詳解電容在電源中所起到的作用
2019/7/1 12:46:11??????點擊：
作(zuo)(zuo)為無(wu)源元件之(zhi)一的電容(rong)，其作(zuo)(zuo)用不外乎以(yi)下幾種(zhong)：
1、應用(yong)于電(dian)(dian)源電(dian)(dian)路(lu)(lu)，實現(xian)旁路(lu)(lu)、去(qu)藕、濾波和(he)儲(chu)能方面電(dian)(dian)容的作用(yong)，下面分類詳述之(zhi)：
1)濾波
濾(lv)波(bo)是(shi)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)的(de)(de)作(zuo)用中很重(zhong)要(yao)的(de)(de)一部分。幾乎所有(you)的(de)(de)電(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)路中都會(hui)用到。從理論(lun)上(即假設(she)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)為純電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong))說，電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)越(yue)大(da)(da)(da)，阻抗越(yue)小(xiao)，通(tong)過(guo)的(de)(de)頻(pin)(pin)率(lv)也(ye)越(yue)高(gao)。但實際上超過(guo)1uF的(de)(de)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)大(da)(da)(da)多為電(dian)(dian)(dian)(dian)解電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)，有(you)很大(da)(da)(da)的(de)(de)電(dian)(dian)(dian)(dian)感成(cheng)份(fen)，所以頻(pin)(pin)率(lv)高(gao)后(hou)反而(er)阻抗會(hui)增大(da)(da)(da)。有(you)時會(hui)看到有(you)一個電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)量較大(da)(da)(da)電(dian)(dian)(dian)(dian)解電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)并聯了(le)一個小(xiao)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)，這時大(da)(da)(da)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)通(tong)低(di)頻(pin)(pin)，小(xiao)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)通(tong)高(gao)頻(pin)(pin)。電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)的(de)(de)作(zuo)用就是(shi)通(tong)高(gao)阻低(di)，通(tong)高(gao)頻(pin)(pin)阻低(di)頻(pin)(pin)。電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)越(yue)大(da)(da)(da)低(di)頻(pin)(pin)越(yue)容(rong)(rong)(rong)(rong)(rong)易(yi)通(tong)過(guo)，電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)越(yue)大(da)(da)(da)高(gao)頻(pin)(pin)越(yue)容(rong)(rong)(rong)(rong)(rong)易(yi)通(tong)過(guo)。具(ju)體(ti)用在(zai)濾(lv)波(bo)中,大(da)(da)(da)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(1000uF)濾(lv)低(di)頻(pin)(pin)，小(xiao)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(20pF)濾(lv)高(gao)頻(pin)(pin)。
曾有網友將濾(lv)(lv)波(bo)電(dian)(dian)(dian)容 比(bi)作“水塘”。由(you)(you)于電(dian)(dian)(dian)容的(de)(de)(de)兩端電(dian)(dian)(dian)壓不會突變，由(you)(you)此可知(zhi)，信號頻(pin)率越(yue)高則衰減越(yue)大，可很(hen)形象(xiang)的(de)(de)(de)說電(dian)(dian)(dian)容像個水塘，不會因(yin)幾(ji)滴(di)水的(de)(de)(de)加入或蒸發而引起(qi)水量的(de)(de)(de)變化。 它把電(dian)(dian)(dian)壓的(de)(de)(de)變動轉化為電(dian)(dian)(dian)流的(de)(de)(de)變化，頻(pin)率越(yue)高，峰值電(dian)(dian)(dian)流就(jiu)越(yue)大，從而緩沖了電(dian)(dian)(dian)壓。濾(lv)(lv)波(bo)就(jiu)是充電(dian)(dian)(dian)，放電(dian)(dian)(dian)的(de)(de)(de)過程。
2)旁路
旁路電(dian)(dian)容(rong)是(shi)為(wei)本地器(qi)(qi)件(jian)(jian)提(ti)供能(neng)量(liang)的(de)儲能(neng)器(qi)(qi)件(jian)(jian)，它(ta)能(neng)使穩壓器(qi)(qi)的(de)輸(shu)出均勻(yun)化，降(jiang)低負載(zai)(zai)需(xu)求。就像小型可(ke)充電(dian)(dian)電(dian)(dian)池一樣，旁路電(dian)(dian)容(rong)能(neng)夠被充電(dian)(dian)，并向器(qi)(qi)件(jian)(jian)進行放 電(dian)(dian)。為(wei)盡(jin)量(liang)減少阻(zu)抗，旁路電(dian)(dian)容(rong)要盡(jin)量(liang)靠(kao)近負載(zai)(zai)器(qi)(qi)件(jian)(jian)的(de)供電(dian)(dian)電(dian)(dian)源(yuan)管腳和(he)地管腳。這能(neng)夠很好(hao)地防(fang)止(zhi)輸(shu)入值過大(da)而導(dao)致的(de)地電(dian)(dian)位抬高和(he)噪聲。地彈是(shi)地連接(jie)處(chu)在通過大(da) 電(dian)(dian)流毛刺(ci)時的(de)電(dian)(dian)壓降(jiang)。
3)去(qu)藕(ou)
去(qu)(qu)(qu)藕(ou)，又稱解藕(ou)。從(cong)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)來說，總是(shi)(shi)可以區分(fen)為驅(qu)(qu)動(dong)的(de)(de)(de)(de)(de)(de)(de)源和被驅(qu)(qu)動(dong)的(de)(de)(de)(de)(de)(de)(de)負(fu)載。如(ru)果(guo)負(fu)載電(dian)(dian)(dian)(dian)(dian)容(rong)比(bi)(bi)較(jiao)(jiao)(jiao)大(da)，驅(qu)(qu)動(dong)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)要把電(dian)(dian)(dian)(dian)(dian)容(rong)充(chong)電(dian)(dian)(dian)(dian)(dian)、放(fang)電(dian)(dian)(dian)(dian)(dian)，才能完成信(xin)號(hao)的(de)(de)(de)(de)(de)(de)(de)跳變，在(zai)上(shang) 升沿比(bi)(bi)較(jiao)(jiao)(jiao)陡峭的(de)(de)(de)(de)(de)(de)(de)時候，電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)比(bi)(bi)較(jiao)(jiao)(jiao)大(da)，這樣(yang)驅(qu)(qu)動(dong)的(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)就(jiu)會(hui)吸收很(hen)大(da)的(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，由于電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)中(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)感，電(dian)(dian)(dian)(dian)(dian)阻(特(te)別是(shi)(shi)芯片(pian)管(guan)腳上(shang)的(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)感，會(hui)產生反彈)，這種電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)相(xiang)對 于正(zheng)常情況來說實際(ji)上(shang)就(jiu)是(shi)(shi)一(yi)(yi)種噪聲(sheng)，會(hui)影響(xiang)前級(ji)的(de)(de)(de)(de)(de)(de)(de)正(zheng)常工作(zuo)。