(bao)漿的原因：
電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)爆漿(jiang)的(de)(de)(de)原(yuan)因(yin)有(you)很(hen)多，比如(ru)電(dian)(dian)(dian)(dian)流大(da)于允許(xu)的(de)(de)(de)穩(wen)波(bo)電(dian)(dian)(dian)(dian)流、使(shi)用(yong)(yong)電(dian)(dian)(dian)(dian)壓(ya)(ya)超(chao)出工作電(dian)(dian)(dian)(dian)壓(ya)(ya)、逆向電(dian)(dian)(dian)(dian)壓(ya)(ya)、頻(pin)繁的(de)(de)(de)充(chong)放電(dian)(dian)(dian)(dian)等。但是(shi)最直接的(de)(de)(de)原(yuan)因(yin)就(jiu)(jiu)(jiu)是(shi)高溫(wen)(wen)(wen)(wen)。我(wo)們知道(dao)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)有(you)一個(ge)重要(yao)的(de)(de)(de)參數就(jiu)(jiu)(jiu)是(shi)耐溫(wen)(wen)(wen)(wen)值，指的(de)(de)(de)就(jiu)(jiu)(jiu)是(shi)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)內部電(dian)(dian)(dian)(dian)解(jie)(jie)(jie)液(ye)的(de)(de)(de)沸(fei)點。當電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)的(de)(de)(de)內部溫(wen)(wen)(wen)(wen)度達(da)到電(dian)(dian)(dian)(dian)解(jie)(jie)(jie)液(ye)的(de)(de)(de)沸(fei)點時(shi)，電(dian)(dian)(dian)(dian)解(jie)(jie)(jie)液(ye)開始沸(fei)騰，電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)內部的(de)(de)(de)壓(ya)(ya)力升高，當壓(ya)(ya)力超(chao)過(guo)(guo)泄爆口(kou)的(de)(de)(de)承受極限就(jiu)(jiu)(jiu)發生(sheng)了爆漿(jiang)。所以說(shuo)溫(wen)(wen)(wen)(wen)度是(shi)導致電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)爆漿(jiang)的(de)(de)(de)直接原(yuan)因(yin)。電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)設計(ji)使(shi)用(yong)(yong)壽(shou)(shou)命大(da)約為(wei)2萬小時(shi)，受環境(jing)(jing)溫(wen)(wen)(wen)(wen)度的(de)(de)(de)影響也很(hen)大(da)。電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)的(de)(de)(de)使(shi)用(yong)(yong)壽(shou)(shou)命隨溫(wen)(wen)(wen)(wen)度的(de)(de)(de)增加(jia)而減小，實驗證明(ming)環境(jing)(jing)溫(wen)(wen)(wen)(wen)度每(mei)升高10℃，電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)的(de)(de)(de)壽(shou)(shou)命就(jiu)(jiu)(jiu)會減半。主(zhu)要(yao)原(yuan)因(yin)就(jiu)(jiu)(jiu)是(shi)溫(wen)(wen)(wen)(wen)度加(jia)速(su)化學反(fan)應而使(shi)介(jie)質(zhi)隨時(shi)間退化失(shi)效，這樣電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)壽(shou)(shou)命終結。為(wei)了保(bao)證電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)的(de)(de)(de)穩(wen)定性，電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)在(zai)插(cha)板前要(yao)經(jing)過(guo)(guo)長(chang)時(shi)間的(de)(de)(de)高溫(wen)(wen)(wen)(wen)環境(jing)(jing)的(de)(de)(de)測試。即使(shi)是(shi)在(zai)100℃，高品(pin)質(zhi)的(de)(de)(de)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)也可(ke)以工作幾(ji)千個(ge)小時(shi)。