模(mo)塊(kuai)(kuai)電(dian)源的誕生(sheng)，無(wu)疑對電(dian)子(zi)電(dian)路設計(ji)有著(zhu)重大的影響。模(mo)塊(kuai)(kuai)電(dian)源的一些特(te)性徹底顛覆了傳統的思路，使人們從(cong)設計(ji)到實際操(cao)作(zuo)都變得簡(jian)單起來。針對不(bu)同的設計(ji)，模(mo)塊(kuai)(kuai)電(dian)源的選(xuan)擇也變得復雜(za)多樣，那么(me)如何按照(zhao)需(xu)要進行選(xuan)擇呢？在本文(wen)中小(xiao)編將為大家(jia)介紹如何從(cong)工(gong)作(zuo)頻(pin)率與隔離度來對模(mo)塊(kuai)(kuai)電(dian)源進行選(xuan)擇。

工作頻率

一般而言，工作頻率越(yue)(yue)高(gao)輸出(chu)紋(wen)波噪聲就(jiu)更(geng)小(xiao)，電(dian)源(yuan)(yuan)動態響應也更(geng)好，但是對元器件特別是磁性材料的(de)(de)(de)要(yao)求(qiu)也越(yue)(yue)高(gao)，成本會有(you)增加，所以(yi)國(guo)內模(mo)(mo)塊電(dian)源(yuan)(yuan)產品開關(guan)頻率多為在300kHz以(yi)下，甚至有(you)的(de)(de)(de)只有(you)100kHz左右，這(zhe)樣(yang)就(jiu)難(nan)以(yi)滿足負載(zai)變條件下動態響應的(de)(de)(de)要(yao)求(qiu)，因此高(gao)要(yao)求(qiu)場合應用要(yao)考(kao)慮采用高(gao)開關(guan)頻率的(de)(de)(de)產品。另外一方面當模(mo)(mo)塊電(dian)源(yuan)(yuan)開關(guan)頻率接近信號(hao)工作頻率時(shi)容易(yi)引起差(cha)拍振蕩(dang)，選用時(shi)也要(yao)考(kao)慮到這(zhe)一點。

隔離度

絕(jue)大(da)多數(shu)的(de)(de)電路都必須實(shi)現隔離(li)(li)，即將(jiang)負(fu)載連同(tong)負(fu)載對本地電源(yuan)的(de)(de)噪聲與電網的(de)(de)其他負(fu)載和噪聲隔開。只有隔離(li)(li)變(bian)換器(qi)(qi)能夠達到這個要(yao)求。采用隔離(li)(li)變(bian)換器(qi)(qi)除(chu)了(le)實(shi)現上述要(yao)求之外(wai)，還(huan)可以實(shi)現差分形式的(de)(de)輸(shu)出(chu)，以及(ji)雙極型輸(shu)出(chu)。此外(wai)，將(jiang)隔離(li)(li)型變(bian)換器(qi)(qi)的(de)(de)輸(shu)出(chu)高(gao)壓端與負(fu)載的(de)(de)電源(yuan)地相連，就(jiu)形成了(le)負(fu)電源(yuan)。由于(yu)電壓參考(kao)點不(bu)是地，因此負(fu)載可以獲(huo)得(de)更高(gao)的(de)(de)電壓。

