臺(tai)(tai)式(shi)(shi)機電源(yuan)電路圖原(yuan)理分析 臺(tai)(tai)式(shi)(shi)機電源(yuan)是如何實現(xian)多種保護功能的

ATX電(dian)(dian)(dian)源(yuan)的(de)控(kong)制電(dian)(dian)(dian)路(lu)如(ru)上圖。控(kong)制電(dian)(dian)(dian)路(lu)采用TL494及(ji)(ji)LM339集成(cheng)電(dian)(dian)(dian)路(lu)（以(yi)下簡稱494和339）。494是(shi)雙排16腳(jiao)(jiao)(jiao)集成(cheng)電(dian)(dian)(dian)路(lu)，工作電(dian)(dian)(dian)壓(ya)7～40V。它含有由{14}腳(jiao)(jiao)(jiao)輸出(chu)的(de)＋5V基準電(dian)(dian)(dian)源(yuan)，輸出(chu)電(dian)(dian)(dian)壓(ya)為(wei)＋5V（±0．05V），最大輸出(chu)電(dian)(dian)(dian)流250mA；一個頻率可調的(de)鋸(ju)齒波產生電(dian)(dian)(dian)路(lu)，振(zhen)蕩頻率由{5}腳(jiao)(jiao)(jiao)外接電(dian)(dian)(dian)容及(ji)(ji){6}腳(jiao)(jiao)(jiao)外接電(dian)(dian)(dian)阻來決定。{13}腳(jiao)(jiao)(jiao)為(wei)高電(dian)(dian)(dian)平(ping)時，由{8}腳(jiao)(jiao)(jiao)及(ji)(ji){11}腳(jiao)(jiao)(jiao)輸出(chu)雙路(lu)反相（即推挽工作方式）的(de)脈寬調制信號。

比較(jiao)器是一(yi)種運(yun)算放大器，符號用(yong)三角(jiao)形表示，它(ta)有一(yi)個(ge)同相(xiang)輸(shu)入端(duan)(duan)“＋”；一(yi)個(ge)反(fan)相(xiang)輸(shu)入端(duan)(duan)“－”和(he)一(yi)個(ge)輸(shu)出端(duan)(duan)。

比(bi)較(jiao)(jiao)器(qi)(qi)(qi)同(tong)相端(duan)(duan)(duan)(duan)電(dian)(dian)(dian)(dian)(dian)平(ping)若高(gao)于(yu)(yu)反相端(duan)(duan)(duan)(duan)電(dian)(dian)(dian)(dian)(dian)平(ping)，則(ze)輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)端(duan)(duan)(duan)(duan)輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)高(gao)電(dian)(dian)(dian)(dian)(dian)平(ping)；反之輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)平(ping)。494內(nei)的(de)(de)比(bi)較(jiao)(jiao)放大器(qi)(qi)(qi)有(you)(you)四個(ge)(ge)(ge)，為(wei)(wei)敘(xu)述方便，在(zai)(zai)上圖中(zhong)用(yong)(yong)小寫(xie)字母a、b、c、d來表示(shi)。其中(zhong)a是(shi)死(si)區(qu)時(shi)間(jian)比(bi)較(jiao)(jiao)器(qi)(qi)(qi)。因兩個(ge)(ge)(ge)作(zuo)逆變(bian)(bian)工作(zuo)的(de)(de)三(san)極(ji)管(guan)(guan)(guan)(guan)串(chuan)聯(lian)后接(jie)到＋310V的(de)(de)直流電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)上，若兩個(ge)(ge)(ge)三(san)極(ji)管(guan)(guan)(guan)(guan)同(tong)時(shi)導(dao)通(tong)(tong)，就(jiu)會形成對(dui)直流電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)短路。兩個(ge)(ge)(ge)三(san)極(ji)管(guan)(guan)(guan)(guan)同(tong)時(shi)導(dao)通(tong)(tong)可(ke)(ke)能(neng)發(fa)生在(zai)(zai)一(yi)(yi)(yi)(yi)(yi)個(ge)(ge)(ge)管(guan)(guan)(guan)(guan)子(zi)(zi)從截止(zhi)轉(zhuan)為(wei)(wei)導(dao)通(tong)(tong)，而(er)另一(yi)(yi)(yi)(yi)(yi)個(ge)(ge)(ge)管(guan)(guan)(guan)(guan)子(zi)(zi)由導(dao)通(tong)(tong)轉(zhuan)為(wei)(wei)截止(zhi)的(de)(de)時(shi)候(hou)。因為(wei)(wei)管(guan)(guan)(guan)(guan)子(zi)(zi)在(zai)(zai)轉(zhuan)換時(shi)有(you)(you)時(shi)間(jian)的(de)(de)延遲，截止(zhi)的(de)(de)管(guan)(guan)(guan)(guan)子(zi)(zi)已經轉(zhuan)為(wei)(wei)導(dao)通(tong)(tong)了(le)，但導(dao)通(tong)(tong)的(de)(de)管(guan)(guan)(guan)(guan)子(zi)(zi)尚未完全轉(zhuan)為(wei)(wei)截止(zhi)，于(yu)(yu)是(shi)兩個(ge)(ge)(ge)管(guan)(guan)(guan)(guan)子(zi)(zi)都呈導(dao)通(tong)(tong)狀態而(er)形成對(dui)直流電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)短路。為(wei)(wei)防止(zhi)這樣的(de)(de)事(shi)情(qing)發(fa)生，494設置了(le)死(si)區(qu)時(shi)間(jian)比(bi)較(jiao)(jiao)器(qi)(qi)(qi)a。從圖中(zhong)可(ke)(ke)以(yi)看出(chu)(chu)(chu)(chu)，在(zai)(zai)比(bi)較(jiao)(jiao)器(qi)(qi)(qi)a的(de)(de)反相輸(shu)(shu)(shu)入(ru)端(duan)(duan)(duan)(duan)串(chuan)聯(lian)了(le)一(yi)(yi)(yi)(yi)(yi)個(ge)(ge)(ge)“電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)”，正極(ji)接(jie)反相端(duan)(duan)(duan)(duan)，負極(ji)接(jie)494的(de)(de){4}腳。A比(bi)較(jiao)(jiao)器(qi)(qi)(qi)同(tong)相端(duan)(duan)(duan)(duan)輸(shu)(shu)(shu)入(ru)的(de)(de)鋸齒(chi)波(bo)信號，只(zhi)(zhi)有(you)(you)大于(yu)(yu)“電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)”電(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)(de)部分才有(you)(you)輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)，在(zai)(zai)三(san)極(ji)管(guan)(guan)(guan)(guan)導(dao)通(tong)(tong)變(bian)(bian)為(wei)(wei)截止(zhi)與截止(zhi)轉(zhuan)為(wei)(wei)導(dao)通(tong)(tong)期間(jian)，也(ye)就(jiu)是(shi)死(si)區(qu)時(shi)間(jian)，494沒有(you)(you)脈沖輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)，避免了(le)對(dui)直流電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)短路。