同時(shi)，我(wo)們提(ti)到的(de)(de)(de)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)的(de)(de)(de)壽(shou)(shou)命是(shi)指電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)在(zai)使(shi)用(yong)(yong)過(guo)(guo)程中，電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)容(rong)(rong)(rong)(rong)(rong)(rong)量不會超(chao)過(guo)(guo)標(biao)準范圍變(bian)化的(de)(de)(de)10%。電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)壽(shou)(shou)命指的(de)(de)(de)是(shi)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)容(rong)(rong)(rong)(rong)(rong)(rong)量的(de)(de)(de)問題，而不是(shi)設計(ji)壽(shou)(shou)命到達(da)之后(hou)就(jiu)(jiu)(jiu)發生(sheng)爆漿(jiang)。只是(shi)無法保(bao)證電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)的(de)(de)(de)設計(ji)的(de)(de)(de)容(rong)(rong)(rong)(rong)(rong)(rong)量標(biao)準。
所以，短(duan)時期內，正常(chang)(chang)使(shi)(shi)用的(de)(de)板卡電(dian)(dian)容(rong)就(jiu)發(fa)生(sheng)爆漿(jiang)的(de)(de)情況(kuang)，這就(jiu)是電(dian)(dian)容(rong)品質問題(ti)。另外(wai)，不(bu)正常(chang)(chang)的(de)(de)使(shi)(shi)用情況(kuang)也有可能(neng)發(fa)生(sheng)電(dian)(dian)容(rong)爆漿(jiang)的(de)(de)情況(kuang)。比如熱插拔電(dian)(dian)腦配件(jian)也會(hui)導致板卡局部電(dian)(dian)路(lu)電(dian)(dian)流、電(dian)(dian)壓的(de)(de)劇(ju)烈變化(hua)，從而引發(fa)電(dian)(dian)容(rong)使(shi)(shi)用故障。
1、應用于電源電路(lu)，實現旁路(lu)、去藕、濾波和儲能方面(mian)電容的作用，下面(mian)分類詳述之：
1)濾(lv)波
濾波是電(dian)(dian)(dian)容(rong)(rong)(rong)的(de)作用中很重要的(de)一(yi)部分(fen)。幾乎所有的(de)電(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)路(lu)中都會用到(dao)。從理論上(即假(jia)設電(dian)(dian)(dian)容(rong)(rong)(rong)為(wei)純(chun)電(dian)(dian)(dian)容(rong)(rong)(rong))說，電(dian)(dian)(dian)容(rong)(rong)(rong)越(yue)(yue)(yue)大(da)(da)，阻抗(kang)越(yue)(yue)(yue)小，通過(guo)(guo)的(de)頻(pin)(pin)(pin)率(lv)(lv)也越(yue)(yue)(yue)高(gao)。但(dan)實際上超過(guo)(guo)1uF的(de)電(dian)(dian)(dian)容(rong)(rong)(rong)大(da)(da)多為(wei)電(dian)(dian)(dian)解(jie)電(dian)(dian)(dian)容(rong)(rong)(rong)，有很大(da)(da)的(de)電(dian)(dian)(dian)感成份，所以頻(pin)(pin)(pin)率(lv)(lv)高(gao)后反而(er)阻抗(kang)會增大(da)(da)。有時會看(kan)到(dao)有一(yi)個(ge)電(dian)(dian)(dian)容(rong)(rong)(rong)量較大(da)(da)電(dian)(dian)(dian)解(jie)電(dian)(dian)(dian)容(rong)(rong)(rong)并聯了一(yi)個(ge)小電(dian)(dian)(dian)容(rong)(rong)(rong)，這時大(da)(da)電(dian)(dian)(dian)容(rong)(rong)(rong)通低(di)(di)頻(pin)(pin)(pin)，小電(dian)(dian)(dian)容(rong)(rong)(rong)通高(gao)頻(pin)(pin)(pin)。電(dian)(dian)(dian)容(rong)(rong)(rong)的(de)作用就是通高(gao)阻低(di)(di)，通高(gao)頻(pin)(pin)(pin)阻低(di)(di)頻(pin)(pin)(pin)。電(dian)(dian)(dian)容(rong)(rong)(rong)越(yue)(yue)(yue)大(da)(da)低(di)(di)頻(pin)(pin)(pin)越(yue)(yue)(yue)容(rong)(rong)(rong)易通過(guo)(guo)，電(dian)(dian)(dian)容(rong)(rong)(rong)越(yue)(yue)(yue)大(da)(da)高(gao)頻(pin)(pin)(pin)越(yue)(yue)(yue)容(rong)(rong)(rong)易通過(guo)(guo)。具(ju)體用在(zai)濾波中,大(da)(da)電(dian)(dian)(dian)容(rong)(rong)(rong)(1000uF)濾低(di)(di)頻(pin)(pin)(pin)，小電(dian)(dian)(dian)容(rong)(rong)(rong)(20pF)濾高(gao)頻(pin)(pin)(pin)。
