利盈娱乐(中国)创新平台有限公司

一、开关电源的电路组成

开(kai)关电(dian)(dian)源(yuan)的(de)主要电(dian)(dian)路(lu)(lu)(lu)是(shi)由输(shu)入电(dian)(dian)磁干扰滤波(bo)器（EMI）、整(zheng)(zheng)流(liu)滤波(bo)电(dian)(dian)路(lu)(lu)(lu)、功率变(bian)换(huan)电(dian)(dian)路(lu)(lu)(lu)、PWM控制(zhi)器电(dian)(dian)路(lu)(lu)(lu)、输(shu)出(chu)整(zheng)(zheng)流(liu)滤波(bo)电(dian)(dian)路(lu)(lu)(lu)组(zu)成。辅助电(dian)(dian)路(lu)(lu)(lu)有输(shu)入过(guo)欠压保护(hu)电(dian)(dian)路(lu)(lu)(lu)、输(shu)出(chu)过(guo)欠压保护(hu)电(dian)(dian)路(lu)(lu)(lu)、输(shu)出(chu)过(guo)流(liu)保护(hu)电(dian)(dian)路(lu)(lu)(lu)、输(shu)出(chu)短路(lu)(lu)(lu)保护(hu)电(dian)(dian)路(lu)(lu)(lu)等。

开关电源的(de)电路组(zu)成方框图如下：

二、输入电路的原理及常见电路

1、AC输入整流滤波电路原理：

①、防雷(lei)电(dian)(dian)(dian)(dian)(dian)(dian)路：当有雷(lei)击，产生高压(ya)(ya)经(jing)电(dian)(dian)(dian)(dian)(dian)(dian)网(wang)导入电(dian)(dian)(dian)(dian)(dian)(dian)源时(shi)，由MOV1、MOV2、MOV3：F1、F2、F3、FDG1组成的电(dian)(dian)(dian)(dian)(dian)(dian)路进行保护(hu)。当加在(zai)压(ya)(ya)敏(min)电(dian)(dian)(dian)(dian)(dian)(dian)阻两(liang)端的电(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)超过其(qi)工作电(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)时(shi)，其(qi)阻值降(jiang)低(di)，使高压(ya)(ya)能量消耗在(zai)压(ya)(ya)敏(min)电(dian)(dian)(dian)(dian)(dian)(dian)阻上(shang)，若电(dian)(dian)(dian)(dian)(dian)(dian)流过大，F1、F2、F3会烧毁保护(hu)后级电(dian)(dian)(dian)(dian)(dian)(dian)路。

②、输入滤(lv)波(bo)电(dian)(dian)(dian)(dian)路：C1、L1、C2、C3组(zu)成的(de)双(shuang)π型滤(lv)波(bo)网(wang)(wang)络(luo)主(zhu)要(yao)是(shi)对(dui)(dui)输入电(dian)(dian)(dian)(dian)源的(de)电(dian)(dian)(dian)(dian)磁(ci)噪声及杂波(bo)信(xin)号进(jin)行抑制，防(fang)止(zhi)对(dui)(dui)电(dian)(dian)(dian)(dian)源干扰，同时(shi)也防(fang)止(zhi)电(dian)(dian)(dian)(dian)源本身(shen)产生(sheng)的(de)高频杂波(bo)对(dui)(dui)电(dian)(dian)(dian)(dian)网(wang)(wang)干扰。当(dang)电(dian)(dian)(dian)(dian)源开(kai)启瞬间，要(yao)对(dui)(dui)C5充电(dian)(dian)(dian)(dian)，由于(yu)瞬间电(dian)(dian)(dian)(dian)流大，加(jia)RT1（热敏(min)电(dian)(dian)(dian)(dian)阻）就(jiu)能(neng)(neng)有效(xiao)的(de)防(fang)止(zhi)浪涌电(dian)(dian)(dian)(dian)流。因瞬时(shi)能(neng)(neng)量全消耗在RT1电(dian)(dian)(dian)(dian)阻上，一定时(shi)间后温(wen)度(du)升高后RT1阻值减(jian)小（RT1是(shi)负(fu)温(wen)系数元件(jian)），这时(shi)它消耗的(de)能(neng)(neng)量非常小，后级电(dian)(dian)(dian)(dian)路可正常工作。

③、整流滤波电路：交流电压经BRG1整流后，经C5滤波后得到较为纯净的(de)直(zhi)流电压。若C5容量变小(xiao)，输出的(de)交流纹波将增大(da)。

2、DC输入滤波电路原理：

①、输入滤波(bo)(bo)电(dian)(dian)路：C1、L1、C2组成的双π型滤波(bo)(bo)网络主要(yao)是对输入电(dian)(dian)源的电(dian)(dian)磁噪声及(ji)杂波(bo)(bo)信(xin)号(hao)进行抑制(zhi)，防止(zhi)对电(dian)(dian)源干扰，同时也防止(zhi)电(dian)(dian)源本身(shen)产生(sheng)的高频杂波(bo)(bo)对电(dian)(dian)网干扰。C3、C4为安规电(dian)(dian)容，L2、L3为差(cha)模电(dian)(dian)感。

②、R1、R2、R3、Z1、C6、Q1、Z2、R4、R5、Q2、RT1、C7组成抗(kang)浪涌电(dian)(dian)路。在起机的(de)瞬(shun)间(jian)(jian)，由于C6的(de)存在Q2不(bu)(bu)导通，电(dian)(dian)流经RT1构成回路。当C6上(shang)的(de)电(dian)(dian)压充至Z1的(de)稳压值时Q2导通。如(ru)果C8漏电(dian)(dian)或后级电(dian)(dian)路短(duan)路现象，在起机的(de)瞬(shun)间(jian)(jian)电(dian)(dian)流在RT1上(shang)产(chan)生的(de)压降(jiang)增大，Q1导通使Q2没有栅极(ji)电(dian)(dian)压不(bu)(bu)导通，RT1将会在很短(duan)的(de)时间(jian)(jian)烧毁，以保护(hu)后级电(dian)(dian)路。

