电容-从10个方面(mian)汇总电容知识(shi)（作用、参(can)数、公式等）-KIA MOS管
信息来源：本站 日期：2019-09-17
电(dian)(dian)(dian)容(rong)（Capacitance）亦(yi)称作“电(dian)(dian)(dian)容(rong)量”，是(shi)指在给定电(dian)(dian)(dian)位差下的电(dian)(dian)(dian)荷(he)(he)(he)(he)储(chu)(chu)藏(zang)量，记为C，国(guo)际单位是(shi)法(fa)拉（F）。一般来说，电(dian)(dian)(dian)荷(he)(he)(he)(he)在电(dian)(dian)(dian)场中(zhong)会受力而移(yi)动(dong)，当导体之间(jian)有了介质，则阻碍(ai)了电(dian)(dian)(dian)荷(he)(he)(he)(he)移(yi)动(dong)而使得电(dian)(dian)(dian)荷(he)(he)(he)(he)累(lei)积在导体上，造(zao)成电(dian)(dian)(dian)荷(he)(he)(he)(he)的累(lei)积储(chu)(chu)存(cun)，储(chu)(chu)存(cun)的电(dian)(dian)(dian)荷(he)(he)(he)(he)量则称为电(dian)(dian)(dian)容(rong)。
电(dian)(dian)(dian)容(rong)(rong)是(shi)指容(rong)(rong)纳电(dian)(dian)(dian)场(chang)的(de)能力。任何静(jing)电(dian)(dian)(dian)场(chang)都是(shi)由许多个电(dian)(dian)(dian)容(rong)(rong)组成(cheng)，有静(jing)电(dian)(dian)(dian)场(chang)就有电(dian)(dian)(dian)容(rong)(rong)，电(dian)(dian)(dian)容(rong)(rong)是(shi)用静(jing)电(dian)(dian)(dian)场(chang)描述的(de)。一般认为(wei)：孤立(li)导体(ti)与(yu)无(wu)穷远(yuan)处构成(cheng)电(dian)(dian)(dian)容(rong)(rong)，导体(ti)接地(di)等(deng)效于(yu)接到无(wu)穷远(yuan)处，并与(yu)大地(di)连接成(cheng)整体(ti)。
电(dian)(dian)(dian)容(rong)（或称电(dian)(dian)(dian)容(rong)量(liang)）是(shi)表现电(dian)(dian)(dian)容(rong)器容(rong)纳电(dian)(dian)(dian)荷(he)本领的(de)物(wu)理量(liang)。电(dian)(dian)(dian)容(rong)从物(wu)理学上讲，它(ta)(ta)是(shi)一种静态电(dian)(dian)(dian)荷(he)存储介质，可能电(dian)(dian)(dian)荷(he)会永久存在，这是(shi)它(ta)(ta)的(de)特征，它(ta)(ta)的(de)用途较广，它(ta)(ta)是(shi)电(dian)(dian)(dian)子(zi)、电(dian)(dian)(dian)力领域中不可缺(que)少的(de)电(dian)(dian)(dian)子(zi)元件。主(zhu)要用于电(dian)(dian)(dian)源(yuan)滤波、信号(hao)滤波、信号(hao)耦合、谐振、滤波、补偿、充放电(dian)(dian)(dian)、储能、隔直(zhi)流等电(dian)(dian)(dian)路中。
作为无(wu)源元件之一的电容，其作用不外(wai)乎(hu)以下(xia)几种：
应用(yong)于电(dian)源电(dian)路(lu)，实现(xian)旁路(lu)、去(qu)藕、滤(lv)波和储(chu)能的作用(yong)。下(xia)面(mian)分类详(xiang)述之(zhi)：
1）旁路
旁(pang)路电(dian)(dian)(dian)容是为(wei)本地(di)器(qi)件提(ti)供能量的(de)储能器(qi)件，它能使稳压(ya)器(qi)的(de)输出均匀化(hua)，降(jiang)(jiang)低负载(zai)(zai)需求(qiu)。就像小型可充电(dian)(dian)(dian)电(dian)(dian)(dian)池一样，旁(pang)路电(dian)(dian)(dian)容能够(gou)(gou)被充电(dian)(dian)(dian)，并向器(qi)件进行放电(dian)(dian)(dian)。为(wei)尽量减少阻抗(kang)，旁(pang)路电(dian)(dian)(dian)容要尽量靠近负载(zai)(zai)器(qi)件的(de)供电(dian)(dian)(dian)电(dian)(dian)(dian)源管(guan)脚(jiao)和(he)地(di)管(guan)脚(jiao)。这能够(gou)(gou)很好地(di)防止(zhi)输入值过大(da)而导致的(de)地(di)电(dian)(dian)(dian)位抬高和(he)噪声。地(di)弹是地(di)连接处在通过大(da)电(dian)(dian)(dian)流毛刺(ci)时(shi)的(de)电(dian)(dian)(dian)压(ya)降(jiang)(jiang)。
2）去藕(ou)
去(qu)藕，又称解藕。从电(dian)路来说，总是可以(yi)区分(fen)为(wei)驱(qu)(qu)(qu)动的(de)源(yuan)和被驱(qu)(qu)(qu)动的(de)负(fu)载。如果负(fu)载电(dian)容(rong)比(bi)较(jiao)大，驱(qu)(qu)(qu)动电(dian)路要把电(dian)容(rong)充电(dian)、放电(dian)，才能完成信号的(de)跳变，在上升沿比(bi)较(jiao)陡峭的(de)时候，电(dian)流比(bi)较(jiao)大，这(zhei)样驱(qu)(qu)(qu)动的(de)电(dian)流就会(hui)吸收(shou)很大的(de)电(dian)源(yuan)电(dian)流，由于(yu)电(dian)路中的(de)电(dian)感(gan)，电(dian)阻（特(te)别(bie)是芯片(pian)管脚上的(de)电(dian)感(gan)，会(hui)产生反(fan)弹），这(zhei)种(zhong)电(dian)流相对于(yu)正(zheng)(zheng)常情况来说实际上就是一种(zhong)噪声，会(hui)影响前级的(de)正(zheng)(zheng)常工作，这(zhei)就是所谓的(de)“耦合”。
去藕(ou)电容就是起到一个“电池”的(de)作用(yong)，满(man)足驱动电路(lu)电流的(de)变化，避(bi)免相互(hu)间的(de)耦(ou)合(he)干扰。将旁路(lu)电容和去藕(ou)电容结合(he)起来将更容易理解。
旁(pang)路(lu)电容(rong)实际(ji)也是去藕合的(de)，只是旁(pang)路(lu)电容(rong)一(yi)般(ban)是指高频(pin)旁(pang)路(lu)，也就是给(ji)高频(pin)的(de)开关噪声提高一(yi)条低阻(zu)抗(kang)泄(xie)防途径(jing)。高频(pin)旁(pang)路(lu)电容(rong)一(yi)般(ban)比较(jiao)小，根据谐振频(pin)率一(yi)般(ban)取 0.1μF、0.01μF 等；而(er)去耦合电容(rong)的(de)容(rong)量一(yi)般(ban)较(jiao)大，可(ke)能是 10μF 或者更(geng)大，依据电路(lu)中分布参数、以及驱动电流的(de)变化大小来(lai)确定。
旁路(lu)是(shi)把输(shu)入(ru)信号中的干(gan)(gan)(gan)扰(rao)作为(wei)滤(lv)除对象，而去耦是(shi)把输(shu)出信号的干(gan)(gan)(gan)扰(rao)作为(wei)滤(lv)除对象，防(fang)止干(gan)(gan)(gan)扰(rao)信号返回(hui)电(dian)源。这应该是(shi)他们的本质区(qu)别。