曾有網友將濾波(bo)電(dian)(dian)容(rong) 比作“水塘”。由于電(dian)(dian)容(rong)的兩端電(dian)(dian)壓(ya)不會突變(bian)，由此可(ke)知，信號(hao)頻率(lv)越(yue)(yue)高則(ze)衰減越(yue)(yue)大，可(ke)很形象的說電(dian)(dian)容(rong)像個水塘，不會因幾滴水的加入或蒸發(fa)而(er)(er)引起水量(liang)的變(bian)化。 它把電(dian)(dian)壓(ya)的變(bian)動轉化為電(dian)(dian)流(liu)的變(bian)化，頻率(lv)越(yue)(yue)高，峰(feng)值電(dian)(dian)流(liu)就(jiu)越(yue)(yue)大，從而(er)(er)緩(huan)沖(chong)了電(dian)(dian)壓(ya)。濾波(bo)就(jiu)是充電(dian)(dian)，放電(dian)(dian)的過程。
2)旁(pang)路
旁(pang)(pang)路電(dian)(dian)容是(shi)為本地(di)器(qi)件提供能(neng)(neng)量(liang)的(de)儲能(neng)(neng)器(qi)件，它能(neng)(neng)使(shi)穩(wen)壓器(qi)的(de)輸(shu)出均(jun)勻化(hua)，降低負(fu)載需(xu)求。就像(xiang)小型(xing)可充電(dian)(dian)電(dian)(dian)池一樣，旁(pang)(pang)路電(dian)(dian)容能(neng)(neng)夠被充電(dian)(dian)，并向(xiang)器(qi)件進(jin)行(xing)放 電(dian)(dian)。為盡量(liang)減少阻抗(kang)，旁(pang)(pang)路電(dian)(dian)容要盡量(liang)靠近負(fu)載器(qi)件的(de)供電(dian)(dian)電(dian)(dian)源管腳(jiao)和地(di)管腳(jiao)。這能(neng)(neng)夠很好地(di)防(fang)止輸(shu)入值過大而導(dao)致的(de)地(di)電(dian)(dian)位抬高和噪聲。地(di)彈是(shi)地(di)連接處在(zai)通過大 電(dian)(dian)流毛刺時(shi)的(de)電(dian)(dian)壓降。
3)去藕
去(qu)(qu)藕(ou)，又稱(cheng)解藕(ou)。從電(dian)(dian)(dian)(dian)(dian)路來(lai)說，總是(shi)(shi)(shi)(shi)(shi)可(ke)以區(qu)分為驅(qu)動(dong)(dong)(dong)的(de)(de)(de)(de)(de)源和(he)被驅(qu)動(dong)(dong)(dong)的(de)(de)(de)(de)(de)負載。如果負載電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)比(bi)較(jiao)(jiao)大，驅(qu)動(dong)(dong)(dong)電(dian)(dian)(dian)(dian)(dian)路要把電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)充電(dian)(dian)(dian)(dian)(dian)、放電(dian)(dian)(dian)(dian)(dian)，才能完成信(xin)(xin)號的(de)(de)(de)(de)(de)跳變(bian)，在上 升(sheng)沿比(bi)較(jiao)(jiao)陡(dou)峭的(de)(de)(de)(de)(de)時候(hou)，電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)比(bi)較(jiao)(jiao)大，這(zhe)(zhe)樣驅(qu)動(dong)(dong)(dong)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)就(jiu)(jiu)(jiu)會吸收很大的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，由于(yu)電(dian)(dian)(dian)(dian)(dian)路中(zhong)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)感，電(dian)(dian)(dian)(dian)(dian)阻(特(te)別(bie)是(shi)(shi)(shi)(shi)(shi)芯片管腳上的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)感，會產生(sheng)反彈)，這(zhe)(zhe)種電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)相對 于(yu)正(zheng)常情況來(lai)說實際(ji)上就(jiu)(jiu)(jiu)是(shi)(shi)(shi)(shi)(shi)一(yi)(yi)(yi)種噪聲(sheng)，會影響前級的(de)(de)(de)(de)(de)正(zheng)常工作。這(zhe)(zhe)就(jiu)(jiu)(jiu)是(shi)(shi)(shi)(shi)(shi)耦(ou)合(he)。