臺(tai)式機電源(yuan)電路圖原(yuan)理分析(xi) 臺(tai)式機電源(yuan)是(shi)如(ru)何實現多種保護功(gong)能的

ATX電(dian)源(yuan)的控制電(dian)路(lu)(lu)如上圖。控制電(dian)路(lu)(lu)采用TL494及LM339集(ji)成電(dian)路(lu)(lu)（以下簡(jian)稱494和339）。494是雙(shuang)排16腳(jiao)(jiao)集(ji)成電(dian)路(lu)(lu)，工(gong)作電(dian)壓7～40V。它(ta)含有(you)由{14}腳(jiao)(jiao)輸出的＋5V基準電(dian)源(yuan)，輸出電(dian)壓為(wei)＋5V（±0．05V），最大輸出電(dian)流(liu)250mA；一個頻率可(ke)調(diao)的鋸(ju)齒(chi)波產生電(dian)路(lu)(lu)，振蕩頻率由{5}腳(jiao)(jiao)外接電(dian)容及{6}腳(jiao)(jiao)外接電(dian)阻(zu)來決定。{13}腳(jiao)(jiao)為(wei)高電(dian)平時，由{8}腳(jiao)(jiao)及{11}腳(jiao)(jiao)輸出雙(shuang)路(lu)(lu)反相（即(ji)推挽(wan)工(gong)作方式）的脈(mo)寬(kuan)調(diao)制信號。

比(bi)較器是一(yi)種運算放大(da)器，符(fu)號用(yong)三角(jiao)形表示，它有(you)一(yi)個(ge)同相(xiang)輸入端“＋”；一(yi)個(ge)反相(xiang)輸入端“－”和(he)一(yi)個(ge)輸出端。

