开关电源 电路

开关电源

开关模(mo)式电(dian)(dian)(dian)源(yuan)(yuan)(yuan)（Switch Mode Power Supply，简称SMPS），又称交(jiao)(jiao)换(huan)式电(dian)(dian)(dian)源(yuan)(yuan)(yuan)、开关变换(huan)器(qi)，是(shi)一种高频化电(dian)(dian)(dian)能转换(huan)装置(zhi)，是(shi)电(dian)(dian)(dian)源(yuan)(yuan)(yuan)供(gong)应器(qi)的(de)一种。其功能是(shi)将一个位准的(de)电(dian)(dian)(dian)压(ya)，透过不同形式的(de)架构(gou)转换(huan)为用(yong)户(hu)端(duan)所(suo)需(xu)求的(de)电(dian)(dian)(dian)压(ya)或电(dian)(dian)(dian)流(liu)。开关电(dian)(dian)(dian)源(yuan)(yuan)(yuan)的(de)输(shu)入(ru)多半(ban)是(shi)交(jiao)(jiao)流(liu)电(dian)(dian)(dian)源(yuan)(yuan)(yuan)（例如市电(dian)(dian)(dian)）或是(shi)直流(liu)电(dian)(dian)(dian)源(yuan)(yuan)(yuan)，而输(shu)出多半(ban)是(shi)需(xu)要直流(liu)电(dian)(dian)(dian)源(yuan)(yuan)(yuan)的(de)设备，例如个人电(dian)(dian)(dian)脑，而开关电(dian)(dian)(dian)源(yuan)(yuan)(yuan)就进行两者之间电(dian)(dian)(dian)压(ya)及电(dian)(dian)(dian)流(liu)的(de)转换(huan)。

开关电源用途

开(kai)关电(dian)源产品广泛(fan)应用(yong)于工(gong)(gong)业自动化控(kong)制(zhi)、军工(gong)(gong)设(she)(she)备(bei)、科研设(she)(she)备(bei)、LED照明、工(gong)(gong)控(kong)设(she)(she)备(bei)、通讯设(she)(she)备(bei)、电(dian)力(li)设(she)(she)备(bei)、仪(yi)器仪(yi)表(biao)、医(yi)疗设(she)(she)备(bei)、半(ban)导体制(zhi)冷制(zhi)热、空气净(jing)化器，电(dian)子(zi)冰箱，液晶显示器，LED灯(deng)具，通讯设(she)(she)备(bei)，视(shi)听(ting)产品，安防监控(kong)，LED灯(deng)带，电(dian)脑机箱，数码(ma)产品和仪(yi)器类(lei)等领域。

开关电源工作原理及各功能电路详解

一(yi)、 开关电(dian)(dian)(dian)源的(de)电(dian)(dian)(dian)路(lu)(lu)(lu)组成[/b]：开关电(dian)(dian)(dian)源的(de)主要电(dian)(dian)(dian)路(lu)(lu)(lu)是由输(shu)(shu)(shu)(shu)入电(dian)(dian)(dian)磁(ci)干扰滤波(bo)器(qi)（EMI）、整(zheng)流滤波(bo)电(dian)(dian)(dian)路(lu)(lu)(lu)、功率变(bian)换电(dian)(dian)(dian)路(lu)(lu)(lu)、PWM控制器(qi)电(dian)(dian)(dian)路(lu)(lu)(lu)、输(shu)(shu)(shu)(shu)出整(zheng)流滤波(bo)电(dian)(dian)(dian)路(lu)(lu)(lu)组成。辅助(zhu)电(dian)(dian)(dian)路(lu)(lu)(lu)有输(shu)(shu)(shu)(shu)入过欠(qian)压保护电(dian)(dian)(dian)路(lu)(lu)(lu)、输(shu)(shu)(shu)(shu)出过欠(qian)压保护电(dian)(dian)(dian)路(lu)(lu)(lu)、输(shu)(shu)(shu)(shu)出过流保护电(dian)(dian)(dian)路(lu)(lu)(lu)、输(shu)(shu)(shu)(shu)出短路(lu)(lu)(lu)保护电(dian)(dian)(dian)路(lu)(lu)(lu)等(deng)。

