臺(tai)式機電源電路圖(tu)原理分析 臺(tai)式機電源是如何實現多種保(bao)護(hu)功能的

ATX電(dian)(dian)(dian)源的控(kong)制(zhi)電(dian)(dian)(dian)路如上圖。控(kong)制(zhi)電(dian)(dian)(dian)路采(cai)用TL494及(ji)(ji)LM339集成電(dian)(dian)(dian)路（以(yi)下簡稱494和339）。494是雙(shuang)(shuang)排16腳集成電(dian)(dian)(dian)路，工(gong)作電(dian)(dian)(dian)壓(ya)7～40V。它含有由{14}腳輸(shu)出的＋5V基準電(dian)(dian)(dian)源，輸(shu)出電(dian)(dian)(dian)壓(ya)為＋5V（±0．05V），最大輸(shu)出電(dian)(dian)(dian)流(liu)250mA；一個頻率可調(diao)的鋸齒(chi)波產生(sheng)電(dian)(dian)(dian)路，振(zhen)蕩頻率由{5}腳外(wai)接(jie)電(dian)(dian)(dian)容(rong)及(ji)(ji){6}腳外(wai)接(jie)電(dian)(dian)(dian)阻來(lai)決(jue)定。{13}腳為高電(dian)(dian)(dian)平時，由{8}腳及(ji)(ji){11}腳輸(shu)出雙(shuang)(shuang)路反相（即推挽(wan)工(gong)作方式）的脈寬調(diao)制(zhi)信號(hao)。

比較器是(shi)一種運算(suan)放大器，符號用三角形(xing)表示(shi)，它有(you)一個(ge)同相(xiang)輸(shu)入(ru)端“＋”；一個(ge)反(fan)相(xiang)輸(shu)入(ru)端“－”和(he)一個(ge)輸(shu)出端。