這就(jiu)是(shi)(shi)耦合(he)。去(qu)(qu)(qu)藕(ou)電(dian)(dian)(dian)(dian)(dian)容(rong)就(jiu)是(shi)(shi)起到一(yi)(yi)個(ge)電(dian)(dian)(dian)(dian)(dian)池的(de)(de)(de)(de)(de)(de)(de)作(zuo)用，滿足驅(qu)(qu)動(dong)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)(de)(de)(de)變化，避免相(xiang)互間的(de)(de)(de)(de)(de)(de)(de)耦合(he)干(gan)擾(rao)。將(jiang)旁(pang)路(lu)(lu)(lu)(lu)電(dian)(dian)(dian)(dian)(dian)容(rong)和去(qu)(qu)(qu)藕(ou)電(dian)(dian)(dian)(dian)(dian)容(rong)結合(he)起來將(jiang)更容(rong)易理解。旁(pang)路(lu)(lu)(lu)(lu)電(dian)(dian)(dian)(dian)(dian)容(rong)實際(ji)也是(shi)(shi)去(qu)(qu)(qu)藕(ou)合(he)的(de)(de)(de)(de)(de)(de)(de)，只是(shi)(shi)旁(pang)路(lu)(lu)(lu)(lu)電(dian)(dian)(dian)(dian)(dian)容(rong)一(yi)(yi)般是(shi)(shi)指高(gao)(gao)頻(pin)旁(pang)路(lu)(lu)(lu)(lu)，也就(jiu)是(shi)(shi)給(gei)高(gao)(gao)頻(pin)的(de)(de)(de)(de)(de)(de)(de)開關噪聲(sheng)提高(gao)(gao)一(yi)(yi)條低阻抗泄防 途徑。高(gao)(gao)頻(pin)旁(pang)路(lu)(lu)(lu)(lu)電(dian)(dian)(dian)(dian)(dian)容(rong)一(yi)(yi)般比(bi)(bi)較(jiao)(jiao)(jiao)小，根據(ju)諧振頻(pin)率一(yi)(yi)般是(shi)(shi)0.1u，0.01u等，而(er)去(qu)(qu)(qu)耦合(he)電(dian)(dian)(dian)(dian)(dian)容(rong)一(yi)(yi)般比(bi)(bi)較(jiao)(jiao)(jiao)大(da)，是(shi)(shi)10uF或者更大(da)，依據(ju)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)中(zhong)(zhong)分(fen)布參數(shu)，以及驅(qu)(qu)動(dong) 電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)(de)(de)(de)變化大(da)小來確(que)定(ding)。旁(pang)路(lu)(lu)(lu)(lu)是(shi)(shi)把輸入信(xin)號(hao)中(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)干(gan)擾(rao)作(zuo)為濾除(chu)對象，而(er)去(qu)(qu)(qu)耦是(shi)(shi)把輸出信(xin)號(hao)的(de)(de)(de)(de)(de)(de)(de)干(gan)擾(rao)作(zuo)為濾除(chu)對象，防止干(gan)擾(rao)信(xin)號(hao)返(fan)回電(dian)(dian)(dian)(dian)(dian)源。這應(ying)該是(shi)(shi)他們(men)的(de)(de)(de)(de)(de)(de)(de)本(ben)質區別。
4)儲能
儲能型電(dian)容器(qi)(qi)通過整流器(qi)(qi)收(shou)集電(dian)荷(he)，并(bing)將存儲的(de)能量通過變換器(qi)(qi)引線(xian)傳(chuan)送至電(dian)源(yuan)的(de)輸出端(duan)。電(dian)壓額定值為40～450VDC、電(dian)容值在220～150 000uF之間的(de)鋁電(dian)解電(dian)容器(qi)(qi)(如EPCOS公司的(de) B43504或(huo)B43505)是較為常用(yong)的(de)。根(gen)據不同(tong)的(de)電(dian)源(yuan)要求(qiu)，器(qi)(qi)件有時會采用(yong)串聯(lian)、并(bing)聯(lian)或(huo)其(qi)組合(he)的(de)形式， 對于功率級(ji)超過10KW的(de)電(dian)源(yuan)，通常采用(yong)體積較大的(de)罐形螺旋端(duan)子電(dian)容器(qi)(qi)。
2、應用于信(xin)號電路，主要完(wan)成耦合、振蕩/同步及時(shi)間常(chang)數的作用：
1)耦合
舉個例子來講，晶體管放大器發射極有一(yi)個自給偏(pian)壓(ya)電(dian)阻(zu)，它同時又使信號產生壓(ya)降(jiang)反饋到輸入(ru)端(duan)形(xing)成了輸入(ru)輸出(chu)信號耦(ou)合，這個電(dian)阻(zu)就是產生了耦(ou)合的(de)元件(jian)，如果(guo)在這個電(dian)阻(zu)兩(liang)端(duan)并聯(lian)一(yi)個電(dian)容(rong)，由于適當容(rong)量的(de)電(dian)容(rong)器對交(jiao)流信號較小的(de)阻(zu)抗,這樣就減小了電(dian)阻(zu)產生的(de)耦(ou)合效應，故稱此電(dian)容(rong)為去耦(ou)電(dian)容(rong)。
2)振蕩/同步
包括RC、LC振蕩(dang)器及晶(jing)體的負(fu)載電(dian)容都(dou)屬于這一(yi)范(fan)疇(chou)。
3)時間常數
這(zhe)就是(shi)常見的(de) R、C 串聯構成的(de)積分電(dian)(dian)路。當輸入信號電(dian)(dian)壓(ya)(ya)加在輸入端時，電(dian)(dian)容(C)上的(de)電(dian)(dian)壓(ya)(ya)逐漸上升。而其充電(dian)(dian)電(dian)(dian)流(liu)則隨著電(dian)(dian)壓(ya)(ya)的(de)上升而減小。電(dian)(dian)流(liu)通過(guo)電(dian)(dian)阻(zu)(R)、電(dian)(dian)容(C)的(de)特性通過(guo)下面的(de)公(gong)式描述：
i = (V/R)e-(t/CR)
我們知道(dao)了電(dian)容的(de)作用以后下面來(lai)談談電(dian)容在使用中的(de)注意事項
A. 什么是好電容。
1.電容(rong)(rong)容(rong)(rong)量越(yue)(yue)大(da)越(yue)(yue)好(hao)。
很多人在(zai)電(dian)(dian)(dian)(dian)(dian)容(rong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)替(ti)換中往往愛用大(da)(da)(da)容(rong)量(liang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)容(rong)。我們(men)知(zhi)道雖然電(dian)(dian)(dian)(dian)(dian)容(rong)越(yue)(yue)大(da)(da)(da)，為IC提(ti)供的(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)補(bu)償(chang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)能力越(yue)(yue)強。且不說(shuo)電(dian)(dian)(dian)(dian)(dian)容(rong)容(rong)量(liang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)增大(da)(da)(da)帶來的(de)(de)(de)(de)(de)(de)(de)(de)(de)體(ti)積(ji)變大(da)(da)(da)，增加成本(ben)的(de)(de)(de)(de)(de)(de)(de)(de)(de)同時(shi)(shi)還影響空(kong)氣(qi)流(liu)動和散熱。關鍵在(zai)于(yu)電(dian)(dian)(dian)(dian)(dian)容(rong)上存(cun)在(zai)寄生電(dian)(dian)(dian)(dian)(dian)感，電(dian)(dian)(dian)(dian)(dian)容(rong)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)回(hui)路會(hui)在(zai)某個頻(pin)點(dian)上發生諧振(zhen)。