开关电(dian)源的电(dian)路组成方(fang)框图如(ru)下：

二、 输(shu)入电路的原理(li)及(ji)常见电路[/b]：：

1、AC输入整流滤波电路原理：

① 防雷(lei)电(dian)(dian)(dian)(dian)(dian)路：当有(you)雷(lei)击，产生高压(ya)经电(dian)(dian)(dian)(dian)(dian)网导入电(dian)(dian)(dian)(dian)(dian)源(yuan)时，由MOV1、MOV2、MOV3：F1、F2、F3、FDG1组成(cheng)的电(dian)(dian)(dian)(dian)(dian)路进行保(bao)护(hu)。当加在压(ya)敏电(dian)(dian)(dian)(dian)(dian)阻两端的电(dian)(dian)(dian)(dian)(dian)压(ya)超过(guo)其工作(zuo)电(dian)(dian)(dian)(dian)(dian)压(ya)时，其阻值降(jiang)低(di)，使高压(ya)能量消(xiao)耗在压(ya)敏电(dian)(dian)(dian)(dian)(dian)阻上，若电(dian)(dian)(dian)(dian)(dian)流过(guo)大，F1、F2、F3会(hui)烧(shao)毁保(bao)护(hu)后级电(dian)(dian)(dian)(dian)(dian)路。

② 输入滤(lv)波电(dian)(dian)路：C1、L1、C2、C3组(zu)成的(de)(de)双π型滤(lv)波网络主要(yao)是(shi)对输入电(dian)(dian)源(yuan)的(de)(de)电(dian)(dian)磁噪声及(ji)杂(za)波信(xin)号(hao)进行抑制，防止(zhi)对电(dian)(dian)源(yuan)干扰，同时也防止(zhi)电(dian)(dian)源(yuan)本身产生(sheng)的(de)(de)高频(pin)杂(za)波对电(dian)(dian)网干扰。当电(dian)(dian)源(yuan)开启瞬(shun)间(jian)(jian)，要(yao)对C5充(chong)电(dian)(dian)，由于瞬(shun)间(jian)(jian)电(dian)(dian)流大，加(jia)RT1（热敏电(dian)(dian)阻）就能有(you)效的(de)(de)防止(zhi)浪涌电(dian)(dian)流。因瞬(shun)时能量(liang)全消耗在(zai)RT1电(dian)(dian)阻上，一(yi)定时间(jian)(jian)后温度升高后RT1阻值(zhi)减小（RT1是(shi)负温系数(shu)元件(jian)），这时它消耗的(de)(de)能量(liang)非常小，后级(ji)电(dian)(dian)路可正常工(gong)作。

③ 整流滤波电路：交(jiao)流电压经BRG1整流后，经C5滤波后得(de)到较为(wei)纯净的直流电压。若C5容量变(bian)小，输出(chu)的交(jiao)流纹波将增大。

2、 DC输入滤(lv)波电路原理：

① 输入滤(lv)波(bo)电(dian)(dian)路：C1、L1、C2组成的双(shuang)π型滤(lv)波(bo)网(wang)络主(zhu)要是对输入电(dian)(dian)源的电(dian)(dian)磁噪声及杂波(bo)信号进行抑制，防(fang)止对电(dian)(dian)源干(gan)扰(rao)，同时也防(fang)止电(dian)(dian)源本身(shen)产生的高频杂波(bo)对电(dian)(dian)网(wang)干(gan)扰(rao)。C3、C4为安规电(dian)(dian)容，L2、L3为差模电(dian)(dian)感(gan)。