3）滤(lv)波
从(cong)理论上(shang)（即假(jia)设电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)为纯电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)）说(shuo)，电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)越(yue)大(da)，阻抗(kang)越(yue)小(xiao)，通(tong)(tong)过的(de)(de)频(pin)(pin)率也(ye)越(yue)高(gao)(gao)。但实际(ji)上(shang)超过 1μF 的(de)(de)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)大(da)多为电(dian)(dian)解(jie)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)，有很大(da)的(de)(de)电(dian)(dian)感成份，所以频(pin)(pin) 率高(gao)(gao)后反而阻抗(kang)会增大(da)。有时(shi)会看到有一个(ge)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)量较大(da)电(dian)(dian)解(jie)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)并联了一个(ge)小(xiao)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)，这时(shi)大(da)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)通(tong)(tong)低(di)频(pin)(pin)，小(xiao)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)通(tong)(tong)高(gao)(gao)频(pin)(pin)。电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)的(de)(de)作用就(jiu)是通(tong)(tong)高(gao)(gao)阻低(di)，通(tong)(tong)高(gao)(gao)频(pin)(pin)阻低(di)频(pin)(pin)。电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)越(yue)大(da)低(di)频(pin)(pin)越(yue)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)易(yi)通(tong)(tong)过，电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)越(yue)大(da)高(gao)(gao)频(pin)(pin)越(yue)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)易(yi)通(tong)(tong)过。具体(ti)用在滤(lv)波中，大(da)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)（1000μF）滤(lv)低(di)频(pin)(pin)，小(xiao)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)（20pF）滤(lv)高(gao)(gao)频(pin)(pin)。
曾有网友形象地将滤(lv)(lv)波电(dian)容(rong)比(bi)作“水塘”。由于电(dian)容(rong)的(de)(de)两(liang)端电(dian)压(ya)不会(hui)突(tu)变(bian)(bian)，由此可知，信(xin)号频率(lv)(lv)越高则衰减越大(da)，可很形象的(de)(de)说电(dian)容(rong)像个水塘，不会(hui)因几滴水的(de)(de)加入或(huo)蒸(zheng)发而(er)引起水量的(de)(de)变(bian)(bian)化(hua)。它把电(dian)压(ya)的(de)(de)变(bian)(bian)动转(zhuan)化(hua)为电(dian)流的(de)(de)变(bian)(bian)化(hua)，频率(lv)(lv)越高，峰值电(dian)流就越大(da)，从而(er)缓(huan)冲了电(dian)压(ya)。滤(lv)(lv)波就是充(chong)电(dian)，放电(dian)的(de)(de)过程。
4）储能
储能型电(dian)容(rong)(rong)器通过整流器收集电(dian)荷，并将存储的(de)(de)(de)能量通过变换(huan)器引线传送至电(dian)源的(de)(de)(de)输出端。电(dian)压额定值为(wei) 40～450VDC、电(dian)容(rong)(rong)值在 220～150 000μF 之间(jian)的(de)(de)(de)铝电(dian)解电(dian)容(rong)(rong)器是较(jiao)为(wei)常(chang)用(yong)(yong)的(de)(de)(de)。根不同的(de)(de)(de)电(dian)源要求，器件(jian)有时(shi)会采用(yong)(yong)串联(lian)、并联(lian)或其组合的(de)(de)(de)形(xing)式，对于功(gong)率(lv)级超(chao)过 10KW 的(de)(de)(de)电(dian)源，通常(chang)采用(yong)(yong)体积较(jiao)大的(de)(de)(de)罐形(xing)螺旋端子电(dian)容(rong)(rong)器。
应用于信号电路，主要完成耦合、振荡/同步及时间常数的作用：
1）耦合
举个例子来讲，晶体管放大器发射极(ji)有一个自给偏压(ya)电(dian)(dian)阻，它同时又使信(xin)(xin)号(hao) 产(chan)生(sheng)(sheng)压(ya)降(jiang)反馈到输入端形成了(le)输入输出信(xin)(xin)号(hao)耦合，这个电(dian)(dian)阻就是产(chan)生(sheng)(sheng)了(le)耦合的元件，如(ru)果在这个电(dian)(dian)阻两(liang)端并联(lian)一个电(dian)(dian)容(rong)，由于适当(dang)容(rong)量的电(dian)(dian)容(rong)器对交流(liu)信(xin)(xin)号(hao) 较小(xiao)(xiao)的阻抗，这样就减小(xiao)(xiao)了(le)电(dian)(dian)阻产(chan)生(sheng)(sheng)的耦合效应，故称(cheng)此电(dian)(dian)容(rong)为去耦电(dian)(dian)容(rong)。
2）振荡/同步(bu)
包括 RC、LC 振荡器及晶体(ti)的负载电容都属(shu)于这一(yi)范(fan)畴。
3）时(shi)间常数
这就是常见的(de) R、C 串联构成的(de)积分电(dian)路(lu)。当输入信号电(dian)压(ya)加在(zai)输入端(duan)时，电(dian)容(rong)（C）上(shang)的(de)电(dian)压(ya)逐渐上(shang)升。而其(qi)充电(dian)电(dian)流则随着电(dian)压(ya)的(de)上(shang)升而减小。电(dian)流通过电(dian)阻（R）、电(dian)容(rong)（C）的(de)特性通过下(xia)面的(de)公式描述(shu)：
i=(V/R)e-(t/CR)