比(bi)較器(qi)(qi)(qi)(qi)同相(xiang)端(duan)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)若高于反(fan)(fan)相(xiang)端(duan)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)，則輸(shu)(shu)(shu)(shu)(shu)出(chu)端(duan)輸(shu)(shu)(shu)(shu)(shu)出(chu)高電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)；反(fan)(fan)之輸(shu)(shu)(shu)(shu)(shu)出(chu)低電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)。494內的(de)(de)(de)(de)(de)(de)(de)(de)比(bi)較放大(da)(da)器(qi)(qi)(qi)(qi)有(you)(you)(you)四(si)個(ge)(ge)(ge)，為(wei)敘述方便，在上(shang)(shang)圖中用小寫字(zi)母a、b、c、d來表示。其中a是(shi)死區(qu)時(shi)(shi)間(jian)比(bi)較器(qi)(qi)(qi)(qi)。因兩個(ge)(ge)(ge)作逆(ni)變(bian)工作的(de)(de)(de)(de)(de)(de)(de)(de)三極(ji)管串(chuan)聯后(hou)接到(dao)＋310V的(de)(de)(de)(de)(de)(de)(de)(de)直流電(dian)(dian)(dian)(dian)(dian)源(yuan)上(shang)(shang)，若兩個(ge)(ge)(ge)三極(ji)管同時(shi)(shi)導(dao)(dao)通(tong)(tong)，就(jiu)會形成對直流電(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)(de)(de)(de)(de)短(duan)(duan)路(lu)。兩個(ge)(ge)(ge)三極(ji)管同時(shi)(shi)導(dao)(dao)通(tong)(tong)可(ke)能發(fa)生(sheng)在一(yi)(yi)個(ge)(ge)(ge)管子從截(jie)止(zhi)轉(zhuan)為(wei)導(dao)(dao)通(tong)(tong)，而另一(yi)(yi)個(ge)(ge)(ge)管子由導(dao)(dao)通(tong)(tong)轉(zhuan)為(wei)截(jie)止(zhi)的(de)(de)(de)(de)(de)(de)(de)(de)時(shi)(shi)候。因為(wei)管子在轉(zhuan)換時(shi)(shi)有(you)(you)(you)時(shi)(shi)間(jian)的(de)(de)(de)(de)(de)(de)(de)(de)延(yan)遲，截(jie)止(zhi)的(de)(de)(de)(de)(de)(de)(de)(de)管子已經轉(zhuan)為(wei)導(dao)(dao)通(tong)(tong)了(le)(le)，但導(dao)(dao)通(tong)(tong)的(de)(de)(de)(de)(de)(de)(de)(de)管子尚未完全轉(zhuan)為(wei)截(jie)止(zhi)，于是(shi)兩個(ge)(ge)(ge)管子都呈導(dao)(dao)通(tong)(tong)狀態而形成對直流電(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)(de)(de)(de)(de)短(duan)(duan)路(lu)。為(wei)防(fang)止(zhi)這(zhe)樣(yang)的(de)(de)(de)(de)(de)(de)(de)(de)事情發(fa)生(sheng)，494設置了(le)(le)死區(qu)時(shi)(shi)間(jian)比(bi)較器(qi)(qi)(qi)(qi)a。從圖中可(ke)以看出(chu)，在比(bi)較器(qi)(qi)(qi)(qi)a的(de)(de)(de)(de)(de)(de)(de)(de)反(fan)(fan)相(xiang)輸(shu)(shu)(shu)(shu)(shu)入(ru)(ru)(ru)端(duan)串(chuan)聯了(le)(le)一(yi)(yi)個(ge)(ge)(ge)“電(dian)(dian)(dian)(dian)(dian)源(yuan)”，正極(ji)接反(fan)(fan)相(xiang)端(duan)，負極(ji)接494的(de)(de)(de)(de)(de)(de)(de)(de){4}腳(jiao)(jiao)(jiao)。A比(bi)較器(qi)(qi)(qi)(qi)同相(xiang)端(duan)輸(shu)(shu)(shu)(shu)(shu)入(ru)(ru)(ru)的(de)(de)(de)(de)(de)(de)(de)(de)鋸(ju)齒(chi)波信號，只(zhi)有(you)(you)(you)大(da)(da)于“電(dian)(dian)(dian)(dian)(dian)源(yuan)”電(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)(de)(de)(de)(de)(de)(de)(de)部(bu)分(fen)才有(you)(you)(you)輸(shu)(shu)(shu)(shu)(shu)出(chu)，在三極(ji)管導(dao)(dao)通(tong)(tong)變(bian)為(wei)截(jie)止(zhi)與(yu)截(jie)止(zhi)轉(zhuan)為(wei)導(dao)(dao)通(tong)(tong)期間(jian)，也就(jiu)是(shi)死區(qu)時(shi)(shi)間(jian)，494沒有(you)(you)(you)脈(mo)沖(chong)(chong)輸(shu)(shu)(shu)(shu)(shu)出(chu)，避免了(le)(le)對直流電(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)(de)(de)(de)(de)短(duan)(duan)路(lu)。