死(si)區(qu)時(shi)間(jian)還可(ke)(ke)由{4}腳外接(jie)的(de)(de)電(dian)(dian)(dian)(dian)(dian)平(ping)來控(kong)制(zhi)，{4}腳的(de)(de)電(dian)(dian)(dian)(dian)(dian)平(ping)上升，死(si)區(qu)時(shi)間(jian)變(bian)(bian)寬，494輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)的(de)(de)脈沖就(jiu)變(bian)(bian)窄了(le)，若{4}腳的(de)(de)電(dian)(dian)(dian)(dian)(dian)平(ping)超(chao)過了(le)鋸齒(chi)波(bo)的(de)(de)峰值電(dian)(dian)(dian)(dian)(dian)壓(ya)，494就(jiu)進入(ru)了(le)保護狀態，{8}腳和(he){11}腳就(jiu)不輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)脈沖了(le)。494內(nei)部還有(you)(you)3個(ge)(ge)(ge)二輸(shu)(shu)(shu)入(ru)端(duan)(duan)(duan)(duan)與門(men)（用(yong)(yong)1、2、3表示(shi)）、兩個(ge)(ge)(ge)二輸(shu)(shu)(shu)入(ru)端(duan)(duan)(duan)(duan)與非門(men)、反相器(qi)(qi)(qi)、T觸發(fa)器(qi)(qi)(qi)等(deng)電(dian)(dian)(dian)(dian)(dian)路。與門(men)是(shi)這樣一(yi)(yi)(yi)(yi)(yi)種電(dian)(dian)(dian)(dian)(dian)路，只(zhi)(zhi)有(you)(you)所(suo)有(you)(you)的(de)(de)輸(shu)(shu)(shu)入(ru)端(duan)(duan)(duan)(duan)都是(shi)高(gao)電(dian)(dian)(dian)(dian)(dian)平(ping)，輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)端(duan)(duan)(duan)(duan)才能(neng)輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)高(gao)電(dian)(dian)(dian)(dian)(dian)平(ping)；若有(you)(you)一(yi)(yi)(yi)(yi)(yi)個(ge)(ge)(ge)輸(shu)(shu)(shu)入(ru)端(duan)(duan)(duan)(duan)為(wei)(wei)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)平(ping)，則(ze)輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)端(duan)(duan)(duan)(duan)輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)平(ping)。反相器(qi)(qi)(qi)的(de)(de)作(zuo)用(yong)(yong)是(shi)把輸(shu)(shu)(shu)入(ru)信號隔離放大后反相輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)。與非門(men)則(ze)相當于(yu)(yu)一(yi)(yi)(yi)(yi)(yi)個(ge)(ge)(ge)與門(men)和(he)一(yi)(yi)(yi)(yi)(yi)個(ge)(ge)(ge)反相器(qi)(qi)(qi)的(de)(de)組合(he)。T觸發(fa)器(qi)(qi)(qi)的(de)(de)作(zuo)用(yong)(yong)是(shi)：每輸(shu)(shu)(shu)入(ru)一(yi)(yi)(yi)(yi)(yi)個(ge)(ge)(ge)脈沖，輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)端(duan)(duan)(duan)(duan)的(de)(de)電(dian)(dian)(dian)(dian)(dian)平(ping)就(jiu)變(bian)(bian)化一(yi)(yi)(yi)(yi)(yi)次(ci)。如輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)端(duan)(duan)(duan)(duan)Q為(wei)(wei)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)平(ping)，輸(shu)(shu)(shu)入(ru)一(yi)(yi)(yi)(yi)(yi)個(ge)(ge)(ge)脈沖后，Q變(bian)(bian)為(wei)(wei)高(gao)電(dian)(dian)(dian)(dian)(dian)平(ping)，再輸(shu)(shu)(shu)入(ru)一(yi)(yi)(yi)(yi)(yi)個(ge)(ge)(ge)脈沖，Q又回到低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)平(ping)。

339是四比較(jiao)(jiao)器(qi)集(ji)(ji)成電(dian)(dian)(dian)(dian)(dian)(dian)路。 LM339集(ji)(ji)成塊內部裝有四個(ge)獨立的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓比較(jiao)(jiao)器(qi)，每個(ge)比較(jiao)(jiao)器(qi)有兩個(ge)輸(shu)(shu)(shu)(shu)(shu)入端(duan)(duan)(duan)(duan)(duan)(duan)和(he)(he)一(yi)(yi)個(ge)輸(shu)(shu)(shu)(shu)(shu)出(chu)端(duan)(duan)(duan)(duan)(duan)(duan)。兩個(ge)輸(shu)(shu)(shu)(shu)(shu)入端(duan)(duan)(duan)(duan)(duan)(duan)一(yi)(yi)個(ge)稱(cheng)為(wei)(wei)(wei)同相(xiang)輸(shu)(shu)(shu)(shu)(shu)入端(duan)(duan)(duan)(duan)(duan)(duan)，用(yong)(yong)“+”表示(shi)，另一(yi)(yi)個(ge)稱(cheng)為(wei)(wei)(wei)反相(xiang)輸(shu)(shu)(shu)(shu)(shu)入端(duan)(duan)(duan)(duan)(duan)(duan)，用(yong)(yong)“-”表示(shi)。