② R1、R2、R3、Z1、C6、Q1、Z2、R4、R5、Q2、RT1、C7组(zu)成(cheng)抗浪涌电(dian)路。在起(qi)机(ji)的(de)(de)瞬间(jian)，由于C6的(de)(de)存在Q2不导(dao)(dao)通，电(dian)流(liu)经RT1构成(cheng)回路。当(dang)C6上的(de)(de)电(dian)压(ya)充至Z1的(de)(de)稳压(ya)值时Q2导(dao)(dao)通。如果C8漏电(dian)或(huo)后(hou)(hou)级电(dian)路短路现象，在起(qi)机(ji)的(de)(de)瞬间(jian)电(dian)流(liu)在RT1上产生的(de)(de)压(ya)降增大(da)，Q1导(dao)(dao)通使Q2没有(you)栅(zha)极电(dian)压(ya)不导(dao)(dao)通，RT1将会在很短的(de)(de)时间(jian)烧毁，以(yi)保护(hu)后(hou)(hou)级电(dian)路。

三、 功率变(bian)换电(dian)路[/b]：

1、 MOS管的(de)(de)工作原理：目前(qian)应用最(zui)广(guang)泛的(de)(de)绝缘栅(zha)场(chang)效(xiao)应管是(shi)MOSFET（MOS管），是(shi)利用半(ban)导体表(biao)面的(de)(de)电(dian)(dian)(dian)声(sheng)效(xiao)应进行工作的(de)(de)。也(ye)称(cheng)为表(biao)面场(chang)效(xiao)应器件。由(you)于(yu)(yu)它的(de)(de)栅(zha)极(ji)处于(yu)(yu)不导电(dian)(dian)(dian)状态，所(suo)以输入电(dian)(dian)(dian)阻可以大(da)大(da)提高，最(zui)高可达105欧姆(mu)，MOS管是(shi)利用栅(zha)源电(dian)(dian)(dian)压的(de)(de)大(da)小，来改变半(ban)导体表(biao)面感生电(dian)(dian)(dian)荷的(de)(de)多少，从而控制漏极(ji)电(dian)(dian)(dian)流的(de)(de)大(da)小。

2、 常见的原理图(tu)：

3、工(gong)作(zuo)原理：

R4、C3、R5、R6、C4、D1、D2组(zu)成缓冲器，和(he)开(kai)(kai)关(guan)(guan)MOS管(guan)(guan)(guan)并接(jie)，使开(kai)(kai)关(guan)(guan)管(guan)(guan)(guan)电(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)应力减少，EMI减少，不发生二次击穿。在开(kai)(kai)关(guan)(guan)管(guan)(guan)(guan)Q1关(guan)(guan)断时，变压(ya)(ya)(ya)器的(de)(de)(de)原(yuan)边线(xian)圈易(yi)产生尖峰(feng)(feng)电(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)和(he)尖峰(feng)(feng)电(dian)(dian)(dian)(dian)(dian)流，这些(xie)元件(jian)组(zu)合一起(qi)，能(neng)很(hen)(hen)好(hao)地吸收尖峰(feng)(feng)电(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)和(he)电(dian)(dian)(dian)(dian)(dian)流。从R3测得的(de)(de)(de)电(dian)(dian)(dian)(dian)(dian)流峰(feng)(feng)值信号(hao)参与(yu)当(dang)前(qian)工作周波(bo)(bo)的(de)(de)(de)占(zhan)空(kong)比控制(zhi)，因此是当(dang)前(qian)工作周波(bo)(bo)的(de)(de)(de)电(dian)(dian)(dian)(dian)(dian)流限制(zhi)。当(dang)R5上的(de)(de)(de)电(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)达到1V时，UC3842停止工作，开(kai)(kai)关(guan)(guan)管(guan)(guan)(guan)Q1立即关(guan)(guan)断 。 R1和(he)Q1中的(de)(de)(de)结电(dian)(dian)(dian)(dian)(dian)容(rong)CGS、CGD一起(qi)组(zu)成RC网络，电(dian)(dian)(dian)(dian)(dian)容(rong)的(de)(de)(de)充放电(dian)(dian)(dian)(dian)(dian)直接(jie)影响着开(kai)(kai)关(guan)(guan)管(guan)(guan)(guan)的(de)(de)(de)开(kai)(kai)关(guan)(guan)速(su)度。R1过(guo)小，易(yi)引起(qi)振荡，电(dian)(dian)(dian)(dian)(dian)磁干扰也会(hui)很(hen)(hen)大；R1过(guo)大，会(hui)降(jiang)低(di)开(kai)(kai)关(guan)(guan)管(guan)(guan)(guan)的(de)(de)(de)开(kai)(kai)关(guan)(guan)速(su)度。Z1通常将MOS管(guan)(guan)(guan)的(de)(de)(de)GS电(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)限制(zhi)在18V以(yi)下(xia)，从而保护了MOS管(guan)(guan)(guan)。