死區(qu)時(shi)(shi)間(jian)還可(ke)由{4}腳(jiao)(jiao)(jiao)外(wai)接的(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)來控(kong)制，{4}腳(jiao)(jiao)(jiao)的(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)上(shang)(shang)升(sheng)，死區(qu)時(shi)(shi)間(jian)變(bian)寬，494輸(shu)(shu)(shu)(shu)(shu)出(chu)的(de)(de)(de)(de)(de)(de)(de)(de)脈(mo)沖(chong)(chong)就(jiu)變(bian)窄(zhai)了(le)(le)，若{4}腳(jiao)(jiao)(jiao)的(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)超過了(le)(le)鋸(ju)齒(chi)波的(de)(de)(de)(de)(de)(de)(de)(de)峰值電(dian)(dian)(dian)(dian)(dian)壓(ya)，494就(jiu)進入(ru)(ru)(ru)了(le)(le)保護狀態，{8}腳(jiao)(jiao)(jiao)和{11}腳(jiao)(jiao)(jiao)就(jiu)不輸(shu)(shu)(shu)(shu)(shu)出(chu)脈(mo)沖(chong)(chong)了(le)(le)。494內部(bu)還有(you)(you)(you)3個(ge)(ge)(ge)二輸(shu)(shu)(shu)(shu)(shu)入(ru)(ru)(ru)端(duan)與(yu)門(men)(men)（用1、2、3表示）、兩個(ge)(ge)(ge)二輸(shu)(shu)(shu)(shu)(shu)入(ru)(ru)(ru)端(duan)與(yu)非(fei)門(men)(men)、反(fan)(fan)相(xiang)器(qi)(qi)(qi)(qi)、T觸發(fa)器(qi)(qi)(qi)(qi)等電(dian)(dian)(dian)(dian)(dian)路(lu)。與(yu)門(men)(men)是(shi)這(zhe)樣(yang)一(yi)(yi)種電(dian)(dian)(dian)(dian)(dian)路(lu)，只(zhi)有(you)(you)(you)所(suo)有(you)(you)(you)的(de)(de)(de)(de)(de)(de)(de)(de)輸(shu)(shu)(shu)(shu)(shu)入(ru)(ru)(ru)端(duan)都是(shi)高電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)，輸(shu)(shu)(shu)(shu)(shu)出(chu)端(duan)才能輸(shu)(shu)(shu)(shu)(shu)出(chu)高電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)；若有(you)(you)(you)一(yi)(yi)個(ge)(ge)(ge)輸(shu)(shu)(shu)(shu)(shu)入(ru)(ru)(ru)端(duan)為(wei)低電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)，則輸(shu)(shu)(shu)(shu)(shu)出(chu)端(duan)輸(shu)(shu)(shu)(shu)(shu)出(chu)低電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)。反(fan)(fan)相(xiang)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)(de)(de)(de)作用是(shi)把輸(shu)(shu)(shu)(shu)(shu)入(ru)(ru)(ru)信號隔離放大(da)(da)后(hou)反(fan)(fan)相(xiang)輸(shu)(shu)(shu)(shu)(shu)出(chu)。與(yu)非(fei)門(men)(men)則相(xiang)當于一(yi)(yi)個(ge)(ge)(ge)與(yu)門(men)(men)和一(yi)(yi)個(ge)(ge)(ge)反(fan)(fan)相(xiang)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)(de)(de)(de)組合。T觸發(fa)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)(de)(de)(de)作用是(shi)：每(mei)輸(shu)(shu)(shu)(shu)(shu)入(ru)(ru)(ru)一(yi)(yi)個(ge)(ge)(ge)脈(mo)沖(chong)(chong)，輸(shu)(shu)(shu)(shu)(shu)出(chu)端(duan)的(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)就(jiu)變(bian)化一(yi)(yi)次。如(ru)輸(shu)(shu)(shu)(shu)(shu)出(chu)端(duan)Q為(wei)低電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)，輸(shu)(shu)(shu)(shu)(shu)入(ru)(ru)(ru)一(yi)(yi)個(ge)(ge)(ge)脈(mo)沖(chong)(chong)后(hou)，Q變(bian)為(wei)高電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)，再(zai)輸(shu)(shu)(shu)(shu)(shu)入(ru)(ru)(ru)一(yi)(yi)個(ge)(ge)(ge)脈(mo)沖(chong)(chong)，Q又回到(dao)低電(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)。