用(yong)(yong)作比較(jiao)(jiao)兩個(ge)電(dian)(dian)(dian)(dian)(dian)(dian)壓時(shi)，任意一(yi)(yi)個(ge)輸(shu)(shu)(shu)(shu)(shu)入端(duan)(duan)(duan)(duan)(duan)(duan)加(jia)一(yi)(yi)個(ge)固定電(dian)(dian)(dian)(dian)(dian)(dian)壓做(zuo)參考電(dian)(dian)(dian)(dian)(dian)(dian)壓（也稱(cheng)為(wei)(wei)(wei)門限電(dian)(dian)(dian)(dian)(dian)(dian)平(ping)，它可選(xuan)擇LM339輸(shu)(shu)(shu)(shu)(shu)入共模范圍的(de)(de)(de)任何一(yi)(yi)點），另一(yi)(yi)端(duan)(duan)(duan)(duan)(duan)(duan)加(jia)一(yi)(yi)個(ge)待比較(jiao)(jiao)的(de)(de)(de)信(xin)號電(dian)(dian)(dian)(dian)(dian)(dian)壓。當“+”端(duan)(duan)(duan)(duan)(duan)(duan)電(dian)(dian)(dian)(dian)(dian)(dian)壓高(gao)于(yu)(yu)“-”端(duan)(duan)(duan)(duan)(duan)(duan)時(shi)，輸(shu)(shu)(shu)(shu)(shu)出(chu)管(guan)(guan)截(jie)止，相(xiang)當于(yu)(yu)輸(shu)(shu)(shu)(shu)(shu)出(chu)端(duan)(duan)(duan)(duan)(duan)(duan)開(kai)路。當“-”端(duan)(duan)(duan)(duan)(duan)(duan)電(dian)(dian)(dian)(dian)(dian)(dian)壓高(gao)于(yu)(yu)“+”端(duan)(duan)(duan)(duan)(duan)(duan)時(shi)，輸(shu)(shu)(shu)(shu)(shu)出(chu)管(guan)(guan)飽和(he)(he)，相(xiang)當于(yu)(yu)輸(shu)(shu)(shu)(shu)(shu)出(chu)端(duan)(duan)(duan)(duan)(duan)(duan)接(jie)低電(dian)(dian)(dian)(dian)(dian)(dian)位。兩個(ge)輸(shu)(shu)(shu)(shu)(shu)入端(duan)(duan)(duan)(duan)(duan)(duan)電(dian)(dian)(dian)(dian)(dian)(dian)壓差別大于(yu)(yu)10mV就(jiu)能確(que)保輸(shu)(shu)(shu)(shu)(shu)出(chu)能從一(yi)(yi)種狀態可靠地轉(zhuan)換(huan)到另一(yi)(yi)種狀態， LM339的(de)(de)(de)輸(shu)(shu)(shu)(shu)(shu)出(chu)端(duan)(duan)(duan)(duan)(duan)(duan)相(xiang)當于(yu)(yu)一(yi)(yi)只不接(jie)集(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)極電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)的(de)(de)(de)晶體三極管(guan)(guan)，在使用(yong)(yong)時(shi)輸(shu)(shu)(shu)(shu)(shu)出(chu)端(duan)(duan)(duan)(duan)(duan)(duan)到正電(dian)(dian)(dian)(dian)(dian)(dian)源一(yi)(yi)般(ban)須(xu)接(jie)一(yi)(yi)只電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)（稱(cheng)為(wei)(wei)(wei)上(shang)(shang)拉電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)，選(xuan)3-15K）。選(xuan)不同阻(zu)值的(de)(de)(de)上(shang)(shang)拉電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)會影響輸(shu)(shu)(shu)(shu)(shu)出(chu)端(duan)(duan)(duan)(duan)(duan)(duan)高(gao)電(dian)(dian)(dian)(dian)(dian)(dian)位的(de)(de)(de)值。因為(wei)(wei)(wei)當輸(shu)(shu)(shu)(shu)(shu)出(chu)晶體三極管(guan)(guan)截(jie)止時(shi)，它的(de)(de)(de)集(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)極電(dian)(dian)(dian)(dian)(dian)(dian)壓基本(ben)上(shang)(shang)取決于(yu)(yu)上(shang)(shang)拉電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)與負(fu)載的(de)(de)(de)值。

按管腳的順(shun)序把內部四個比較器設為(wei)A、B 、C 、D 比較器。494和339再(zai)配合其他電(dian)路，共同完成(cheng)ATX電(dian)源的穩壓，產生PW－OK信號及各種保護(hu)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)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)接通(tong)市電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)后(hou)(hou)，輔(fu)助電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)立(li)即工(gong)作(zuo)。一(yi)方面輸(shu)出(chu)(chu)(chu)(chu)(chu) ＋5VSB電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)，同時(shi)向494的(de)(de)(de)(de)(de){12}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)提供十(shi)幾伏到(dao)二(er)十(shi)多伏的(de)(de)(de)(de)(de)直流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)。494從(cong)(cong){14}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)出(chu)(chu)(chu)(chu)(chu)＋5V基(ji)準電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)，鋸(ju)齒(chi)波振蕩(dang)器(qi)(qi)(qi)(qi)也(ye)開始起振工(gong)作(zuo)。