在(zai)諧振(zhen)點(dian)，電(dian)(dian)(dian)(dian)(dian)容(rong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)阻(zu)抗(kang)小。因此(ci)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)回(hui)路的(de)(de)(de)(de)(de)(de)(de)(de)(de)阻(zu)抗(kang)最(zui)小，補(bu)充能量(liang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)效(xiao)果也最(zui)好。但當頻(pin)率(lv)超過諧振(zhen)點(dian)時(shi)(shi)，放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)回(hui)路的(de)(de)(de)(de)(de)(de)(de)(de)(de)阻(zu)抗(kang)開始(shi)增加，電(dian)(dian)(dian)(dian)(dian)容(rong)提(ti)供電(dian)(dian)(dian)(dian)(dian)流(liu)能力便(bian)開始(shi)下降。電(dian)(dian)(dian)(dian)(dian)容(rong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)容(rong)值越(yue)(yue)大(da)(da)(da)，諧振(zhen)頻(pin)率(lv)越(yue)(yue)低，電(dian)(dian)(dian)(dian)(dian)容(rong)能有(you)效(xiao)補(bu)償(chang)電(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)頻(pin)率(lv)范圍也越(yue)(yue)小。從保證(zheng)電(dian)(dian)(dian)(dian)(dian)容(rong)提(ti)供高頻(pin)電(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)能力的(de)(de)(de)(de)(de)(de)(de)(de)(de)角度(du)來說(shuo)，電(dian)(dian)(dian)(dian)(dian)容(rong)越(yue)(yue)大(da)(da)(da)越(yue)(yue)好的(de)(de)(de)(de)(de)(de)(de)(de)(de)觀點(dian)是錯誤的(de)(de)(de)(de)(de)(de)(de)(de)(de)，一(yi)(yi)般的(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)路設計中都有(you)一(yi)(yi)個參考值的(de)(de)(de)(de)(de)(de)(de)(de)(de)。
2.同樣容量的電容，并聯(lian)越多的小電容越好(hao)
耐(nai)壓(ya)值(zhi)(zhi)、耐(nai)溫值(zhi)(zhi)、容值(zhi)(zhi)、ESR(等效(xiao)電(dian)(dian)(dian)阻(zu)(zu))等是(shi)(shi)電(dian)(dian)(dian)容的幾個(ge)重(zhong)要參數，對于ESR自然(ran)是(shi)(shi)越(yue)低(di)越(yue)好(hao)。ESR與(yu)電(dian)(dian)(dian)容的容量、頻率、電(dian)(dian)(dian)壓(ya)、溫度等都有關系。當電(dian)(dian)(dian)壓(ya)固定(ding)時候，容量越(yue)大，ESR越(yue)低(di)。在板卡設計(ji)中采(cai)用多(duo)個(ge)小(xiao)(xiao)電(dian)(dian)(dian)容并(bing)(bing)連多(duo)是(shi)(shi)出與(yu)PCB空間的限制，這樣有的人(ren)就(jiu)認為，越(yue)多(duo)的并(bing)(bing)聯小(xiao)(xiao)電(dian)(dian)(dian)阻(zu)(zu)，ESR越(yue)低(di)，效(xiao)果越(yue)好(hao)。理論上是(shi)(shi)如此，但(dan)是(shi)(shi)要考(kao)慮到電(dian)(dian)(dian)容接(jie)腳(jiao)焊點的阻(zu)(zu)抗，采(cai)用多(duo)個(ge)小(xiao)(xiao)電(dian)(dian)(dian)容并(bing)(bing)聯，效(xiao)果并(bing)(bing)不一定(ding)突(tu)出。
3.ESR越低(di)，效(xiao)果越好(hao)。
結合我們(men)上面的(de)(de)提高(gao)(gao)的(de)(de)供電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)路(lu)(lu)來說，對于輸(shu)入(ru)電(dian)(dian)(dian)(dian)容(rong)(rong)來說，輸(shu)入(ru)電(dian)(dian)(dian)(dian)容(rong)(rong)的(de)(de)容(rong)(rong)量要(yao)(yao)大一點(dian)。相對容(rong)(rong)量的(de)(de)要(yao)(yao)求(qiu)，對ESR的(de)(de)要(yao)(yao)求(qiu)可以適當的(de)(de)降低(di)。因(yin)(yin)為(wei)(wei)輸(shu)入(ru)電(dian)(dian)(dian)(dian)容(rong)(rong)主要(yao)(yao)是耐(nai)壓，其次是吸收MOSFET的(de)(de)開(kai)關脈沖。對于輸(shu)出電(dian)(dian)(dian)(dian)容(rong)(rong)來說，耐(nai)壓的(de)(de)要(yao)(yao)求(qiu)和(he)容(rong)(rong)量可以適當的(de)(de)降低(di)一點(dian)。ESR的(de)(de)要(yao)(yao)求(qiu)則高(gao)(gao)一點(dian)，因(yin)(yin)為(wei)(wei)這里(li)(li)要(yao)(yao)保證(zheng)的(de)(de)是足夠的(de)(de)電(dian)(dian)(dian)(dian)流通(tong)過(guo)量。但(dan)這里(li)(li)要(yao)(yao)注意的(de)(de)是ESR并不是越低(di)越好，低(di)ESR電(dian)(dian)(dian)(dian)容(rong)(rong)會(hui)引起開(kai)關電(dian)(dian)(dian)(dian)路(lu)(lu)振(zhen)蕩(dang)。而消(xiao)振(zhen)電(dian)(dian)(dian)(dian)路(lu)(lu)復雜(za)同時會(hui)導(dao)(dao)致成(cheng)本(ben)的(de)(de)增加(jia)。板卡(ka)設計(ji)中，這里(li)(li)一般有(you)一個參考(kao)值，此作為(wei)(wei)元件(jian)選用參數，避免(mian)消(xiao)振(zhen)電(dian)(dian)(dian)(dian)路(lu)(lu)而導(dao)(dao)致成(cheng)本(ben)的(de)(de)增加(jia)。
4.好電容代表著(zhu)高品質。
“唯電(dian)(dian)容論”曾(ceng)經盛極一(yi)(yi)時，一(yi)(yi)些(xie)廠(chang)商和媒(mei)體也(ye)刻(ke)意(yi)的(de)(de)(de)把這個事情做成(cheng)一(yi)(yi)個賣(mai)點。在板卡設(she)計中，電(dian)(dian)路設(she)計水平是關鍵(jian)。和有的(de)(de)(de)廠(chang)商可以用(yong)(yong)兩(liang)相供(gong)電(dian)(dian)做出比一(yi)(yi)些(xie)廠(chang)商采用(yong)(yong)四(si)相供(gong)電(dian)(dian)更穩定(ding)的(de)(de)(de)產(chan)品一(yi)(yi)樣(yang)，一(yi)(yi)味的(de)(de)(de)采用(yong)(yong)高(gao)價電(dian)(dian)容，不一(yi)(yi)定(ding)能做出好產(chan)品。衡量一(yi)(yi)個產(chan)品，一(yi)(yi)定(ding)要全方(fang)位多(duo)角度的(de)(de)(de)去考慮(lv)，切(qie)不可把電(dian)(dian)容的(de)(de)(de)作用(yong)(yong)有意(yi)無意(yi)的(de)(de)(de)夸大。
B. 電容(rong)爆漿之面面談(tan)
爆漿的種(zhong)類：
分(fen)兩類，輸(shu)入(ru)電(dian)容爆漿(jiang)和輸(shu)出(chu)電(dian)容爆漿(jiang)。