比(bi)較器(qi)(qi)同(tong)(tong)相(xiang)(xiang)端(duan)(duan)(duan)(duan)(duan)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)若(ruo)高(gao)于(yu)反(fan)相(xiang)(xiang)端(duan)(duan)(duan)(duan)(duan)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)，則輸(shu)(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)(duan)(duan)輸(shu)(shu)(shu)出(chu)(chu)高(gao)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)；反(fan)之輸(shu)(shu)(shu)出(chu)(chu)低(di)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)。494內的(de)(de)(de)(de)(de)比(bi)較放(fang)大(da)器(qi)(qi)有四(si)個(ge)(ge)(ge)，為(wei)(wei)敘述方便，在上圖中(zhong)用(yong)小寫字母a、b、c、d來表示(shi)。其(qi)中(zhong)a是(shi)(shi)死(si)(si)(si)區時(shi)(shi)(shi)間比(bi)較器(qi)(qi)。因兩個(ge)(ge)(ge)作逆(ni)變(bian)工(gong)作的(de)(de)(de)(de)(de)三極管(guan)(guan)(guan)串聯后接到(dao)＋310V的(de)(de)(de)(de)(de)直流電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)上，若(ruo)兩個(ge)(ge)(ge)三極管(guan)(guan)(guan)同(tong)(tong)時(shi)(shi)(shi)導(dao)(dao)通(tong)，就(jiu)(jiu)(jiu)會形成對直流電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)的(de)(de)(de)(de)(de)短(duan)路。兩個(ge)(ge)(ge)三極管(guan)(guan)(guan)同(tong)(tong)時(shi)(shi)(shi)導(dao)(dao)通(tong)可(ke)能發(fa)生在一(yi)個(ge)(ge)(ge)管(guan)(guan)(guan)子(zi)(zi)從(cong)截(jie)(jie)止(zhi)轉(zhuan)(zhuan)為(wei)(wei)導(dao)(dao)通(tong)，而(er)另一(yi)個(ge)(ge)(ge)管(guan)(guan)(guan)子(zi)(zi)由導(dao)(dao)通(tong)轉(zhuan)(zhuan)為(wei)(wei)截(jie)(jie)止(zhi)的(de)(de)(de)(de)(de)時(shi)(shi)(shi)候。因為(wei)(wei)管(guan)(guan)(guan)子(zi)(zi)在轉(zhuan)(zhuan)換時(shi)(shi)(shi)有時(shi)(shi)(shi)間的(de)(de)(de)(de)(de)延遲，截(jie)(jie)止(zhi)的(de)(de)(de)(de)(de)管(guan)(guan)(guan)子(zi)(zi)已經轉(zhuan)(zhuan)為(wei)(wei)導(dao)(dao)通(tong)了(le)(le)，但導(dao)(dao)通(tong)的(de)(de)(de)(de)(de)管(guan)(guan)(guan)子(zi)(zi)尚(shang)未(wei)完全轉(zhuan)(zhuan)為(wei)(wei)截(jie)(jie)止(zhi)，于(yu)是(shi)(shi)兩個(ge)(ge)(ge)管(guan)(guan)(guan)子(zi)(zi)都(dou)呈(cheng)導(dao)(dao)通(tong)狀態而(er)形成對直流電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)的(de)(de)(de)(de)(de)短(duan)路。為(wei)(wei)防止(zhi)這樣的(de)(de)(de)(de)(de)事(shi)情發(fa)生，494設置了(le)(le)死(si)(si)(si)區時(shi)(shi)(shi)間比(bi)較器(qi)(qi)a。從(cong)圖中(zhong)可(ke)以看(kan)出(chu)(chu)，在比(bi)較器(qi)(qi)a的(de)(de)(de)(de)(de)反(fan)相(xiang)(xiang)輸(shu)(shu)(shu)入(ru)端(duan)(duan)(duan)(duan)(duan)串聯了(le)(le)一(yi)個(ge)(ge)(ge)“電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)”，正極接反(fan)相(xiang)(xiang)端(duan)(duan)(duan)(duan)(duan)，負(fu)極接494的(de)(de)(de)(de)(de){4}腳(jiao)。A比(bi)較器(qi)(qi)同(tong)(tong)相(xiang)(xiang)端(duan)(duan)(duan)(duan)(duan)輸(shu)(shu)(shu)入(ru)的(de)(de)(de)(de)(de)鋸齒(chi)波信號，只有大(da)于(yu)“電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)”電(dian)(dian)(dian)(dian)(dian)壓的(de)(de)(de)(de)(de)部分才(cai)有輸(shu)(shu)(shu)出(chu)(chu)，在三極管(guan)(guan)(guan)導(dao)(dao)通(tong)變(bian)為(wei)(wei)截(jie)(jie)止(zhi)與(yu)截(jie)(jie)止(zhi)轉(zhuan)(zhuan)為(wei)(wei)導(dao)(dao)通(tong)期間，也就(jiu)(jiu)(jiu)是(shi)(shi)死(si)(si)(si)區時(shi)(shi)(shi)間，494沒有脈(mo)(mo)沖(chong)輸(shu)(shu)(shu)出(chu)(chu)，避免了(le)(le)對直流電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)的(de)(de)(de)(de)(de)短(duan)路。死(si)(si)(si)區時(shi)(shi)(shi)間還可(ke)由{4}腳(jiao)外接的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)來控制，{4}腳(jiao)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)上升，死(si)(si)(si)區時(shi)(shi)(shi)間變(bian)寬，494輸(shu)(shu)(shu)出(chu)(chu)的(de)(de)(de)(de)(de)脈(mo)(mo)沖(chong)就(jiu)(jiu)(jiu)變(bian)窄了(le)(le)，若(ruo){4}腳(jiao)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)超過了(le)(le)鋸齒(chi)波的(de)(de)(de)(de)(de)峰值電(dian)(dian)(dian)(dian)(dian)壓，494就(jiu)(jiu)(jiu)進入(ru)了(le)(le)保護狀態，{8}腳(jiao)和{11}腳(jiao)就(jiu)(jiu)(jiu)不輸(shu)(shu)(shu)出(chu)(chu)脈(mo)(mo)沖(chong)了(le)(le)。494內部還有3個(ge)(ge)(ge)二輸(shu)(shu)(shu)入(ru)端(duan)(duan)(duan)(duan)(duan)與(yu)門(men)（用(yong)1、2、3表示(shi)）、兩個(ge)(ge)(ge)二輸(shu)(shu)(shu)入(ru)端(duan)(duan)(duan)(duan)(duan)與(yu)非門(men)、反(fan)相(xiang)(xiang)器(qi)(qi)、T觸發(fa)器(qi)(qi)等電(dian)(dian)(dian)(dian)(dian)路。與(yu)門(men)是(shi)(shi)這樣一(yi)種電(dian)(dian)(dian)(dian)(dian)路，只有所有的(de)(de)(de)(de)(de)輸(shu)(shu)(shu)入(ru)端(duan)(duan)(duan)(duan)(duan)都(dou)是(shi)(shi)高(gao)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)，輸(shu)(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)(duan)(duan)才(cai)能輸(shu)(shu)(shu)出(chu)(chu)高(gao)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)；若(ruo)有一(yi)個(ge)(ge)(ge)輸(shu)(shu)(shu)入(ru)端(duan)(duan)(duan)(duan)(duan)為(wei)(wei)低(di)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)，則輸(shu)(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)(duan)(duan)輸(shu)(shu)(shu)出(chu)(chu)低(di)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)。反(fan)相(xiang)(xiang)器(qi)(qi)的(de)(de)(de)(de)(de)作用(yong)是(shi)(shi)把(ba)輸(shu)(shu)(shu)入(ru)信號隔離(li)放(fang)大(da)后反(fan)相(xiang)(xiang)輸(shu)(shu)(shu)出(chu)(chu)。與(yu)非門(men)則相(xiang)(xiang)當于(yu)一(yi)個(ge)(ge)(ge)與(yu)門(men)和一(yi)個(ge)(ge)(ge)反(fan)相(xiang)(xiang)器(qi)(qi)的(de)(de)(de)(de)(de)組(zu)合。T觸發(fa)器(qi)(qi)的(de)(de)(de)(de)(de)作用(yong)是(shi)(shi)：每(mei)輸(shu)(shu)(shu)入(ru)一(yi)個(ge)(ge)(ge)脈(mo)(mo)沖(chong)，輸(shu)(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)(duan)(duan)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)就(jiu)(jiu)(jiu)變(bian)化一(yi)次。如輸(shu)(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)(duan)(duan)Q為(wei)(wei)低(di)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)，輸(shu)(shu)(shu)入(ru)一(yi)個(ge)(ge)(ge)脈(mo)(mo)沖(chong)后，Q變(bian)為(wei)(wei)高(gao)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)，再輸(shu)(shu)(shu)入(ru)一(yi)個(ge)(ge)(ge)脈(mo)(mo)沖(chong)，Q又回(hui)到(dao)低(di)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)。