三、功率变换电路

1、MOS管的工作原理：目前应用最广泛的绝缘栅场效应管是MOSFET（MOS管），是利用半导体表面的电声效应进行工作的。也称为表面场效应器件。由于它的栅极处于不导电状态，所以输入电阻可以大大提高，最高可达105欧姆，MOS管是利用栅源电压的大小，来改变半导体表面感生电荷的多少，从而控制漏极电流的大小。

2、常见的原理图：

3、工作原理：

R4、C3、R5、R6、C4、D1、D2组(zu)(zu)成缓冲器，和(he)(he)开(kai)关MOS管(guan)(guan)并接(jie)，使(shi)开(kai)关管(guan)(guan)电(dian)(dian)压(ya)(ya)应力减少，EMI减少，不发生二次击穿。在(zai)开(kai)关管(guan)(guan)Q1关断时(shi)，变(bian)压(ya)(ya)器的(de)(de)(de)(de)原(yuan)边(bian)线圈易产生尖峰(feng)电(dian)(dian)压(ya)(ya)和(he)(he)尖峰(feng)电(dian)(dian)流(liu)，这些元件组(zu)(zu)合(he)一(yi)起，能很好地吸(xi)收尖峰(feng)电(dian)(dian)压(ya)(ya)和(he)(he)电(dian)(dian)流(liu)。从(cong)R3测得的(de)(de)(de)(de)电(dian)(dian)流(liu)峰(feng)值(zhi)信号(hao)参与当(dang)前工(gong)作周波的(de)(de)(de)(de)占(zhan)空比控(kong)制，因此是当(dang)前工(gong)作周波的(de)(de)(de)(de)电(dian)(dian)流(liu)限制。当(dang)R5上的(de)(de)(de)(de)电(dian)(dian)压(ya)(ya)达(da)到1V时(shi)，UC3842停止工(gong)作，开(kai)关管(guan)(guan)Q1立即关断。R1和(he)(he)Q1中的(de)(de)(de)(de)结电(dian)(dian)容CGS、CGD一(yi)起组(zu)(zu)成RC网(wang)络(luo)，电(dian)(dian)容的(de)(de)(de)(de)充(chong)放电(dian)(dian)直(zhi)接(jie)影响着开(kai)关管(guan)(guan)的(de)(de)(de)(de)开(kai)关速度。R1过(guo)小，易引起振荡(dang)，电(dian)(dian)磁干扰(rao)也(ye)会(hui)(hui)很大；R1过(guo)大，会(hui)(hui)降低开(kai)关管(guan)(guan)的(de)(de)(de)(de)开(kai)关速度。Z1通常将MOS管(guan)(guan)的(de)(de)(de)(de)GS电(dian)(dian)压(ya)(ya)限制在(zai)18V以下，从(cong)而保(bao)护了(le)(le)MOS管(guan)(guan)。Q1的(de)(de)(de)(de)栅极受控(kong)电(dian)(dian)压(ya)(ya)为(wei)锯(ju)形(xing)波，当(dang)其(qi)占(zhan)空比越(yue)大时(shi)，Q1导通时(shi)间越(yue)长，变(bian)压(ya)(ya)器所储(chu)存(cun)的(de)(de)(de)(de)能量也(ye)就越(yue)多(duo)；当(dang)Q1截止时(shi)，变(bian)压(ya)(ya)器通过(guo)D1、D2、R5、R4、C3释放能量，同时(shi)也(ye)达(da)到了(le)(le)磁场复位的(de)(de)(de)(de)目的(de)(de)(de)(de)，为(wei)变(bian)压(ya)(ya)器的(de)(de)(de)(de)下一(yi)次存(cun)储(chu)、传递能量做(zuo)好了(le)(le)准备。IC根据输出(chu)电(dian)(dian)压(ya)(ya)和(he)(he)电(dian)(dian)流(liu)时(shi)刻(ke)调整(zheng)着⑥脚(jiao)锯(ju)形(xing)波占(zhan)空比的(de)(de)(de)(de)大小，从(cong)而稳定了(le)(le)整(zheng)机的(de)(de)(de)(de)输出(chu)电(dian)(dian)流(liu)和(he)(he)电(dian)(dian)压(ya)(ya)。C4和(he)(he)R6为(wei)尖峰(feng)电(dian)(dian)压(ya)(ya)吸(xi)收回路。

4、推挽式功率变换电路：

Q1和(he)Q2将轮流导(dao)通。

5、有驱动变压器的功率变换电路：

T2为驱动变压器，T1为开关(guan)变压器，TR1为电流环。

四、输出整流滤波电路

1、正激式整流电路：

T1为(wei)(wei)(wei)开(kai)关变压(ya)器，其初极(ji)和次极(ji)的(de)相位同相。D1为(wei)(wei)(wei)整流二极(ji)管，D2为(wei)(wei)(wei)续流二极(ji)管，R1、C1、R2、C2为(wei)(wei)(wei)削尖峰电路。L1为(wei)(wei)(wei)续流电感，C4、L2、C5组成π型滤波器。

2、反激式整流电路：

T1为开关变压器，其初极(ji)(ji)和次极(ji)(ji)的相位相反。D1为整流(liu)二(er)极(ji)(ji)管(guan)，R1、C1为削尖峰电路。L1为续流(liu)电感，R2为假负载，C4、L2、C5组成π型滤波(bo)器。