去(qu)(qu)藕(ou)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)就(jiu)(jiu)(jiu)是(shi)(shi)(shi)(shi)(shi)起到一(yi)(yi)(yi)個電(dian)(dian)(dian)(dian)(dian)池的(de)(de)(de)(de)(de)作用(yong)，滿(man)足驅(qu)動(dong)(dong)(dong)電(dian)(dian)(dian)(dian)(dian)路電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)(de)變(bian)化，避免相互間(jian)的(de)(de)(de)(de)(de)耦(ou)合(he)干(gan)(gan)擾(rao)(rao)。將(jiang)旁(pang)(pang)路電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)和(he)去(qu)(qu)藕(ou)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)結合(he)起來(lai)將(jiang)更容(rong)(rong)(rong)(rong)易理解。旁(pang)(pang)路電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)實際(ji)也是(shi)(shi)(shi)(shi)(shi)去(qu)(qu)藕(ou)合(he)的(de)(de)(de)(de)(de)，只是(shi)(shi)(shi)(shi)(shi)旁(pang)(pang)路電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)一(yi)(yi)(yi)般(ban)(ban)是(shi)(shi)(shi)(shi)(shi)指(zhi)高頻(pin)(pin)旁(pang)(pang)路，也就(jiu)(jiu)(jiu)是(shi)(shi)(shi)(shi)(shi)給高頻(pin)(pin)的(de)(de)(de)(de)(de)開關(guan)噪聲(sheng)提高一(yi)(yi)(yi)條低(di)阻抗泄防(fang) 途徑。高頻(pin)(pin)旁(pang)(pang)路電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)一(yi)(yi)(yi)般(ban)(ban)比(bi)較(jiao)(jiao)小(xiao)，根據(ju)諧振頻(pin)(pin)率一(yi)(yi)(yi)般(ban)(ban)是(shi)(shi)(shi)(shi)(shi)0.1u，0.01u等，而去(qu)(qu)耦(ou)合(he)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)一(yi)(yi)(yi)般(ban)(ban)比(bi)較(jiao)(jiao)大，是(shi)(shi)(shi)(shi)(shi)10uF或者更大，依據(ju)電(dian)(dian)(dian)(dian)(dian)路中(zhong)分布參數，以及驅(qu)動(dong)(dong)(dong) 電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)(de)變(bian)化大小(xiao)來(lai)確(que)定。旁(pang)(pang)路是(shi)(shi)(shi)(shi)(shi)把輸入信(xin)(xin)號中(zhong)的(de)(de)(de)(de)(de)干(gan)(gan)擾(rao)(rao)作為濾除對象，而去(qu)(qu)耦(ou)是(shi)(shi)(shi)(shi)(shi)把輸出信(xin)(xin)號的(de)(de)(de)(de)(de)干(gan)(gan)擾(rao)(rao)作為濾除對象，防(fang)止(zhi)干(gan)(gan)擾(rao)(rao)信(xin)(xin)號返(fan)回電(dian)(dian)(dian)(dian)(dian)源。這(zhe)(zhe)應該是(shi)(shi)(shi)(shi)(shi)他(ta)們的(de)(de)(de)(de)(de)本質區(qu)別(bie)。
4)儲能
儲(chu)能型電(dian)(dian)容(rong)器(qi)通(tong)(tong)過整流器(qi)收集(ji)電(dian)(dian)荷(he)，并(bing)將存儲(chu)的(de)能量通(tong)(tong)過變換器(qi)引線傳(chuan)送至電(dian)(dian)源(yuan)的(de)輸出端(duan)。電(dian)(dian)壓額定值為(wei)40～450VDC、電(dian)(dian)容(rong)值在220～150 000uF之間的(de)鋁電(dian)(dian)解電(dian)(dian)容(rong)器(qi)(如EPCOS公司(si)的(de) B43504或B43505)是較(jiao)為(wei)常用(yong)的(de)。根據不(bu)同的(de)電(dian)(dian)源(yuan)要求，器(qi)件有時會(hui)采用(yong)串聯、并(bing)聯或其(qi)組合的(de)形式， 對于(yu)功率級超過10KW的(de)電(dian)(dian)源(yuan)，通(tong)(tong)常采用(yong)體(ti)積較(jiao)大的(de)罐形螺(luo)旋端(duan)子電(dian)(dian)容(rong)器(qi)。
2、應用于信號(hao)電路，主要完成耦合、振(zhen)蕩/同步及(ji)時間(jian)常數(shu)的作(zuo)用：
1)耦(ou)合(he)