若主機(ji)(ji)未(wei)開機(ji)(ji)，PS－ON信(xin)號(hao)(hao)(hao)(hao)(hao)(hao)為(wei)(wei)(wei)(wei)高(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，經(jing)(jing)(jing)(jing)(jing)R37使(shi)(shi)339的(de)(de)(de)(de)(de)B比(bi)(bi)較(jiao)(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi){6}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)亦(yi)(yi)為(wei)(wei)(wei)(wei)高(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，因電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻R37小于R44，{6}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)高(gao)(gao)(gao)于{7}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，B比(bi)(bi)較(jiao)(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)輸(shu)出(chu)(chu)(chu)(chu)(chu)端(duan)(duan)(duan)(duan)(duan){1}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)出(chu)(chu)(chu)(chu)(chu)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，經(jing)(jing)(jing)(jing)(jing)D36的(de)(de)(de)(de)(de)鉗位作(zuo)用，A比(bi)(bi)較(jiao)(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)反相(xiang)端(duan)(duan)(duan)(duan)(duan){4}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)亦(yi)(yi)為(wei)(wei)(wei)(wei)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，其(qi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)低(di)(di)(di)于同相(xiang)端(duan)(duan)(duan)(duan)(duan){5}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，輸(shu)出(chu)(chu)(chu)(chu)(chu)端(duan)(duan)(duan)(duan)(duan){2}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)呈(cheng)高(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，經(jing)(jing)(jing)(jing)(jing)R41使(shi)(shi)494的(de)(de)(de)(de)(de){4}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)為(wei)(wei)(wei)(wei)高(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，故(gu)494內部的(de)(de)(de)(de)(de)死區(qu)時(shi)間比(bi)(bi)較(jiao)(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)a輸(shu)出(chu)(chu)(chu)(chu)(chu)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，與(yu)門(men)1也(ye)因此(ci)(ci)(ci)(ci)輸(shu)出(chu)(chu)(chu)(chu)(chu)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)并進而使(shi)(shi)與(yu)門(men)2和(he)與(yu)門(men)3輸(shu)出(chu)(chu)(chu)(chu)(chu)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，封鎖(suo)了振蕩(dang)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)輸(shu)出(chu)(chu)(chu)(chu)(chu)，{8}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)、{11}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)無脈(mo)(mo)沖輸(shu)出(chu)(chu)(chu)(chu)(chu)，ATX電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)無±5V、±12V、＋3．3V電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)輸(shu)出(chu)(chu)(chu)(chu)(chu)，主機(ji)(ji)處(chu)于待機(ji)(ji)狀態。因＋5V、＋12V電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)輸(shu)出(chu)(chu)(chu)(chu)(chu)為(wei)(wei)(wei)(wei)零(ling)，經(jing)(jing)(jing)(jing)(jing)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻R15、R16使(shi)(shi)494的(de)(de)(de)(de)(de){1}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)亦(yi)(yi)為(wei)(wei)(wei)(wei)零(ling)，494的(de)(de)(de)(de)(de)c比(bi)(bi)較(jiao)(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)輸(shu)出(chu)(chu)(chu)(chu)(chu)端(duan)(duan)(duan)(duan)(duan){3}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)出(chu)(chu)(chu)(chu)(chu)亦(yi)(yi)為(wei)(wei)(wei)(wei)零(ling)，經(jing)(jing)(jing)(jing)(jing)R48使(shi)(shi)339的(de)(de)(de)(de)(de){9}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)亦(yi)(yi)為(wei)(wei)(wei)(wei)零(ling)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，故(gu)339的(de)(de)(de)(de)(de)C比(bi)(bi)較(jiao)(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)輸(shu)出(chu)(chu)(chu)(chu)(chu)端(duan)(duan)(duan)(duan)(duan){14}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)為(wei)(wei)(wei)(wei)零(ling)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)。另外，339的(de)(de)(de)(de)(de){1}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)信(xin)號(hao)(hao)(hao)(hao)(hao)(hao)因D34的(de)(de)(de)(de)(de)鉗位作(zuo)用，也(ye)使(shi)(shi){14}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)為(wei)(wei)(wei)(wei)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，經(jing)(jing)(jing)(jing)(jing)R50和(he)R63使(shi)(shi){11}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)亦(yi)(yi)為(wei)(wei)(wei)(wei)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)。