339是四比較(jiao)器(qi)集成(cheng)電(dian)(dian)(dian)路。 LM339集成(cheng)塊內(nei)部裝有四個獨立的(de)電(dian)(dian)(dian)壓(ya)(ya)(ya)比較(jiao)器(qi)，每(mei)個比較(jiao)器(qi)有兩個輸(shu)(shu)(shu)(shu)(shu)入端(duan)(duan)(duan)和(he)(he)一(yi)(yi)(yi)個輸(shu)(shu)(shu)(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)。兩個輸(shu)(shu)(shu)(shu)(shu)入端(duan)(duan)(duan)一(yi)(yi)(yi)個稱(cheng)為同(tong)相(xiang)(xiang)輸(shu)(shu)(shu)(shu)(shu)入端(duan)(duan)(duan)，用(yong)(yong)“+”表(biao)示，另一(yi)(yi)(yi)個稱(cheng)為反相(xiang)(xiang)輸(shu)(shu)(shu)(shu)(shu)入端(duan)(duan)(duan)，用(yong)(yong)“-”表(biao)示。用(yong)(yong)作(zuo)比較(jiao)兩個電(dian)(dian)(dian)壓(ya)(ya)(ya)時(shi)，任(ren)意一(yi)(yi)(yi)個輸(shu)(shu)(shu)(shu)(shu)入端(duan)(duan)(duan)加一(yi)(yi)(yi)個固(gu)定電(dian)(dian)(dian)壓(ya)(ya)(ya)做參考電(dian)(dian)(dian)壓(ya)(ya)(ya)（也稱(cheng)為門(men)限電(dian)(dian)(dian)平，它可選擇LM339輸(shu)(shu)(shu)(shu)(shu)入共模范圍的(de)任(ren)何(he)一(yi)(yi)(yi)點），另一(yi)(yi)(yi)端(duan)(duan)(duan)加一(yi)(yi)(yi)個待比較(jiao)的(de)信(xin)號電(dian)(dian)(dian)壓(ya)(ya)(ya)。當(dang)“+”端(duan)(duan)(duan)電(dian)(dian)(dian)壓(ya)(ya)(ya)高于(yu)(yu)“-”端(duan)(duan)(duan)時(shi)，輸(shu)(shu)(shu)(shu)(shu)出(chu)(chu)管截(jie)止(zhi)，相(xiang)(xiang)當(dang)于(yu)(yu)輸(shu)(shu)(shu)(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)開路。當(dang)“-”端(duan)(duan)(duan)電(dian)(dian)(dian)壓(ya)(ya)(ya)高于(yu)(yu)“+”端(duan)(duan)(duan)時(shi)，輸(shu)(shu)(shu)(shu)(shu)出(chu)(chu)管飽和(he)(he)，相(xiang)(xiang)當(dang)于(yu)(yu)輸(shu)(shu)(shu)(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)接(jie)低電(dian)(dian)(dian)位。兩個輸(shu)(shu)(shu)(shu)(shu)入端(duan)(duan)(duan)電(dian)(dian)(dian)壓(ya)(ya)(ya)差別大(da)于(yu)(yu)10mV就能確保輸(shu)(shu)(shu)(shu)(shu)出(chu)(chu)能從一(yi)(yi)(yi)種狀態(tai)可靠(kao)地轉換到另一(yi)(yi)(yi)種狀態(tai)， LM339的(de)輸(shu)(shu)(shu)(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)相(xiang)(xiang)當(dang)于(yu)(yu)一(yi)(yi)(yi)只(zhi)不接(jie)集電(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)阻(zu)的(de)晶體三極(ji)管，在(zai)使用(yong)(yong)時(shi)輸(shu)(shu)(shu)(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)到正電(dian)(dian)(dian)源(yuan)一(yi)(yi)(yi)般須接(jie)一(yi)(yi)(yi)只(zhi)電(dian)(dian)(dian)阻(zu)（稱(cheng)為上(shang)(shang)拉(la)電(dian)(dian)(dian)阻(zu)，選3-15K）。選不同(tong)阻(zu)值(zhi)的(de)上(shang)(shang)拉(la)電(dian)(dian)(dian)阻(zu)會影(ying)響(xiang)輸(shu)(shu)(shu)(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)高電(dian)(dian)(dian)位的(de)值(zhi)。因為當(dang)輸(shu)(shu)(shu)(shu)(shu)出(chu)(chu)晶體三極(ji)管截(jie)止(zhi)時(shi)，它的(de)集電(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)壓(ya)(ya)(ya)基本上(shang)(shang)取決于(yu)(yu)上(shang)(shang)拉(la)電(dian)(dian)(dian)阻(zu)與負載(zai)的(de)值(zhi)。

按(an)管腳的順(shun)序(xu)把(ba)內(nei)部(bu)四個比(bi)較器設為A、B 、C 、D 比(bi)較器。494和339再配合(he)其(qi)他電(dian)路，共同完成(cheng)ATX電(dian)源(yuan)的穩(wen)壓，產生PW－OK信號及各種保護功能。

一、 產生PW－OK信號

PC主機要求各路電源穩定之后才工作，以保護各元器件不致因電壓不穩而損壞，故設置了PW－OK信號（約＋5V），主機在獲得此信號后才開始工作。接通電源時，要求PW－OK信號比±5V、±12V、＋3．3V電源延遲數百毫秒才產生，關機時PW－OK信號應比直流電源先消失數百毫秒，以便主機先停止工作，硬盤的磁頭回復到著陸區，以保護硬盤。