339是四比較(jiao)(jiao)器集(ji)成電(dian)(dian)(dian)(dian)(dian)路。 LM339集(ji)成塊內部裝有(you)四個(ge)(ge)獨(du)立的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)比較(jiao)(jiao)器，每個(ge)(ge)比較(jiao)(jiao)器有(you)兩個(ge)(ge)輸(shu)(shu)入(ru)端(duan)(duan)(duan)和一(yi)(yi)(yi)(yi)個(ge)(ge)輸(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)。兩個(ge)(ge)輸(shu)(shu)入(ru)端(duan)(duan)(duan)一(yi)(yi)(yi)(yi)個(ge)(ge)稱(cheng)為(wei)同相輸(shu)(shu)入(ru)端(duan)(duan)(duan)，用(yong)“+”表(biao)示，另一(yi)(yi)(yi)(yi)個(ge)(ge)稱(cheng)為(wei)反相輸(shu)(shu)入(ru)端(duan)(duan)(duan)，用(yong)“-”表(biao)示。用(yong)作比較(jiao)(jiao)兩個(ge)(ge)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)時(shi)(shi)，任意一(yi)(yi)(yi)(yi)個(ge)(ge)輸(shu)(shu)入(ru)端(duan)(duan)(duan)加(jia)一(yi)(yi)(yi)(yi)個(ge)(ge)固定電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)做參考(kao)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)（也(ye)稱(cheng)為(wei)門限電(dian)(dian)(dian)(dian)(dian)平，它可選擇LM339輸(shu)(shu)入(ru)共模范圍的(de)(de)(de)(de)任何(he)一(yi)(yi)(yi)(yi)點(dian)），另一(yi)(yi)(yi)(yi)端(duan)(duan)(duan)加(jia)一(yi)(yi)(yi)(yi)個(ge)(ge)待比較(jiao)(jiao)的(de)(de)(de)(de)信號(hao)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)。當(dang)“+”端(duan)(duan)(duan)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)高(gao)于(yu)“-”端(duan)(duan)(duan)時(shi)(shi)，輸(shu)(shu)出(chu)(chu)管(guan)截止(zhi)，相當(dang)于(yu)輸(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)開路。當(dang)“-”端(duan)(duan)(duan)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)高(gao)于(yu)“+”端(duan)(duan)(duan)時(shi)(shi)，輸(shu)(shu)出(chu)(chu)管(guan)飽和，相當(dang)于(yu)輸(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)接(jie)低電(dian)(dian)(dian)(dian)(dian)位。兩個(ge)(ge)輸(shu)(shu)入(ru)端(duan)(duan)(duan)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)差別大于(yu)10mV就能確保輸(shu)(shu)出(chu)(chu)能從一(yi)(yi)(yi)(yi)種狀態(tai)可靠(kao)地(di)轉換(huan)到另一(yi)(yi)(yi)(yi)種狀態(tai)， LM339的(de)(de)(de)(de)輸(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)相當(dang)于(yu)一(yi)(yi)(yi)(yi)只(zhi)不接(jie)集(ji)電(dian)(dian)(dian)(dian)(dian)極電(dian)(dian)(dian)(dian)(dian)阻的(de)(de)(de)(de)晶體(ti)三極管(guan)，在使用(yong)時(shi)(shi)輸(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)到正(zheng)電(dian)(dian)(dian)(dian)(dian)源一(yi)(yi)(yi)(yi)般須(xu)接(jie)一(yi)(yi)(yi)(yi)只(zhi)電(dian)(dian)(dian)(dian)(dian)阻（稱(cheng)為(wei)上(shang)拉(la)電(dian)(dian)(dian)(dian)(dian)阻，選3-15K）。選不同阻值的(de)(de)(de)(de)上(shang)拉(la)電(dian)(dian)(dian)(dian)(dian)阻會影響輸(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)高(gao)電(dian)(dian)(dian)(dian)(dian)位的(de)(de)(de)(de)值。因(yin)為(wei)當(dang)輸(shu)(shu)出(chu)(chu)晶體(ti)三極管(guan)截止(zhi)時(shi)(shi)，它的(de)(de)(de)(de)集(ji)電(dian)(dian)(dian)(dian)(dian)極電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)基本上(shang)取決于(yu)上(shang)拉(la)電(dian)(dian)(dian)(dian)(dian)阻與負載的(de)(de)(de)(de)值。

