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电容器的容量大小与什么有关?为什么?

2021-7-18 20:35| 编辑:电工学习网| 查看: 13975| 评论: 0

    电容器器件种类繁多,包括现在的贴片电容器等,但它的基本结构都是由二片金属,中间用绝缘介质隔开做成的,所以电容器容量大小与金属面的面积有关,即面积越大则容量越大;其次与组成电容器的介质材料有关,不同介质材料的电容器,其电容量不同,这种特性材料我们仅仅只要知道即可,一般电容器生产厂家非常清楚。

    再者,与组成电(dian)容器(qi)的(de)金属、介质(zhi)、金属的(de)极板(ban)间距有(you)关(guan)。例如一(yi)种由铝材料组成的(de)由空气为介质(zhi)的(de)可(ke)变电(dian)容器(qi),它的(de)容量就比(bi)较大(da)(为2×365pF)。并且这种结构的(de)电(dian)容器(qi)的(de)承受(shou)电(dian)压比(bi)较高(gao)。见下图所示

    电容器是由绝缘体(电介质)分隔开的两个导体(电极)的组合。电容器是具有充放电能量的一种电子元器件;它可以用来容纳和存储电荷的装置。

    ★电(dian)容(rong)器也是电(dian)子(zi)元器件(jian)之一(yi)(yi),属于一(yi)(yi)种基本元件(jian)。顾(gu)名思义(yi),“容(rong)”是容(rong)器,容(rong)器是一(yi)(yi)种可以储(chu)存(cun)东西,电(dian)容(rong)器是储(chu)存(cun)电(dian)荷的(de)(de)容(rong)器,简(jian)称(cheng)电(dian)容(rong),常用(yong)英(ying)语字母“C”表示。那么能够储(chu)存(cun)电(dian)荷的(de)(de)数量的(de)(de)本领叫电(dian)容(rong)量。电(dian)容(rong)量的(de)(de)表示单位(wei)是“法(fa)(fa)拉(la)”,,简(jian)称(cheng)“法(fa)(fa)”,用(yong)字母“F”表示。但实际应用(yong)中(zhong)由于“法(fa)(fa)拉(la)”这一(yi)(yi)单位(wei)实在是太大(da)了,正常使用(yong)中(zhong)人们习(xi)惯(guan)性用(yong)的(de)(de)单位(wei)比法(fa)(fa)拉(la)要小很多,如(ru)“微法(fa)(fa)”(μf)和“微微法(fa)(fa)”(pF)。其换算关系(xi)如(ru)下(xia):

    1F(法(fa)(fa)拉)=1000000μF(微法(fa)(fa))=10⁶μF(微法(fa)(fa))

    1μF(微(wei)(wei)法)=1000000pF(微(wei)(wei)微(wei)(wei)法)=10⁶μF(微(wei)(wei)微(wei)(wei)法)

    电(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)器(qi)具有储(chu)存(cun)(cun)(cun)电(dian)(dian)(dian)(dian)(dian)(dian)荷能力特(te)性(xing):电(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)器(qi)中(zhong)(zhong)所(suo)(suo)充电(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)电(dian)(dian)(dian)(dian)(dian)(dian)荷会(hui)自(zi)(zi)动储(chu)存(cun)(cun)(cun)在(zai)电(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)器(qi)中(zhong)(zhong),只要外部电(dian)(dian)(dian)(dian)(dian)(dian)路中(zhong)(zhong)不存(cun)(cun)(cun)在(zai)让电(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)器(qi)放电(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)条件,电(dian)(dian)(dian)(dian)(dian)(dian)荷就一直会(hui)储(chu)存(cun)(cun)(cun)在(zai)电(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)器(qi)中(zhong)(zhong)。不过这(zhei)是一种(zhong)理论上的(de)(de)条件,事实上由于组成电(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)器(qi)的(de)(de)材料(liao)和电(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)器(qi)所(suo)(suo)处(chu)环(huan)(huan)境,由于空气湿度存(cun)(cun)(cun)在(zai)水(shui)份,所(suo)(suo)以电(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)器(qi)也会(hui)自(zi)(zi)然环(huan)(huan)境中(zhong)(zhong)慢慢的(de)(de)放电(dian)(dian)(dian)(dian)(dian)(dian),而将(jiang)电(dian)(dian)(dian)(dian)(dian)(dian)荷失(shi)去部分。