通常，应(ying)该如何为(wei)我们的电(dian)(dian)路(lu)选(xuan)择一(yi)颗合适(shi)的电(dian)(dian)容呢？笔者认为(wei)，应(ying)基于(yu)以下几点考(kao)虑：
1）静(jing)电容量；
2）额定耐(nai)压(ya)；
3）容值误差；
4）直流偏压下的(de)电(dian)容变化量(liang)；
5）噪声等(deng)级(ji)；
6）电(dian)容的类型；
7）电容的(de)规格(ge)。
那么，是否(fou)有捷径可寻呢？其实(shi)，电容作为器件(jian)(jian)的外围(wei)元件(jian)(jian)，几乎每个器件(jian)(jian)的 Datasheet 或(huo)者 Solutions，都比较明(ming)确地指(zhi)明(ming)了外围(wei)元件(jian)(jian)的选择参(can)数，也(ye)就是说(shuo)，据此可以获得基本(ben)的器件(jian)(jian)选择要求，然后再(zai)进一(yi)步(bu)完善(shan)细(xi)化之。
其实选用(yong)电(dian)容(rong)(rong)时(shi)不仅(jin)仅(jin)是只看(kan)容(rong)(rong)量和封装(zhuang)，具体要看(kan)产品(pin)所使用(yong)环境，特(te)殊的(de)电(dian)路必(bi)须用(yong)特(te)殊的(de)电(dian)容(rong)(rong)。
下面(mian)是 chip capacitor 根据电介质(zhi)的(de)介电常数分类，介电常数直接(jie)影响电路的(de)稳定性。
NP0 or CH （K < 150）：电(dian)气性能最稳定(ding)，基本上(shang)不(bu)随温度﹑电(dian)压(ya)与(yu)时间的(de)改(gai)变而改(gai)变，适用于对稳定(ding)性要(yao)求高的(de)高频电(dian)路。鉴于 K 值较小，所以在 0402、0603、0805 封装下(xia)很难有(you)大容(rong)量的(de)电(dian)容(rong)。如 0603 一般最大的(de) 10nF 以下(xia)。
X7R or YB （2000 < K < 4000）：电气性能较(jiao)稳(wen)定，在(zai)温度、电压与时间改变时性能的变化并(bing)不显著（?C < ±10%）。适用于隔直、偶合、旁路(lu)与对容量稳(wen)定性要求不太高(gao)的全频鉴电路(lu)。
Y5V or YF（K > 15000）：容量稳(wen)定性较 X7R 差（?C < +20% ～ -8 0%），容量损耗对温(wen)度(du)、电压等测试条件较敏感，但由(you)于(yu)其(qi) K 值较大，所以适用于(yu)一(yi)些容值要求较高的场(chang)合(he)。
电容的(de)分(fen)类方式及种类很多，基于电容的(de)材料特性，其可分(fen)为以下(xia)几(ji)大类：
1）铝电解电容
电(dian)容(rong)(rong)容(rong)(rong)量范围为 0.1μF ～ 22000μF，高脉动电(dian)流、长寿命、大容(rong)(rong)量的不二之(zhi)选，广(guang)泛(fan)应用于电(dian)源滤波、解藕(ou)等场合。
2）薄膜电容(rong)
电(dian)(dian)容容量范围为(wei) 0.1pF ～ 10μF，具有较小公差(cha)、较高容量稳定性及极低的压电(dian)(dian)效(xiao)应，因此(ci)是 X、Y 安全电(dian)(dian)容、EMI/EMC 的首(shou)选。
3）钽电容
电(dian)(dian)容(rong)(rong)容(rong)(rong)量范(fan)围为 2.2μF ～ 560μF，低等(deng)效(xiao)串联电(dian)(dian)阻（ESR）、低等(deng)效(xiao)串联电(dian)(dian)感（ESL）。脉动吸收、瞬态响应(ying)及噪声抑制(zhi)都优(you)于铝电(dian)(dian)解电(dian)(dian)容(rong)(rong)，是高稳定电(dian)(dian)源的理想选择(ze)。
4）陶瓷电容
电容(rong)容(rong)量范围为 0.5pF ～ 100μF，独特的(de)(de)材料和薄膜技术的(de)(de)结晶，迎合了当今“更轻、更薄、更节(jie)能“的(de)(de)设(she)计(ji)理(li)念。
5）超级(ji)电容
电(dian)容容量范围(wei)为(wei) 0.022F ～ 70F，极高的容值，因此(ci)又称做“金(jin)电(dian)容”或者“法(fa)拉电(dian)容”。主要(yao)特(te)点是：超(chao)高容值、良好的充/放电(dian)特(te)性(xing)，适合于(yu)电(dian)能存(cun)储和(he)电(dian)源备份(fen)。缺(que)点是耐压较(jiao)低(di)，工作温度范围(wei)较(jiao)窄。
对于电(dian)容而言(yan)，小型化(hua)和高容量是永(yong)恒不变的发(fa)展(zhan)趋势。其(qi)中，要数多层陶瓷电(dian)容（MLCC）的发(fa)展(zhan)最快。
多层陶瓷(ci)电(dian)容(rong)在便携(xie)产品(pin)中广(guang)泛(fan)应用(yong)极为(wei)广(guang)泛(fan)，但近年来数字产品(pin)的技术进步对其提出了新要(yao)求(qiu)。例如，手(shou)机要(yao)求(qiu)更高(gao)的传输速(su)率(lv)和(he)更高(gao)的性能；基带(dai)处理 器(qi)要(yao)求(qiu)高(gao)速(su)度(du)、低电(dian)压；LCD 模块(kuai)要(yao)求(qiu)低厚度(du)（0.5mm）、大容(rong)量电(dian)容(rong)。而汽车环境的苛刻性对多层陶瓷(ci)电(dian)
容更有特殊的要(yao)求：首先是耐高温，放置于其(qi)中的多层陶(tao)瓷电容必须能满足 150℃ 的工(gong)作温度；其(qi)次(ci)是在电池电路(lu)上需要(yao)短路(lu)失 效保护(hu)设(she)计。
也(ye)就是说，小型化(hua)、高(gao)(gao)速度和高(gao)(gao)性能(neng)、耐高(gao)(gao)温条(tiao)件、高(gao)(gao)可靠(kao)性已成为陶瓷电容(rong)的关键特性。
陶瓷电(dian)容的容量随直(zhi)流偏置(zhi)电(dian)压(ya)的变化而变化。直(zhi)流偏置(zhi)电(dian)压(ya)降低了介(jie)电(dian)常数，因此需要从材(cai)料方面，降低介(jie)电(dian)常数对电(dian)压(ya)的依赖，优化直(zhi)流偏置(zhi)电(dian)压(ya)特性(xing)。
应(ying)用(yong)中较为常见的是 X7R（X5R）类多层陶(tao)瓷(ci)电(dian)(dian)容(rong)， 它(ta)的容(rong)量主要集(ji)中在1000pF以上，该类电(dian)(dian)容(rong)器主要性能(neng)指标(biao)是等效串联电(dian)(dian)阻(zu)（ESR），在高波纹电(dian)(dian)流的电(dian)(dian)源去耦、滤波及低频信号耦合电(dian)(dian)路的低功耗表现比较突出。