Q1的(de)栅(zha)极受控电压(ya)为(wei)锯形(xing)波，当(dang)其占空比越大(da)时(shi)，Q1导(dao)通(tong)时(shi)间(jian)越长，变压(ya)器(qi)(qi)所(suo)储存的(de)能(neng)量也(ye)就越多；当(dang)Q1截止时(shi)，变压(ya)器(qi)(qi)通(tong)过(guo)D1、D2、R5、R4、C3释放能(neng)量，同时(shi)也(ye)达到了磁场(chang)复位的(de)目(mu)的(de)，为(wei)变压(ya)器(qi)(qi)的(de)下一次存储、传(chuan)递能(neng)量做好了准备。IC根据输(shu)出电压(ya)和(he)(he)电流时(shi)刻调整着⑥脚锯形(xing)波占空比的(de)大(da)小，从而稳定了整机的(de)输(shu)出电流和(he)(he)电压(ya)。 C4和(he)(he)R6为(wei)尖峰(feng)电压(ya)吸收回路。

4、推挽式功率变(bian)换电(dian)路： Q1和Q2将轮(lun)流导通。

5、有(you)驱动变(bian)压(ya)器的功率变(bian)换(huan)电路：T2为(wei)驱动变(bian)压(ya)器，T1为(wei)开关变(bian)压(ya)器，TR1为(wei)电流环(huan)。

四(si)、 输(shu)出整流滤波电(dian)路[/b]：：

1、 正激式整流电路：

T1为开关(guan)变压器，其初极(ji)和次极(ji)的(de)相位同相。D1为整流二(er)极(ji)管，D2为续流二(er)极(ji)管，R1、C1、R2、C2为削尖峰电(dian)(dian)路。L1为续流电(dian)(dian)感(gan)，C4、L2、C5组成π型滤(lv)波器。

2、 反(fan)激(ji)式整流电路：

T1为开(kai)关变压器，其初极和次极的相位同相。D1为整(zheng)流二极管(guan)，D2为续(xu)流二极管(guan)，R1、C1、R2、C2为削尖峰(feng)电(dian)(dian)路。L1为续(xu)流电(dian)(dian)感(gan)，C4、L2、C5组成π型滤波器。

3、 反激式(shi)整流电路：

4、工(gong)作原理：当变压器次级上端为(wei)(wei)正时，电(dian)(dian)流经(jing)C2、R5、R6、R7使Q2导通，电(dian)(dian)路构(gou)成(cheng)回路，Q2为(wei)(wei)整流管。Q1栅(zha)极由于(yu)处于(yu)反(fan)偏而(er)截止。当变压器次级下端为(wei)(wei)正时，电(dian)(dian)流经(jing)C3、R4、R2使Q1导通，Q1为(wei)(wei)续(xu)流管。Q2栅(zha)极由于(yu)处于(yu)反(fan)偏而(er)截止。L2为(wei)(wei)续(xu)流电(dian)(dian)感(gan)，C6、L1、C7组成(cheng)π型滤波器。R1、C1、R9、C4为(wei)(wei)削(xue)尖峰(feng)电(dian)(dian)路。