3、同步整流电路：

工作原理：当(dang)变压器(qi)次级(ji)上端为(wei)正(zheng)时，电流(liu)(liu)经C2、R5、R6、R7使(shi)Q2导通，电路构成回(hui)路，Q2为(wei)整流(liu)(liu)管。Q1栅极由于(yu)处(chu)于(yu)反偏而(er)截(jie)止(zhi)。当(dang)变压器(qi)次级(ji)下端为(wei)正(zheng)时，电流(liu)(liu)经C3、R4、R2使(shi)Q1导通，Q1为(wei)续流(liu)(liu)管。Q2栅极由于(yu)处(chu)于(yu)反偏而(er)截(jie)止(zhi)。L2为(wei)续流(liu)(liu)电感，C6、L1、C7组成π型滤波器(qi)。R1、C1、R9、C4为(wei)削尖峰电路。

五、稳(wen)压(ya)环路原理(li)

1、反馈电路原理图：

2、工作原理：

当(dang)输(shu)出(chu)(chu)U0升(sheng)高(gao)(gao)，经取样电(dian)阻(zu)R7、R8、R10、VR1分(fen)压后(hou)，U1③脚(jiao)(jiao)(jiao)电(dian)压升(sheng)高(gao)(gao)，当(dang)其超过(guo)U1②脚(jiao)(jiao)(jiao)基准电(dian)压后(hou)U1①脚(jiao)(jiao)(jiao)输(shu)出(chu)(chu)高(gao)(gao)电(dian)平，使Q1导(dao)通，光(guang)耦(ou)OT1发(fa)光(guang)二极(ji)管(guan)(guan)发(fa)光(guang)，光(guang)电(dian)三极(ji)管(guan)(guan)导(dao)通，UC3842①脚(jiao)(jiao)(jiao)电(dian)位相应变低(di)，从而(er)(er)改(gai)(gai)变U1⑥脚(jiao)(jiao)(jiao)输(shu)出(chu)(chu)占(zhan)(zhan)空(kong)比减小(xiao)，U0降(jiang)低(di)。当(dang)输(shu)出(chu)(chu)U0降(jiang)低(di)时，U1③脚(jiao)(jiao)(jiao)电(dian)压降(jiang)低(di)，当(dang)其低(di)过(guo)U1②脚(jiao)(jiao)(jiao)基准电(dian)压后(hou)U1①脚(jiao)(jiao)(jiao)输(shu)出(chu)(chu)低(di)电(dian)平，Q1不(bu)(bu)导(dao)通，光(guang)耦(ou)OT1发(fa)光(guang)二极(ji)管(guan)(guan)不(bu)(bu)发(fa)光(guang)，光(guang)电(dian)三极(ji)管(guan)(guan)不(bu)(bu)导(dao)通，UC3842①脚(jiao)(jiao)(jiao)电(dian)位升(sheng)高(gao)(gao)，从而(er)(er)改(gai)(gai)变U1⑥脚(jiao)(jiao)(jiao)输(shu)出(chu)(chu)占(zhan)(zhan)空(kong)比增大，U0降(jiang)低(di)。周而(er)(er)复始(shi)，从而(er)(er)使输(shu)出(chu)(chu)电(dian)压保持稳定(ding)。调节VR1可改(gai)(gai)变输(shu)出(chu)(chu)电(dian)压值(zhi)。

反馈环路是影响开(kai)关电源稳定性的重要电路。如反馈电阻电容错、漏、虚焊(han)等，会产生(sheng)自激振(zhen)荡，故障(zhang)现象(xiang)为：波形异常，空、满载振(zhen)荡，输(shu)出(chu)电压(ya)不稳定等。

六、开关式稳压电源的基本工作原理

开关(guan)(guan)式(shi)稳压电源(yuan)(yuan)接控(kong)制(zhi)方式(shi)分为调宽式(shi)和调频式(shi)两种，在实(shi)际的应(ying)用中(zhong)，调宽式(shi)使(shi)(shi)用得(de)较多，在目(mu)前开发(fa)和使(shi)(shi)用的开关(guan)(guan)电源(yuan)(yuan)集成电路中(zhong)，绝(jue)大多数也为脉(mai)宽调制(zhi)型。因此(ci)下面就(jiu)主(zhu)要介绍调宽式(shi)开关(guan)(guan)稳压电源(yuan)(yuan)。

调宽式开关稳压电源的基本原理(li)可参见(jian)下图。

对(dui)于(yu)单极性矩(ju)(ju)形脉冲(chong)来说，其直(zhi)流平(ping)均(jun)电(dian)压Uo取(qu)决于(yu)矩(ju)(ju)形脉冲(chong)的宽度(du)，脉冲(chong)越(yue)宽，其直(zhi)流平(ping)均(jun)电(dian)压值(zhi)就越(yue)高(gao)。直(zhi)流平(ping)均(jun)电(dian)压Ｕ。可由公式计算(suan)，

即Uo=Um×T1/T

式中Um为矩(ju)形脉冲(chong)最(zui)大电压值；T为矩(ju)形脉冲(chong)周(zhou)期(qi)；T1为矩(ju)形脉冲(chong)宽度。

从上式可(ke)以(yi)(yi)看(kan)出，当Um 与T 不变(bian)时，直流平均电压(ya)Uo 将与脉冲(chong)宽度(du)T1 成正比。这样，只要我们设法(fa)使脉冲(chong)宽度(du)随稳压(ya)电源输出电压(ya)的(de)(de)(de)增高(gao)而变(bian)窄，就可(ke)以(yi)(yi)达到稳定电压(ya)的(de)(de)(de)目的(de)(de)(de)。

七、开关式稳压电源的原理电路

1、基本电路

图(tu)二 开(kai)关电源基本电路框(kuang)图(tu)