對(dui)于(yu)輸(shu)入電(dian)(dian)(dian)容來說(shuo)，就(jiu)是我是說(shuo)的(de)(de)C1，C1對(dui)由電(dian)(dian)(dian)源(yuan)(yuan)接(jie)收到的(de)(de)電(dian)(dian)(dian)流進行過(guo)(guo)濾(lv)。輸(shu)入電(dian)(dian)(dian)容爆漿(jiang)和電(dian)(dian)(dian)源(yuan)(yuan)輸(shu)入電(dian)(dian)(dian)流的(de)(de)品質有(you)關。過(guo)(guo)多的(de)(de)毛(mao)刺電(dian)(dian)(dian)壓，峰值電(dian)(dian)(dian)壓過(guo)(guo)高，電(dian)(dian)(dian)流不穩定等(deng)都使電(dian)(dian)(dian)容過(guo)(guo)于(yu)充放電(dian)(dian)(dian)過(guo)(guo)于(yu)頻繁，長時間處于(yu)這類工作(zuo)環境下的(de)(de)電(dian)(dian)(dian)容，內部溫度(du)升高很快。超過(guo)(guo)泄爆口的(de)(de)承受極(ji)限(xian)就(jiu)會發生(sheng)爆漿(jiang)。
對(dui)于輸出電(dian)(dian)容來說，就我說的(de)(de)C2，對(dui)經電(dian)(dian)源模塊調整后的(de)(de)電(dian)(dian)流進行濾波。此(ci)處電(dian)(dian)流經過一次過濾，比較(jiao)平穩，發生爆漿(jiang)的(de)(de)可能性相對(dui)來說小(xiao)了不(bu)少。但如果環境溫度過高，電(dian)(dian)容同樣容易發生爆漿(jiang)。爆，報也。采用垃圾東西自(zi)然要爆，報應啊。欲(yu)知過去(qu)因者，見(jian)其現在(zai)果;欲(yu)知未來果者，見(jian)其現在(zai)因。
電解電容爆漿的(de)原因：
電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)爆(bao)漿(jiang)的(de)(de)(de)(de)(de)原(yuan)(yuan)(yuan)因有(you)很多，比如電(dian)(dian)(dian)(dian)(dian)(dian)流大于(yu)允許的(de)(de)(de)(de)(de)穩波電(dian)(dian)(dian)(dian)(dian)(dian)流、使(shi)用電(dian)(dian)(dian)(dian)(dian)(dian)壓超出工作電(dian)(dian)(dian)(dian)(dian)(dian)壓、逆向電(dian)(dian)(dian)(dian)(dian)(dian)壓、頻繁的(de)(de)(de)(de)(de)充放(fang)電(dian)(dian)(dian)(dian)(dian)(dian)等。但(dan)是(shi)最直(zhi)接的(de)(de)(de)(de)(de)原(yuan)(yuan)(yuan)因就(jiu)是(shi)高(gao)(gao)溫(wen)。我們知道電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)有(you)一個重要(yao)的(de)(de)(de)(de)(de)參數就(jiu)是(shi)耐溫(wen)值，指(zhi)的(de)(de)(de)(de)(de)就(jiu)是(shi)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)內(nei)(nei)部(bu)電(dian)(dian)(dian)(dian)(dian)(dian)解液的(de)(de)(de)(de)(de)沸(fei)(fei)點。當(dang)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)的(de)(de)(de)(de)(de)內(nei)(nei)部(bu)溫(wen)度(du)達(da)到電(dian)(dian)(dian)(dian)(dian)(dian)解液的(de)(de)(de)(de)(de)沸(fei)(fei)點時(shi)，電(dian)(dian)(dian)(dian)(dian)(dian)解液開始(shi)沸(fei)(fei)騰，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)內(nei)(nei)部(bu)的(de)(de)(de)(de)(de)壓力升(sheng)高(gao)(gao)，當(dang)壓力超過(guo)(guo)泄爆(bao)口的(de)(de)(de)(de)(de)承(cheng)受(shou)極限就(jiu)發生了爆(bao)漿(jiang)。所(suo)以說溫(wen)度(du)是(shi)導致電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)爆(bao)漿(jiang)的(de)(de)(de)(de)(de)直(zhi)接原(yuan)(yuan)(yuan)因。電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)設計使(shi)用壽(shou)命(ming)(ming)大約(yue)為2萬小(xiao)時(shi)，受(shou)環境溫(wen)度(du)的(de)(de)(de)(de)(de)影響(xiang)也很大。電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)的(de)(de)(de)(de)(de)使(shi)用壽(shou)命(ming)(ming)隨(sui)溫(wen)度(du)的(de)(de)(de)(de)(de)增加而(er)(er)(er)減(jian)小(xiao)，實(shi)驗證(zheng)(zheng)明環境溫(wen)度(du)每升(sheng)高(gao)(gao)10℃，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)的(de)(de)(de)(de)(de)壽(shou)命(ming)(ming)就(jiu)會減(jian)半。主要(yao)原(yuan)(yuan)(yuan)因就(jiu)是(shi)溫(wen)度(du)加速化(hua)(hua)學反應(ying)而(er)(er)(er)使(shi)介質(zhi)隨(sui)時(shi)間退化(hua)(hua)失效(xiao)，這(zhe)樣電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)壽(shou)命(ming)(ming)終結(jie)。為了保(bao)證(zheng)(zheng)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)的(de)(de)(de)(de)(de)穩定性，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)在插板前要(yao)經(jing)過(guo)(guo)長時(shi)間的(de)(de)(de)(de)(de)高(gao)(gao)溫(wen)環境的(de)(de)(de)(de)(de)測試。即使(shi)是(shi)在100℃，高(gao)(gao)品質(zhi)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)也可以工作幾千個小(xiao)時(shi)。同時(shi)，我們提到的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)的(de)(de)(de)(de)(de)壽(shou)命(ming)(ming)是(shi)指(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)在使(shi)用過(guo)(guo)程中(zhong)，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)容(rong)(rong)(rong)(rong)量不(bu)會超過(guo)(guo)標(biao)準(zhun)(zhun)范圍變化(hua)(hua)的(de)(de)(de)(de)(de)10%。電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)壽(shou)命(ming)(ming)指(zhi)的(de)(de)(de)(de)(de)是(shi)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)容(rong)(rong)(rong)(rong)量的(de)(de)(de)(de)(de)問題，而(er)(er)(er)不(bu)是(shi)設計壽(shou)命(ming)(ming)到達(da)之后就(jiu)發生爆(bao)漿(jiang)。只(zhi)是(shi)無(wu)法保(bao)證(zheng)(zheng)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)的(de)(de)(de)(de)(de)設計的(de)(de)(de)(de)(de)容(rong)(rong)(rong)(rong)量標(biao)準(zhun)(zhun)。
所(suo)以，短時期(qi)內，正(zheng)常使(shi)(shi)用的板(ban)卡(ka)(ka)電(dian)(dian)容就發(fa)(fa)生爆漿(jiang)的情(qing)況，這就是(shi)電(dian)(dian)容品質問題。另外，不正(zheng)常的使(shi)(shi)用情(qing)況也(ye)(ye)有可能發(fa)(fa)生電(dian)(dian)容爆漿(jiang)的情(qing)況。比(bi)如熱插拔電(dian)(dian)腦配(pei)件(jian)也(ye)(ye)會(hui)導致板(ban)卡(ka)(ka)局部電(dian)(dian)路電(dian)(dian)流、電(dian)(dian)壓的劇烈變(bian)化，從而引發(fa)(fa)電(dian)(dian)容使(shi)(shi)用故障(zhang)。
