電容的阻(zu)抗與頻(pin)率成反比,所以電容可以阻(zu)擋低頻(pin)通過。電感正相反——所以二者適當組合,就可過濾各種(zhong)頻(pin)率信號。如在整(zheng)流電路中(zhong),將(jiang)電容并在負載上或(huo)將(jiang)電感串聯在負載上,可濾去交(jiao)流紋波。
由于(yu)電(dian)解(jie)電(dian)容的作用(yong)是過濾掉電(dian)流(liu)中的低頻信號,但即(ji)使是低頻信號,其頻率也分為了好幾個(ge)數量(liang)級。因此為了適合在不同頻率下使用(yong),電(dian)解(jie)電(dian)容也分為高頻電(dian)容和低頻電(dian)容(這里的高頻是相對而言)。
低頻(pin)(pin)濾(lv)波(bo)(bo)(bo)電(dian)(dian)容(rong)(rong)主要用于市電(dian)(dian)濾(lv)波(bo)(bo)(bo)或變壓器整流(liu)后的(de)濾(lv)波(bo)(bo)(bo),其(qi)工作頻(pin)(pin)率與市電(dian)(dian)一致為50Hz;而(er)高(gao)(gao)(gao)頻(pin)(pin)濾(lv)波(bo)(bo)(bo)電(dian)(dian)容(rong)(rong)主要工作在開關電(dian)(dian)源整流(liu)后的(de)濾(lv)波(bo)(bo)(bo),其(qi)工作頻(pin)(pin)率為幾(ji)千Hz到幾(ji)萬(wan)Hz。當我們將(jiang)低頻(pin)(pin)濾(lv)波(bo)(bo)(bo)電(dian)(dian)容(rong)(rong)用于高(gao)(gao)(gao)頻(pin)(pin)電(dian)(dian)路(lu)時,由于低頻(pin)(pin)濾(lv)波(bo)(bo)(bo)電(dian)(dian)容(rong)(rong)高(gao)(gao)(gao)頻(pin)(pin)特性不好,它在高(gao)(gao)(gao)頻(pin)(pin)充放電(dian)(dian)時內阻較(jiao)大,等效電(dian)(dian)感較(jiao)高(gao)(gao)(gao)。因(yin)此在使用中會因(yin)電(dian)(dian)解液(ye)(ye)的(de)頻(pin)(pin)繁極(ji)化而(er)產生較(jiao)大的(de)熱(re)量。而(er)較(jiao)高(gao)(gao)(gao)的(de)溫(wen)度將(jiang)使電(dian)(dian)容(rong)(rong)內部的(de)電(dian)(dian)解液(ye)(ye)氣化,電(dian)(dian)容(rong)(rong)內壓力升高(gao)(gao)(gao),最終(zhong)導致電(dian)(dian)容(rong)(rong)的(de)鼓包(bao)和爆裂。
電(dian)源(yuan)濾(lv)(lv)波(bo)電(dian)容(rong)(rong)器(qi)的(de)大(da)(da)小,平時做設(she)計(ji),前級用(yong)4.7u,用(yong)于濾(lv)(lv)低頻,二級用(yong)0.1u,用(yong)于濾(lv)(lv)高頻,4.7uF的(de)電(dian)容(rong)(rong)作用(yong)是減小輸出(chu)脈動和(he)低頻干擾,0.1uF的(de)電(dian)容(rong)(rong)應該是減小由于負載(zai)電(dian)流瞬時變化(hua)引(yin)起(qi)的(de)高頻干擾。一般前面那個越(yue)大(da)(da)越(yue)好,兩個電(dian)容(rong)(rong)值相差大(da)(da)概100倍(bei)左右。電(dian)源(yuan)濾(lv)(lv)波(bo),開關電(dian)源(yuan),要(yao)看你的(de)ESR(電(dian)容(rong)(rong)的(de)等效串(chuan)聯電(dian)阻(zu))有多大(da)(da),而高頻電(dian)容(rong)(rong)的(de)選擇(ze)最好在其自(zi)(zi)諧振(zhen)頻率(lv)上。大(da)(da)電(dian)容(rong)(rong)是防止浪(lang)涌,機理就(jiu)好比大(da)(da)水庫防洪(hong)能力更強一樣(yang);小電(dian)容(rong)(rong)濾(lv)(lv)高頻干擾,任何器(qi)件都可以(yi)(yi)等效成(cheng)一個電(dian)阻(zu)、電(dian)感、電(dian)容(rong)(rong)的(de)串(chuan)并聯電(dian)路,也就(jiu)有了自(zi)(zi)諧振(zhen),只有在這個自(zi)(zi)諧振(zhen)頻率(lv)上,等效電(dian)阻(zu)最小,所以(yi)(yi)濾(lv)(lv)波(bo)最好。
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