开关式稳压电(dian)源的(de)基(ji)本电(dian)路(lu)框图如图二所示。

交流(liu)(liu)电(dian)压(ya)(ya)经整流(liu)(liu)电(dian)路(lu)及滤波(bo)(bo)电(dian)路(lu)整流(liu)(liu)滤波(bo)(bo)后，变(bian)成(cheng)含有一(yi)定脉动成(cheng)份的(de)(de)直(zhi)流(liu)(liu)电(dian)压(ya)(ya)，该电(dian)压(ya)(ya)进人高频变(bian)换(huan)器被转换(huan)成(cheng)所需(xu)电(dian)压(ya)(ya)值的(de)(de)方波(bo)(bo)，最后再将(jiang)这个方波(bo)(bo)电(dian)压(ya)(ya)经整流(liu)(liu)滤波(bo)(bo)变(bian)为所需(xu)要的(de)(de)直(zhi)流(liu)(liu)电(dian)压(ya)(ya)。

控制(zhi)电(dian)(dian)(dian)路(lu)(lu)为一脉冲宽(kuan)度调(diao)制(zhi)器，它主要由(you)取(qu)样器、比较器、振(zhen)荡器、脉宽(kuan)调(diao)制(zhi)及基准电(dian)(dian)(dian)压等电(dian)(dian)(dian)路(lu)(lu)构成。这部(bu)分电(dian)(dian)(dian)路(lu)(lu)目前已集(ji)成化，制(zhi)成了各种(zhong)开关(guan)电(dian)(dian)(dian)源用(yong)集(ji)成电(dian)(dian)(dian)路(lu)(lu)。控制(zhi)电(dian)(dian)(dian)路(lu)(lu)用(yong)来调(diao)整高频开关(guan)元件的开关(guan)时(shi)间比例，以达到稳定输出电(dian)(dian)(dian)压的目的。

２、单端反激式开关电源

单端(duan)反(fan)激式开(kai)关(guan)电源(yuan)的(de)典型电路(lu)如图(tu)三所示(shi)。电路(lu)中(zhong)(zhong)所谓的(de)单端(duan)是(shi)指高频变换器(qi)的(de)磁芯(xin)仅工(gong)作在磁滞回线的(de)一侧。所谓的(de)反(fan)激，是(shi)指当(dang)开(kai)关(guan)管(guan)VT1 导通时，高频变压器(qi)Ｔ初级绕(rao)组的(de)感应电压为上正(zheng)下(xia)负，整流二极管(guan)VD1处于(yu)截(jie)止状态，在初级绕(rao)组中(zhong)(zhong)储(chu)存能量(liang)。当(dang)开(kai)关(guan)管(guan)VT1截(jie)止时，变压器(qi)Ｔ初级绕(rao)组中(zhong)(zhong)存储(chu)的(de)能量(liang)，通过次级绕(rao)组及(ji)VD1 整流和电容Ｃ滤波(bo)后向负载输出(chu)。

单端反激式开关电(dian)(dian)源是一(yi)种成本(ben)最低的(de)电(dian)(dian)源电(dian)(dian)路，输出功率(lv)为20－100Ｗ，可以同(tong)时输出不同(tong)的(de)电(dian)(dian)压，且有较好的(de)电(dian)(dian)压调整率(lv)。唯一(yi)的(de)缺点(dian)是输出的(de)纹波电(dian)(dian)压较大(da)，外特性差，适用于(yu)相(xiang)对固定的(de)负载。

单端反(fan)激(ji)式开关电(dian)源(yuan)使用的(de)(de)开关管VT1 承受的(de)(de)最(zui)大反(fan)向电(dian)压(ya)是电(dian)路工作(zuo)电(dian)压(ya)值的(de)(de)两倍，工作(zuo)频(pin)率在20－200kHz之间。

３、单端正激式开关电源

单(dan)端(duan)(duan)正激(ji)式(shi)开关(guan)(guan)电(dian)(dian)源(yuan)的(de)典型(xing)电(dian)(dian)路(lu)如图四所(suo)示。这(zhei)(zhei)种(zhong)电(dian)(dian)路(lu)在形(xing)(xing)式(shi)上与单(dan)端(duan)(duan)反激(ji)式(shi)电(dian)(dian)路(lu)相似，但工作情形(xing)(xing)不同。当开关(guan)(guan)管VT1导通(tong)时(shi)，VD2也导通(tong)，这(zhei)(zhei)时(shi)电(dian)(dian)网向(xiang)负载(zai)(zai)传送能(neng)量，滤波电(dian)(dian)感(gan)Ｌ储(chu)存(cun)能(neng)量；当开关(guan)(guan)管VT1截止时(shi)，电(dian)(dian)感(gan)Ｌ通(tong)过(guo)续流二极(ji)管VD3 继续向(xiang)负载(zai)(zai)释放能(neng)量。

在(zai)(zai)电(dian)(dian)(dian)路(lu)(lu)中(zhong)还设有钳位线圈与(yu)二极管VD2，它可以将(jiang)开(kai)关管VT1的(de)最高电(dian)(dian)(dian)压(ya)限(xian)制(zhi)在(zai)(zai)两倍电(dian)(dian)(dian)源电(dian)(dian)(dian)压(ya)之(zhi)间。为满足磁(ci)(ci)芯复位条件，即(ji)磁(ci)(ci)通(tong)建(jian)立和复位时(shi)间应相等，所(suo)以电(dian)(dian)(dian)路(lu)(lu)中(zhong)脉冲的(de)占空比不能(neng)大于(yu)５０％。由于(yu)这种(zhong)电(dian)(dian)(dian)路(lu)(lu)在(zai)(zai)开(kai)关管VT1导(dao)通(tong)时(shi)，通(tong)过变(bian)压(ya)器向(xiang)负载传(chuan)送能(neng)量(liang)，所(suo)以输(shu)出功(gong)率范围大，可输(shu)出50－200 Ｗ的(de)功(gong)率。电(dian)(dian)(dian)路(lu)(lu)使用的(de)变(bian)压(ya)器结构复杂，体(ti)积也较大，正(zheng)因(yin)为这个原因(yin)，这种(zhong)电(dian)(dian)(dian)路(lu)(lu)的(de)实际应用较少。