另一类(lei)(lei)多层陶瓷电(dian)(dian)(dian)容(rong)是(shi)C0G类(lei)(lei)，它的(de)(de)容(rong)量多在(zai) 1000pF 以下，该类(lei)(lei)电(dian)(dian)(dian)容(rong)器(qi)主要性(xing)能(neng)指标是(shi)损(sun)耗角正切值(zhi) tgδ(DF)。传统的(de)(de)贵(gui)金属(shu)电(dian)(dian)(dian)极（NME）的(de)(de) C0G 产(chan)品(pin)(pin) DF 值(zhi)范围是(shi)（2.0 ～ 8.0）× 10-4，而技术创新型贱(jian)金属(shu)电(dian)(dian)(dian)极（BME）的(de)(de)C0G产(chan)品(pin)(pin)DF值(zhi)范围为(wei) (1.0 ～ 2.5)×10-4，约(yue)是(shi)前者的(de)(de)31 ～ 50%。该类(lei)(lei)产(chan)品(pin)(pin)在(zai)载有T/R模块电(dian)(dian)(dian)路(lu)的(de)(de)GSM、CDMA、无绳电(dian)(dian)(dian)话、蓝(lan)牙、GPS系统中低功耗特性(xing)较为(wei)显著。较多用(yong)于(yu)各(ge)种高频电(dian)(dian)(dian)路(lu)，如振荡/同(tong)步器(qi)、定(ding)时器(qi)电(dian)(dian)(dian)路(lu)等。
通常(chang)的(de)(de)(de)看(kan)法是(shi)钽电(dian)(dian)(dian)容(rong)(rong)性能比铝电(dian)(dian)(dian)容(rong)(rong)好，因为钽电(dian)(dian)(dian)容(rong)(rong)的(de)(de)(de)介(jie)质(zhi)(zhi)(zhi)为阳极氧化后生成(cheng)的(de)(de)(de)五氧化二(er)钽，它(ta)的(de)(de)(de)介(jie)电(dian)(dian)(dian)能力（通常(chang)用 ε 表示）比铝电(dian)(dian)(dian)容(rong)(rong)的(de)(de)(de)三氧化二(er)铝介(jie)质(zhi)(zhi)(zhi)要高。因此在同样容(rong)(rong)量的(de)(de)(de)情(qing)况下，钽电(dian)(dian)(dian)容(rong)(rong)的(de)(de)(de)体(ti)积能比铝电(dian)(dian)(dian)容(rong)(rong)做得(de)更小。（电(dian)(dian)(dian)解(jie)电(dian)(dian)(dian)容(rong)(rong)的(de)(de)(de)电(dian)(dian)(dian)容(rong)(rong)量取决于介(jie)质(zhi)(zhi)(zhi)的(de)(de)(de)介(jie)电(dian)(dian)(dian)能力和体(ti)积，在容(rong)(rong)量一定的(de)(de)(de)情(qing)况下，介(jie)电(dian)(dian)(dian)能力越高，体(ti)积就可以做得(de)越小，反之，体(ti)积就需要做得(de)越大(da)）再加(jia)上钽的(de)(de)(de)性质(zhi)(zhi)(zhi)比较稳定，所(suo)以通常(chang)认为钽电(dian)(dian)(dian)容(rong)(rong)性能比铝电(dian)(dian)(dian)容(rong)(rong)好。
但这(zhei)种(zhong)凭阳(yang)极(ji)(ji)(ji)(ji)判断(duan)电(dian)(dian)(dian)容(rong)性(xing)能的(de)(de)(de)方(fang)法已经过时了(le)，目前决定电(dian)(dian)(dian)解(jie)电(dian)(dian)(dian)容(rong)性(xing)能的(de)(de)(de)关键并不在(zai)于阳(yang)极(ji)(ji)(ji)(ji)，而(er)在(zai)于电(dian)(dian)(dian)解(jie)质，也就(jiu)是(shi)阴(yin)极(ji)(ji)(ji)(ji)。因(yin)为不同(tong)(tong)(tong)的(de)(de)(de)阴(yin)极(ji)(ji)(ji)(ji)和不同(tong)(tong)(tong)的(de)(de)(de)阳(yang)极(ji)(ji)(ji)(ji)可以组合成不同(tong)(tong)(tong)种(zhong)类(lei)的(de)(de)(de)电(dian)(dian)(dian)解(jie)电(dian)(dian)(dian)容(rong)，其性(xing)能也大不相同(tong)(tong)(tong)。采用同(tong)(tong)(tong)一种(zhong)阳(yang)极(ji)(ji)(ji)(ji)的(de)(de)(de)电(dian)(dian)(dian)容(rong)由于电(dian)(dian)(dian)解(jie)质的(de)(de)(de)不同(tong)(tong)(tong)，性(xing)能可以差距很大，总之阳(yang)极(ji)(ji)(ji)(ji)对于电(dian)(dian)(dian)容(rong)性(xing)能的(de)(de)(de)影(ying)响远远小于阴(yin)极(ji)(ji)(ji)(ji)。
还(hai)有一种看(kan)法是认(ren)为钽电(dian)(dian)(dian)容(rong)(rong)(rong)比铝电(dian)(dian)(dian)容(rong)(rong)(rong)性能(neng)好，主要(yao)是由于钽加上二氧(yang)化锰阴(yin)极(ji)助威后才有明(ming)显好于铝电(dian)(dian)(dian)解液(ye)电(dian)(dian)(dian)容(rong)(rong)(rong)的(de)(de)表现。如果把铝电(dian)(dian)(dian)解液(ye)电(dian)(dian)(dian)容(rong)(rong)(rong)的(de)(de)阴(yin)极(ji)更换为二氧(yang)化锰， 那么它(ta)的(de)(de)性能(neng)其实(shi)也能(neng)提升不少(shao)。
可(ke)(ke)以肯定，ESR 是衡(heng)量一(yi)个电容特(te)性的主要参数之一(yi)。但(dan)是，选择电容，应避免(mian) ESR 越(yue)(yue)(yue)低越(yue)(yue)(yue)好(hao)，品质越(yue)(yue)(yue)高越(yue)(yue)(yue)好(hao)等误区。衡(heng)量一(yi)个产(chan)品，一(yi)定要全方位、多(duo)角度的去考虑，切不(bu)可(ke)(ke)把电容的作用有(you)意(yi)无意(yi)的夸大。
嵌入式(shi)设计中，要求 MCU 从耗电量很大的(de)处理密集(ji)型工作模(mo)式(shi)进入耗电量很少的(de)空闲/休(xiu)眠(mian)模(mo)式(shi)。这些(xie)转换很容易引起线路损耗的(de)急剧增(zeng)加，增(zeng)加的(de)速率很高，达到 20A/ms 甚至更快。
通常采用旁(pang)路(lu)电(dian)(dian)容(rong)(rong)来(lai)解决稳(wen)压(ya)(ya)(ya)器(qi)(qi)(qi)(qi)无法适应系统中高速器(qi)(qi)(qi)(qi)件(jian)引起的(de)负载(zai)变化(hua)，以确保电(dian)(dian)源输(shu)出的(de)稳(wen)定(ding)性(xing)及良(liang)好的(de)瞬态响应。旁(pang)路(lu)电(dian)(dian)容(rong)(rong)是为(wei)本地器(qi)(qi)(qi)(qi)件(jian)提(ti)供能(neng)(neng)量(liang)的(de)储能(neng)(neng)器(qi)(qi)(qi)(qi)件(jian)，它能(neng)(neng)使稳(wen)压(ya)(ya)(ya)器(qi)(qi)(qi)(qi)的(de)输(shu)出均匀化(hua)，降(jiang)低负载(zai)需求。就像小(xiao)型可充电(dian)(dian)电(dian)(dian)池一样，旁(pang)路(lu)电(dian)(dian)容(rong)(rong)能(neng)(neng)够(gou)被充电(dian)(dian)，并向器(qi)(qi)(qi)(qi)件(jian)进行(xing)放(fang)电(dian)(dian)。为(wei)尽量(liang)减少阻抗，旁(pang)路(lu)电(dian)(dian)容(rong)(rong)要尽量(liang)靠近(jin)负载(zai)器(qi)(qi)(qi)(qi)件(jian)的(de)供电(dian)(dian)电(dian)(dian)源管脚和(he)地管脚。这能(neng)(neng)够(gou)很(hen)好地防止输(shu)入值过(guo)(guo)大(da)而导致的(de)地电(dian)(dian)位抬高和(he)噪声。地弹(dan)是地连接处在(zai)通过(guo)(guo)大(da)电(dian)(dian)流(liu)毛(mao)刺时的(de)电(dian)(dian)压(ya)(ya)(ya)降(jiang)。