1、應用(yong)于電(dian)(dian)源電(dian)(dian)路(lu)(lu)，實現(xian)旁路(lu)(lu)、去(qu)藕、濾波和(he)儲(chu)能方面電(dian)(dian)容的作用(yong)，下面分類詳述之(zhi)：
1)濾波
濾(lv)波(bo)是(shi)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)的(de)(de)作(zuo)用中很重(zhong)要(yao)的(de)(de)一部分。幾乎所有(you)的(de)(de)電(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)路中都會(hui)用到。從理論(lun)上(即假設(she)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)為純電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong))說，電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)越(yue)大(da)(da)(da)，阻抗越(yue)小(xiao)，通(tong)過(guo)的(de)(de)頻(pin)(pin)率(lv)也(ye)越(yue)高(gao)。但實際上超過(guo)1uF的(de)(de)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)大(da)(da)(da)多為電(dian)(dian)(dian)(dian)解電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)，有(you)很大(da)(da)(da)的(de)(de)電(dian)(dian)(dian)(dian)感成(cheng)份(fen)，所以頻(pin)(pin)率(lv)高(gao)后(hou)反而(er)阻抗會(hui)增大(da)(da)(da)。有(you)時會(hui)看到有(you)一個電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)量較大(da)(da)(da)電(dian)(dian)(dian)(dian)解電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)并聯了(le)一個小(xiao)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)，這時大(da)(da)(da)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)通(tong)低(di)頻(pin)(pin)，小(xiao)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)通(tong)高(gao)頻(pin)(pin)。電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)的(de)(de)作(zuo)用就是(shi)通(tong)高(gao)阻低(di)，通(tong)高(gao)頻(pin)(pin)阻低(di)頻(pin)(pin)。電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)越(yue)大(da)(da)(da)低(di)頻(pin)(pin)越(yue)容(rong)(rong)(rong)(rong)(rong)易(yi)通(tong)過(guo)，電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)越(yue)大(da)(da)(da)高(gao)頻(pin)(pin)越(yue)容(rong)(rong)(rong)(rong)(rong)易(yi)通(tong)過(guo)。具(ju)體(ti)用在(zai)濾(lv)波(bo)中,大(da)(da)(da)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(1000uF)濾(lv)低(di)頻(pin)(pin)，小(xiao)電(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(20pF)濾(lv)高(gao)頻(pin)(pin)。
曾有網友將濾(lv)(lv)波(bo)電(dian)(dian)(dian)容 比(bi)作“水塘”。由(you)(you)于電(dian)(dian)(dian)容的(de)(de)(de)兩端電(dian)(dian)(dian)壓不會突變，由(you)(you)此可知(zhi)，信號頻(pin)率越(yue)高則衰減越(yue)大，可很(hen)形象(xiang)的(de)(de)(de)說電(dian)(dian)(dian)容像個水塘，不會因(yin)幾(ji)滴(di)水的(de)(de)(de)加入或蒸發而引起(qi)水量的(de)(de)(de)變化。 它把電(dian)(dian)(dian)壓的(de)(de)(de)變動轉化為電(dian)(dian)(dian)流的(de)(de)(de)變化，頻(pin)率越(yue)高，峰值電(dian)(dian)(dian)流就(jiu)越(yue)大，從而緩沖了電(dian)(dian)(dian)壓。濾(lv)(lv)波(bo)就(jiu)是充電(dian)(dian)(dian)，放電(dian)(dian)(dian)的(de)(de)(de)過程。
2)旁路
旁路電(dian)(dian)容(rong)是(shi)為(wei)本地器(qi)(qi)件(jian)(jian)提(ti)供能(neng)量(liang)的(de)儲能(neng)器(qi)(qi)件(jian)(jian)，它(ta)能(neng)使穩壓器(qi)(qi)的(de)輸(shu)出均勻(yun)化，降(jiang)低負載(zai)(zai)需(xu)求。就像小型可(ke)充電(dian)(dian)電(dian)(dian)池一樣，旁路電(dian)(dian)容(rong)能(neng)夠被充電(dian)(dian)，并向器(qi)(qi)件(jian)(jian)進行放 電(dian)(dian)。為(wei)盡(jin)量(liang)減少阻(zu)抗，旁路電(dian)(dian)容(rong)要盡(jin)量(liang)靠(kao)近負載(zai)(zai)器(qi)(qi)件(jian)(jian)的(de)供電(dian)(dian)電(dian)(dian)源(yuan)管腳和(he)地管腳。這能(neng)夠很好(hao)地防(fang)止(zhi)輸(shu)入值過大(da)而導(dao)致的(de)地電(dian)(dian)位抬高和(he)噪聲。地彈是(shi)地連接(jie)處(chu)在通過大(da) 電(dian)(dian)流毛刺(ci)時的(de)電(dian)(dian)壓降(jiang)。
3)去(qu)藕(ou)
去(qu)(qu)(qu)藕(ou)，又稱解藕(ou)。從(cong)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)來說，總是(shi)(shi)可以區分(fen)為驅(qu)(qu)動(dong)的(de)(de)(de)(de)(de)(de)(de)源和被驅(qu)(qu)動(dong)的(de)(de)(de)(de)(de)(de)(de)負(fu)載。如(ru)果(guo)負(fu)載電(dian)(dian)(dian)(dian)(dian)容(rong)比(bi)(bi)較(jiao)(jiao)(jiao)大(da)，驅(qu)(qu)動(dong)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)要把電(dian)(dian)(dian)(dian)(dian)容(rong)充(chong)電(dian)(dian)(dian)(dian)(dian)、放(fang)電(dian)(dian)(dian)(dian)(dian)，才能完成信(xin)號(hao)的(de)(de)(de)(de)(de)(de)(de)跳變，在(zai)上(shang) 升沿比(bi)(bi)較(jiao)(jiao)(jiao)陡峭的(de)(de)(de)(de)(de)(de)(de)時候，電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)比(bi)(bi)較(jiao)(jiao)(jiao)大(da)，這樣(yang)驅(qu)(qu)動(dong)的(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)就(jiu)會(hui)吸收很(hen)大(da)的(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，由于電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)中(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)感，電(dian)(dian)(dian)(dian)(dian)阻(特(te)別是(shi)(shi)芯片(pian)管(guan)腳上(shang)的(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)感，會(hui)產生反彈)，這種電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)相(xiang)對 于正(zheng)常情況來說實際(ji)上(shang)就(jiu)是(shi)(shi)一(yi)(yi)種噪聲(sheng)，會(hui)影響(xiang)前級(ji)的(de)(de)(de)(de)(de)(de)(de)正(zheng)常工作(zuo)。