按管腳的順序把內部四(si)個(ge)比較器(qi)設為A、B 、C 、D 比較器(qi)。494和(he)339再配合(he)其他電路(lu)，共同完成ATX電源的穩壓，產生(sheng)PW－OK信號及各種保護功能(neng)。

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)接通市電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)后(hou)，輔(fu)助電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)立即(ji)(ji)工(gong)作。一方面(mian)輸(shu)(shu)(shu)(shu)(shu)(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)(shi)(shi)向494的(de)(de)(de)(de)(de){12}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)提供十幾伏到(dao)(dao)二十多(duo)伏的(de)(de)(de)(de)(de)直(zhi)流電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)。494從(cong){14}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)＋5V基準電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)，鋸齒波振(zhen)蕩(dang)器(qi)(qi)(qi)(qi)也開始起振(zhen)工(gong)作。若主(zhu)機(ji)未開機(ji)，PS－ON信(xin)號(hao)(hao)為高(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)，經(jing)(jing)R37使(shi)339的(de)(de)(de)(de)(de)B比(bi)(bi)(bi)較(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi){6}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)亦(yi)為高(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)，因電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)R37小于(yu)(yu)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)高(gao)(gao)(gao)于(yu)(yu){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)，B比(bi)(bi)(bi)較(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)輸(shu)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)端{1}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)低(di)(di)(di)(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)，經(jing)(jing)D36的(de)(de)(de)(de)(de)鉗位作用(yong)，A比(bi)(bi)(bi)較(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)反(fan)(fan)(fan)相(xiang)端{4}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)亦(yi)為低(di)(di)(di)(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)，其(qi)(qi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)低(di)(di)(di)(di)(di)(di)于(yu)(yu)同相(xiang)端{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)，輸(shu)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)端{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)，經(jing)(jing)R41使(shi)494的(de)(de)(de)(de)(de){4}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)為高(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)，故494內(nei)部(bu)的(de)(de)(de)(de)(de)死(si)區(qu)時(shi)(shi)(shi)間比(bi)(bi)(bi)較(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)a輸(shu)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)低(di)(di)(di)(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)，與門(men)1也因此(ci)(ci)(ci)(ci)(ci)輸(shu)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)低(di)(di)(di)(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)并進而使(shi)與門(men)2和與門(men)3輸(shu)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)低(di)(di)(di)(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)，封鎖了(le)振(zhen)蕩(dang)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)輸(shu)(shu)(shu)(shu)(shu)(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)(mo)沖(chong)輸(shu)(shu)(shu)(shu)(shu)(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)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)，主(zhu)機(ji)處于(yu)(yu)待(dai)機(ji)狀(zhuang)態。因＋5V、＋12V電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)輸(shu)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)為零，經(jing)(jing)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)R15、R16使(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)亦(yi)為零，494的(de)(de)(de)(de)(de)c比(bi)(bi)(bi)較(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)輸(shu)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)端{3}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)亦(yi)為零，經(jing)(jing)R48使(shi)339的(de)(de)(de)(de)(de){9}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)亦(yi)為零電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)，故339的(de)(de)(de)(de)(de)C比(bi)(bi)(bi)較(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)輸(shu)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)端{14}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)為零電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)。另(ling)外，339的(de)(de)(de)(de)(de){1}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)低(di)(di)(di)(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)信(xin)號(hao)(hao)因D34的(de)(de)(de)(de)(de)鉗位作用(yong)，也使(shi){14}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)為低(di)(di)(di)(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)，經(jing)(jing)R50和R63使(shi){11}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)亦(yi)為低(di)(di)(di)(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)。因此(ci)(ci)(ci)(ci)(ci)D比(bi)(bi)(bi)較(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)輸(shu)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)端{13}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)為低(di)(di)(di)(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)，也就是(shi)PW－OK信(xin)號(hao)(hao)為低(di)(di)(di)(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)，主(zhu)機(ji)不(bu)會工(gong)作。開啟主(zhu)機(ji)時(shi)(shi)(shi)，通過(guo)人工(gong)或(huo)遙控(kong)操作閉合了(le)與PS－ON相(xiang)關的(de)(de)(de)(de)(de)開關，PS－ON呈(cheng)低(di)(di)(di)(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)，經(jing)(jing)R37使(shi)339的(de)(de)(de)(de)(de)反(fan)(fan)(fan)相(xiang)端{6}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)為低(di)(di)(di)(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)，B比(bi)(bi)(bi)較(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi){1}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)(shu)(shu)(shu)(shu)(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)，D35、D36反(fan)(fan)(fan)偏截止，A比(bi)(bi)(bi)較(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)輸(shu)(shu)(shu)(shu)(shu)(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)則由{5}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)與{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)決定(ding)。正常(chang)(chang)工(gong)作時(shi)(shi)(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)低(di)(di)(di)(di)(di)(di)于(yu)(yu){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)，{2}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)低(di)(di)(di)(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)，經(jing)(jing)R41送(song)到(dao)(dao)494的(de)(de)(de)(de)(de){4}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)，使(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)變為低(di)(di)(di)(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)，鋸齒波振(zhen)蕩(dang)信(xin)號(hao)(hao)可(ke)以從(cong)死(si)區(qu)時(shi)(shi)(shi)間比(bi)(bi)(bi)較(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)a輸(shu)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)脈(mo)(mo)(mo)沖(chong)信(xin)號(hao)(hao)，另(ling)一方面(mian)，振(zhen)蕩(dang)信(xin)號(hao)(hao)送(song)到(dao)(dao)了(le)PWM比(bi)(bi)(bi)較(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)b的(de)(de)(de)(de)(de)同相(xiang)輸(shu)(shu)(shu)(shu)(shu)(shu)入(ru)端，PWM比(bi)(bi)(bi)較(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)輸(shu)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)的(de)(de)(de)(de)(de)脈(mo)(mo)(mo)沖(chong)信(xin)號(hao)(hao)的(de)(de)(de)(de)(de)寬度，則是(shi)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)（也就是(shi)負載的(de)(de)(de)(de)(de)大(da)(da)小）與{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)來決定(ding)。PWM比(bi)(bi)(bi)較(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi)輸(shu)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)的(de)(de)(de)(de)(de)脈(mo)(mo)(mo)沖(chong)信(xin)號(hao)(hao)，最后(hou)經(jing)(jing)緩沖(chong)放大(da)(da)器(qi)(qi)(qi)(qi)放大(da)(da)后(hou)，從(cong){8}、{11}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)(shu)(shu)(shu)(shu)(shu)出(chu)(chu)(chu)(chu)(chu)脈(mo)(mo)(mo)沖(chong)信(xin)號(hao)(hao)，ATX電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)向主(zhu)機(ji)輸(shu)(shu)(shu)(shu)(shu)(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)(ci)過(guo)程因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(bai)毫(hao)秒的(de)(de)(de)(de)(de)延時(shi)(shi)(shi)，但對主(zhu)機(ji)開機(ji)并無影響(xiang)。494的(de)(de)(de)(de)(de){1}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)從(cong)＋5V、＋12V經(jing)(jing)取樣(yang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)R15、R16得到(dao)(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓，其(qi)(qi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)略高(gao)(gao)(gao)于(yu)(yu){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)，{3}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)(shu)(shu)(shu)(shu)(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)，經(jing)(jing)R48使(shi)339的(de)(de)(de)(de)(de){9}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)得到(dao)(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)，其(qi)(qi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)(ping)(ping)(ping)(ping)(ping)(ping)(ping)高(gao)(gao)(gao)于(yu)(yu){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)，因而{14}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)(shu)(shu)(shu)(shu)(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)，此(ci)(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)經(jing)(jing)R50與基準＋5V電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)經(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)數百(bai)毫(hao)秒后(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)升到(dao)(dao)高(gao)(gao)(gao)于(yu)(yu){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)時(shi)(shi)(shi)，D比(bi)(bi)(bi)較(jiao)(jiao)(jiao)器(qi)(qi)(qi)(qi){13}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)(shu)(shu)(shu)(shu)(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)，此(ci)(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)經(jing)(jing)R49反(fan)(fan)(fan)饋至{11}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)，維(wei)持{11}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)處于(yu)(yu)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)狀(zhuang)態，故{13}腳(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)(jiao)輸(shu)(shu)(shu)(shu)(shu)(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) PW－OK信(xin)號(hao)(hao)，主(zhu)機(ji)檢測到(dao)(dao)此(ci)(ci)(ci)(ci)(ci)信(xin)號(hao)(hao)后(hou)即(ji)(ji)開始正常(chang)(chang)工(gong)作。

