一、 電容(rong)簡介(jie)
電容器由兩個夾有絕緣材料（介質）的金屬極組成。由于絕緣材料不同，電容器的類型也不同：
按結構(gou)可分為(wei)：固定電容、可變電容、微調(diao)電容。
根據介(jie)(jie)質(zhi)材料的不同(tong)，可分為：氣(qi)體(ti)(ti)介(jie)(jie)質(zhi)電(dian)(dian)容(rong)、液體(ti)(ti)介(jie)(jie)質(zhi)電(dian)(dian)容(rong)、無固體(ti)(ti)介(jie)(jie)質(zhi)電(dian)(dian)容(rong)、有固體(ti)(ti)介(jie)(jie)質(zhi)電(dian)(dian)容(rong)、電(dian)(dian)解電(dian)(dian)容(rong)。
按極性(xing)可分為極性(xing)電(dian)容和非極性(xing)電(dian)容。我們看到的常見的是電(dian)解電(dian)容。
電(dian)容在電(dian)路中(zhong)既能切斷直流電(dian)又能通過交流電(dian)，因此常被(bei)用于級間耦合(he)、濾(lv)波、去耦、旁路和(he)信(xin)號(hao)調理。
二、用(yong)于信號電路，主要完成(cheng)耦合(he)、振(zhen)蕩/同步、時間(jian)常數(shu)等功(gong)能
1） 耦合：例如晶體(ti)管放大器的(de)發射(she)極具(ju)有獨立的(de)偏(pian)置電(dian)(dian)(dian)阻，同時(shi)使信號產生電(dian)(dian)(dian)壓降并反饋到(dao)輸(shu)入端形(xing)成(cheng)輸(shu)入輸(shu)出信號耦合。這(zhe)個電(dian)(dian)(dian)阻是產生耦合的(de)元(yuan)件(jian)。如果一個電(dian)(dian)(dian)容(rong)器并聯在該電(dian)(dian)(dian)阻的(de)兩端，由于電(dian)(dian)(dian)容(rong)器對交流信號的(de)阻抗(kang)較(jiao)小(xiao)，這(zhe)將減(jian)小(xiao)該電(dian)(dian)(dian)容(rong)器因電(dian)(dian)(dian)阻引起的(de)耦合效應(ying)而(er)被稱(cheng)為去耦電(dian)(dian)(dian)容(rong)器。
2） 振(zhen)蕩(dang)/同步：包括RC、LC振(zhen)蕩(dang)器和晶體的負載電容都屬于(yu)這一類。
3） 時間(jian)常(chang)數：這是常(chang)用的R，C串聯積分電(dian)路(lu)。當(dang)輸(shu)入信號電(dian)壓施加(jia)到(dao)輸(shu)入端子時，電(dian)容器（c）上的電(dian)壓逐(zhu)漸升高。充電(dian)電(dian)流隨(sui)電(dian)壓的增加(jia)而減小。
三、 用(yong)于電源電路中實現旁路、去(qu)耦、濾波和儲能。詳細分類(lei)如下(xia)：
1） 旁(pang)路：旁(pang)路電(dian)(dian)(dian)容器是一(yi)種為(wei)本地(di)設備提(ti)供能(neng)(neng)量(liang)的(de)(de)儲能(neng)(neng)裝(zhuang)置(zhi)。它可(ke)以使調(diao)節器的(de)(de)輸(shu)(shu)出均勻(yun)，降(jiang)低負載要求(qiu)。就(jiu)像一(yi)個(ge)小型的(de)(de)可(ke)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)池，旁(pang)路電(dian)(dian)(dian)容器可(ke)以充(chong)放電(dian)(dian)(dian)到設備上。為(wei)了盡(jin)可(ke)能(neng)(neng)降(jiang)低阻抗，旁(pang)路電(dian)(dian)(dian)容應盡(jin)可(ke)能(neng)(neng)靠近(jin)負載裝(zhuang)置(zhi)的(de)(de)電(dian)(dian)(dian)源引(yin)腳(jiao)和(he)接地(di)引(yin)腳(jiao)。這樣可(ke)以很好地(di)防止由于輸(shu)(shu)入值(zhi)過大而引(yin)起(qi)的(de)(de)接地(di)電(dian)(dian)(dian)位升高和(he)噪聲。接地(di)彈是接地(di)體通過大電(dian)(dian)(dian)流毛刺時的(de)(de)電(dian)(dian)(dian)壓降(jiang)。