ATX電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)接通(tong)市(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)后(hou)，輔助電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)立即工作(zuo)(zuo)(zuo)(zuo)。一(yi)方面輸(shu)(shu)出(chu) ＋5VSB電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)，同(tong)時(shi)(shi)(shi)向494的(de)(de)(de)(de)(de)(de)(de)(de)(de){12}腳(jiao)(jiao)提供十幾伏到二十多伏的(de)(de)(de)(de)(de)(de)(de)(de)(de)直(zhi)流電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)。494從(cong){14}腳(jiao)(jiao)輸(shu)(shu)出(chu)＋5V基準(zhun)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)，鋸齒(chi)波振(zhen)(zhen)蕩(dang)器也(ye)開(kai)始起振(zhen)(zhen)工作(zuo)(zuo)(zuo)(zuo)。若主(zhu)(zhu)機未開(kai)機，PS－ON信(xin)(xin)(xin)號為(wei)(wei)(wei)(wei)(wei)(wei)高(gao)(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，經(jing)(jing)(jing)R37使(shi)(shi)339的(de)(de)(de)(de)(de)(de)(de)(de)(de)B比(bi)(bi)(bi)較(jiao)(jiao)(jiao)(jiao)(jiao)器{6}腳(jiao)(jiao)亦(yi)(yi)為(wei)(wei)(wei)(wei)(wei)(wei)高(gao)(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，因(yin)(yin)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻R37小(xiao)于(yu)(yu)(yu)R44，{6}腳(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)高(gao)(gao)(gao)(gao)于(yu)(yu)(yu){7}腳(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，B比(bi)(bi)(bi)較(jiao)(jiao)(jiao)(jiao)(jiao)器輸(shu)(shu)出(chu)端(duan)(duan){1}腳(jiao)(jiao)輸(shu)(shu)出(chu)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，經(jing)(jing)(jing)D36的(de)(de)(de)(de)(de)(de)(de)(de)(de)鉗位作(zuo)(zuo)(zuo)(zuo)用(yong)，A比(bi)(bi)(bi)較(jiao)(jiao)(jiao)(jiao)(jiao)器的(de)(de)(de)(de)(de)(de)(de)(de)(de)反相(xiang)端(duan)(duan){4}腳(jiao)(jiao)亦(yi)(yi)為(wei)(wei)(wei)(wei)(wei)(wei)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，其(qi)(qi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)低(di)(di)(di)于(yu)(yu)(yu)同(tong)相(xiang)端(duan)(duan){5}腳(jiao)(jiao)的(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，輸(shu)(shu)出(chu)端(duan)(duan){2}腳(jiao)(jiao)呈高(gao)(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，經(jing)(jing)(jing)R41使(shi)(shi)494的(de)(de)(de)(de)(de)(de)(de)(de)(de){4}腳(jiao)(jiao)為(wei)(wei)(wei)(wei)(wei)(wei)高(gao)(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，故(gu)494內(nei)部(bu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)死區(qu)時(shi)(shi)(shi)間(jian)(jian)比(bi)(bi)(bi)較(jiao)(jiao)(jiao)(jiao)(jiao)器a輸(shu)(shu)出(chu)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，與(yu)(yu)(yu)門1也(ye)因(yin)(yin)此(ci)輸(shu)(shu)出(chu)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)并進(jin)而使(shi)(shi)與(yu)(yu)(yu)門2和(he)與(yu)(yu)(yu)門3輸(shu)(shu)出(chu)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，封鎖了(le)振(zhen)(zhen)蕩(dang)器的(de)(de)(de)(de)(de)(de)(de)(de)(de)輸(shu)(shu)出(chu)，{8}腳(jiao)(jiao)、{11}腳(jiao)(jiao)無(wu)脈沖輸(shu)(shu)出(chu)，ATX電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)無(wu)±5V、±12V、＋3．3V電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)輸(shu)(shu)出(chu)，主(zhu)(zhu)機處(chu)于(yu)(yu)(yu)待機狀態。因(yin)(yin)＋5V、＋12V電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)輸(shu)(shu)出(chu)為(wei)(wei)(wei)(wei)(wei)(wei)零，經(jing)(jing)(jing)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻R15、R16使(shi)(shi)494的(de)(de)(de)(de)(de)(de)(de)(de)(de){1}腳(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)亦(yi)(yi)為(wei)(wei)(wei)(wei)(wei)(wei)零，494的(de)(de)(de)(de)(de)(de)(de)(de)(de)c比(bi)(bi)(bi)較(jiao)(jiao)(jiao)(jiao)(jiao)器的(de)(de)(de)(de)(de)(de)(de)(de)(de)輸(shu)(shu)出(chu)端(duan)(duan){3}腳(jiao)(jiao)輸(shu)(shu)出(chu)亦(yi)(yi)為(wei)(wei)(wei)(wei)(wei)(wei)零，經(jing)(jing)(jing)R48使(shi)(shi)339的(de)(de)(de)(de)(de)(de)(de)(de)(de){9}腳(jiao)(jiao)亦(yi)(yi)為(wei)(wei)(wei)(wei)(wei)(wei)零電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，故(gu)339的(de)(de)(de)(de)(de)(de)(de)(de)(de)C比(bi)(bi)(bi)較(jiao)(jiao)(jiao)(jiao)(jiao)器的(de)(de)(de)(de)(de)(de)(de)(de)(de)輸(shu)(shu)出(chu)端(duan)(duan){14}腳(jiao)(jiao)為(wei)(wei)(wei)(wei)(wei)(wei)零電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)。另(ling)外(wai)，339的(de)(de)(de)(de)(de)(de)(de)(de)(de){1}腳(jiao)(jiao)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)信(xin)(xin)(xin)號因(yin)(yin)D34的(de)(de)(de)(de)(de)(de)(de)(de)(de)鉗位作(zuo)(zuo)(zuo)(zuo)用(yong)，也(ye)使(shi)(shi){14}腳(jiao)(jiao)為(wei)(wei)(wei)(wei)(wei)(wei)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，經(jing)(jing)(jing)R50和(he)R63使(shi)(shi){11}腳(jiao)(jiao)亦(yi)(yi)為(wei)(wei)(wei)(wei)(wei)(wei)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)。因(yin)(yin)此(ci)D比(bi)(bi)(bi)較(jiao)(jiao)(jiao)(jiao)(jiao)器的(de)(de)(de)(de)(de)(de)(de)(de)(de)輸(shu)(shu)出(chu)端(duan)(duan){13}腳(jiao)(jiao)為(wei)(wei)(wei)(wei)(wei)(wei)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，也(ye)就是PW－OK信(xin)(xin)(xin)號為(wei)(wei)(wei)(wei)(wei)(wei)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，主(zhu)(zhu)機不會工作(zuo)(zuo)(zuo)(zuo)。