關機時，主機內開關使(shi)(shi)PS－ON呈高電(dian)平(ping)(ping)，此(ci)時(shi)339的(de){6}腳(jiao)(jiao)(jiao)電(dian)平(ping)(ping)高于(yu){7}腳(jiao)(jiao)(jiao)，{1}腳(jiao)(jiao)(jiao)輸出低(di)(di)(di)電(dian)平(ping)(ping)，因(yin)二極管(guan)D34的(de)鉗(qian)位作用，{14}腳(jiao)(jiao)(jiao)呈低(di)(di)(di)電(dian)平(ping)(ping)，C39對C比較器及(ji)B比較器放(fang)電(dian)，很(hen)快{11}腳(jiao)(jiao)(jiao)呈低(di)(di)(di)電(dian)平(ping)(ping)，{13}腳(jiao)(jiao)(jiao)輸出低(di)(di)(di)電(dian)平(ping)(ping)，即PW－OK信號呈低(di)(di)(di)電(dian)平(ping)(ping)。在339的(de){1}腳(jiao)(jiao)(jiao)為(wei)低(di)(di)(di)電(dian)平(ping)(ping)時(shi)，經D36使(shi)(shi){4}臆腳(jiao)(jiao)(jiao)為(wei)低(di)(di)(di)電(dian)平(ping)(ping)，{2}腳(jiao)(jiao)(jiao)輸出高電(dian)平(ping)(ping)，經R41傳(chuan)送到494的(de){4}腳(jiao)(jiao)(jiao)，但因(yin)C35電(dian)位不能突變(bian)，經數(shu)百毫秒的(de)放(fang)電(dian)后方使(shi)(shi)494的(de){4}腳(jiao)(jiao)(jiao)轉為(wei)高電(dian)平(ping)(ping)，從而封鎖(suo)正(zheng)負脈沖的(de)輸出 ，主(zhu)機進入(ru)待(dai)機狀態(tai)。上(shang)述的(de)過程中，關機時(shi)C39和(he)C35都要(yao)(yao)放(fang)電(dian)，但因(yin)放(fang)電(dian)時(shi)間常(chang)數(shu)不同，C39放(fang)電(dian)較快，故(gu)PW－OK信號先于(yu)各電(dian)源變(bian)成低(di)(di)(di)電(dian)平(ping)(ping)，滿足了主(zhu)機關機的(de)需(xu)要(yao)(yao)。此(ci)外，關機時(shi)因(yin)各路輸出電(dian)源的(de)電(dian)解(jie)電(dian)容放(fang)電(dian)需(xu)要(yao)(yao)時(shi)間，也使(shi)(shi)PW－OK信號先于(yu)各電(dian)源回到低(di)(di)(di)電(dian)平(ping)(ping)。

二、 穩壓

494的(de){2}腳(jiao)(jiao)(jiao)經R47與(yu)基準電(dian)(dian)壓(ya)＋5V相連，維(wei)持較(jiao)(jiao)好的(de)穩定電(dian)(dian)壓(ya)，而{1}腳(jiao)(jiao)(jiao)則與(yu)取樣電(dian)(dian)阻(zu)R15、R16與(yu)＋5V、＋12V相連接，正常的(de)情況下，{1}腳(jiao)(jiao)(jiao)電(dian)(dian)平(ping)與(yu){2}腳(jiao)(jiao)(jiao)電(dian)(dian)平(ping)相等或(huo)略高(gao)。當(dang)輸(shu)出(chu)電(dian)(dian)壓(ya)升(sheng)高(gao)時（無論(lun)＋5V或(huo)＋12V），{1}腳(jiao)(jiao)(jiao)電(dian)(dian)平(ping)高(gao)于{2}腳(jiao)(jiao)(jiao)電(dian)(dian)平(ping)，c比(bi)(bi)較(jiao)(jiao)器輸(shu)出(chu)誤差電(dian)(dian)壓(ya)與(yu)鋸齒(chi)波振(zhen)蕩(dang)脈沖(chong)(chong)在(zai)PWM比(bi)(bi)較(jiao)(jiao)器b進行(xing)比(bi)(bi)較(jiao)(jiao)使輸(shu)出(chu)脈沖(chong)(chong)寬度(du)變窄，輸(shu)出(chu)電(dian)(dian)壓(ya)回落到標準值，反之則促使振(zhen)蕩(dang)脈沖(chong)(chong)寬度(du)增(zeng)(zeng)加，輸(shu)出(chu)電(dian)(dian)壓(ya)回升(sheng)。由于494內的(de)放(fang)大(da)器增(zeng)(zeng)益(yi)很(hen)高(gao)，故穩壓(ya)精度(du)很(hen)好。從穩壓(ya)的(de)原(yuan)理，我們可(ke)以得到ATX電(dian)(dian)源輸(shu)出(chu)電(dian)(dian)壓(ya)偏高(gao)或(huo)偏低的(de)維(wei)修方法。如果輸(shu)出(chu)電(dian)(dian)壓(ya)偏低，可(ke)在(zai)494的(de){1}腳(jiao)(jiao)(jiao)對(dui)地并聯(lian)電(dian)(dian)阻(zu)，或(huo)是把R47的(de)電(dian)(dian)阻(zu)增(zeng)(zeng)大(da)。要(yao)是電(dian)(dian)源的(de)輸(shu)出(chu)偏高(gao)，則可(ke)在(zai){2}腳(jiao)(jiao)(jiao)對(dui)地并聯(lian)電(dian)(dian)阻(zu)，也(ye)可(ke)以用增(zeng)(zeng)大(da)R33或(huo)取下R69、R35來降低輸(shu)出(chu)電(dian)(dian)壓(ya)。