应该明(ming)白，大容(rong)(rong)量(liang)和小(xiao)容(rong)(rong)量(liang)的(de)(de)(de)(de)(de)旁路电(dian)容(rong)(rong)都可能(neng)(neng)是(shi)必需(xu)的(de)(de)(de)(de)(de)，有的(de)(de)(de)(de)(de)甚至是(shi)多个(ge)陶瓷电(dian)容(rong)(rong)和钽电(dian)容(rong)(rong)。这样的(de)(de)(de)(de)(de)组合能(neng)(neng)够(gou)(gou)解决上述(shu)负(fu)载电(dian)流(liu)或(huo)许(xu)为(wei)阶梯变(bian)化所带来(lai)的(de)(de)(de)(de)(de)问题，而(er)且还能(neng)(neng)提(ti)供足够(gou)(gou)的(de)(de)(de)(de)(de)去耦(ou)以(yi)抑(yi)制(zhi)(zhi)电(dian)压和电(dian)流(liu)毛刺。在负(fu)载变(bian)化非常剧(ju)烈(lie)的(de)(de)(de)(de)(de)情况下，则需(xu)要三个(ge)或(huo)更多不同容(rong)(rong)量(liang)的(de)(de)(de)(de)(de)电(dian)容(rong)(rong)，以(yi)保证(zheng)在稳(wen)压器(qi)稳(wen)压前(qian)提(ti)供足够(gou)(gou)的(de)(de)(de)(de)(de)电(dian)流(liu)。快(kuai)速的(de)(de)(de)(de)(de)瞬态过程由高频小(xiao)容(rong)(rong)量(liang)电(dian)容(rong)(rong)来(lai)抑(yi)制(zhi)(zhi)，中(zhong)速的(de)(de)(de)(de)(de)瞬态过程由低频大容(rong)(rong)量(liang)来(lai)抑(yi)制(zhi)(zhi)，剩下则交给稳(wen)压器(qi)完成了。
还应(ying)记住一点(dian)，稳压(ya)器也(ye)要求电容尽量靠近(jin)电压(ya)输出端。
普遍(bian)的(de)观点(dian)是(shi)：一个等效(xiao)串联电(dian)(dian)阻（ESR）很小的(de)相对较(jiao)大容(rong)(rong)量(liang)的(de)外部电(dian)(dian)容(rong)(rong)能很好地吸收快速转换时(shi)的(de)峰值（纹(wen)波）电(dian)(dian)流。但是(shi)，有时(shi)这样的(de)选择(ze)容(rong)(rong)易引起稳(wen)压(ya)器(qi)（特别(bie)是(shi)线(xian)性稳(wen)压(ya)器(qi) LDO）的(de)不(bu)稳(wen)定，所以必须合理(li)选择(ze)小容(rong)(rong)量(liang)和(he)大容(rong)(rong)量(liang)电(dian)(dian)容(rong)(rong)的(de)容(rong)(rong)值。永远记住，稳(wen)压(ya)器(qi)就是(shi)一个放(fang)大器(qi)，放(fang)大器(qi)可能出现(xian)的(de)各(ge)种情况 它都会出现(xian)。
由于 DC/DC 转(zhuan)换(huan)器(qi)(qi)的(de)(de)(de)(de)响应(ying)速度相(xiang)对较慢，输出去耦电(dian)容(rong)(rong)(rong)在负载阶跃的(de)(de)(de)(de)初始(shi)阶段(duan)起主导(dao)的(de)(de)(de)(de)作(zuo)用，因此需(xu)要额外大(da)容(rong)(rong)(rong)量的(de)(de)(de)(de)电(dian)容(rong)(rong)(rong)来减缓(huan)相(xiang)对于 DC/DC 转(zhuan)换(huan)器(qi)(qi)的(de)(de)(de)(de)快速转(zhuan)换(huan)，同时用高频电(dian)容(rong)(rong)(rong)减缓(huan)相(xiang)对于大(da)电(dian)容(rong)(rong)(rong)的(de)(de)(de)(de)快速变(bian)换(huan)。通常，大(da)容(rong)(rong)(rong)量电(dian)容(rong)(rong)(rong)的(de)(de)(de)(de)等效(xiao)串联电(dian)阻应(ying)该选择为合适(shi)的(de)(de)(de)(de)值(zhi)(zhi)，以便使输出电(dian)压(ya)的(de)(de)(de)(de)峰(feng)值(zhi)(zhi)和毛刺在器(qi)(qi)件的(de)(de)(de)(de) Dasheet 规(gui)定之内。
高频(pin)转换中，小(xiao)容(rong)量电(dian)(dian)容(rong)在 0.01μF 到 0.1μF 量级(ji)就(jiu)能很好(hao)满足要求。表贴(tie)陶瓷电(dian)(dian)容(rong)或者多(duo)层陶瓷电(dian)(dian)容(rong)（MLCC）具有(you)更(geng)小(xiao)的(de)(de) ESR。另外，在这些容(rong)值(zhi)下，它们的(de)(de)体积和(he) BOM 成本都比较合理。如果局(ju)部低(di)频(pin)去耦(ou)不(bu)充分(fen)，则从低(di)频(pin)向(xiang)高频(pin)转换时(shi)将引起(qi)输入(ru)电(dian)(dian)压(ya)(ya)降低(di)。电(dian)(dian)压(ya)(ya)下降过程可能持续数毫秒，时(shi)间长短(duan)主要取(qu)决于稳压(ya)(ya)器调节增(zeng)益(yi)和(he)提供较大负载电(dian)(dian)流的(de)(de)时(shi)间。
用 ESR 大(da)的(de)电容(rong)并联比(bi)用 ESR 恰好那么低(di)的(de)单个电容(rong)当然(ran)更具成本(ben)效(xiao)益。然(ran)而(er)，这需要(yao)你在 PCB 面积(ji)、器件数(shu)目与成本(ben)之间寻求折衷。
这(zhei)里的电(dian)解电(dian)容(rong)器主要指铝电(dian)解电(dian)容(rong)器，其基(ji)本的电(dian)参数(shu)包括下(xia)列(lie)五点：
1）电容(rong)值