五、 稳压环路原理[/b]：

1、反馈电路原(yuan)理图(tu)：

2、工作原理： 当输出(chu)U0升(sheng)高(gao)，经取样电(dian)(dian)(dian)(dian)(dian)阻R7、R8、R10、VR1分压(ya)(ya)(ya)后(hou)，U1③脚(jiao)(jiao)(jiao)电(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)升(sheng)高(gao)，当其(qi)超过U1②脚(jiao)(jiao)(jiao)基准电(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)后(hou)U1①脚(jiao)(jiao)(jiao)输出(chu)高(gao)电(dian)(dian)(dian)(dian)(dian)平(ping)，使Q1导通(tong)，光(guang)耦OT1发(fa)光(guang)二极管发(fa)光(guang)，光(guang)电(dian)(dian)(dian)(dian)(dian)三极管导通(tong)，UC3842①脚(jiao)(jiao)(jiao)电(dian)(dian)(dian)(dian)(dian)位相应(ying)变低，从而(er)(er)改(gai)变U1⑥脚(jiao)(jiao)(jiao)输出(chu)占空比减(jian)小，U0降(jiang)低。 当输出(chu)U0降(jiang)低时(shi)，U1③脚(jiao)(jiao)(jiao)电(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)降(jiang)低，当其(qi)低过U1②脚(jiao)(jiao)(jiao)基准电(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)后(hou)U1①脚(jiao)(jiao)(jiao)输出(chu)低电(dian)(dian)(dian)(dian)(dian)平(ping)，Q1不导通(tong)，光(guang)耦OT1发(fa)光(guang)二极管不发(fa)光(guang)，光(guang)电(dian)(dian)(dian)(dian)(dian)三极管不导通(tong)，UC3842①脚(jiao)(jiao)(jiao)电(dian)(dian)(dian)(dian)(dian)位升(sheng)高(gao)，从而(er)(er)改(gai)变U1⑥脚(jiao)(jiao)(jiao)输出(chu)占空比增大，U0降(jiang)低。周而(er)(er)复始，从而(er)(er)使输出(chu)电(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)保持稳(wen)定(ding)。调节VR1可改(gai)变输出(chu)电(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)值。 反馈环路(lu)(lu)是影(ying)响开(kai)关电(dian)(dian)(dian)(dian)(dian)源(yuan)稳(wen)定(ding)性的重要电(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。如反馈电(dian)(dian)(dian)(dian)(dian)阻电(dian)(dian)(dian)(dian)(dian)容错(cuo)、漏、虚焊等，会产生(sheng)自激振(zhen)荡(dang)，故障(zhang)现(xian)象为：波形异常，空、满(man)载振(zhen)荡(dang)，输出(chu)电(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)不稳(wen)定(ding)等。

六、短(duan)路保护电路：

1、在(zai)输出端短(duan)路的情(qing)况下，PWM控(kong)制电路能够把输出电流(liu)限制在(zai)一个(ge)安全范(fan)围内，它(ta)可以用多种方法(fa)来实现限流(liu)电路，当功率(lv)限流(liu)在(zai)短(duan)路时不起作(zuo)用时，只有另(ling)增设一部分电路。

2、短路(lu)保(bao)护(hu)电路(lu)通常有(you)两种，下图(tu)是小功率(lv)短路(lu)保(bao)护(hu)电路(lu)，其原(yuan)理简(jian)述如下：