采用(yong)(yong)隔離(li)型變(bian)(bian)換器(qi)(qi)的(de)(de)另一個(ge)(ge)妙處是：可以將多個(ge)(ge)具有(you)(you)不(bu)同輸出電(dian)(dian)壓的(de)(de)變(bian)(bian)換器(qi)(qi)級聯起來，構成一個(ge)(ge)電(dian)(dian)源。對于(yu)那些(xie)單(dan)個(ge)(ge)變(bian)(bian)換器(qi)(qi)的(de)(de)輸出電(dian)(dian)壓達不(bu)到工作電(dian)(dian)壓要求的(de)(de)設(she)備，這種(zhong)特(te)性非常有(you)(you)用(yong)(yong)。在一定時限內（通常是1秒）變(bian)(bian)換器(qi)(qi)所(suo)能承受(shou)(shou)的(de)(de)、施(shi)加在輸入端和輸出端之間(jian)的(de)(de)最高電(dian)(dian)壓，稱為變(bian)(bian)換器(qi)(qi)的(de)(de)隔離(li)強度(du)。而變(bian)(bian)換器(qi)(qi)的(de)(de)額定工作電(dian)(dian)壓是指變(bian)(bian)換器(qi)(qi)能長時間(jian)承受(shou)(shou)的(de)(de)加在輸入端的(de)(de)電(dian)(dian)壓，這個(ge)(ge)電(dian)(dian)壓低于(yu)隔離(li)強度(du)。

在選(xuan)擇隔(ge)(ge)離(li)(li)(li)(li)型變(bian)換器時還需要(yao)考慮(lv)器件的(de)(de)泄(xie)漏(lou)電(dian)(dian)(dian)(dian)(dian)流(liu)指標，泄(xie)漏(lou)電(dian)(dian)(dian)(dian)(dian)流(liu)是(shi)指因(yin)輸(shu)入回路和輸(shu)出回路之間(jian)的(de)(de)耦合電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)而產生的(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)。只要(yao)給定(ding)隔(ge)(ge)離(li)(li)(li)(li)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)的(de)(de)值，并且(qie)確定(ding)噪聲(sheng)頻率(lv)，就可以根(gen)據(ju)阻抗計算出泄(xie)漏(lou)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)的(de)(de)大小。泄(xie)漏(lou)電(dian)(dian)(dian)(dian)(dian)流(liu)隨(sui)噪聲(sheng)電(dian)(dian)(dian)(dian)(dian)壓的(de)(de)增(zeng)(zeng)加(jia)而增(zeng)(zeng)大，隨(sui)隔(ge)(ge)離(li)(li)(li)(li)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)的(de)(de)減小而減小。因(yin)此，設計低(di)噪聲(sheng)電(dian)(dian)(dian)(dian)(dian)源時，應該選(xuan)擇隔(ge)(ge)離(li)(li)(li)(li)強度高而隔(ge)(ge)離(li)(li)(li)(li)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)低(di)的(de)(de)DC/DC變(bian)換器，以減小泄(xie)漏(lou)電(dian)(dian)(dian)(dian)(dian)流(liu)。

通常在醫療設(she)備里需要(yao)很高的(de)隔離電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，這是因(yin)為高隔離電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)能(neng)夠產生最(zui)小的(de)漏電(dian)(dian)(dian)(dian)(dian)(dian)流，對身(shen)體的(de)危害就小。一般(ban)場合使(shi)用(yong)對模塊電(dian)(dian)(dian)(dian)(dian)(dian)源隔離電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)要(yao)求(qiu)不是很高，但是更(geng)高的(de)隔離電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)可以保(bao)證模塊電(dian)(dian)(dian)(dian)(dian)(dian)源具有更(geng)小的(de)漏電(dian)(dian)(dian)(dian)(dian)(dian)流，更(geng)高的(de)安全(quan)性和可靠性，并且EMC特性也(ye)更(geng)好一些(xie)，因(yin)此目(mu)前業界普(pu)遍的(de)隔離電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)水平為1500VDC以上。

從(cong)隔離度與工(gong)作(zuo)頻率這兩(liang)個方面(mian)，可以看到(dao)對模(mo)塊(kuai)電源的選擇(ze)不僅會影響到(dao)產(chan)品(pin)的最(zui)終(zhong)(zhong)效率，當應用在醫療領域時，還(huan)對使用者的人身安全(quan)負(fu)有責任。因此(ci)熟悉怎樣的模(mo)塊(kuai)電源才是(shi)適合產(chan)品(pin)的最(zui)終(zhong)(zhong)選擇(ze)就變(bian)得非常重要，希(xi)望大(da)家在閱讀過本文后(hou)能夠(gou)有所收獲哦。