电(dian)(dian)(dian)(dian)(dian)(dian)(dian)解电(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)器的(de)(de)(de)容(rong)值(zhi)，取决于在(zai)交(jiao)流(liu)(liu)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)下工(gong)作时所呈现的(de)(de)(de)阻抗。因此容(rong)值(zhi)，也就是交(jiao)流(liu)(liu)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)值(zhi)，随着(zhe)工(gong)作频(pin)率、电(dian)(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)以及测量(liang)方法的(de)(de)(de)变化而变化。在(zai)标准(zhun) JISC 5102 规定：铝电(dian)(dian)(dian)(dian)(dian)(dian)(dian)解电(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)的(de)(de)(de)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)量(liang)的(de)(de)(de)测量(liang)条件(jian)是在(zai)频(pin)率为 120Hz，最大交(jiao)流(liu)(liu)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)为 0.5Vrms，DC bias 电(dian)(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)为 1.5 ～ 2.0V 的(de)(de)(de)条件(jian)下进行。可以断言(yan)，铝电(dian)(dian)(dian)(dian)(dian)(dian)(dian)解电(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)器的(de)(de)(de)容(rong)量(liang)随频(pin)率的(de)(de)(de)增加而减小。
2）损耗角正切值 Tan δ
在(zai)电(dian)容器的(de)(de)(de)等效电(dian)路中，串联等效电(dian)阻 ESR 同容抗 1/ωC 之比称之为 Tan δ， 这里的(de)(de)(de) ESR 是(shi)在(zai) 120Hz 下计算获得的(de)(de)(de)值。显(xian)然，Tan δ 随着(zhe)测量频率的(de)(de)(de)增加而变(bian)大，随测量温度的(de)(de)(de)下降而增大。
3）阻抗 Z
在(zai)特定的(de)(de)频率(lv)下(xia)，阻碍交(jiao)流(liu)电(dian)(dian)(dian)流(liu)通过的(de)(de)电(dian)(dian)(dian)阻即为所谓的(de)(de)阻抗（Z）。它与电(dian)(dian)(dian)容等(deng)效电(dian)(dian)(dian)路中的(de)(de)电(dian)(dian)(dian)容值(zhi)、电(dian)(dian)(dian)感(gan)值(zhi)密切相关，且与 ESR 也有关系。
Z = √ [ESR2 + (XL - XC)2 ]
式中，XC = 1 / ωC = 1 / 2πfC
XL = ωL = 2πfL
电容(rong)的(de)(de)容(rong)抗(kang)(kang)（XC）在(zai)低频(pin)(pin)(pin)率范(fan)围(wei)内随着频(pin)(pin)(pin)率的(de)(de)增(zeng)(zeng)加(jia)逐步减小(xiao)，频(pin)(pin)(pin)率继续增(zeng)(zeng)加(jia)达到中频(pin)(pin)(pin)范(fan)围(wei)时电抗(kang)(kang)（XL）降至 ESR 的(de)(de)值。当频(pin)(pin)(pin)率达到高频(pin)(pin)(pin)范(fan)围(wei)时感(gan)抗(kang)(kang)（XL）变为主(zhu)导，所(suo)以阻抗(kang)(kang)是随着频(pin)(pin)(pin)率的(de)(de)增(zeng)(zeng)加(jia)而增(zeng)(zeng)加(jia)。
4）漏电流(liu)
电(dian)容器的(de)介质(zhi)(zhi)对直(zhi)流(liu)电(dian)流(liu)具有(you)很大的(de)阻碍作(zuo)用。然而，由于铝(lv)氧(yang)化(hua)膜介质(zhi)(zhi)上浸(jin)有(you)电(dian)解液，在施加电(dian)压(ya)(ya)时(shi)，重新形成(cheng)的(de)以及修复氧(yang)化(hua)膜的(de)时(shi)候会(hui)产(chan)生(sheng)一(yi)种很小的(de)称之为漏电(dian)流(liu)的(de)电(dian)流(liu)。通常，漏电(dian)流(liu)会(hui)随着温度(du)和电(dian)压(ya)(ya)的(de)升(sheng)高而增(zeng)大。
5）纹波电(dian)流和纹波电(dian)压
在(zai)一些资料中将此二者称做(zuo)“涟波电流”和(he)“涟波电压(ya)”，其实就是(shi) ripple current，ripple voltage。含义(yi)即(ji)为电容(rong)器所能耐受纹波电流/电压(ya)值。它们和(he) ESR 之(zhi)间的关系密切，可以用(yong)下面的式子表(biao)示：
Urms = Irms × R
式中，Vrms 表示纹波电压
Irms 表示纹波电流
R 表示电容的 ESR
由上可见，当纹(wen)波(bo)电(dian)(dian)流(liu)增大的(de)(de)(de)(de)(de)时候(hou)，即(ji)使(shi)在 ESR 保持不变(bian)的(de)(de)(de)(de)(de)情况(kuang)下，涟波(bo)电(dian)(dian)压(ya)也(ye)(ye)(ye)会(hui)成(cheng)倍提高。换(huan)言(yan)之，当纹(wen)波(bo)电(dian)(dian)压(ya)增大时，纹(wen)波(bo)电(dian)(dian)流(liu)也(ye)(ye)(ye)随(sui)之增大，这也(ye)(ye)(ye)是要求(qiu)电(dian)(dian)容具(ju)备更低(di)(di) ESR 值的(de)(de)(de)(de)(de)原因。叠加(jia)入纹(wen)波(bo)电(dian)(dian)流(liu)后(hou)，由于电(dian)(dian)容内(nei)部的(de)(de)(de)(de)(de)等(deng)效(xiao)串(chuan)连电(dian)(dian)阻（ESR）引起发热，从而影响到电(dian)(dian)容器(qi)的(de)(de)(de)(de)(de)使(shi)用寿命。一般的(de)(de)(de)(de)(de)，纹(wen)波(bo)电(dian)(dian)流(liu)与频率(lv)成(cheng)正比(bi)，因此低(di)(di)频时纹(wen)波(bo)电(dian)(dian)流(liu)也(ye)(ye)(ye)比(bi)较低(di)(di)。
1）容量（法拉）
英制：C = ( 0.224 × K · A) / TD
公制：C = ( 0.0884 × K · A) / TD
2）电容(rong)器中存储的能量
1/2CV2
3）电容器的线性充(chong)电量
I = C (dV/dt)
4）电容的(de)总阻抗(kang)（欧姆）
Z = √ [ RS2 + (XC – XL)2 ]5）容(rong)性电抗（欧姆）
5）容性电抗（欧姆）
XC= 1/(2πfC)
6）相位角 Ф理想电容器：超前当前电压(ya) 90o
理想电感器：滞后(hou)当前电压 90o
理想(xiang)电阻器：与(yu)当前(qian)电压的相位(wei)相同
7）耗散系数 (%)
D.F. = tan δ （损(sun)耗角）
= ESR / XC
= (2πfC)(ESR)
8）品(pin)质因素
Q = cotan δ = 1/ DF
9）等(deng)效串联(lian)电阻 ESR（欧姆）
ESR = (DF) XC = DF/ 2πfC
10）功(gong)率(lv)消(xiao)耗
Power Loss = (2πfCV2 ) (DF)
11）功率因数
PF = sin δ (loss angle) – cos Ф (相位角)