因此(ci)(ci)(ci)(ci)D比(bi)(bi)較(jiao)(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)輸(shu)出(chu)(chu)(chu)(chu)(chu)端(duan)(duan)(duan)(duan)(duan){13}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)為(wei)(wei)(wei)(wei)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，也(ye)就是PW－OK信(xin)號(hao)(hao)(hao)(hao)(hao)(hao)為(wei)(wei)(wei)(wei)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，主機(ji)(ji)不會工(gong)作(zuo)。開啟主機(ji)(ji)時(shi)，通(tong)過人(ren)工(gong)或遙控操作(zuo)閉(bi)合了與(yu)PS－ON相(xiang)關的(de)(de)(de)(de)(de)開關，PS－ON呈(cheng)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，經(jing)(jing)(jing)(jing)(jing)R37使(shi)(shi)339的(de)(de)(de)(de)(de)反相(xiang)端(duan)(duan)(duan)(duan)(duan){6}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)為(wei)(wei)(wei)(wei)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，B比(bi)(bi)較(jiao)(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi){1}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)出(chu)(chu)(chu)(chu)(chu)高(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，D35、D36反偏截止(zhi)，A比(bi)(bi)較(jiao)(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)輸(shu)出(chu)(chu)(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)則由{5}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)與(yu){4}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)決(jue)定(ding)。正(zheng)常工(gong)作(zuo)時(shi)，{5}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)低(di)(di)(di)于{4}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，{2}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)出(chu)(chu)(chu)(chu)(chu)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，經(jing)(jing)(jing)(jing)(jing)R41送到(dao)494的(de)(de)(de)(de)(de){4}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)，使(shi)(shi){4}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)變(bian)為(wei)(wei)(wei)(wei)低(di)(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，鋸(ju)齒(chi)波振蕩(dang)信(xin)號(hao)(hao)(hao)(hao)(hao)(hao)可以從(cong)(cong)死區(qu)時(shi)間比(bi)(bi)較(jiao)(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)a輸(shu)出(chu)(chu)(chu)(chu)(chu)脈(mo)(mo)沖信(xin)號(hao)(hao)(hao)(hao)(hao)(hao)，另一(yi)方面，振蕩(dang)信(xin)號(hao)(hao)(hao)(hao)(hao)(hao)送到(dao)了PWM比(bi)(bi)較(jiao)(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)b的(de)(de)(de)(de)(de)同相(xiang)輸(shu)入端(duan)(duan)(duan)(duan)(duan)，PWM比(bi)(bi)較(jiao)(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)輸(shu)出(chu)(chu)(chu)(chu)(chu)的(de)(de)(de)(de)(de)脈(mo)(mo)沖信(xin)號(hao)(hao)(hao)(hao)(hao)(hao)的(de)(de)(de)(de)(de)寬度，則是由494的(de)(de)(de)(de)(de){1}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)（也(ye)就是負(fu)載的(de)(de)(de)(de)(de)大(da)小）與(yu){16}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)來決(jue)定(ding)。PWM比(bi)(bi)較(jiao)(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)輸(shu)出(chu)(chu)(chu)(chu)(chu)的(de)(de)(de)(de)(de)脈(mo)(mo)沖信(xin)號(hao)(hao)(hao)(hao)(hao)(hao)，最后(hou)(hou)經(jing)(jing)(jing)(jing)(jing)緩沖放大(da)器(qi)(qi)(qi)(qi)放大(da)后(hou)(hou)，從(cong)(cong){8}、{11}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)出(chu)(chu)(chu)(chu)(chu)脈(mo)(mo)沖信(xin)號(hao)(hao)(hao)(hao)(hao)(hao)，ATX電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)向主機(ji)(ji)輸(shu)出(chu)(chu)(chu)(chu)(chu)±5V、±12V、＋3.3V電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)。此(ci)(ci)(ci)(ci)過程(cheng)因C35的(de)(de)(de)(de)(de)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)有數百毫(hao)秒(miao)的(de)(de)(de)(de)(de)延時(shi)，但對主機(ji)(ji)開機(ji)(ji)并無影(ying)響。