開(kai)啟(qi)主(zhu)(zhu)機時(shi)(shi)(shi)，通(tong)過人工或遙控操(cao)作(zuo)(zuo)(zuo)(zuo)閉(bi)合(he)了(le)與(yu)(yu)(yu)PS－ON相(xiang)關的(de)(de)(de)(de)(de)(de)(de)(de)(de)開(kai)關，PS－ON呈低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，經(jing)(jing)(jing)R37使(shi)(shi)339的(de)(de)(de)(de)(de)(de)(de)(de)(de)反相(xiang)端(duan)(duan){6}腳(jiao)(jiao)為(wei)(wei)(wei)(wei)(wei)(wei)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，B比(bi)(bi)(bi)較(jiao)(jiao)(jiao)(jiao)(jiao)器{1}腳(jiao)(jiao)輸(shu)(shu)出(chu)高(gao)(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，D35、D36反偏截止，A比(bi)(bi)(bi)較(jiao)(jiao)(jiao)(jiao)(jiao)器的(de)(de)(de)(de)(de)(de)(de)(de)(de)輸(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)則由(you){5}腳(jiao)(jiao)與(yu)(yu)(yu){4}腳(jiao)(jiao)的(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)決(jue)定(ding)。正常(chang)工作(zuo)(zuo)(zuo)(zuo)時(shi)(shi)(shi)，{5}腳(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)低(di)(di)(di)于(yu)(yu)(yu){4}腳(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，{2}腳(jiao)(jiao)輸(shu)(shu)出(chu)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，經(jing)(jing)(jing)R41送到494的(de)(de)(de)(de)(de)(de)(de)(de)(de){4}腳(jiao)(jiao)，使(shi)(shi){4}腳(jiao)(jiao)的(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)變為(wei)(wei)(wei)(wei)(wei)(wei)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，鋸齒(chi)波振(zhen)(zhen)蕩(dang)信(xin)(xin)(xin)號可(ke)以從(cong)死區(qu)時(shi)(shi)(shi)間(jian)(jian)比(bi)(bi)(bi)較(jiao)(jiao)(jiao)(jiao)(jiao)器a輸(shu)(shu)出(chu)脈沖信(xin)(xin)(xin)號，另(ling)一(yi)方面，振(zhen)(zhen)蕩(dang)信(xin)(xin)(xin)號送到了(le)PWM比(bi)(bi)(bi)較(jiao)(jiao)(jiao)(jiao)(jiao)器b的(de)(de)(de)(de)(de)(de)(de)(de)(de)同(tong)相(xiang)輸(shu)(shu)入端(duan)(duan)，PWM比(bi)(bi)(bi)較(jiao)(jiao)(jiao)(jiao)(jiao)器輸(shu)(shu)出(chu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)脈沖信(xin)(xin)(xin)號的(de)(de)(de)(de)(de)(de)(de)(de)(de)寬度，則是由(you)494的(de)(de)(de)(de)(de)(de)(de)(de)(de){1}腳(jiao)(jiao)的(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)（也(ye)就是負載的(de)(de)(de)(de)(de)(de)(de)(de)(de)大小(xiao)）與(yu)(yu)(yu){16}腳(jiao)(jiao)的(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)來決(jue)定(ding)。PWM比(bi)(bi)(bi)較(jiao)(jiao)(jiao)(jiao)(jiao)器輸(shu)(shu)出(chu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)脈沖信(xin)(xin)(xin)號，最(zui)后(hou)經(jing)(jing)(jing)緩沖放(fang)大器放(fang)大后(hou)，從(cong){8}、{11}腳(jiao)(jiao)輸(shu)(shu)出(chu)脈沖信(xin)(xin)(xin)號，ATX電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)向主(zhu)(zhu)機輸(shu)(shu)出(chu)±5V、±12V、＋3.3V電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)。此(ci)過程因(yin)(yin)C35的(de)(de)(de)(de)(de)(de)(de)(de)(de)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)有數百毫秒(miao)(miao)的(de)(de)(de)(de)(de)(de)(de)(de)(de)延時(shi)(shi)(shi)，但對(dui)(dui)主(zhu)(zhu)機開(kai)機并無(wu)影響。494的(de)(de)(de)(de)(de)(de)(de)(de)(de){1}腳(jiao)(jiao)從(cong)＋5V、＋12V經(jing)(jing)(jing)取樣電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻R15、R16得到電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓，其(qi)(qi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)略(lve)高(gao)(gao)(gao)(gao)于(yu)(yu)(yu){2}腳(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，{3}腳(jiao)(jiao)輸(shu)(shu)出(chu)高(gao)(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，經(jing)(jing)(jing)R48使(shi)(shi)339的(de)(de)(de)(de)(de)(de)(de)(de)(de){9}腳(jiao)(jiao)得到高(gao)(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，其(qi)(qi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)高(gao)(gao)(gao)(gao)于(yu)(yu)(yu){8}腳(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，因(yin)(yin)而{14}腳(jiao)(jiao)輸(shu)(shu)出(chu)高(gao)(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，此(ci)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)經(jing)(jing)(jing)R50與(yu)(yu)(yu)基準(zhun)＋5V電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)經(jing)(jing)(jing)R64共同(tong)對(dui)(dui)C39充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，經(jing)(jing)(jing)數百毫秒(miao)(miao)后(hou)，{11}腳(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)升到高(gao)(gao)(gao)(gao)于(yu)(yu)(yu){10}腳(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)時(shi)(shi)(shi)，D比(bi)(bi)(bi)較(jiao)(jiao)(jiao)(jiao)(jiao)器{13}腳(jiao)(jiao)輸(shu)(shu)出(chu)高(gao)(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，此(ci)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)經(jing)(jing)(jing)R49反饋至{11}腳(jiao)(jiao)，維(wei)持{11}腳(jiao)(jiao)處(chu)于(yu)(yu)(yu)高(gao)(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)狀態，故(gu){13}腳(jiao)(jiao)輸(shu)(shu)出(chu)穩(wen)定(ding)的(de)(de)(de)(de)(de)(de)(de)(de)(de)高(gao)(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping) PW－OK信(xin)(xin)(xin)號，主(zhu)(zhu)機檢(jian)測(ce)到此(ci)信(xin)(xin)(xin)號后(hou)即開(kai)始正常(chang)工作(zuo)(zuo)(zuo)(zuo)。