４、自激式开关稳压电源

自激式开(kai)关稳压(ya)电源(yuan)的(de)典型电路(lu)如图五所示。这是(shi)一(yi)种利(li)用(yong)间歇振荡电路(lu)组(zu)成的(de)开(kai)关电源(yuan)，也是(shi)目前(qian)广泛使用(yong)的(de)基本电源(yuan)之一(yi)。

当接入电(dian)(dian)(dian)(dian)源后在R1给(ji)开关管(guan)VT1提(ti)供(gong)启动(dong)电(dian)(dian)(dian)(dian)流，使(shi)(shi)(shi)(shi)VT1开始(shi)导通(tong)，其集电(dian)(dian)(dian)(dian)极(ji)(ji)电(dian)(dian)(dian)(dian)流Ic在L1中(zhong)(zhong)线性增长，在L2 中(zhong)(zhong)感(gan)应出使(shi)(shi)(shi)(shi)VT1 基(ji)极(ji)(ji)为正，发(fa)射极(ji)(ji)为负(fu)的(de)(de)正反(fan)馈(kui)电(dian)(dian)(dian)(dian)压(ya)，使(shi)(shi)(shi)(shi)VT1 很快饱和(he)。与(yu)此同时(shi)，感(gan)应电(dian)(dian)(dian)(dian)压(ya)给(ji)C1充电(dian)(dian)(dian)(dian)，随着C1充电(dian)(dian)(dian)(dian)电(dian)(dian)(dian)(dian)压(ya)的(de)(de)增高，VT1基(ji)极(ji)(ji)电(dian)(dian)(dian)(dian)位逐(zhu)渐(jian)变低，致使(shi)(shi)(shi)(shi)VT1退出饱和(he)区，Ic 开始(shi)减小，在L2 中(zhong)(zhong)感(gan)应出使(shi)(shi)(shi)(shi)VT1 基(ji)极(ji)(ji)为负(fu)、发(fa)射极(ji)(ji)为正的(de)(de)电(dian)(dian)(dian)(dian)压(ya)，使(shi)(shi)(shi)(shi)VT1 迅速截止(zhi)，这(zhei)时(shi)二极(ji)(ji)管(guan)VD1导通(tong)，高频变压(ya)器Ｔ初级绕(rao)组(zu)中(zhong)(zhong)的(de)(de)储能释(shi)放给(ji)负(fu)载。在VT1截止(zhi)时(shi)，L2中(zhong)(zhong)没有感(gan)应电(dian)(dian)(dian)(dian)压(ya)，直流供(gong)电(dian)(dian)(dian)(dian)输(shu)(shu)人电(dian)(dian)(dian)(dian)压(ya)又经R1给(ji)C1反(fan)向充电(dian)(dian)(dian)(dian)，逐(zhu)渐(jian)提(ti)高VT1基(ji)极(ji)(ji)电(dian)(dian)(dian)(dian)位，使(shi)(shi)(shi)(shi)其重新导通(tong)，再次翻(fan)转达到(dao)饱和(he)状态，电(dian)(dian)(dian)(dian)路就这(zhei)样重复振荡下去。这(zhei)里(li)就像单端反(fan)激式(shi)开关电(dian)(dian)(dian)(dian)源那(nei)样，由变压(ya)器Ｔ的(de)(de)次级绕(rao)组(zu)向负(fu)载输(shu)(shu)出所(suo)需要(yao)的(de)(de)电(dian)(dian)(dian)(dian)压(ya)。

自激式(shi)开关(guan)电(dian)源中(zhong)(zhong)的开关(guan)管起(qi)着开关(guan)及振荡的双重作(zuo)从(cong)，也省去了控制电(dian)路。电(dian)路中(zhong)(zhong)由于负载位于变压器(qi)的次(ci)级且工作(zuo)在(zai)反激状态，具有输(shu)人和输(shu)出相互隔离的优(you)点。这种电(dian)路不仅适(shi)用(yong)于大功率电(dian)源，亦适(shi)用(yong)于小功率电(dian)源。

５、推挽式开关电源

推(tui)挽式开关电(dian)源的(de)(de)典型电(dian)路如(ru)图(tu)六所示。它属于双端(duan)式变(bian)(bian)换(huan)电(dian)路，高频(pin)变(bian)(bian)压器的(de)(de)磁芯工(gong)作在(zai)磁滞(zhi)回线的(de)(de)两侧。电(dian)路使用(yong)两个开关管(guan)VT1和VT2，两个开关管(guan)在(zai)外激励方波(bo)信号的(de)(de)控制下交替(ti)的(de)(de)导通(tong)与截止，在(zai)变(bian)(bian)压器Ｔ次级统(tong)组得到方波(bo)电(dian)压，经(jing)整流(liu)滤(lv)波(bo)变(bian)(bian)为(wei)所需要的(de)(de)直(zhi)流(liu)电(dian)压。

这种电(dian)路(lu)的(de)优点是两个开(kai)关(guan)管容(rong)易驱动(dong)，主要(yao)缺点是开(kai)关(guan)管的(de)耐(nai)压(ya)要(yao)达到两倍电(dian)路(lu)峰(feng)值电(dian)压(ya)。电(dian)路(lu)的(de)输出功率较大，一般在(zai)100-500 Ｗ范围(wei)内。