這就(jiu)是(shi)(shi)耦合(he)。去(qu)(qu)(qu)藕(ou)電(dian)(dian)(dian)(dian)(dian)容(rong)就(jiu)是(shi)(shi)起到一(yi)(yi)個(ge)電(dian)(dian)(dian)(dian)(dian)池的(de)(de)(de)(de)(de)(de)(de)作(zuo)用，滿足驅(qu)(qu)動(dong)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)(de)(de)(de)變化，避免相(xiang)互間的(de)(de)(de)(de)(de)(de)(de)耦合(he)干(gan)擾(rao)。將(jiang)旁(pang)路(lu)(lu)(lu)(lu)電(dian)(dian)(dian)(dian)(dian)容(rong)和去(qu)(qu)(qu)藕(ou)電(dian)(dian)(dian)(dian)(dian)容(rong)結合(he)起來將(jiang)更容(rong)易理解。旁(pang)路(lu)(lu)(lu)(lu)電(dian)(dian)(dian)(dian)(dian)容(rong)實際(ji)也是(shi)(shi)去(qu)(qu)(qu)藕(ou)合(he)的(de)(de)(de)(de)(de)(de)(de)，只是(shi)(shi)旁(pang)路(lu)(lu)(lu)(lu)電(dian)(dian)(dian)(dian)(dian)容(rong)一(yi)(yi)般是(shi)(shi)指高(gao)(gao)頻(pin)旁(pang)路(lu)(lu)(lu)(lu)，也就(jiu)是(shi)(shi)給(gei)高(gao)(gao)頻(pin)的(de)(de)(de)(de)(de)(de)(de)開關噪聲(sheng)提高(gao)(gao)一(yi)(yi)條低阻抗泄防 途徑。高(gao)(gao)頻(pin)旁(pang)路(lu)(lu)(lu)(lu)電(dian)(dian)(dian)(dian)(dian)容(rong)一(yi)(yi)般比(bi)(bi)較(jiao)(jiao)(jiao)小，根據(ju)諧振頻(pin)率一(yi)(yi)般是(shi)(shi)0.1u，0.01u等，而(er)去(qu)(qu)(qu)耦合(he)電(dian)(dian)(dian)(dian)(dian)容(rong)一(yi)(yi)般比(bi)(bi)較(jiao)(jiao)(jiao)大(da)，是(shi)(shi)10uF或者更大(da)，依據(ju)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)中(zhong)(zhong)分(fen)布參數(shu)，以及驅(qu)(qu)動(dong) 電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)(de)(de)(de)變化大(da)小來確(que)定(ding)。旁(pang)路(lu)(lu)(lu)(lu)是(shi)(shi)把輸入信(xin)號(hao)中(zhong)(zhong)的(de)(de)(de)(de)(de)(de)(de)干(gan)擾(rao)作(zuo)為濾除(chu)對象，而(er)去(qu)(qu)(qu)耦是(shi)(shi)把輸出信(xin)號(hao)的(de)(de)(de)(de)(de)(de)(de)干(gan)擾(rao)作(zuo)為濾除(chu)對象，防止干(gan)擾(rao)信(xin)號(hao)返(fan)回電(dian)(dian)(dian)(dian)(dian)源。這應(ying)該是(shi)(shi)他們(men)的(de)(de)(de)(de)(de)(de)(de)本(ben)質區別。
4)儲能
儲能型電(dian)容器(qi)(qi)通過整流器(qi)(qi)收(shou)集電(dian)荷(he)，并(bing)將存儲的(de)能量通過變換器(qi)(qi)引線(xian)傳(chuan)送至電(dian)源(yuan)的(de)輸出端(duan)。電(dian)壓額定值為40～450VDC、電(dian)容值在220～150 000uF之間的(de)鋁電(dian)解電(dian)容器(qi)(qi)(如EPCOS公司的(de) B43504或(huo)B43505)是較為常用(yong)的(de)。根(gen)據不同(tong)的(de)電(dian)源(yuan)要求(qiu)，器(qi)(qi)件有時會采用(yong)串聯(lian)、并(bing)聯(lian)或(huo)其(qi)組合(he)的(de)形式， 對于功率級(ji)超過10KW的(de)電(dian)源(yuan)，通常采用(yong)體積較大的(de)罐形螺旋端(duan)子電(dian)容器(qi)(qi)。
2、應用于信(xin)號電路，主要完(wan)成耦合、振蕩/同步及時(shi)間常(chang)數的作用：
1)耦合
舉個例子來講，晶體管放大器發射極有一(yi)個自給偏(pian)壓(ya)電(dian)阻(zu)，它同時又使信號產生壓(ya)降(jiang)反饋到輸入(ru)端(duan)形(xing)成了輸入(ru)輸出(chu)信號耦(ou)合，這個電(dian)阻(zu)就是產生了耦(ou)合的(de)元件(jian)，如果(guo)在這個電(dian)阻(zu)兩(liang)端(duan)并聯(lian)一(yi)個電(dian)容(rong)，由于適當容(rong)量的(de)電(dian)容(rong)器對交(jiao)流信號較小的(de)阻(zu)抗,這樣就減小了電(dian)阻(zu)產生的(de)耦(ou)合效應，故稱此電(dian)容(rong)為去耦(ou)電(dian)容(rong)。
2)振蕩/同步
包括RC、LC振蕩(dang)器及晶(jing)體的負(fu)載電(dian)容都(dou)屬于這一(yi)范(fan)疇(chou)。
3)時間常數
這(zhe)就是(shi)常見的(de) R、C 串聯構成的(de)積分電(dian)(dian)路。當輸入信號電(dian)(dian)壓(ya)(ya)加在輸入端時，電(dian)(dian)容(C)上的(de)電(dian)(dian)壓(ya)(ya)逐漸上升。而其充電(dian)(dian)電(dian)(dian)流(liu)則隨著電(dian)(dian)壓(ya)(ya)的(de)上升而減小。電(dian)(dian)流(liu)通過(guo)電(dian)(dian)阻(zu)(R)、電(dian)(dian)容(C)的(de)特性通過(guo)下面的(de)公(gong)式描述：
i = (V/R)e-(t/CR)
我們知道(dao)了電(dian)容的(de)作用以后下面來(lai)談談電(dian)容在使用中的(de)注意事項
A. 什么是好電容。
1.電容(rong)(rong)容(rong)(rong)量越(yue)(yue)大(da)越(yue)(yue)好(hao)。
很多人在(zai)電(dian)(dian)(dian)(dian)(dian)容(rong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)替(ti)換中往往愛用大(da)(da)(da)容(rong)量(liang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)容(rong)。我們(men)知(zhi)道雖然電(dian)(dian)(dian)(dian)(dian)容(rong)越(yue)(yue)大(da)(da)(da)，為IC提(ti)供的(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)補(bu)償(chang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)能力越(yue)(yue)強。且不說(shuo)電(dian)(dian)(dian)(dian)(dian)容(rong)容(rong)量(liang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)增大(da)(da)(da)帶來的(de)(de)(de)(de)(de)(de)(de)(de)(de)體(ti)積(ji)變大(da)(da)(da)，增加成本(ben)的(de)(de)(de)(de)(de)(de)(de)(de)(de)同時(shi)(shi)還影響空(kong)氣(qi)流(liu)動和散熱。關鍵在(zai)于(yu)電(dian)(dian)(dian)(dian)(dian)容(rong)上存(cun)在(zai)寄生電(dian)(dian)(dian)(dian)(dian)感，電(dian)(dian)(dian)(dian)(dian)容(rong)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)回(hui)路會(hui)在(zai)某個頻(pin)點(dian)上發生諧振(zhen)。在(zai)諧振(zhen)點(dian)，電(dian)(dian)(dian)(dian)(dian)容(rong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)阻(zu)抗(kang)小。