關機時，主機內開關(guan)(guan)使(shi)(shi)PS－ON呈(cheng)高(gao)(gao)電(dian)(dian)(dian)平(ping)(ping)(ping)，此(ci)時(shi)(shi)(shi)339的(de)(de)(de)(de){6}腳(jiao)(jiao)電(dian)(dian)(dian)平(ping)(ping)(ping)高(gao)(gao)于{7}腳(jiao)(jiao)，{1}腳(jiao)(jiao)輸(shu)出(chu)(chu)低(di)(di)電(dian)(dian)(dian)平(ping)(ping)(ping)，因(yin)(yin)二極管(guan)D34的(de)(de)(de)(de)鉗位作(zuo)用，{14}腳(jiao)(jiao)呈(cheng)低(di)(di)電(dian)(dian)(dian)平(ping)(ping)(ping)，C39對C比(bi)較器(qi)及B比(bi)較器(qi)放(fang)電(dian)(dian)(dian)，很快(kuai){11}腳(jiao)(jiao)呈(cheng)低(di)(di)電(dian)(dian)(dian)平(ping)(ping)(ping)，{13}腳(jiao)(jiao)輸(shu)出(chu)(chu)低(di)(di)電(dian)(dian)(dian)平(ping)(ping)(ping)，即PW－OK信(xin)(xin)號呈(cheng)低(di)(di)電(dian)(dian)(dian)平(ping)(ping)(ping)。在339的(de)(de)(de)(de){1}腳(jiao)(jiao)為(wei)低(di)(di)電(dian)(dian)(dian)平(ping)(ping)(ping)時(shi)(shi)(shi)，經(jing)(jing)D36使(shi)(shi){4}臆腳(jiao)(jiao)為(wei)低(di)(di)電(dian)(dian)(dian)平(ping)(ping)(ping)，{2}腳(jiao)(jiao)輸(shu)出(chu)(chu)高(gao)(gao)電(dian)(dian)(dian)平(ping)(ping)(ping)，經(jing)(jing)R41傳送到494的(de)(de)(de)(de){4}腳(jiao)(jiao)，但(dan)因(yin)(yin)C35電(dian)(dian)(dian)位不(bu)能突(tu)變，經(jing)(jing)數百毫秒的(de)(de)(de)(de)放(fang)電(dian)(dian)(dian)后方使(shi)(shi)494的(de)(de)(de)(de){4}腳(jiao)(jiao)轉(zhuan)為(wei)高(gao)(gao)電(dian)(dian)(dian)平(ping)(ping)(ping)，從而封鎖正負脈沖的(de)(de)(de)(de)輸(shu)出(chu)(chu) ，主(zhu)機進入待機狀態。上述的(de)(de)(de)(de)過程(cheng)中(zhong)，關(guan)(guan)機時(shi)(shi)(shi)C39和C35都要(yao)(yao)放(fang)電(dian)(dian)(dian)，但(dan)因(yin)(yin)放(fang)電(dian)(dian)(dian)時(shi)(shi)(shi)間(jian)常數不(bu)同(tong)，C39放(fang)電(dian)(dian)(dian)較快(kuai)，故PW－OK信(xin)(xin)號先于各電(dian)(dian)(dian)源變成低(di)(di)電(dian)(dian)(dian)平(ping)(ping)(ping)，滿足了主(zhu)機關(guan)(guan)機的(de)(de)(de)(de)需要(yao)(yao)。此(ci)外，關(guan)(guan)機時(shi)(shi)(shi)因(yin)(yin)各路輸(shu)出(chu)(chu)電(dian)(dian)(dian)源的(de)(de)(de)(de)電(dian)(dian)(dian)解電(dian)(dian)(dian)容放(fang)電(dian)(dian)(dian)需要(yao)(yao)時(shi)(shi)(shi)間(jian)，也使(shi)(shi)PW－OK信(xin)(xin)號先于各電(dian)(dian)(dian)源回到低(di)(di)電(dian)(dian)(dian)平(ping)(ping)(ping)。