当(dang)输(shu)出电(dian)路(lu)短路(lu)，输(shu)出电(dian)压消(xiao)失(shi)(shi)，光耦OT1不导(dao)通，UC3842①脚电(dian)压上升(sheng)至5V左右(you)，R1与R2的(de)分压超过TL431基准，使之导(dao)通，UC3842⑦脚VCC电(dian)位(wei)被拉低(di)，IC停止(zhi)工(gong)(gong)作(zuo)。UC3842停止(zhi)工(gong)(gong)作(zuo)后①脚电(dian)位(wei)消(xiao)失(shi)(shi)，TL431不导(dao)通UC3842⑦脚电(dian)位(wei)上升(sheng)，UC3842重新启动，周(zhou)而复始。当(dang)短路(lu)现象消(xiao)失(shi)(shi)后，电(dian)路(lu)可以自动恢(hui)复成正常工(gong)(gong)作(zuo)状态。

3、下图是中功率短路保(bao)护电路，其原理简述如下：

当输(shu)出短(duan)路(lu)，UC3842①脚(jiao)(jiao)(jiao)电(dian)压(ya)上升,U1 ③脚(jiao)(jiao)(jiao) 电(dian)位高于②脚(jiao)(jiao)(jiao)时(shi)，比(bi)较器翻(fan)转①脚(jiao)(jiao)(jiao)输(shu)出高电(dian)位，给 C1充电(dian)，当C1两端(duan)电(dian)压(ya)超过⑤脚(jiao)(jiao)(jiao)基准电(dian)压(ya)时(shi) U1⑦脚(jiao)(jiao)(jiao)输(shu)出低电(dian)位，UC3842①脚(jiao)(jiao)(jiao)低于1V，UCC3842 停止工作，输(shu)出电(dian)压(ya)为(wei)0V，周(zhou)而(er)复始，当短(duan)路(lu) 消失后电(dian)路(lu)正(zheng)常工作。R2、C1是充放(fang)电(dian)时(shi)间(jian)常数(shu)， 阻值(zhi)不对时(shi)短(duan)路(lu)保护不起作用(yong)。

4、 下图是常见的(de)限流、短路保(bao)护电路。其工(gong)作原理(li)简(jian)述(shu)如(ru)下：

当输(shu)出(chu)电(dian)路(lu)短路(lu)或过流，变压器(qi)原边电(dian)流增(zeng)大，R3 两端电(dian)压降增(zeng)大，③脚电(dian)压升高，UC3842⑥脚输(shu)出(chu)占空 比逐渐增(zeng)大，③脚电(dian)压超过1V时，UC3842关闭(bi)无输(shu)出(chu)。

5、下图是用电(dian)流(liu)互(hu)感器取样电(dian)流(liu)的保护电(dian)路(lu)

有(you)着功(gong)耗小，但(dan)成本高(gao)和电(dian)路(lu)较为复(fu)杂，其工作(zuo)原 理(li)简述(shu)如下： 输出(chu)电(dian)路(lu)短(duan)路(lu)或(huo)电(dian)流过大，TR1次(ci)级(ji)线圈(quan)感 应的电(dian)压(ya)就越高(gao)，当UC3842③脚超(chao)过1伏，UC3842 停止(zhi)工作(zuo)，周而复(fu)始(shi)，当短(duan)路(lu)或(huo)过载消失，电(dian)路(lu)自行恢复(fu)。

七、输出端限流保护(hu)：

上(shang)(shang)图是常见的输出端(duan)限流保(bao)护电(dian)(dian)路，其工作原理简述如上(shang)(shang)图：当输出电(dian)(dian)流过大时，RS（锰铜丝）两端(duan)电(dian)(dian)压上(shang)(shang)升(sheng)，U1③脚(jiao)(jiao)电(dian)(dian)压高于②脚(jiao)(jiao)基准电(dian)(dian)压，U1①脚(jiao)(jiao)输出高电(dian)(dian)压，Q1导通，光(guang)耦发(fa)生光(guang)电(dian)(dian)效应，UC3842①脚(jiao)(jiao)电(dian)(dian)压降低，输出电(dian)(dian)压降低，从而达到输出过载(zai)限流的目的。