494的(de)(de)(de)(de)(de){1}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)從(cong)(cong)＋5V、＋12V經(jing)(jing)(jing)(jing)(jing)取樣電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻R15、R16得到(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓，其(qi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)略高(gao)(gao)(gao)于{2}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，{3}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)出(chu)(chu)(chu)(chu)(chu)高(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，經(jing)(jing)(jing)(jing)(jing)R48使(shi)(shi)339的(de)(de)(de)(de)(de){9}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)得到(dao)高(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，其(qi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)高(gao)(gao)(gao)于{8}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，因而{14}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)出(chu)(chu)(chu)(chu)(chu)高(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，此(ci)(ci)(ci)(ci)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)經(jing)(jing)(jing)(jing)(jing)R50與(yu)基(ji)準＋5V電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)經(jing)(jing)(jing)(jing)(jing)R64共同對C39充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，經(jing)(jing)(jing)(jing)(jing)數百毫(hao)秒(miao)后(hou)(hou)，{11}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)升到(dao)高(gao)(gao)(gao)于{10}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)時(shi)，D比(bi)(bi)較(jiao)(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi){13}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)出(chu)(chu)(chu)(chu)(chu)高(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，此(ci)(ci)(ci)(ci)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)經(jing)(jing)(jing)(jing)(jing)R49反饋至{11}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)，維持(chi){11}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)處(chu)于高(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)狀態，故(gu){13}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)出(chu)(chu)(chu)(chu)(chu)穩定(ding)的(de)(de)(de)(de)(de)高(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping) PW－OK信(xin)號(hao)(hao)(hao)(hao)(hao)(hao)，主機(ji)(ji)檢測到(dao)此(ci)(ci)(ci)(ci)信(xin)號(hao)(hao)(hao)(hao)(hao)(hao)后(hou)(hou)即開始正(zheng)常工(gong)作(zuo)。

關機時，主機內(nei)開關(guan)(guan)使(shi)PS－ON呈(cheng)高電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)，此時339的(de)(de)(de)(de){6}腳(jiao)(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)高于(yu){7}腳(jiao)(jiao)(jiao)，{1}腳(jiao)(jiao)(jiao)輸(shu)出低(di)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)，因(yin)(yin)二極管(guan)D34的(de)(de)(de)(de)鉗位作用，{14}腳(jiao)(jiao)(jiao)呈(cheng)低(di)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)，C39對C比(bi)較(jiao)器(qi)及B比(bi)較(jiao)器(qi)放(fang)電(dian)(dian)(dian)(dian)(dian)，很快{11}腳(jiao)(jiao)(jiao)呈(cheng)低(di)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)，{13}腳(jiao)(jiao)(jiao)輸(shu)出低(di)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)，即PW－OK信號(hao)(hao)(hao)呈(cheng)低(di)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)。在339的(de)(de)(de)(de){1}腳(jiao)(jiao)(jiao)為低(di)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)時，經D36使(shi){4}臆腳(jiao)(jiao)(jiao)為低(di)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)，{2}腳(jiao)(jiao)(jiao)輸(shu)出高電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)，經R41傳送到494的(de)(de)(de)(de){4}腳(jiao)(jiao)(jiao)，但因(yin)(yin)C35電(dian)(dian)(dian)(dian)(dian)位不(bu)能(neng)突變，經數(shu)百毫秒的(de)(de)(de)(de)放(fang)電(dian)(dian)(dian)(dian)(dian)后方使(shi)494的(de)(de)(de)(de){4}腳(jiao)(jiao)(jiao)轉為高電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)，從(cong)而(er)封(feng)鎖(suo)正負脈沖的(de)(de)(de)(de)輸(shu)出 ，主機(ji)進入待機(ji)狀態。