舉個例子來講，晶(jing)體管放大器發(fa)射極有(you)一個自給偏壓電(dian)(dian)阻(zu)，它(ta)同(tong)時又(you)使(shi)信號產生(sheng)(sheng)壓降反饋到輸(shu)入端(duan)形成了(le)輸(shu)入輸(shu)出信號耦合，這個電(dian)(dian)阻(zu)就是產生(sheng)(sheng)了(le)耦合的(de)元(yuan)件，如果在(zai)這個電(dian)(dian)阻(zu)兩端(duan)并聯一個電(dian)(dian)容(rong)，由于適當(dang)容(rong)量的(de)電(dian)(dian)容(rong)器對(dui)交(jiao)流(liu)信號較小的(de)阻(zu)抗,這樣就減小了(le)電(dian)(dian)阻(zu)產生(sheng)(sheng)的(de)耦合效應，故(gu)稱(cheng)此電(dian)(dian)容(rong)為去耦電(dian)(dian)容(rong)。
2)振蕩/同步(bu)
包括RC、LC振(zhen)蕩(dang)器及晶體的負載電(dian)容都屬于這一范疇。
3)時間常數(shu)
這就是常(chang)見的(de)(de) R、C 串(chuan)聯(lian)構成(cheng)的(de)(de)積分電(dian)路。當輸(shu)入信號(hao)電(dian)壓加在輸(shu)入端時，電(dian)容(C)上(shang)(shang)的(de)(de)電(dian)壓逐漸(jian)上(shang)(shang)升(sheng)。而其充電(dian)電(dian)流則隨著電(dian)壓的(de)(de)上(shang)(shang)升(sheng)而減小。電(dian)流通過電(dian)阻(zu)(R)、電(dian)容(C)的(de)(de)特性通過下面的(de)(de)公式描述：
i = (V/R)e-(t/CR)
我們知道(dao)了電容的作用(yong)以后下面來談談電容在使用(yong)中的注(zhu)意事項
A. 什(shen)么(me)是好電容。
1.電(dian)容容量越(yue)大越(yue)好。
很多人(ren)在(zai)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)的(de)(de)(de)替換中往(wang)往(wang)愛用大容(rong)(rong)(rong)量(liang)(liang)(liang)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)。我們知道(dao)雖然電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)越(yue)(yue)大，為IC提(ti)供(gong)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流補償(chang)的(de)(de)(de)能力(li)越(yue)(yue)強。且不說(shuo)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)容(rong)(rong)(rong)量(liang)(liang)(liang)的(de)(de)(de)增(zeng)大帶來的(de)(de)(de)體積(ji)變大，增(zeng)加成本的(de)(de)(de)同時(shi)還影響空(kong)氣流動和散熱。關(guan)鍵在(zai)于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)上存在(zai)寄(ji)生(sheng)電(dian)(dian)(dian)(dian)(dian)(dian)感，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)放電(dian)(dian)(dian)(dian)(dian)(dian)回(hui)路(lu)會在(zai)某個頻(pin)(pin)(pin)點(dian)上發(fa)生(sheng)諧振(zhen)(zhen)。在(zai)諧振(zhen)(zhen)點(dian)，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)的(de)(de)(de)阻抗(kang)(kang)小(xiao)。因此放電(dian)(dian)(dian)(dian)(dian)(dian)回(hui)路(lu)的(de)(de)(de)阻抗(kang)(kang)最(zui)小(xiao)，補充能量(liang)(liang)(liang)的(de)(de)(de)效果也(ye)(ye)最(zui)好(hao)。但當頻(pin)(pin)(pin)率(lv)超過(guo)諧振(zhen)(zhen)點(dian)時(shi)，放電(dian)(dian)(dian)(dian)(dian)(dian)回(hui)路(lu)的(de)(de)(de)阻抗(kang)(kang)開(kai)(kai)始增(zeng)加，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)提(ti)供(gong)電(dian)(dian)(dian)(dian)(dian)(dian)流能力(li)便開(kai)(kai)始下降。電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)的(de)(de)(de)容(rong)(rong)(rong)值越(yue)(yue)大，諧振(zhen)(zhen)頻(pin)(pin)(pin)率(lv)越(yue)(yue)低，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)能有效補償(chang)電(dian)(dian)(dian)(dian)(dian)(dian)流的(de)(de)(de)頻(pin)(pin)(pin)率(lv)范(fan)圍也(ye)(ye)越(yue)(yue)小(xiao)。