６、降压式开关电源

降压式开关(guan)电(dian)(dian)源的(de)(de)典型电(dian)(dian)路(lu)如图七所示(shi)。当开关(guan)管VT1 导(dao)通时(shi)，二(er)极(ji)(ji)管VD1 截止，输(shu)人的(de)(de)整流(liu)电(dian)(dian)压经VT1和L向Ｃ充电(dian)(dian)，这一电(dian)(dian)流(liu)使电(dian)(dian)感Ｌ中的(de)(de)储能增加。当开关(guan)管VT1截止时(shi)，电(dian)(dian)感Ｌ感应出(chu)左负(fu)(fu)右(you)正的(de)(de)电(dian)(dian)压，经负(fu)(fu)载RL和续流(liu)二(er)极(ji)(ji)管VD1释放电(dian)(dian)感Ｌ中存储的(de)(de)能量，维持输(shu)出(chu)直流(liu)电(dian)(dian)压不(bu)变。电(dian)(dian)路(lu)输(shu)出(chu)直流(liu)电(dian)(dian)压的(de)(de)高低由加在VT1基极(ji)(ji)上的(de)(de)脉冲宽度确定。

这种电路使用(yong)元件少(shao)，它同下面介(jie)绍的另外两种电路一样(yang)，只需要利用(yong)电感、电容和二极管即可实(shi)现。

７、升压式开关电源

升(sheng)压(ya)(ya)式开关(guan)(guan)电(dian)(dian)源的(de)稳压(ya)(ya)电(dian)(dian)路如图八所示。当(dang)开关(guan)(guan)管 VT1 导通时，电(dian)(dian)感Ｌ储存(cun)能量。当(dang)开关(guan)(guan)管VT1 截止时，电(dian)(dian)感Ｌ感应出左负右正(zheng)的(de)电(dian)(dian)压(ya)(ya)，该(gai)电(dian)(dian)压(ya)(ya)叠加在(zai)输(shu)人电(dian)(dian)压(ya)(ya)上(shang)，经二极管VD1向负载(zai)供电(dian)(dian)，使输(shu)出电(dian)(dian)压(ya)(ya)大于输(shu)人电(dian)(dian)压(ya)(ya)，形成升(sheng)压(ya)(ya)式开关(guan)(guan)电(dian)(dian)源。

８、反转式开关电源

反转式开(kai)关电源(yuan)的典型电路如图(tu)九所示。这(zhei)种电路又称为升降压(ya)式开(kai)关电源(yuan)。无论开(kai)关管VT1之前的脉动直流电压(ya)高于或低于输出端(duan)的稳定电压(ya)，电路均能正常工作。

当开关管(guan) VT1 导通时(shi)，电(dian)(dian)感(gan)L 储存(cun)能量(liang)，二(er)极(ji)管(guan)VD1 截止，负(fu)(fu)载RL靠电(dian)(dian)容C上次的(de)充(chong)电(dian)(dian)电(dian)(dian)荷供(gong)电(dian)(dian)。当开关管(guan)VT1截止时(shi)，电(dian)(dian)感(gan)Ｌ中(zhong)的(de)电(dian)(dian)流继续(xu)流通，并感(gan)应出(chu)上负(fu)(fu)下(xia)正的(de)电(dian)(dian)压(ya)，经(jing)二(er)极(ji)管(guan)VD1向负(fu)(fu)载供(gong)电(dian)(dian)，同时(shi)给电(dian)(dian)容Ｃ充(chong)电(dian)(dian)。

以上(shang)介绍了(le)脉(mai)冲宽(kuan)度调制(zhi)式(shi)开关稳压电(dian)源的(de)基本工作(zuo)原理和各(ge)种电(dian)路(lu)(lu)类(lei)型，在实(shi)际应用中，会有各(ge)种各(ge)样(yang)的(de)实(shi)际控制(zhi)电(dian)路(lu)(lu)，但无论(lun)怎(zen)样(yang)，也(ye)都(dou)是在这些(xie)基础上(shang)发展出来的(de)。

八、短路保护电路

1、在输(shu)出(chu)端短路的情况下，PWM控制(zhi)电(dian)路能(neng)够把(ba)输(shu)出(chu)电(dian)流限制(zhi)在一个(ge)安全范围内，它可以用(yong)多(duo)种(zhong)方法来实现限流电(dian)路，当(dang)功(gong)率限流在短路时不(bu)起(qi)作(zuo)用(yong)时，只有另增设(she)一部分电(dian)路。

2、短(duan)路(lu)(lu)保(bao)护(hu)电路(lu)(lu)通常有两种(zhong)，下(xia)图是小功率短(duan)路(lu)(lu)保(bao)护(hu)电路(lu)(lu)，其(qi)原理简述如下(xia)：

当输(shu)出(chu)电(dian)路(lu)短路(lu)，输(shu)出(chu)电(dian)压消(xiao)失(shi)，光(guang)耦OT1不(bu)导通，UC3842①脚(jiao)(jiao)电(dian)压上升(sheng)至5V左右，R1与(yu)R2的分压超过TL431基准，使之(zhi)导通，UC3842⑦脚(jiao)(jiao)VCC电(dian)位(wei)被拉低，IC停止工作(zuo)(zuo)。UC3842停止工作(zuo)(zuo)后(hou)①脚(jiao)(jiao)电(dian)位(wei)消(xiao)失(shi)，TL431不(bu)导通UC3842⑦脚(jiao)(jiao)电(dian)位(wei)上升(sheng)，UC3842重新启动(dong)，周(zhou)而复(fu)始。当短路(lu)现象消(xiao)失(shi)后(hou)，电(dian)路(lu)可以自动(dong)恢复(fu)成(cheng)正常(chang)工作(zuo)(zuo)状态。