上述(shu)的(de)(de)(de)(de)過程中，關(guan)(guan)機(ji)時C39和C35都要放(fang)電(dian)(dian)(dian)(dian)(dian)，但因(yin)(yin)放(fang)電(dian)(dian)(dian)(dian)(dian)時間常數(shu)不(bu)同，C39放(fang)電(dian)(dian)(dian)(dian)(dian)較(jiao)快，故PW－OK信號(hao)(hao)(hao)先于(yu)各(ge)(ge)電(dian)(dian)(dian)(dian)(dian)源變成低(di)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)，滿足(zu)了(le)主機(ji)關(guan)(guan)機(ji)的(de)(de)(de)(de)需要。此外，關(guan)(guan)機(ji)時因(yin)(yin)各(ge)(ge)路輸(shu)出電(dian)(dian)(dian)(dian)(dian)源的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)解電(dian)(dian)(dian)(dian)(dian)容放(fang)電(dian)(dian)(dian)(dian)(dian)需要時間，也使(shi)PW－OK信號(hao)(hao)(hao)先于(yu)各(ge)(ge)電(dian)(dian)(dian)(dian)(dian)源回到低(di)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)。

二、 穩壓

494的(de){2}腳經R47與基準電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)＋5V相連(lian)，維持較好的(de)穩定電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，而(er){1}腳則與取樣電(dian)(dian)(dian)(dian)(dian)(dian)阻R15、R16與＋5V、＋12V相連(lian)接，正常的(de)情況(kuang)下，{1}腳電(dian)(dian)(dian)(dian)(dian)(dian)平(ping)與{2}腳電(dian)(dian)(dian)(dian)(dian)(dian)平(ping)相等(deng)或略高。當輸(shu)出(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)升高時（無(wu)論＋5V或＋12V），{1}腳電(dian)(dian)(dian)(dian)(dian)(dian)平(ping)高于(yu){2}腳電(dian)(dian)(dian)(dian)(dian)(dian)平(ping)，c比(bi)較器輸(shu)出(chu)(chu)(chu)誤差電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)與鋸齒波振(zhen)蕩脈沖在(zai)PWM比(bi)較器b進行比(bi)較使輸(shu)出(chu)(chu)(chu)脈沖寬度變(bian)窄，輸(shu)出(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)回落(luo)到(dao)標準值，反之則促使振(zhen)蕩脈沖寬度增(zeng)加，輸(shu)出(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)回升。由于(yu)494內的(de)放(fang)大器增(zeng)益很高，故(gu)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)(dian)(dian)源(yuan)輸(shu)出(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)偏(pian)(pian)高或偏(pian)(pian)低(di)的(de)維修方法。如果輸(shu)出(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)偏(pian)(pian)低(di)，可在(zai)494的(de){1}腳對地并聯電(dian)(dian)(dian)(dian)(dian)(dian)阻，或是(shi)把R47的(de)電(dian)(dian)(dian)(dian)(dian)(dian)阻增(zeng)大。要是(shi)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)輸(shu)出(chu)(chu)(chu)偏(pian)(pian)高，則可在(zai){2}腳對地并聯電(dian)(dian)(dian)(dian)(dian)(dian)阻，也可以用增(zeng)大R33或取下R69、R35來降低(di)輸(shu)出(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)。

三、 過流保護

過(guo)流保(bao)護(hu)的(de)(de)(de)(de)(de)(de)(de)原理是(shi)基于負載(zai)愈大(da)，Q3、Q4集電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)的(de)(de)(de)(de)(de)(de)(de)脈沖(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)也(ye)(ye)愈高(gao)(gao)，也(ye)(ye)即是(shi)R13（1．5kΩ）上的(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)也(ye)(ye)愈高(gao)(gao)，從(cong)這(zhe)里采(cai)樣經(jing)D14整流和C36濾波，再(zai)經(jing)R54、R55并(bing)聯(lian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻與R51、R56、R58等組成的(de)(de)(de)(de)(de)(de)(de)分壓(ya)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路送(song)到494的(de)(de)(de)(de)(de)(de)(de){16}腳(jiao)(jiao)(jiao)(jiao)。隨(sui)(sui)著負載(zai)的(de)(de)(de)(de)(de)(de)(de)加重，{16}腳(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)也(ye)(ye)隨(sui)(sui)之上升，當(dang)超過(guo){15}腳(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)時，誤(wu)(wu)差(cha)放大(da)器輸(shu)出(chu)的(de)(de)(de)(de)(de)(de)(de)誤(wu)(wu)差(cha)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)促使調制(zhi)脈沖(chong)的(de)(de)(de)(de)(de)(de)(de)寬度變(bian)窄從(cong)而使負載(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流減小。