八、输出过压(ya)保护电路的(de)原理(li)

输(shu)出(chu)过(guo)压(ya)保(bao)护(hu)电路(lu)的作用(yong)是：当输(shu)出(chu)电压(ya)超过(guo)设(she)计值(zhi)时，把输(shu)出(chu)电压(ya)限定在(zai)一安全值(zhi)的范围内(nei)。当开关电源(yuan)内(nei)部稳压(ya)环路(lu)出(chu)现(xian)故障(zhang)或者由(you)于用(yong)户操作不当引起(qi)输(shu)出(chu)过(guo)压(ya)现(xian)象时，过(guo)压(ya)保(bao)护(hu)电路(lu)进行保(bao)护(hu)以防(fang)止(zhi)损坏后级(ji)用(yong)电设(she)备。

应用(yong)最为(wei)普遍的过压(ya)保护电路有如下(xia)几种(zhong)：

1、可控(kong)硅触发(fa)保(bao)护电路：

如上(shang)图，当(dang)Uo1输出升高，稳压管(guan)（Z3）击穿导通(tong)，可(ke)控(kong)硅（SCR1）的控(kong)制(zhi)端得到触发电(dian)(dian)压，因此可(ke)控(kong)硅导通(tong)。Uo2电(dian)(dian)压对地(di)短(duan)路，过(guo)流保(bao)护电(dian)(dian)路或短(duan)路保(bao)护电(dian)(dian)路就会(hui)工作(zuo)(zuo)，停止整个(ge)电(dian)(dian)源电(dian)(dian)路的工作(zuo)(zuo)。当(dang)输出过(guo)压现象排除(chu)，可(ke)控(kong)硅的控(kong)制(zhi)端触发电(dian)(dian)压通(tong)过(guo)R对地(di)泄放(fang)，可(ke)控(kong)硅恢复断开状态

2、光电(dian)耦合保护(hu)电(dian)路：

如上图，当Uo有过压(ya)现(xian)象时，稳压(ya)管击穿(chuan)导(dao)通，经光耦(ou)（OT2）R6到地(di)产(chan)生电(dian)流(liu)流(liu)过，光电(dian)耦(ou)合器(qi)的(de)发(fa)光二极管发(fa)光，从而使(shi)光电(dian)耦(ou)合器(qi)的(de)光敏三极管导(dao)通。Q1基极得电(dian)导(dao)通， 3842的(de)③脚电(dian)降低，使(shi)IC关闭，停止(zhi)整个(ge)电(dian)源的(de)工作，Uo为零，周而复(fu)始，。

3、输(shu)(shu)出(chu)限压(ya)(ya)保护(hu)电(dian)路： 输(shu)(shu)出(chu)限压(ya)(ya)保护(hu)电(dian)路如下(xia)图，当(dang)输(shu)(shu)出(chu)电(dian)压(ya)(ya)升(sheng)高(gao)，稳(wen)压(ya)(ya)管导(dao)通光耦导(dao)通，Q1基(ji)极有驱动(dong)电(dian)压(ya)(ya)而道通，UC3842③电(dian)压(ya)(ya)升(sheng)高(gao)，输(shu)(shu)出(chu)降低(di)，稳(wen)压(ya)(ya)管不导(dao)通，UC3842③电(dian)压(ya)(ya)降低(di)，输(shu)(shu)出(chu)电(dian)压(ya)(ya)升(sheng)高(gao)。周(zhou)而复始，输(shu)(shu)出(chu)电(dian)压(ya)(ya)将稳(wen)定在(zai)一范(fan)围内（取决于稳(wen)压(ya)(ya)管的稳(wen)压(ya)(ya)值）。

4、输出过(guo)压锁(suo)死电(dian)路：

5、工作原理(li)