從(cong)保(bao)證電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)提(ti)供(gong)高頻(pin)(pin)(pin)電(dian)(dian)(dian)(dian)(dian)(dian)流的(de)(de)(de)能力(li)的(de)(de)(de)角度來說(shuo)，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)越(yue)(yue)大越(yue)(yue)好(hao)的(de)(de)(de)觀點(dian)是錯誤的(de)(de)(de)，一般的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)設計中都有一個參考值的(de)(de)(de)。
2.同樣容(rong)量的(de)電(dian)容(rong)，并聯越多(duo)的(de)小電(dian)容(rong)越好
耐(nai)壓(ya)(ya)值(zhi)、耐(nai)溫值(zhi)、容(rong)值(zhi)、ESR(等效電阻)等是(shi)(shi)電容(rong)的(de)(de)幾個重要參(can)數，對(dui)于ESR自然是(shi)(shi)越(yue)低(di)越(yue)好(hao)。ESR與(yu)電容(rong)的(de)(de)容(rong)量(liang)、頻率、電壓(ya)(ya)、溫度等都有關(guan)系。當電壓(ya)(ya)固定時候(hou)，容(rong)量(liang)越(yue)大，ESR越(yue)低(di)。在板卡(ka)設計中采用(yong)多(duo)個小(xiao)(xiao)電容(rong)并連多(duo)是(shi)(shi)出(chu)與(yu)PCB空間(jian)的(de)(de)限制，這(zhe)樣有的(de)(de)人就認為，越(yue)多(duo)的(de)(de)并聯小(xiao)(xiao)電阻，ESR越(yue)低(di)，效果(guo)越(yue)好(hao)。理論上是(shi)(shi)如此，但是(shi)(shi)要考慮到電容(rong)接腳焊點的(de)(de)阻抗，采用(yong)多(duo)個小(xiao)(xiao)電容(rong)并聯，效果(guo)并不一(yi)定突出(chu)。
3.ESR越低(di)，效果越好。
結(jie)合我們上(shang)面的(de)(de)(de)提高(gao)的(de)(de)(de)供電(dian)(dian)(dian)電(dian)(dian)(dian)路(lu)(lu)來(lai)說(shuo)(shuo)，對(dui)于輸(shu)(shu)入(ru)電(dian)(dian)(dian)容(rong)來(lai)說(shuo)(shuo)，輸(shu)(shu)入(ru)電(dian)(dian)(dian)容(rong)的(de)(de)(de)容(rong)量(liang)要(yao)(yao)(yao)大一點。相對(dui)容(rong)量(liang)的(de)(de)(de)要(yao)(yao)(yao)求，對(dui)ESR的(de)(de)(de)要(yao)(yao)(yao)求可以(yi)適當的(de)(de)(de)降低。因為(wei)輸(shu)(shu)入(ru)電(dian)(dian)(dian)容(rong)主(zhu)要(yao)(yao)(yao)是耐壓，其次(ci)是吸收MOSFET的(de)(de)(de)開(kai)關脈沖。對(dui)于輸(shu)(shu)出(chu)電(dian)(dian)(dian)容(rong)來(lai)說(shuo)(shuo)，耐壓的(de)(de)(de)要(yao)(yao)(yao)求和容(rong)量(liang)可以(yi)適當的(de)(de)(de)降低一點。ESR的(de)(de)(de)要(yao)(yao)(yao)求則高(gao)一點，因為(wei)這里要(yao)(yao)(yao)保(bao)證的(de)(de)(de)是足夠的(de)(de)(de)電(dian)(dian)(dian)流通過量(liang)。但(dan)這里要(yao)(yao)(yao)注意的(de)(de)(de)是ESR并不是越(yue)低越(yue)好，低ESR電(dian)(dian)(dian)容(rong)會引起(qi)開(kai)關電(dian)(dian)(dian)路(lu)(lu)振(zhen)蕩(dang)。而消振(zhen)電(dian)(dian)(dian)路(lu)(lu)復雜同時會導致成本(ben)(ben)的(de)(de)(de)增加。板卡設計中，這里一般有一個(ge)參(can)考值，此作為(wei)元(yuan)件選用參(can)數，避免消振(zhen)電(dian)(dian)(dian)路(lu)(lu)而導致成本(ben)(ben)的(de)(de)(de)增加。
4.好(hao)電容代(dai)表著高品質。