三、 過流保護

過(guo)(guo)(guo)(guo)流(liu)保護的(de)(de)(de)(de)原理是基于(yu)負載(zai)(zai)愈大，Q3、Q4集電(dian)(dian)(dian)極(ji)的(de)(de)(de)(de)脈(mo)(mo)沖(chong)電(dian)(dian)(dian)壓(ya)也(ye)(ye)愈高(gao)(gao)(gao)(gao)，也(ye)(ye)即是R13（1．5kΩ）上的(de)(de)(de)(de)電(dian)(dian)(dian)壓(ya)也(ye)(ye)愈高(gao)(gao)(gao)(gao)，從(cong)這里采(cai)樣經(jing)D14整流(liu)和C36濾波，再經(jing)R54、R55并聯(lian)電(dian)(dian)(dian)阻與(yu)R51、R56、R58等組(zu)成(cheng)的(de)(de)(de)(de)分壓(ya)電(dian)(dian)(dian)路送(song)(song)(song)到(dao)(dao)494的(de)(de)(de)(de){16}腳(jiao)(jiao)(jiao)(jiao)。隨著負載(zai)(zai)的(de)(de)(de)(de)加重，{16}腳(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)電(dian)(dian)(dian)平(ping)也(ye)(ye)隨之上升，當(dang)超過(guo)(guo)(guo)(guo){15}腳(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)電(dian)(dian)(dian)平(ping)時(shi)，誤(wu)差放(fang)大器輸(shu)出(chu)的(de)(de)(de)(de)誤(wu)差電(dian)(dian)(dian)壓(ya)促使(shi)調制(zhi)脈(mo)(mo)沖(chong)的(de)(de)(de)(de)寬度變窄從(cong)而使(shi)負載(zai)(zai)電(dian)(dian)(dian)流(liu)減小。另外，從(cong)R56、R58并聯(lian)電(dian)(dian)(dian)阻獲得的(de)(de)(de)(de)分壓(ya)再經(jing)R52送(song)(song)(song)到(dao)(dao)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)超過(guo)(guo)(guo)(guo){4}腳(jiao)(jiao)(jiao)(jiao)時(shi)，{2}腳(jiao)(jiao)(jiao)(jiao)即輸(shu)出(chu)高(gao)(gao)(gao)(gao)電(dian)(dian)(dian)平(ping)送(song)(song)(song)到(dao)(dao)494的(de)(de)(de)(de){4}腳(jiao)(jiao)(jiao)(jiao)，494停止(zhi)(zhi)輸(shu)出(chu)脈(mo)(mo)沖(chong)信(xin)號，終(zhong)止(zhi)(zhi)±5V、±12V、＋3．3V電(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)(de)(de)輸(shu)出(chu)，達到(dao)(dao)過(guo)(guo)(guo)(guo)流(liu)及短路保護的(de)(de)(de)(de)目的(de)(de)(de)(de)。需要說明的(de)(de)(de)(de)是：494的(de)(de)(de)(de){16}腳(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)平(ping)的(de)(de)(de)(de)高(gao)(gao)(gao)(gao)低只(zhi)能(neng)改(gai)變輸(shu)出(chu)脈(mo)(mo)沖(chong)的(de)(de)(de)(de)寬度，但(dan)不(bu)影(ying)響(xiang)494的(de)(de)(de)(de){4}腳(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)平(ping)狀態(tai)，而339的(de)(de)(de)(de){5}腳(jiao)(jiao)(jiao)(jiao)電(dian)(dian)(dian)平(ping)一旦超過(guo)(guo)(guo)(guo){4}腳(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)電(dian)(dian)(dian)平(ping)，339的(de)(de)(de)(de){2}腳(jiao)(jiao)(jiao)(jiao)就(jiu)送(song)(song)(song)出(chu)高(gao)(gao)(gao)(gao)電(dian)(dian)(dian)平(ping)去封鎖449的(de)(de)(de)(de)脈(mo)(mo)沖(chong)輸(shu)出(chu)，終(zhong)止(zhi)(zhi)±5V、±12V、＋3．3V電(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)(de)(de)輸(shu)出(chu)，同時(shi){2}腳(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)高(gao)(gao)(gao)(gao)電(dian)(dian)(dian)平(ping)經(jing)R59和二極(ji)管D39反(fan)饋(kui)到(dao)(dao){5}腳(jiao)(jiao)(jiao)(jiao)，維持(chi){5}腳(jiao)(jiao)(jiao)(jiao)處于(yu)高(gao)(gao)(gao)(gao)電(dian)(dian)(dian)平(ping)狀態(tai)，此時(shi)若過(guo)(guo)(guo)(guo)載(zai)(zai)或短路狀態(tai)消失(shi)，494的(de)(de)(de)(de){4}腳(jiao)(jiao)(jiao)(jiao)仍維持(chi)高(gao)(gao)(gao)(gao)電(dian)(dian)(dian)平(ping)，±5V與(yu)±12V、＋3．3V電(dian)(dian)(dian)源(yuan)(yuan)仍不(bu)能(neng)輸(shu)出(chu)，只(zhi)有切(qie)斷交流(liu)市電(dian)(dian)(dian)的(de)(de)(de)(de)輸(shu)入，再重新接通交流(liu)電(dian)(dian)(dian)，方(fang)可再次(ci)開機。