3、下图是中功率短路保护电路，其原(yuan)理简述如下：

当输出短(duan)路(lu)，UC3842①脚(jiao)(jiao)(jiao)电(dian)压(ya)上(shang)升,U1③脚(jiao)(jiao)(jiao)电(dian)位高于②脚(jiao)(jiao)(jiao)时(shi)(shi)，比(bi)较器翻转(zhuan)①脚(jiao)(jiao)(jiao)输出高电(dian)位，给C1充电(dian)，当C1两端电(dian)压(ya)超过⑤脚(jiao)(jiao)(jiao)基准电(dian)压(ya)时(shi)(shi)U1⑦脚(jiao)(jiao)(jiao)输出低(di)电(dian)位，UC3842①脚(jiao)(jiao)(jiao)低(di)于1V，UCC3842停止工作(zuo)(zuo)，输出电(dian)压(ya)为0V，周(zhou)而复始(shi)，当短(duan)路(lu)消失后电(dian)路(lu)正常(chang)工作(zuo)(zuo)。R2、C1是充放(fang)电(dian)时(shi)(shi)间常(chang)数，阻值不对时(shi)(shi)短(duan)路(lu)保护不起(qi)作(zuo)(zuo)用。

4、下图是常见的限流、短路(lu)保护电(dian)路(lu)。其(qi)工作原理(li)简述(shu)如下：

当输出(chu)电(dian)路短(duan)路或过流，变压器(qi)原边电(dian)流增(zeng)大，R3两端(duan)电(dian)压降增(zeng)大，③脚电(dian)压升高，UC3842⑥脚输出(chu)占空比(bi)逐(zhu)渐增(zeng)大，③脚电(dian)压超过1V时，UC3842关(guan)闭(bi)无输出(chu)。

5、下(xia)图是用电(dian)流(liu)互感器取样电(dian)流(liu)的保护(hu)电(dian)路，有着功耗小，但(dan)成本高(gao)和电(dian)路较为复杂，其工作原理简述如下(xia)：

输出电路短路或(huo)电流过(guo)大，TR1次(ci)级(ji)线(xian)圈(quan)感应的电压就越高(gao)，当UC3842③脚超(chao)过(guo)1伏，UC3842停(ting)止(zhi)工(gong)作(zuo)，周而复始，当短路或(huo)过(guo)载消(xiao)失，电路自行恢复。

九、输出端限流保护

上图是常(chang)见的输(shu)(shu)(shu)出端限流保护电(dian)(dian)(dian)路，其工作原理简(jian)述如上图：当(dang)输(shu)(shu)(shu)出电(dian)(dian)(dian)流过大时，RS（锰铜丝）两端电(dian)(dian)(dian)压(ya)(ya)上升，U1③脚电(dian)(dian)(dian)压(ya)(ya)高于②脚基准电(dian)(dian)(dian)压(ya)(ya)，U1①脚输(shu)(shu)(shu)出高电(dian)(dian)(dian)压(ya)(ya)，Q1导通，光(guang)(guang)耦发(fa)生光(guang)(guang)电(dian)(dian)(dian)效应，UC3842①脚电(dian)(dian)(dian)压(ya)(ya)降低，输(shu)(shu)(shu)出电(dian)(dian)(dian)压(ya)(ya)降低，从而达(da)到(dao)输(shu)(shu)(shu)出过载(zai)限流的目的。

十、输出过压保护电路的原理

输出过(guo)(guo)(guo)压(ya)保(bao)护电(dian)路的(de)作用是(shi)：当(dang)输出电(dian)压(ya)超过(guo)(guo)(guo)设计值(zhi)时(shi)，把输出电(dian)压(ya)限定在一安全值(zhi)的(de)范(fan)围内。当(dang)开关电(dian)源内部(bu)稳压(ya)环路出现故障或者(zhe)由于(yu)用户操作不当(dang)引起输出过(guo)(guo)(guo)压(ya)现象时(shi)，过(guo)(guo)(guo)压(ya)保(bao)护电(dian)路进行保(bao)护以防止损(sun)坏后级用电(dian)设备。应(ying)用最为普遍(bian)的(de)过(guo)(guo)(guo)压(ya)保(bao)护电(dian)路有如下几种：

1、可控硅触发保护电路：

如上图，当Uo1输出(chu)(chu)升高，稳压(ya)管（Z3）击穿导通，可(ke)控(kong)硅(gui)（SCR1）的控(kong)制端(duan)得到触(chu)发电(dian)(dian)压(ya)，因此可(ke)控(kong)硅(gui)导通。Uo2电(dian)(dian)压(ya)对地短路(lu)(lu)，过流保护(hu)电(dian)(dian)路(lu)(lu)或(huo)短路(lu)(lu)保护(hu)电(dian)(dian)路(lu)(lu)就会工作，停(ting)止(zhi)整个电(dian)(dian)源(yuan)电(dian)(dian)路(lu)(lu)的工作。当输出(chu)(chu)过压(ya)现象排除，可(ke)控(kong)硅(gui)的控(kong)制端(duan)触(chu)发电(dian)(dian)压(ya)通过R对地泄放(fang)，可(ke)控(kong)硅(gui)恢复断开(kai)状(zhuang)态。

2、光电耦合保护电路：

如上图，当Uo有过(guo)压(ya)现象时(shi)，稳压(ya)管(guan)(guan)击(ji)穿导(dao)通，经光(guang)耦(ou)（OT2）R6到地产生电(dian)流流过(guo)，光(guang)电(dian)耦(ou)合器的(de)(de)发(fa)光(guang)二极(ji)管(guan)(guan)发(fa)光(guang)，从而使(shi)光(guang)电(dian)耦(ou)合器的(de)(de)光(guang)敏三(san)极(ji)管(guan)(guan)导(dao)通。Q1基极(ji)得电(dian)导(dao)通，3842的(de)(de)③脚(jiao)电(dian)降低，使(shi)IC关闭，停止(zhi)整个电(dian)源的(de)(de)工作，Uo为零(ling)，周而复始，。