“唯電(dian)(dian)容(rong)(rong)論”曾(ceng)經盛極(ji)一(yi)(yi)(yi)(yi)時(shi)，一(yi)(yi)(yi)(yi)些(xie)廠商(shang)和媒體也刻意的(de)(de)(de)把這個事情做(zuo)成一(yi)(yi)(yi)(yi)個賣點。在板(ban)卡設計(ji)中(zhong)，電(dian)(dian)路設計(ji)水平是關鍵。和有的(de)(de)(de)廠商(shang)可以(yi)用(yong)兩相供電(dian)(dian)做(zuo)出(chu)比一(yi)(yi)(yi)(yi)些(xie)廠商(shang)采用(yong)四相供電(dian)(dian)更穩定(ding)(ding)的(de)(de)(de)產(chan)品(pin)一(yi)(yi)(yi)(yi)樣，一(yi)(yi)(yi)(yi)味(wei)的(de)(de)(de)采用(yong)高價電(dian)(dian)容(rong)(rong)，不(bu)一(yi)(yi)(yi)(yi)定(ding)(ding)能做(zuo)出(chu)好產(chan)品(pin)。衡量一(yi)(yi)(yi)(yi)個產(chan)品(pin)，一(yi)(yi)(yi)(yi)定(ding)(ding)要(yao)全方位多角度(du)的(de)(de)(de)去考慮，切不(bu)可把電(dian)(dian)容(rong)(rong)的(de)(de)(de)作用(yong)有意無意的(de)(de)(de)夸大。
B. 電容(rong)爆漿之面面談
爆(bao)漿(jiang)的種類：
分(fen)兩類，輸入(ru)電(dian)容爆漿和輸出電(dian)容爆漿。
對(dui)于輸入電(dian)(dian)(dian)(dian)容來說，就是(shi)我(wo)是(shi)說的C1，C1對(dui)由電(dian)(dian)(dian)(dian)源接收到的電(dian)(dian)(dian)(dian)流(liu)進行(xing)過(guo)(guo)濾。輸入電(dian)(dian)(dian)(dian)容爆漿和電(dian)(dian)(dian)(dian)源輸入電(dian)(dian)(dian)(dian)流(liu)的品質有關。過(guo)(guo)多的毛刺(ci)電(dian)(dian)(dian)(dian)壓，峰值電(dian)(dian)(dian)(dian)壓過(guo)(guo)高，電(dian)(dian)(dian)(dian)流(liu)不穩定(ding)等(deng)都使電(dian)(dian)(dian)(dian)容過(guo)(guo)于充放電(dian)(dian)(dian)(dian)過(guo)(guo)于頻繁，長(chang)時間處(chu)于這(zhe)類工作環境(jing)下的電(dian)(dian)(dian)(dian)容，內部溫度升(sheng)高很(hen)快。超(chao)過(guo)(guo)泄爆口的承受極限(xian)就會(hui)發生爆漿。
對于輸出電(dian)容來說，就(jiu)我說的(de)C2，對經電(dian)源模(mo)塊(kuai)調整后的(de)電(dian)流(liu)(liu)進行濾波。此處電(dian)流(liu)(liu)經過一(yi)次(ci)過濾，比較平穩，發(fa)生爆漿的(de)可能(neng)性相對來說小了不少。但如(ru)果(guo)(guo)環境(jing)溫度(du)過高，電(dian)容同樣容易發(fa)生爆漿。爆，報也。采用垃圾東(dong)西自然(ran)要爆，報應啊。欲(yu)知過去因者，見其現在果(guo)(guo);欲(yu)知未來果(guo)(guo)者，見其現在因。
電解電容爆(bao)漿的原因：
電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)爆漿(jiang)的(de)(de)(de)原(yuan)因(yin)有(you)很(hen)多，比如(ru)電(dian)(dian)(dian)(dian)流大(da)于允許(xu)的(de)(de)(de)穩(wen)波(bo)電(dian)(dian)(dian)(dian)流、使(shi)用(yong)(yong)電(dian)(dian)(dian)(dian)壓(ya)(ya)超(chao)出工作電(dian)(dian)(dian)(dian)壓(ya)(ya)、逆向電(dian)(dian)(dian)(dian)壓(ya)(ya)、頻(pin)繁的(de)(de)(de)充(chong)放電(dian)(dian)(dian)(dian)等。但是(shi)最直接的(de)(de)(de)原(yuan)因(yin)就(jiu)(jiu)(jiu)是(shi)高溫(wen)(wen)(wen)(wen)。我(wo)們知道(dao)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)有(you)一個(ge)重要(yao)的(de)(de)(de)參數就(jiu)(jiu)(jiu)是(shi)耐溫(wen)(wen)(wen)(wen)值，指的(de)(de)(de)就(jiu)(jiu)(jiu)是(shi)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)內部電(dian)(dian)(dian)(dian)解(jie)(jie)(jie)液(ye)的(de)(de)(de)沸(fei)點。當電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)的(de)(de)(de)內部溫(wen)(wen)(wen)(wen)度達(da)到電(dian)(dian)(dian)(dian)解(jie)(jie)(jie)液(ye)的(de)(de)(de)沸(fei)點時(shi)，電(dian)(dian)(dian)(dian)解(jie)(jie)(jie)液(ye)開始沸(fei)騰，電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)內部的(de)(de)(de)壓(ya)(ya)力升高，當壓(ya)(ya)力超(chao)過(guo)(guo)泄爆口(kou)的(de)(de)(de)承受極限就(jiu)(jiu)(jiu)發生(sheng)了爆漿(jiang)。