12）均方根
rms = 0.707 × Vp
13）千伏安 KVA （千瓦）
KVA = 2πfCV2 × 10-3
14）电容器(qi)的温度系数(shu)
T.C. = [ (Ct – C25) / C25 (Tt – 25) ] × 106
15）容量损耗(%)
CD = [ (C1 – C2) / C1 ] × 100
16）陶(tao)瓷电容的可(ke)靠性
L0 / Lt = (Vt / V0)X (Tt / T0)Y
17）串联时的容值
n 个电容串联：1/CT = 1/C1 + 1/C2 + …. + 1/Cn
两个电容(rong)串联：CT = C1 · C2 / (C1 + C2)
18）并联(lian)时(shi)的(de)容值
CT = C1 + C2 + …. + Cn
19）重复次数（Againg Rate）
A.R. = % ?C / decade of time
上述公式中的(de)符号说(shuo)明(ming)如下(xia)：
K = 介电常数；
A = 面积；
TD = 绝缘层厚度；
V = 电压；
RS = 串联电阻；
f = 频率；
L = 电感(gan)感(gan)性系数；
δ = 损耗角(jiao)；
Ф = 相位角；
L0 = 使用寿命；
Lt = 试验寿(shou)命；
Vt = 测试电压；
V0 = 工作电压；
Tt = 测试温度(du)；
T0 = 工作温度；
X , Y = 电(dian)压与温度的效应指数。
在交流(liu)电源输入端(duan)，一(yi)般需要(yao)增(zeng)加三个电容(rong)来抑制 EMI 传导干扰。
交流电(dian)(dian)(dian)(dian)(dian)源的(de)(de)输入一(yi)般(ban)可分为三根(gen)线：火线（L）/零(ling)线（N）/地(di)(di)(di)线（G）。在火线和地(di)(di)(di)线之(zhi)间及在零(ling)线和地(di)(di)(di)线之(zhi)间并接(jie)的(de)(de)电(dian)(dian)(dian)(dian)(dian)容(rong)，一(yi)般(ban)称之(zhi)为 Y 电(dian)(dian)(dian)(dian)(dian)容(rong)。这两(liang)个 Y 电(dian)(dian)(dian)(dian)(dian)容(rong)连接(jie)的(de)(de)位(wei)置(zhi)比较(jiao)关(guan)键，必须(xu)需要符合相(xiang)关(guan)安(an)全(quan)标(biao)准，以(yi)防引(yin)起电(dian)(dian)(dian)(dian)(dian)子设备漏电(dian)(dian)(dian)(dian)(dian) 或机(ji)壳带电(dian)(dian)(dian)(dian)(dian)，容(rong)易危及人(ren)身安(an)全(quan)及生命，所以(yi)它(ta)们都属于安(an)全(quan)电(dian)(dian)(dian)(dian)(dian)容(rong)，要求电(dian)(dian)(dian)(dian)(dian)容(rong)值(zhi)不(bu)能偏大(da)，而耐压必须(xu)较(jiao)高。一(yi)般(ban)地(di)(di)(di)，工(gong)作(zuo)(zuo)在亚热带的(de)(de)机(ji)器(qi)，要求对地(di)(di)(di)漏电(dian)(dian)(dian)(dian)(dian)电(dian)(dian)(dian)(dian)(dian)流不(bu)能超过 0.7mA；工(gong)作(zuo)(zuo)在温带机(ji)器(qi)，要求对地(di)(di)(di)漏电(dian)(dian)(dian)(dian)(dian)电(dian)(dian)(dian)(dian)(dian)流不(bu)能超过 0.35mA。
因此， Y 电(dian)容(rong)(rong)的总容(rong)(rong)量一(yi)般都不能超过 4700pF，特别提(ti)示(shi)：Y 电(dian)(dian)容(rong)(rong)为安(an)全(quan)电(dian)(dian)容(rong)(rong)，必(bi)须取得安(an)全(quan)检(jian)测机(ji)构(gou)的认证。Y 电(dian)(dian)容(rong)(rong)的耐压(ya)一(yi)般都标有安(an)全(quan)认证标志和 AC250V 或(huo) AC275V 字样(yang)，但其真(zhen)正的直(zhi)流耐压(ya)高达 5000V 以上。因(yin)此，Y 电(dian)(dian)容(rong)(rong)不能随意使(shi)用(yong)标称耐压(ya) AC250V，或(huo) DC400V 之类的普通电(dian)(dian)容(rong)(rong)来代(dai)用(yong)。
在火线和零线抑制之(zhi)间(jian)并(bing)联的(de)(de)电(dian)(dian)容(rong)(rong)，一般(ban)称之(zhi)为(wei) X 电(dian)(dian)容(rong)(rong)。由(you)于这个电(dian)(dian)容(rong)(rong)连接的(de)(de)位置也(ye)比(bi)较关键，同样(yang)需要(yao)符(fu)合(he)安(an)(an)全(quan)(quan)标准(zhun)。因此，X 电(dian)(dian)容(rong)(rong)同样(yang)也(ye)属于安(an)(an)全(quan)(quan)电(dian)(dian)容(rong)(rong) 之(zhi)一。X 电(dian)(dian)容(rong)(rong)的(de)(de)容(rong)(rong)值允(yun)许(xu)比(bi) Y 电(dian)(dian)容(rong)(rong)大，但必(bi)须在 X 电(dian)(dian)容(rong)(rong)的(de)(de)两端(duan)并(bing)联一个安(an)(an)全(quan)(quan)电(dian)(dian)阻(zu)，用于防止电(dian)(dian)源(yuan)线拔插(cha)(cha)时(shi)，由(you)于该电(dian)(dian)容(rong)(rong)的(de)(de)充放电(dian)(dian)过程而(er)致电(dian)(dian)源(yuan)线插(cha)(cha)头长时(shi)间(jian)带(dai)电(dian)(dian)。安(an)(an)全(quan)(quan)标准(zhun)规定(ding)，当正在工作(zuo)之(zhi)中的(de)(de)机器(qi)电(dian)(dian)源(yuan)线被拔掉时(shi)，在两秒钟内，电(dian)(dian)源(yuan)线插(cha)(cha)头两端(duan)带(dai)电(dian)(dian)的(de)(de)电(dian)(dian)压(ya)(或对地电(dian)(dian)位)必(bi)须小于原来额定(ding)工作(zuo)电(dian)(dian)压(ya)的(de)(de) 30%。
同理，X 电(dian)容(rong)也是安全(quan)电(dian)容(rong)，必须取得安全(quan)检测机构的(de)认证。X 电(dian)容(rong)的(de)耐(nai)压一(yi)般都标(biao)有安全(quan)认证标(biao)志和 AC250V 或 AC275V 字样，但其(qi)真(zhen)正的(de)直流(liu)耐(nai)压高达 2000V 以上，使用(yong)(yong)(yong)的(de)时候不要随意使用(yong)(yong)(yong)标(biao)称(cheng)耐(nai)压 AC250V，或 DC400V 之类的(de)普(pu)通电(dian)容(rong)来代用(yong)(yong)(yong)。