输入电(dian)(dian)压(ya)(ya)经L1、L2、L3等组成的EMI滤波器(qi)，BRG1整流一(yi)路(lu)送(song)PFC电(dian)(dian)感，另(ling)一(yi)路(lu)经R1、R2分压(ya)(ya)后送(song)入PFC控(kong)制(zhi)器(qi)作为输入电(dian)(dian)压(ya)(ya)的取(qu)样，用(yong)以(yi)调整控(kong)制(zhi)信号(hao)(hao)的占空比(bi)，即改变(bian)Q1的导(dao)通(tong)和关(guan)(guan)断时间，稳(wen)(wen)定PFC输出(chu)电(dian)(dian)压(ya)(ya)。L4是PFC电(dian)(dian)感，它在(zai)Q1导(dao)通(tong)时储(chu)存能量(liang)，在(zai)Q1关(guan)(guan)断时施放(fang)能量(liang)。D1是启动二(er)极(ji)管。D2是PFC整流二(er)极(ji)管，C6、C7滤波。PFC电(dian)(dian)压(ya)(ya)一(yi)路(lu)送(song)后级(ji)电(dian)(dian)路(lu)，另(ling)一(yi)路(lu)经R3、R4分压(ya)(ya)后送(song)入PFC控(kong)制(zhi)器(qi)作为PFC输出(chu)电(dian)(dian)压(ya)(ya)的取(qu)样，用(yong)以(yi)调整控(kong)制(zhi)信号(hao)(hao)的占空比(bi)，稳(wen)(wen)定PFC输出(chu)电(dian)(dian)压(ya)(ya)。

十、输入过欠压保护：

1、 原理图(tu)：

2、 工(gong)作原理

AC输(shu)入(ru)(ru)和DC输(shu)入(ru)(ru)的开关(guan)电(dian)(dian)(dian)(dian)源(yuan)的输(shu)入(ru)(ru)过(guo)欠压(ya)保(bao)护(hu)原理(li)大致相同。保(bao)护(hu)电(dian)(dian)(dian)(dian)路(lu)的取(qu)样(yang)电(dian)(dian)(dian)(dian)压(ya)均来自输(shu)入(ru)(ru)滤波后的电(dian)(dian)(dian)(dian)压(ya)。 取(qu)样(yang)电(dian)(dian)(dian)(dian)压(ya)分(fen)为两路(lu)，一(yi)路(lu)经(jing)R1、R2、R3、R4分(fen)压(ya)后输(shu)入(ru)(ru)比(bi)较器(qi)(qi)(qi)3脚(jiao)，如取(qu)样(yang)电(dian)(dian)(dian)(dian)压(ya)高(gao)于2脚(jiao)基准(zhun)(zhun)电(dian)(dian)(dian)(dian)压(ya)，比(bi)较器(qi)(qi)(qi)1脚(jiao)输(shu)出(chu)高(gao)电(dian)(dian)(dian)(dian)平(ping)去(qu)控制主(zhu)控制器(qi)(qi)(qi)使(shi)其(qi)关(guan)断，电(dian)(dian)(dian)(dian)源(yuan)无输(shu)出(chu)。另一(yi)路(lu)经(jing)R7、R8、R9、R10分(fen)压(ya)后输(shu)入(ru)(ru)比(bi)较器(qi)(qi)(qi)6脚(jiao)，如取(qu)样(yang)电(dian)(dian)(dian)(dian)压(ya)低于5脚(jiao)基准(zhun)(zhun)电(dian)(dian)(dian)(dian)压(ya)，比(bi)较器(qi)(qi)(qi)7脚(jiao)输(shu)出(chu)高(gao)电(dian)(dian)(dian)(dian)平(ping)去(qu)控制主(zhu)控制器(qi)(qi)(qi)使(shi)其(qi)关(guan)断，电(dian)(dian)(dian)(dian)源(yuan)无输(shu)出(chu)。

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