    ★电容(rong)器的特性正好与电感(gan)恰恰相(xiang)反,对于交流(liu)电的阻力却很小。这(zhei)种阻力叫做“容(rong)抗”。容(rong)抗是(shi)(shi)指交流(liu)电能够通过电容(rong)器,但(dan)是(shi)(shi)电容(rong)器极(ji)板上(shang)所带电荷容(rong)抗虽然(ran)很小,但(dan)它(ta)还是(shi)(shi)对定(ding)向移动的电荷具有阻碍(ai)作(zuo)用,物理学(xue)上(shang)把这(zhei)种阻碍(ai)作(zuo)用称为容(rong)抗,用字母Xc表示。

    Xc=1/2πfC

    式中的2π为常数,计算时用(yong)2×3.14=6.28;

    f为交流电源的频率,单位为赫兹(Hz);

    C为(wei)(wei)电容(rong)器的容(rong)量(liang),单位为(wei)(wei)法(fa)拉(F)。

    从容抗计算公(gong)式中可以(yi)看出(chu)来(lai),由(you)于直流(liu)(liu)(liu)电(dian)(dian)的频(pin)(pin)率为零(ling),所以(yi)它(ta)的容抗为无穷大∝,故,直流(liu)(liu)(liu)电(dian)(dian)是不能通(tong)(tong)过电(dian)(dian)容器的。电(dian)(dian)子(zi)电(dian)(dian)路中常利(li)用(yong)电(dian)(dian)容器的这种(zhong)特性来(lai)隔断直流(liu)(liu)(liu)电(dian)(dian),而让交(jiao)流(liu)(liu)(liu)电(dian)(dian)(交(jiao)流(liu)(liu)(liu)信号)通(tong)(tong)过。构成各种(zhong)类型滤(lv)波(bo)器,来(lai)分离高频(pin)(pin)和低频(pin)(pin)信号。

    ★电(dian)(dian)(dian)(dian)容(rong)(rong)器(qi)充电(dian)(dian)(dian)(dian)后(hou),极(ji)板所带电(dian)(dian)(dian)(dian)量(liang)用q表示,它与施加在(zai)极(ji)板两端的(de)电(dian)(dian)(dian)(dian)压(ya)U的(de)大小成(cheng)正比(bi),即q=CU。式中(zhong)的(de)比(bi)例(li)常数C就是电(dian)(dian)(dian)(dian)容(rong)(rong)器(qi)的(de)电(dian)(dian)(dian)(dian)容(rong)(rong)量(liang)。也可以(yi)改写为C=q/U。所以(yi)电(dian)(dian)(dian)(dian)容(rong)(rong)量(liang)也可以(yi)说是在(zai)单(dan)(dan)位电(dian)(dian)(dian)(dian)压(ya)下,极(ji)板上(shang)所带电(dian)(dian)(dian)(dian)量(liang)的(de)大小。在(zai)上(shang)面(mian)的(de)两个式子中(zhong),电(dian)(dian)(dian)(dian)量(liang)q的(de)单(dan)(dan)位是库,电(dian)(dian)(dian)(dian)压(ya)你(ni)的(de)单(dan)(dan)位是伏,电(dian)(dian)(dian)(dian)容(rong)(rong)量(liang)C为法(fa)拉。

    电(dian)容(rong)在串(chuan)、并联时,计(ji)算总(zong)电(dian)容(rong)的公式正好与电(dian)阻串(chuan)、 并联时的计(ji)算公式相反。在电(dian)容(rong)并联时,总(zong)电(dian)容(rong)为各并联电(dian)容(rong)之和,即(ji)总(zong)电(dian)容(rong)为:

    C = C ₁+ C₂ + C ₃+ ……

    在(zai)电容器串联(lian)时,总(zong)电容的(de)倒(dao)数等于各(ge)串联(lian)电容倒(dao)数之和,

    即1/C=1/C₁+1/C₂+1/C₃+……。

    ★电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)器(qi)(qi)品种繁多(duo),常见(jian)的(de)(de)有无(wu)极(ji)(ji)性(xing)(xing)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)和有极(ji)(ji)性(xing)(xing)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)器(qi)(qi)。无(wu)极(ji)(ji)性(xing)(xing)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)常见(jian)有云(yun)母(mu)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)、涤纶电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)、玻璃(li)釉电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)、瓷介(jie)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)、、纸(zhi)介(jie)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)和色环电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)等。有极(ji)(ji)性(xing)(xing)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)也(ye)称为电(dian)(dian)解电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)器(qi)(qi);它(ta)具有正负极(ji)(ji)之(zhi)分。无(wu)极(ji)(ji)性(xing)(xing)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)串(chuan)联不存在极(ji)(ji)性(xing)(xing)可以随意连(lian)接,但电(dian)(dian)解电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)器(qi)(qi)串(chuan)联必须(xu)将(jiang)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)的(de)(de)正负极(ji)(ji)进行连(lian)接,否则就可能损(sun)坏串(chuan)联的(de)(de)电(dian)(dian)解电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)器(qi)(qi)。不同材料组成的(de)(de)电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)器(qi)(qi)其耐(nai)(nai)压(ya)(ya)值也(ye)特(te)别(bie)重要,在使用(yong)更换它(ta)时,除体积(ji)之(zhi)外一定要考虑用(yong)耐(nai)(nai)压(ya)(ya)值高(gao)的(de)(de)替换耐(nai)(nai)压(ya)(ya)值低的(de)(de),不然容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)易引(yin)起过电(dian)(dian)压(ya)(ya)造成电(dian)(dian)容(rong)(rong)(rong)(rong)(rong)(rong)(rong)(rong)器(qi)(qi)炸裂损(sun)坏。

    ★最后说一说电容器的基本作用

    ①隔直(zhi)通交;即(ji)可(ke)以顺利通过交流信号阻断直(zhi)流信号通过。

    ②耦合(he)电容器(qi);在(zai)电子信号放(fang)大(da)器(qi)中,作为上(shang)一(yi)级传(chuan)递(di)至下一(yi)级放(fang)大(da)电路的桥梁作用。

    ③旁路(lu)电容;电路(lu)中(zhong)如果需要从信(xin)号中(zhong)去除某一频率(lv)段的信(xin)号,常用于(yu)高频电路(lu)中(zhong)。

    ④滤(lv)波(bo)电(dian)(dian)容;电(dian)(dian)容C用(yong)在(zai)滤(lv)波(bo)电(dian)(dian)路(lu)中(zhong),在(zai)电(dian)(dian)源(yuan)滤(lv)波(bo)和(he)各种滤(lv)波(bo)电(dian)(dian)路(lu)中(zhong)使用(yong)这种电(dian)(dian)容电(dian)(dian)路(lu),滤(lv)波(bo)电(dian)(dian)容将(jiang)一定(ding)频率的信号在(zai)电(dian)(dian)路(lu)中(zhong)去(qu)除。

    ⑤谐振电容;用在信号中并联或(huo)串(chuan)联电路中,产生谐振,进行变频、或(huo)者选频。

    ⑥退(tui)耦电(dian)容;电(dian)容器在(zai)多(duo)级放(fang)大器的直流电(dian)源(yuan)中使用,消除每(mei)级放(fang)大器之间的有害低(di)频交(jiao)连。

    ⑦中和电容;这种电容容量(liang)不大(1 ~ 10 p)在收音机(ji)高频(pin)与中频(pin),上下级之间(jian)交链(lian)处串联,以(yi)消(xiao)除自激。

    ⑧定时电(dian)容;通过可变(bian)电(dian)阻器调节,改(gai)变(bian)电(dian)容充放电(dian)时间,来控制放大电(dian)路的(de)时间常数。

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