2） 去耦：在電(dian)(dian)(dian)路(lu)方面，通常(chang)分為驅(qu)動(dong)源和(he)驅(qu)動(dong)負載(zai)。當負載(zai)電(dian)(dian)(dian)容較大時，驅(qu)動(dong)電(dian)(dian)(dian)路(lu)需要對電(dian)(dian)(dian)容進行充放電(dian)(dian)(dian)以(yi)完成信(xin)號跳變。當上(shang)升(sheng)沿較陡時，電(dian)(dian)(dian)流(liu)較大，因此驅(qu)動(dong)電(dian)(dian)(dian)流(liu)會吸收大量的(de)功率電(dian)(dian)(dian)流(liu)。由于電(dian)(dian)(dian)路(lu)中的(de)電(dian)(dian)(dian)感、電(dian)(dian)(dian)阻（特別是芯片(pian)引腳上(shang)的(de)電(dian)(dian)(dian)感會反彈），這種(zhong)電(dian)(dian)(dian)流(liu)實際上(shang)是相對于正(zheng)常(chang)情況的(de)，是一種(zhong)會影響前一級(ji)正(zheng)常(chang)工作(zuo)的(de)噪聲，稱為“耦合”。
去(qu)耦電(dian)容(rong)器是起(qi)到“電(dian)池(chi)”作用，以滿足驅動電(dian)路電(dian)流的變化，避免互耦干擾(rao)。
3） 濾(lv)波：理(li)論上（即假設電(dian)(dian)(dian)容(rong)(rong)為純(chun)電(dian)(dian)(dian)容(rong)(rong)），電(dian)(dian)(dian)容(rong)(rong)越(yue)大(da)(da)(da)，阻(zu)抗越(yue)小，通過(guo)頻(pin)率越(yue)高(gao)。但事(shi)實上，1μf以(yi)上的(de)電(dian)(dian)(dian)容(rong)(rong)器大(da)(da)(da)多是電(dian)(dian)(dian)感分量較(jiao)大(da)(da)(da)的(de)電(dian)(dian)(dian)解電(dian)(dian)(dian)容(rong)(rong)器，因(yin)此(ci)當頻(pin)率較(jiao)高(gao)時，阻(zu)抗會(hui)增大(da)(da)(da)。有時可以(yi)看到，有一個(ge)大(da)(da)(da)容(rong)(rong)量的(de)電(dian)(dian)(dian)解電(dian)(dian)(dian)容(rong)(rong)器并聯在一個(ge)小電(dian)(dian)(dian)容(rong)(rong)器上。此(ci)時大(da)(da)(da)電(dian)(dian)(dian)容(rong)(rong)接低頻(pin)，小電(dian)(dian)(dian)容(rong)(rong)接高(gao)頻(pin)。電(dian)(dian)(dian)容(rong)(rong)器的(de)作用(yong)是通過(guo)高(gao)阻(zu)和低阻(zu)、高(gao)頻(pin)和低頻(pin)。電(dian)(dian)(dian)容(rong)(rong)越(yue)大(da)(da)(da)，低頻(pin)越(yue)容(rong)(rong)易通過(guo)，電(dian)(dian)(dian)容(rong)(rong)越(yue)大(da)(da)(da)，高(gao)頻(pin)越(yue)容(rong)(rong)易通過(guo)。專門用(yong)于濾(lv)波，大(da)(da)(da)電(dian)(dian)(dian)容(rong)(rong)（1000μf）濾(lv)波器低頻(pin)，小電(dian)(dian)(dian)容(rong)(rong)（20pF）濾(lv)波器高(gao)頻(pin)。
4） 儲能：儲能電(dian)容器通(tong)(tong)過整(zheng)流器收集電(dian)荷(he)，通(tong)(tong)過換流導線將儲能傳輸到電(dian)源輸出端。常用鋁電(dian)解電(dian)容器（如EPCOS公司的(de)b43504或b43505），額(e)定電(dian)壓(ya)40-450vdc，電(dian)容值(zhi)220-150000μf。根據不(bu)同(tong)的(de)功率要求，器件(jian)有時采用串(chuan)聯、并聯或組合的(de)形(xing)式(shi)。