X 电(dian)(dian)(dian)容(rong)(rong)一般都选用(yong)纹波(bo)电(dian)(dian)(dian)流比较大(da)的(de)(de)(de)聚脂薄(bo)膜类电(dian)(dian)(dian)容(rong)(rong)，这种电(dian)(dian)(dian)容(rong)(rong)体积一般都很大(da)，但(dan)其允许(xu)瞬间充(chong)放电(dian)(dian)(dian)的(de)(de)(de)电(dian)(dian)(dian)流也很大(da)，而其内阻相(xiang)应较小。普通电(dian)(dian)(dian)容(rong)(rong)纹波(bo)电(dian)(dian)(dian)流的(de)(de)(de)指标(biao)都很低，动态(tai)内阻较高。用(yong)普通电(dian)(dian)(dian)容(rong)(rong)代替 X 电(dian)(dian)(dian)容(rong)(rong)，除(chu)了耐压条件不能 满足(zu)以(yi)外，一般纹波(bo)电(dian)(dian)(dian)流指标(biao)也是(shi)难以(yi)满足(zu)要求的(de)(de)(de)。
实际上，仅仅依赖(lai)于(yu) Y 电(dian)(dian)容(rong)(rong)(rong)和(he) X 电(dian)(dian)容(rong)(rong)(rong)来完全滤(lv)除掉传导(dao)干扰信(xin)号是不(bu)(bu)太可能(neng)的(de)(de)(de)(de)(de)。因为干扰信(xin)号的(de)(de)(de)(de)(de)频(pin)(pin)谱非常宽，基(ji)本覆(fu)盖了几十 KHz 到(dao)几百 MHz，甚(shen)至上千 MHz 的(de)(de)(de)(de)(de)频(pin)(pin)率(lv)(lv)范围(wei)。通常，对(dui)低端干扰信(xin)号的(de)(de)(de)(de)(de)滤(lv)除需(xu)要很大(da)容(rong)(rong)(rong)量的(de)(de)(de)(de)(de)滤(lv)波电(dian)(dian)容(rong)(rong)(rong)，但(dan)受到(dao)安全条件的(de)(de)(de)(de)(de)限制，Y 电(dian)(dian)容(rong)(rong)(rong)和(he) X 电(dian)(dian)容(rong)(rong)(rong)的(de)(de)(de)(de)(de)容(rong)(rong)(rong)量都(dou)(dou)不(bu)(bu)能(neng)用大(da)；对(dui)高端干扰信(xin)号的(de)(de)(de)(de)(de)滤(lv)除，大(da)容(rong)(rong)(rong)量电(dian)(dian)容(rong)(rong)(rong)的(de)(de)(de)(de)(de)滤(lv)波性(xing)能(neng)又极差，特别是聚(ju)脂(zhi)薄(bo)膜电(dian)(dian)容(rong)(rong)(rong)的(de)(de)(de)(de)(de)高频(pin)(pin)性(xing)能(neng)一般(ban)都(dou)(dou)比(bi)较(jiao)差，因为它是用卷(juan)绕工(gong)艺生产的(de)(de)(de)(de)(de)，并且聚(ju)脂(zhi)薄(bo)膜介(jie)质高频(pin)(pin)响(xiang)应(ying)特性(xing)与陶瓷(ci)或(huo)云母相(xiang)比(bi)相(xiang)差很远，一般(ban)聚(ju)脂(zhi)薄(bo)膜介(jie)质都(dou)(dou)具有吸附(fu)效应(ying)，它会降低电(dian)(dian)容(rong)(rong)(rong)器的(de)(de)(de)(de)(de)工(gong)作(zuo)(zuo)频(pin)(pin)率(lv)(lv)，聚(ju)脂(zhi)薄(bo)膜电(dian)(dian)容(rong)(rong)(rong)工(gong)作(zuo)(zuo)频(pin)(pin)率(lv)(lv)范围(wei)大(da)约都(dou)(dou)在 1MHz 左右，超过 1MHz 其阻抗将显著增加。
因此，为(wei)抑制电(dian)(dian)(dian)子(zi)设备产生的(de)(de)(de)传导(dao)干(gan)(gan)扰，除了选用(yong)(yong)(yong) Y 电(dian)(dian)(dian)容(rong)和(he) X 电(dian)(dian)(dian)容(rong)之外，还要同时选用(yong)(yong)(yong)多个类型的(de)(de)(de)电(dian)(dian)(dian)感(gan)(gan)(gan)滤(lv)波(bo)(bo)器(qi)，组合(he)(he)起(qi)来一起(qi)滤(lv)除干(gan)(gan)扰。电(dian)(dian)(dian)感(gan)(gan)(gan)滤(lv)波(bo)(bo)器(qi)多属于低(di)通滤(lv)波(bo)(bo)器(qi)，但电(dian)(dian)(dian)感(gan)(gan)(gan)滤(lv)波(bo)(bo)器(qi)也(ye)有很(hen)(hen)多规格(ge)类型，例如有：差(cha)模(mo)、共模(mo)，以及高频(pin)(pin)(pin)、低(di)频(pin)(pin)(pin)等。每(mei)种电(dian)(dian)(dian)感(gan)(gan)(gan)主要都是针对某一小(xiao)段频(pin)(pin)(pin)率(lv)的(de)(de)(de)干(gan)(gan)扰信(xin)号滤(lv)除而(er)(er)起(qi)作用(yong)(yong)(yong)，对其它(ta)频(pin)(pin)(pin)率(lv)的(de)(de)(de)干(gan)(gan)扰信(xin)号的(de)(de)(de)滤(lv)除效果(guo)不(bu)大(da)。通常，电(dian)(dian)(dian)感(gan)(gan)(gan)量很(hen)(hen)大(da)的(de)(de)(de)电(dian)(dian)(dian)感(gan)(gan)(gan)，其线圈(quan)匝数较(jiao)多，那么电(dian)(dian)(dian)感(gan)(gan)(gan)的(de)(de)(de)分(fen)布电(dian)(dian)(dian)容(rong)也(ye)很(hen)(hen)大(da)。高频(pin)(pin)(pin)干(gan)(gan)扰信(xin)号将通过分(fen)布电(dian)(dian)(dian)容(rong)旁路(lu)掉。而(er)(er)且，导(dao)磁(ci)(ci)率(lv)很(hen)(hen)高的(de)(de)(de)磁(ci)(ci)芯(xin)(xin)(xin)，其工作频(pin)(pin)(pin)率(lv)则较(jiao)低(di)。目前(qian)，大(da)量使用(yong)(yong)(yong)的(de)(de)(de)电(dian)(dian)(dian)感(gan)(gan)(gan)滤(lv)波(bo)(bo)器(qi)磁(ci)(ci)芯(xin)(xin)(xin)的(de)(de)(de)工作频(pin)(pin)(pin)率(lv)大(da)多数都在 75MHz 以下。对于工作频(pin)(pin)(pin)率(lv)要求比较(jiao)高的(de)(de)(de)场合(he)(he)，必(bi)须选用(yong)(yong)(yong)高频(pin)(pin)(pin)环形磁(ci)(ci)芯(xin)(xin)(xin)，高频(pin)(pin)(pin)环形磁(ci)(ci)芯(xin)(xin)(xin)导(dao)磁(ci)(ci)率(lv)一般(ban)都不(bu)高，但漏感(gan)(gan)(gan)特别(bie)小(xiao)，比如，非晶合(he)(he)金磁(ci)(ci)芯(xin)(xin)(xin)，坡莫合(he)(he)金等。
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