四、過壓保護

過(guo)電(dian)(dian)(dian)壓保護(hu)由(you)R17和穩壓管Z02并聯電(dian)(dian)(dian)路從＋5V采(cai)樣，經D37送到(dao)339的(de)(de)(de){5}腳。若(ruo)＋5V電(dian)(dian)(dian)源(yuan)由(you)于某種原因(yin)升(sheng)(sheng)高(gao)，339的(de)(de)(de){5}腳電(dian)(dian)(dian)平也會隨之升(sheng)(sheng)高(gao)，當超過(guo){4}腳電(dian)(dian)(dian)平時(shi)，{2}腳即送出(chu)(chu)高(gao)電(dian)(dian)(dian)平去494的(de)(de)(de){4}腳，封鎖±5V、±12V、＋3．3V電(dian)(dian)(dian)源(yuan)的(de)(de)(de)輸出(chu)(chu)，達到(dao)過(guo)電(dian)(dian)(dian)壓保護(hu)的(de)(de)(de)目的(de)(de)(de)。正(zheng)常工(gong)作時(shi)，R17上(shang)(shang)的(de)(de)(de)壓降(jiang)不大，Z02截止(zhi)送到(dao){5}腳的(de)(de)(de)電(dian)(dian)(dian)壓較低(di)，若(ruo)＋5V電(dian)(dian)(dian)源(yuan)的(de)(de)(de)電(dian)(dian)(dian)壓上(shang)(shang)升(sheng)(sheng)，使R17上(shang)(shang)的(de)(de)(de)壓降(jiang)超過(guo)Z02的(de)(de)(de)穩壓值，Z02導通，＋5V電(dian)(dian)(dian)源(yuan)上(shang)(shang)升(sheng)(sheng)后的(de)(de)(de)電(dian)(dian)(dian)壓值全部(bu)加到(dao)339的(de)(de)(de){5}腳上(shang)(shang)，促使其(qi)快速封鎖494脈(mo)沖(chong)的(de)(de)(de)輸出(chu)(chu)，以保護(hu)電(dian)(dian)(dian)源(yuan)。

五、欠壓保護

欠(qian)壓(ya)(ya)(ya)(ya)保(bao)(bao)護(hu)從(cong)－5V的(de)D32及(ji)－12V處的(de)R14取樣，經R34和D37送(song)到339的(de){5}腳(jiao)。若因(yin)某種原因(yin)使輸出(chu)電(dian)(dian)壓(ya)(ya)(ya)(ya)過(guo)低時，－12V及(ji) －5V電(dian)(dian)壓(ya)(ya)(ya)(ya)的(de)負值也會隨之減(jian)小(xiao)，也就是電(dian)(dian)壓(ya)(ya)(ya)(ya)值上(shang)升，經R34及(ji)D37送(song)往339的(de){5}腳(jiao)使電(dian)(dian)平上(shang)升，339的(de){2}腳(jiao)送(song)出(chu)高電(dian)(dian)平到494的(de){4}腳(jiao)，從(cong)而封鎖(suo) 449脈沖的(de)輸出(chu)，實現(xian)欠(qian)壓(ya)(ya)(ya)(ya)保(bao)(bao)護(hu)。二極管D32在導通(tong)(tong)時，其(qi)電(dian)(dian)壓(ya)(ya)(ya)(ya)降與通(tong)(tong)過(guo)的(de)電(dian)(dian)流基本無關，保(bao)(bao)持在0．6V～0．7V，于是－5V電(dian)(dian)壓(ya)(ya)(ya)(ya)的(de)減(jian)少量會全部傳送(song)到D32的(de)負端，提高了(le)欠(qian)壓(ya)(ya)(ya)(ya)保(bao)(bao)護(hu)的(de)靈敏度。