因此(ci)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)回(hui)路的(de)(de)(de)(de)(de)(de)(de)(de)(de)阻(zu)抗(kang)最(zui)小，補(bu)充能量(liang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)效(xiao)果也最(zui)好。但當頻(pin)率(lv)超過諧振(zhen)點(dian)時(shi)(shi)，放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)回(hui)路的(de)(de)(de)(de)(de)(de)(de)(de)(de)阻(zu)抗(kang)開始(shi)增加，電(dian)(dian)(dian)(dian)(dian)容(rong)提(ti)供電(dian)(dian)(dian)(dian)(dian)流(liu)能力便(bian)開始(shi)下降。電(dian)(dian)(dian)(dian)(dian)容(rong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)容(rong)值越(yue)(yue)大(da)(da)(da)，諧振(zhen)頻(pin)率(lv)越(yue)(yue)低，電(dian)(dian)(dian)(dian)(dian)容(rong)能有(you)效(xiao)補(bu)償(chang)電(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)頻(pin)率(lv)范圍也越(yue)(yue)小。從保證(zheng)電(dian)(dian)(dian)(dian)(dian)容(rong)提(ti)供高頻(pin)電(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)能力的(de)(de)(de)(de)(de)(de)(de)(de)(de)角度(du)來說(shuo)，電(dian)(dian)(dian)(dian)(dian)容(rong)越(yue)(yue)大(da)(da)(da)越(yue)(yue)好的(de)(de)(de)(de)(de)(de)(de)(de)(de)觀點(dian)是錯誤的(de)(de)(de)(de)(de)(de)(de)(de)(de)，一(yi)(yi)般的(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)路設計中都有(you)一(yi)(yi)個參考值的(de)(de)(de)(de)(de)(de)(de)(de)(de)。
2.同樣容量的電容，并聯(lian)越多的小電容越好(hao)
耐(nai)壓(ya)值(zhi)(zhi)、耐(nai)溫值(zhi)(zhi)、容值(zhi)(zhi)、ESR(等效(xiao)電(dian)(dian)(dian)阻(zu)(zu))等是(shi)(shi)電(dian)(dian)(dian)容的幾個(ge)重(zhong)要參數，對于ESR自然(ran)是(shi)(shi)越(yue)低(di)越(yue)好(hao)。ESR與(yu)電(dian)(dian)(dian)容的容量、頻率、電(dian)(dian)(dian)壓(ya)、溫度等都有關系。當電(dian)(dian)(dian)壓(ya)固定(ding)時候，容量越(yue)大，ESR越(yue)低(di)。在板卡設計(ji)中采(cai)用多(duo)個(ge)小(xiao)(xiao)電(dian)(dian)(dian)容并(bing)(bing)連多(duo)是(shi)(shi)出與(yu)PCB空間的限制，這樣有的人(ren)就(jiu)認為，越(yue)多(duo)的并(bing)(bing)聯小(xiao)(xiao)電(dian)(dian)(dian)阻(zu)(zu)，ESR越(yue)低(di)，效(xiao)果越(yue)好(hao)。理論上是(shi)(shi)如此，但(dan)是(shi)(shi)要考(kao)慮到電(dian)(dian)(dian)容接(jie)腳(jiao)焊點的阻(zu)(zu)抗，采(cai)用多(duo)個(ge)小(xiao)(xiao)電(dian)(dian)(dian)容并(bing)(bing)聯，效(xiao)果并(bing)(bing)不一定(ding)突(tu)出。
3.ESR越低(di)，效(xiao)果越好(hao)。
結合我們(men)上面的(de)(de)提高(gao)(gao)的(de)(de)供電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)路(lu)(lu)來說，對于輸(shu)入(ru)電(dian)(dian)(dian)(dian)容(rong)(rong)來說，輸(shu)入(ru)電(dian)(dian)(dian)(dian)容(rong)(rong)的(de)(de)容(rong)(rong)量要(yao)(yao)大一點(dian)。相對容(rong)(rong)量的(de)(de)要(yao)(yao)求(qiu)，對ESR的(de)(de)要(yao)(yao)求(qiu)可以適當的(de)(de)降低(di)。因(yin)(yin)為(wei)(wei)輸(shu)入(ru)電(dian)(dian)(dian)(dian)容(rong)(rong)主要(yao)(yao)是耐(nai)壓，其次是吸收MOSFET的(de)(de)開(kai)關脈沖。對于輸(shu)出電(dian)(dian)(dian)(dian)容(rong)(rong)來說，耐(nai)壓的(de)(de)要(yao)(yao)求(qiu)和(he)容(rong)(rong)量可以適當的(de)(de)降低(di)一點(dian)。ESR的(de)(de)要(yao)(yao)求(qiu)則高(gao)(gao)一點(dian)，因(yin)(yin)為(wei)(wei)這里(li)(li)要(yao)(yao)保證(zheng)的(de)(de)是足夠的(de)(de)電(dian)(dian)(dian)(dian)流通(tong)過(guo)量。但(dan)這里(li)(li)要(yao)(yao)注意的(de)(de)是ESR并不是越低(di)越好，低(di)ESR電(dian)(dian)(dian)(dian)容(rong)(rong)會(hui)引起開(kai)關電(dian)(dian)(dian)(dian)路(lu)(lu)振(zhen)蕩(dang)。而消(xiao)振(zhen)電(dian)(dian)(dian)(dian)路(lu)(lu)復雜(za)同時會(hui)導(dao)(dao)致成(cheng)本(ben)的(de)(de)增加(jia)。板卡(ka)設計(ji)中，這里(li)(li)一般有(you)一個參考(kao)值，此作為(wei)(wei)元件(jian)選用參數，避免(mian)消(xiao)振(zhen)電(dian)(dian)(dian)(dian)路(lu)(lu)而導(dao)(dao)致成(cheng)本(ben)的(de)(de)增加(jia)。
4.好電容代表著(zhu)高品質。
“唯電(dian)(dian)容論”曾(ceng)經盛極一(yi)(yi)時，一(yi)(yi)些(xie)廠(chang)商和媒(mei)體也(ye)刻(ke)意(yi)的(de)(de)(de)把這個事情做成(cheng)一(yi)(yi)個賣(mai)點。在板卡設(she)計中，電(dian)(dian)路設(she)計水平是關鍵(jian)。和有的(de)(de)(de)廠(chang)商可以用(yong)(yong)兩(liang)相供(gong)電(dian)(dian)做出比一(yi)(yi)些(xie)廠(chang)商采用(yong)(yong)四(si)相供(gong)電(dian)(dian)更穩定(ding)的(de)(de)(de)產(chan)品一(yi)(yi)樣(yang)，一(yi)(yi)味的(de)(de)(de)采用(yong)(yong)高(gao)價電(dian)(dian)容，不一(yi)(yi)定(ding)能做出好產(chan)品。衡量一(yi)(yi)個產(chan)品，一(yi)(yi)定(ding)要全方(fang)位多(duo)角度的(de)(de)(de)去考慮(lv)，切(qie)不可把電(dian)(dian)容的(de)(de)(de)作用(yong)(yong)有意(yi)無意(yi)的(de)(de)(de)夸大。
B. 電容(rong)爆漿之面面談(tan)
爆漿的種(zhong)類：
分(fen)兩類，輸(shu)入(ru)電(dian)容爆漿(jiang)和輸(shu)出(chu)電(dian)容爆漿(jiang)。
對(dui)于(yu)輸(shu)入電(dian)(dian)(dian)容來說(shuo)，就(jiu)是我是說(shuo)的(de)(de)C1，C1對(dui)由電(dian)(dian)(dian)源(yuan)(yuan)接(jie)收到的(de)(de)電(dian)(dian)(dian)流進行過(guo)(guo)濾(lv)。輸(shu)入電(dian)(dian)(dian)容爆漿(jiang)和電(dian)(dian)(dian)源(yuan)(yuan)輸(shu)入電(dian)(dian)(dian)流的(de)(de)品質有(you)關。過(guo)(guo)多的(de)(de)毛(mao)刺電(dian)(dian)(dian)壓，峰值電(dian)(dian)(dian)壓過(guo)(guo)高，電(dian)(dian)(dian)流不穩定等(deng)都使電(dian)(dian)(dian)容過(guo)(guo)于(yu)充放電(dian)(dian)(dian)過(guo)(guo)于(yu)頻繁，長時間處于(yu)這類工作(zuo)環境下的(de)(de)電(dian)(dian)(dian)容，內部溫度(du)升高很快。超過(guo)(guo)泄爆口的(de)(de)承受極(ji)限(xian)就(jiu)會發生(sheng)爆漿(jiang)。