3、输出限压保护电路：

输出(chu)限压(ya)(ya)保护电(dian)路如下图，当输出(chu)电(dian)压(ya)(ya)升高(gao)，稳压(ya)(ya)管导通(tong)(tong)光(guang)耦导通(tong)(tong)，Q1基(ji)极(ji)有驱动电(dian)压(ya)(ya)而道通(tong)(tong)，UC3842③电(dian)压(ya)(ya)升高(gao)，输出(chu)降低，稳压(ya)(ya)管不导通(tong)(tong)，UC3842③电(dian)压(ya)(ya)降低，输出(chu)电(dian)压(ya)(ya)升高(gao)。周而复始，输出(chu)电(dian)压(ya)(ya)将稳定在一范围内（取决(jue)于稳压(ya)(ya)管的稳压(ya)(ya)值(zhi)）。

4、输出过压锁死电路：

图(tu)A的(de)工(gong)作原理(li)是(shi)(shi)，当(dang)输出电(dian)压(ya)(ya)(ya)Uo升(sheng)高(gao)(gao)(gao)，稳压(ya)(ya)(ya)管导通(tong)，光耦导通(tong)，Q2基(ji)极得电(dian)导通(tong)，由(you)于Q2的(de)导通(tong)Q1基(ji)极电(dian)压(ya)(ya)(ya)降(jiang)低也(ye)导通(tong)，Vcc电(dian)压(ya)(ya)(ya)经R1、Q1、R2使Q2始(shi)终(zhong)导通(tong)，UC3842③脚(jiao)始(shi)终(zhong)是(shi)(shi)高(gao)(gao)(gao)电(dian)平而(er)停止工(gong)作。在图(tu)B中，UO升(sheng)高(gao)(gao)(gao)U1③脚(jiao)电(dian)压(ya)(ya)(ya)升(sheng)高(gao)(gao)(gao)，①脚(jiao)输出高(gao)(gao)(gao)电(dian)平，由(you)于D1、R1的(de)存在，U1①脚(jiao)始(shi)终(zhong)输出高(gao)(gao)(gao)电(dian)平Q1始(shi)终(zhong)导通(tong)，UC3842①脚(jiao)始(shi)终(zhong)是(shi)(shi)低电(dian)平而(er)停止工(gong)作。正反(fan)馈

十一、功率因数校正电路（PFC）

1、原理示意图：

2、工作原理：

输入(ru)电压(ya)(ya)经L1、L2、L3等组成(cheng)的(de)EMI滤波(bo)(bo)器，BRG1整(zheng)流一路送(song)PFC电感(gan)，另一路经R1、R2分压(ya)(ya)后送(song)入(ru)PFC控(kong)(kong)制(zhi)(zhi)器作(zuo)为输入(ru)电压(ya)(ya)的(de)取样，用以调整(zheng)控(kong)(kong)制(zhi)(zhi)信号的(de)占(zhan)空(kong)比(bi)，即改变(bian)Q1的(de)导通和关断时(shi)(shi)间(jian)，稳定PFC输出(chu)电压(ya)(ya)。L4是(shi)PFC电感(gan)，它在Q1导通时(shi)(shi)储存(cun)能量，在Q1关断时(shi)(shi)施放能量。D1是(shi)启动二极(ji)管(guan)。D2是(shi)PFC整(zheng)流二极(ji)管(guan)，C6、C7滤波(bo)(bo)。PFC电压(ya)(ya)一路送(song)后级(ji)电路，另一路经R3、R4分压(ya)(ya)后送(song)入(ru)PFC控(kong)(kong)制(zhi)(zhi)器作(zuo)为PFC输出(chu)电压(ya)(ya)的(de)取样，用以调整(zheng)控(kong)(kong)制(zhi)(zhi)信号的(de)占(zhan)空(kong)比(bi)，稳定PFC输出(chu)电压(ya)(ya)。

十二、输入过欠压保护

1、原理图：

2、工作原理：

AC输(shu)入(ru)和DC输(shu)入(ru)的(de)(de)开关电(dian)源(yuan)的(de)(de)输(shu)入(ru)过欠压(ya)(ya)(ya)保护(hu)原(yuan)理大(da)致相(xiang)同。保护(hu)电(dian)路(lu)的(de)(de)取(qu)样电(dian)压(ya)(ya)(ya)均来自输(shu)入(ru)滤波后(hou)(hou)的(de)(de)电(dian)压(ya)(ya)(ya)。取(qu)样电(dian)压(ya)(ya)(ya)分(fen)为两路(lu)，一路(lu)经(jing)R1、R2、R3、R4分(fen)压(ya)(ya)(ya)后(hou)(hou)输(shu)入(ru)比(bi)较器(qi)3脚，如(ru)取(qu)样电(dian)压(ya)(ya)(ya)高于2脚基(ji)准电(dian)压(ya)(ya)(ya)，比(bi)较器(qi)1脚输(shu)出(chu)高电(dian)平去控(kong)制(zhi)(zhi)(zhi)主(zhu)控(kong)制(zhi)(zhi)(zhi)器(qi)使其关断(duan)(duan)，电(dian)源(yuan)无输(shu)出(chu)。另一路(lu)经(jing)R7、R8、R9、R10分(fen)压(ya)(ya)(ya)后(hou)(hou)输(shu)入(ru)比(bi)较器(qi)6脚，如(ru)取(qu)样电(dian)压(ya)(ya)(ya)低(di)于5脚基(ji)准电(dian)压(ya)(ya)(ya)，比(bi)较器(qi)7脚输(shu)出(chu)高电(dian)平去控(kong)制(zhi)(zhi)(zhi)主(zhu)控(kong)制(zhi)(zhi)(zhi)器(qi)使其关断(duan)(duan)，电(dian)源(yuan)无输(shu)出(chu)。

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