二、 穩壓

494的(de){2}腳(jiao)(jiao)經R47與(yu)基(ji)準(zhun)電(dian)(dian)(dian)(dian)壓(ya)(ya)＋5V相連，維持較(jiao)(jiao)好的(de)穩定(ding)電(dian)(dian)(dian)(dian)壓(ya)(ya)，而{1}腳(jiao)(jiao)則(ze)與(yu)取樣電(dian)(dian)(dian)(dian)阻R15、R16與(yu)＋5V、＋12V相連接，正常的(de)情況下(xia)，{1}腳(jiao)(jiao)電(dian)(dian)(dian)(dian)平與(yu){2}腳(jiao)(jiao)電(dian)(dian)(dian)(dian)平相等或(huo)略高(gao)。當輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)壓(ya)(ya)升高(gao)時（無論＋5V或(huo)＋12V），{1}腳(jiao)(jiao)電(dian)(dian)(dian)(dian)平高(gao)于(yu){2}腳(jiao)(jiao)電(dian)(dian)(dian)(dian)平，c比較(jiao)(jiao)器輸(shu)(shu)(shu)出(chu)誤差電(dian)(dian)(dian)(dian)壓(ya)(ya)與(yu)鋸齒波振蕩(dang)脈(mo)沖在PWM比較(jiao)(jiao)器b進行比較(jiao)(jiao)使(shi)輸(shu)(shu)(shu)出(chu)脈(mo)沖寬(kuan)度變(bian)窄(zhai)，輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)壓(ya)(ya)回落(luo)到(dao)標準(zhun)值(zhi)，反之(zhi)則(ze)促使(shi)振蕩(dang)脈(mo)沖寬(kuan)度增(zeng)加，輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)壓(ya)(ya)回升。由于(yu)494內的(de)放(fang)大(da)器增(zeng)益(yi)很高(gao)，故穩壓(ya)(ya)精度很好。從(cong)穩壓(ya)(ya)的(de)原(yuan)理，我們可以得到(dao)ATX電(dian)(dian)(dian)(dian)源(yuan)輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)壓(ya)(ya)偏(pian)高(gao)或(huo)偏(pian)低(di)的(de)維修(xiu)方(fang)法。如果輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)壓(ya)(ya)偏(pian)低(di)，可在494的(de){1}腳(jiao)(jiao)對(dui)地并(bing)聯(lian)電(dian)(dian)(dian)(dian)阻，或(huo)是把R47的(de)電(dian)(dian)(dian)(dian)阻增(zeng)大(da)。要是電(dian)(dian)(dian)(dian)源(yuan)的(de)輸(shu)(shu)(shu)出(chu)偏(pian)高(gao)，則(ze)可在{2}腳(jiao)(jiao)對(dui)地并(bing)聯(lian)電(dian)(dian)(dian)(dian)阻，也(ye)可以用增(zeng)大(da)R33或(huo)取下(xia)R69、R35來降低(di)輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)壓(ya)(ya)。

三、 過流保護

過流(liu)(liu)保護的(de)(de)(de)(de)原理(li)是基于負(fu)載(zai)愈大，Q3、Q4集(ji)電(dian)(dian)(dian)極的(de)(de)(de)(de)脈沖(chong)電(dian)(dian)(dian)壓(ya)也(ye)愈高(gao)，也(ye)即是R13（1．5kΩ）上(shang)的(de)(de)(de)(de)電(dian)(dian)(dian)壓(ya)也(ye)愈高(gao)，從這里采(cai)樣(yang)經D14整流(liu)(liu)和(he)C36濾(lv)波，再(zai)(zai)(zai)經R54、R55并聯電(dian)(dian)(dian)阻與(yu)R51、R56、R58等組成的(de)(de)(de)(de)分壓(ya)電(dian)(dian)(dian)路送到494的(de)(de)(de)(de){16}腳(jiao)(jiao)(jiao)(jiao)。隨著負(fu)載(zai)的(de)(de)(de)(de)加(jia)重(zhong)，{16}腳(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)電(dian)(dian)(dian)平(ping)(ping)也(ye)隨之上(shang)升，當(dang)超(chao)(chao)過{15}腳(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)電(dian)(dian)(dian)平(ping)(ping)時(shi)，誤差放大器輸出(chu)(chu)(chu)(chu)的(de)(de)(de)(de)誤差電(dian)(dian)(dian)壓(ya)促(cu)使(shi)調制脈沖(chong)的(de)(de)(de)(de)寬(kuan)度變窄從而(er)使(shi)負(fu)載(zai)電(dian)(dian)(dian)流(liu)(liu)減小。另(ling)外(wai)，從R56、R58并聯電(dian)(dian)(dian)阻獲得的(de)(de)(de)(de)分壓(ya)再(zai)(zai)(zai)經R52送到339的(de)(de)(de)(de){5}腳(jiao)(jiao)(jiao)(jiao)，當(dang){5}腳(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)電(dian)(dian)(dian)平(ping)(ping)超(chao)(chao)過{4}腳(jiao)(jiao)(jiao)(jiao)時(shi)，{2}腳(jiao)(jiao)(jiao)(jiao)即輸出(chu)(chu)(chu)(chu)高(gao)電(dian)(dian)(dian)平(ping)(ping)送到494的(de)(de)(de)(de){4}腳(jiao)(jiao)(jiao)(jiao)，494停(ting)止輸出(chu)(chu)(chu)(chu)脈沖(chong)信號，終止±5V、±12V、＋3．3V電(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)輸出(chu)(chu)(chu)(chu)，達(da)到過流(liu)(liu)及短路保護的(de)(de)(de)(de)目的(de)(de)(de)(de)。需要說明(ming)的(de)(de)(de)(de)是：494的(de)(de)(de)(de){16}腳(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)平(ping)(ping)的(de)(de)(de)(de)高(gao)低只(zhi)能(neng)改變輸出(chu)(chu)(chu)(chu)脈沖(chong)的(de)(de)(de)(de)寬(kuan)度，但(dan)不影響(xiang)494的(de)(de)(de)(de){4}腳(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)平(ping)(ping)狀態(tai)，而(er)339的(de)(de)(de)(de){5}腳(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)平(ping)(ping)一旦(dan)超(chao)(chao)過{4}腳(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)電(dian)(dian)(dian)平(ping)(ping)，339的(de)(de)(de)(de){2}腳(jiao)(jiao)(jiao)(jiao)就(jiu)送出(chu)(chu)(chu)(chu)高(gao)電(dian)(dian)(dian)平(ping)(ping)去(qu)封鎖449的(de)(de)(de)(de)脈沖(chong)輸出(chu)(chu)(chu)(chu)，終止±5V、±12V、＋3．3V電(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)輸出(chu)(chu)(chu)(chu)，同時(shi){2}腳(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)高(gao)電(dian)(dian)(dian)平(ping)(ping)經R59和(he)二(er)極管D39反饋到{5}腳(jiao)(jiao)(jiao)(jiao)，維(wei)持{5}腳(jiao)(jiao)(jiao)(jiao)處于高(gao)電(dian)(dian)(dian)平(ping)(ping)狀態(tai)，此時(shi)若過載(zai)或短路狀態(tai)消失，494的(de)(de)(de)(de){4}腳(jiao)(jiao)(jiao)(jiao)仍維(wei)持高(gao)電(dian)(dian)(dian)平(ping)(ping)，±5V與(yu)±12V、＋3．3V電(dian)(dian)(dian)源(yuan)仍不能(neng)輸出(chu)(chu)(chu)(chu)，只(zhi)有(you)切斷交流(liu)(liu)市電(dian)(dian)(dian)的(de)(de)(de)(de)輸入，再(zai)(zai)(zai)重(zhong)新接通交流(liu)(liu)電(dian)(dian)(dian)，方(fang)可(ke)再(zai)(zai)(zai)次(ci)開機(ji)。