對(dui)于輸出電(dian)(dian)容來說，就我說的(de)(de)C2，對(dui)經電(dian)(dian)源模塊調整后的(de)(de)電(dian)(dian)流進行濾波。此(ci)處電(dian)(dian)流經過一次過濾，比較(jiao)平穩，發生爆漿(jiang)的(de)(de)可能性相對(dui)來說小(xiao)了不(bu)少。但如果環境溫度過高，電(dian)(dian)容同樣容易發生爆漿(jiang)。爆，報也。采用垃圾東西自(zi)然要爆，報應啊。欲(yu)知過去(qu)因者，見(jian)其現在(zai)果;欲(yu)知未來果者，見(jian)其現在(zai)因。
電解電容爆漿的(de)原因：
電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)爆(bao)漿(jiang)的(de)(de)(de)(de)(de)原(yuan)(yuan)(yuan)因有(you)很多，比如電(dian)(dian)(dian)(dian)(dian)(dian)流大于(yu)允許的(de)(de)(de)(de)(de)穩波電(dian)(dian)(dian)(dian)(dian)(dian)流、使(shi)用電(dian)(dian)(dian)(dian)(dian)(dian)壓超出工作電(dian)(dian)(dian)(dian)(dian)(dian)壓、逆向電(dian)(dian)(dian)(dian)(dian)(dian)壓、頻繁的(de)(de)(de)(de)(de)充放(fang)電(dian)(dian)(dian)(dian)(dian)(dian)等。但(dan)是(shi)最直(zhi)接的(de)(de)(de)(de)(de)原(yuan)(yuan)(yuan)因就(jiu)是(shi)高(gao)(gao)溫(wen)。我們知道電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)有(you)一個重要(yao)的(de)(de)(de)(de)(de)參數就(jiu)是(shi)耐溫(wen)值，指(zhi)的(de)(de)(de)(de)(de)就(jiu)是(shi)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)內(nei)(nei)部(bu)電(dian)(dian)(dian)(dian)(dian)(dian)解液的(de)(de)(de)(de)(de)沸(fei)(fei)點。當(dang)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)的(de)(de)(de)(de)(de)內(nei)(nei)部(bu)溫(wen)度(du)達(da)到電(dian)(dian)(dian)(dian)(dian)(dian)解液的(de)(de)(de)(de)(de)沸(fei)(fei)點時(shi)，電(dian)(dian)(dian)(dian)(dian)(dian)解液開始(shi)沸(fei)(fei)騰，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)內(nei)(nei)部(bu)的(de)(de)(de)(de)(de)壓力升(sheng)高(gao)(gao)，當(dang)壓力超過(guo)(guo)泄爆(bao)口的(de)(de)(de)(de)(de)承(cheng)受(shou)極限就(jiu)發生了爆(bao)漿(jiang)。所(suo)以說溫(wen)度(du)是(shi)導致電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)爆(bao)漿(jiang)的(de)(de)(de)(de)(de)直(zhi)接原(yuan)(yuan)(yuan)因。電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)設計使(shi)用壽(shou)命(ming)(ming)大約(yue)為2萬小(xiao)時(shi)，受(shou)環境溫(wen)度(du)的(de)(de)(de)(de)(de)影響(xiang)也很大。電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)的(de)(de)(de)(de)(de)使(shi)用壽(shou)命(ming)(ming)隨(sui)溫(wen)度(du)的(de)(de)(de)(de)(de)增加而(er)(er)(er)減(jian)小(xiao)，實(shi)驗證(zheng)(zheng)明環境溫(wen)度(du)每升(sheng)高(gao)(gao)10℃，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)的(de)(de)(de)(de)(de)壽(shou)命(ming)(ming)就(jiu)會減(jian)半。主要(yao)原(yuan)(yuan)(yuan)因就(jiu)是(shi)溫(wen)度(du)加速化(hua)(hua)學反應(ying)而(er)(er)(er)使(shi)介質(zhi)隨(sui)時(shi)間退化(hua)(hua)失效(xiao)，這(zhe)樣電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)壽(shou)命(ming)(ming)終結(jie)。為了保(bao)證(zheng)(zheng)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)的(de)(de)(de)(de)(de)穩定性，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)在插板前要(yao)經(jing)過(guo)(guo)長時(shi)間的(de)(de)(de)(de)(de)高(gao)(gao)溫(wen)環境的(de)(de)(de)(de)(de)測試。即使(shi)是(shi)在100℃，高(gao)(gao)品質(zhi)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)也可以工作幾千個小(xiao)時(shi)。同時(shi)，我們提到的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)的(de)(de)(de)(de)(de)壽(shou)命(ming)(ming)是(shi)指(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)在使(shi)用過(guo)(guo)程中(zhong)，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)容(rong)(rong)(rong)(rong)量不(bu)會超過(guo)(guo)標(biao)準(zhun)(zhun)范圍變化(hua)(hua)的(de)(de)(de)(de)(de)10%。電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)壽(shou)命(ming)(ming)指(zhi)的(de)(de)(de)(de)(de)是(shi)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)容(rong)(rong)(rong)(rong)量的(de)(de)(de)(de)(de)問題，而(er)(er)(er)不(bu)是(shi)設計壽(shou)命(ming)(ming)到達(da)之后就(jiu)發生爆(bao)漿(jiang)。只(zhi)是(shi)無(wu)法保(bao)證(zheng)(zheng)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)的(de)(de)(de)(de)(de)設計的(de)(de)(de)(de)(de)容(rong)(rong)(rong)(rong)量標(biao)準(zhun)(zhun)。
所(suo)以，短時期(qi)內，正(zheng)常使(shi)(shi)用的板(ban)卡(ka)(ka)電(dian)(dian)容就發(fa)(fa)生爆漿(jiang)的情(qing)況，這就是(shi)電(dian)(dian)容品質問題。另外，不正(zheng)常的使(shi)(shi)用情(qing)況也(ye)(ye)有可能發(fa)(fa)生電(dian)(dian)容爆漿(jiang)的情(qing)況。比(bi)如熱插拔電(dian)(dian)腦配(pei)件(jian)也(ye)(ye)會(hui)導致板(ban)卡(ka)(ka)局部電(dian)(dian)路電(dian)(dian)流、電(dian)(dian)壓的劇烈變(bian)化，從而引發(fa)(fa)電(dian)(dian)容使(shi)(shi)用故障(zhang)。
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