所以說(shuo)溫(wen)(wen)(wen)(wen)度是(shi)導致電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)爆漿(jiang)的(de)(de)(de)直接原(yuan)因(yin)。電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)設計(ji)使(shi)用(yong)(yong)壽(shou)(shou)命大(da)約為(wei)2萬小時(shi)，受環境(jing)(jing)溫(wen)(wen)(wen)(wen)度的(de)(de)(de)影響也很(hen)大(da)。電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)的(de)(de)(de)使(shi)用(yong)(yong)壽(shou)(shou)命隨溫(wen)(wen)(wen)(wen)度的(de)(de)(de)增加(jia)而減小，實驗證明(ming)環境(jing)(jing)溫(wen)(wen)(wen)(wen)度每(mei)升高10℃，電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)的(de)(de)(de)壽(shou)(shou)命就(jiu)(jiu)(jiu)會減半。主(zhu)要(yao)原(yuan)因(yin)就(jiu)(jiu)(jiu)是(shi)溫(wen)(wen)(wen)(wen)度加(jia)速(su)化學反(fan)應而使(shi)介(jie)質(zhi)隨時(shi)間退化失(shi)效，這樣電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)壽(shou)(shou)命終結。為(wei)了保(bao)證電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)的(de)(de)(de)穩(wen)定性，電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)在(zai)插(cha)板前要(yao)經(jing)過(guo)(guo)長(chang)時(shi)間的(de)(de)(de)高溫(wen)(wen)(wen)(wen)環境(jing)(jing)的(de)(de)(de)測試。即使(shi)是(shi)在(zai)100℃，高品(pin)質(zhi)的(de)(de)(de)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)也可(ke)以工作幾(ji)千個(ge)小時(shi)。同時(shi)，我(wo)們提(ti)到的(de)(de)(de)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)的(de)(de)(de)壽(shou)(shou)命是(shi)指電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)在(zai)使(shi)用(yong)(yong)過(guo)(guo)程中，電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)容(rong)(rong)(rong)(rong)(rong)(rong)量不會超(chao)過(guo)(guo)標(biao)準范圍變(bian)化的(de)(de)(de)10%。電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)壽(shou)(shou)命指的(de)(de)(de)是(shi)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)容(rong)(rong)(rong)(rong)(rong)(rong)量的(de)(de)(de)問題，而不是(shi)設計(ji)壽(shou)(shou)命到達(da)之后(hou)就(jiu)(jiu)(jiu)發生(sheng)爆漿(jiang)。只是(shi)無法保(bao)證電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)的(de)(de)(de)設計(ji)的(de)(de)(de)容(rong)(rong)(rong)(rong)(rong)(rong)量標(biao)準。
所以，短(duan)時期內，正常(chang)(chang)使(shi)(shi)用的(de)(de)板卡電(dian)(dian)容(rong)就(jiu)發(fa)生(sheng)爆漿(jiang)的(de)(de)情況(kuang)，這就(jiu)是電(dian)(dian)容(rong)品質問題(ti)。另外(wai)，不(bu)正常(chang)(chang)的(de)(de)使(shi)(shi)用情況(kuang)也有可能(neng)發(fa)生(sheng)電(dian)(dian)容(rong)爆漿(jiang)的(de)(de)情況(kuang)。比如熱插拔電(dian)(dian)腦配件(jian)也會(hui)導致板卡局部電(dian)(dian)路(lu)電(dian)(dian)流、電(dian)(dian)壓的(de)(de)劇(ju)烈變化(hua)，從而引發(fa)電(dian)(dian)容(rong)使(shi)(shi)用故障。
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