四、過壓保護

過電(dian)(dian)壓(ya)(ya)(ya)保(bao)護由(you)R17和穩(wen)壓(ya)(ya)(ya)管Z02并聯(lian)電(dian)(dian)路從＋5V采樣，經(jing)D37送(song)(song)到339的{5}腳(jiao)。若＋5V電(dian)(dian)源(yuan)(yuan)由(you)于某種原因升高，339的{5}腳(jiao)電(dian)(dian)平(ping)也會隨之升高，當(dang)超過{4}腳(jiao)電(dian)(dian)平(ping)時，{2}腳(jiao)即送(song)(song)出(chu)高電(dian)(dian)平(ping)去494的{4}腳(jiao)，封鎖±5V、±12V、＋3．3V電(dian)(dian)源(yuan)(yuan)的輸出(chu)，達到過電(dian)(dian)壓(ya)(ya)(ya)保(bao)護的目(mu)的。正常(chang)工作(zuo)時，R17上(shang)(shang)的壓(ya)(ya)(ya)降不大(da)，Z02截止(zhi)送(song)(song)到{5}腳(jiao)的電(dian)(dian)壓(ya)(ya)(ya)較低(di)，若＋5V電(dian)(dian)源(yuan)(yuan)的電(dian)(dian)壓(ya)(ya)(ya)上(shang)(shang)升，使(shi)R17上(shang)(shang)的壓(ya)(ya)(ya)降超過Z02的穩(wen)壓(ya)(ya)(ya)值，Z02導通(tong)，＋5V電(dian)(dian)源(yuan)(yuan)上(shang)(shang)升后的電(dian)(dian)壓(ya)(ya)(ya)值全部加到339的{5}腳(jiao)上(shang)(shang)，促使(shi)其(qi)快速封鎖494脈沖的輸出(chu)，以(yi)保(bao)護電(dian)(dian)源(yuan)(yuan)。

五、欠壓保護

欠(qian)壓保(bao)護從(cong)－5V的(de)(de)D32及－12V處的(de)(de)R14取樣，經R34和D37送(song)到339的(de)(de){5}腳。若因某種原因使輸出電(dian)(dian)(dian)壓過低時(shi)，－12V及 －5V電(dian)(dian)(dian)壓的(de)(de)負(fu)(fu)值也會(hui)隨之減小，也就是電(dian)(dian)(dian)壓值上(shang)升，經R34及D37送(song)往339的(de)(de){5}腳使電(dian)(dian)(dian)平(ping)上(shang)升，339的(de)(de){2}腳送(song)出高(gao)電(dian)(dian)(dian)平(ping)到494的(de)(de){4}腳，從(cong)而封鎖 449脈沖的(de)(de)輸出，實(shi)現(xian)欠(qian)壓保(bao)護。二極(ji)管D32在導通(tong)時(shi)，其電(dian)(dian)(dian)壓降與(yu)通(tong)過的(de)(de)電(dian)(dian)(dian)流(liu)基本無關，保(bao)持在0．6V～0．7V，于是－5V電(dian)(dian)(dian)壓的(de)(de)減少(shao)量會(hui)全部(bu)傳(chuan)送(song)到D32的(de)(de)負(fu)(fu)端，提(ti)高(gao)了欠(qian)壓保(bao)護的(de)(de)靈敏(min)度(du)。