另外，從(cong)R56、R58并(bing)聯(lian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻獲得(de)的(de)(de)(de)(de)(de)(de)(de)分壓(ya)再(zai)經(jing)R52送(song)到339的(de)(de)(de)(de)(de)(de)(de){5}腳(jiao)(jiao)(jiao)(jiao)，當(dang){5}腳(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)超過(guo){4}腳(jiao)(jiao)(jiao)(jiao)時，{2}腳(jiao)(jiao)(jiao)(jiao)即輸(shu)出(chu)高(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)送(song)到494的(de)(de)(de)(de)(de)(de)(de){4}腳(jiao)(jiao)(jiao)(jiao)，494停止(zhi)輸(shu)出(chu)脈沖(chong)信號，終止(zhi)±5V、±12V、＋3．3V電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源的(de)(de)(de)(de)(de)(de)(de)輸(shu)出(chu)，達到過(guo)流及短路保(bao)護(hu)的(de)(de)(de)(de)(de)(de)(de)目的(de)(de)(de)(de)(de)(de)(de)。需(xu)要說(shuo)明的(de)(de)(de)(de)(de)(de)(de)是(shi)：494的(de)(de)(de)(de)(de)(de)(de){16}腳(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)的(de)(de)(de)(de)(de)(de)(de)高(gao)(gao)低只(zhi)(zhi)能(neng)改變(bian)輸(shu)出(chu)脈沖(chong)的(de)(de)(de)(de)(de)(de)(de)寬度，但不影響(xiang)494的(de)(de)(de)(de)(de)(de)(de){4}腳(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)狀(zhuang)態(tai)，而339的(de)(de)(de)(de)(de)(de)(de){5}腳(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)一旦(dan)超過(guo){4}腳(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)，339的(de)(de)(de)(de)(de)(de)(de){2}腳(jiao)(jiao)(jiao)(jiao)就(jiu)送(song)出(chu)高(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)去封(feng)鎖449的(de)(de)(de)(de)(de)(de)(de)脈沖(chong)輸(shu)出(chu)，終止(zhi)±5V、±12V、＋3．3V電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源的(de)(de)(de)(de)(de)(de)(de)輸(shu)出(chu)，同時{2}腳(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)(de)(de)(de)高(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)經(jing)R59和二極(ji)管D39反饋到{5}腳(jiao)(jiao)(jiao)(jiao)，維持{5}腳(jiao)(jiao)(jiao)(jiao)處于高(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)狀(zhuang)態(tai)，此時若(ruo)過(guo)載(zai)或(huo)短路狀(zhuang)態(tai)消失，494的(de)(de)(de)(de)(de)(de)(de){4}腳(jiao)(jiao)(jiao)(jiao)仍(reng)維持高(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)，±5V與±12V、＋3．3V電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源仍(reng)不能(neng)輸(shu)出(chu)，只(zhi)(zhi)有切(qie)斷交流市電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)(de)(de)(de)輸(shu)入(ru)，再(zai)重新接(jie)通(tong)交流電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，方可(ke)再(zai)次(ci)開機。

四、過壓保護

過電(dian)(dian)壓(ya)保(bao)護(hu)(hu)由R17和穩壓(ya)管(guan)Z02并聯電(dian)(dian)路從＋5V采樣，經D37送到339的(de)(de)(de){5}腳(jiao)(jiao)。若＋5V電(dian)(dian)源(yuan)由于某種原因升高(gao)，339的(de)(de)(de){5}腳(jiao)(jiao)電(dian)(dian)平(ping)也會隨之升高(gao)，當(dang)超過{4}腳(jiao)(jiao)電(dian)(dian)平(ping)時，{2}腳(jiao)(jiao)即送出(chu)(chu)(chu)高(gao)電(dian)(dian)平(ping)去494的(de)(de)(de){4}腳(jiao)(jiao)，封鎖±5V、±12V、＋3．3V電(dian)(dian)源(yuan)的(de)(de)(de)輸出(chu)(chu)(chu)，達到過電(dian)(dian)壓(ya)保(bao)護(hu)(hu)的(de)(de)(de)目的(de)(de)(de)。正(zheng)常工作時，R17上的(de)(de)(de)壓(ya)降不大，Z02截止送到{5}腳(jiao)(jiao)的(de)(de)(de)電(dian)(dian)壓(ya)較低(di)，若＋5V電(dian)(dian)源(yuan)的(de)(de)(de)電(dian)(dian)壓(ya)上升，使R17上的(de)(de)(de)壓(ya)降超過Z02的(de)(de)(de)穩壓(ya)值(zhi)，Z02導通，＋5V電(dian)(dian)源(yuan)上升后的(de)(de)(de)電(dian)(dian)壓(ya)值(zhi)全部(bu)加到339的(de)(de)(de){5}腳(jiao)(jiao)上，促(cu)使其(qi)快速封鎖494脈(mo)沖的(de)(de)(de)輸出(chu)(chu)(chu)，以(yi)保(bao)護(hu)(hu)電(dian)(dian)源(yuan)。

五、欠壓保護

欠壓保(bao)護(hu)從－5V的D32及(ji)(ji)－12V處的R14取樣(yang)，經R34和D37送到339的{5}腳(jiao)。若(ruo)因(yin)某(mou)種原(yuan)因(yin)使(shi)輸(shu)出(chu)電(dian)(dian)壓過低時，－12V及(ji)(ji) －5V電(dian)(dian)壓的負值也會隨之減小，也就是電(dian)(dian)壓值上升，經R34及(ji)(ji)D37送往339的{5}腳(jiao)使(shi)電(dian)(dian)平上升，339的{2}腳(jiao)送出(chu)高(gao)電(dian)(dian)平到494的{4}腳(jiao)，從而封(feng)鎖(suo) 449脈沖的輸(shu)出(chu)，實現欠壓保(bao)護(hu)。二極管(guan)D32在導(dao)通時，其(qi)電(dian)(dian)壓降與(yu)通過的電(dian)(dian)流基本無關，保(bao)持在0．6V～0．7V，于是－5V電(dian)(dian)壓的減少量會全部傳送到D32的負端(duan)，提高(gao)了欠壓保(bao)護(hu)的靈敏度(du)。