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(guan)电(dian)(dian)(dian)(dian)源的主要(yao)电(dian)(dian)(dian)(dian)路(lu)是由输(shu)(shu)入(ru)电(dian)(dian)(dian)(dian)磁(ci)干扰滤(lv)波(bo)器（EMI）、整流滤(lv)波(bo)电(dian)(dian)(dian)(dian)路(lu)、功率变换电(dian)(dian)(dian)(dian)路(lu)、PWM控制器电(dian)(dian)(dian)(dian)路(lu)、输(shu)(shu)出整流滤(lv)波(bo)电(dian)(dian)(dian)(dian)路(lu)组成。辅助电(dian)(dian)(dian)(dian)路(lu)有输(shu)(shu)入(ru)过欠压保(bao)护(hu)电(dian)(dian)(dian)(dian)路(lu)、输(shu)(shu)出过欠压保(bao)护(hu)电(dian)(dian)(dian)(dian)路(lu)、输(shu)(shu)出过流保(bao)护(hu)电(dian)(dian)(dian)(dian)路(lu)、输(shu)(shu)出短路(lu)保(bao)护(hu)电(dian)(dian)(dian)(dian)路(lu)等。

开关电(dian)(dian)源的电(dian)(dian)路(lu)组成方框图(tu)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(fang)雷电路：当(dang)(dang)有雷击(ji)，产生高压(ya)经电网导入电源时(shi)，由MOV1、MOV2、MOV3：F1、F2、F3、FDG1组成的(de)电路进行保护(hu)。当(dang)(dang)加在压(ya)敏(min)电阻两端的(de)电压(ya)超过其(qi)(qi)工(gong)作电压(ya)时(shi)，其(qi)(qi)阻值(zhi)降低(di)，使高压(ya)能量消耗(hao)在压(ya)敏(min)电阻上，若电流过大(da)，F1、F2、F3会烧(shao)毁保护(hu)后级电路。

②、输入滤波电(dian)(dian)(dian)路(lu)(lu)：C1、L1、C2、C3组(zu)成(cheng)的(de)双π型滤波网(wang)络主要(yao)是对输入电(dian)(dian)(dian)源的(de)电(dian)(dian)(dian)磁噪声(sheng)及杂波信号进(jin)行(xing)抑制，防止对电(dian)(dian)(dian)源干扰，同(tong)时(shi)也防止电(dian)(dian)(dian)源本身产生的(de)高频杂波对电(dian)(dian)(dian)网(wang)干扰。当电(dian)(dian)(dian)源开启(qi)瞬间，要(yao)对C5充(chong)电(dian)(dian)(dian)，由(you)于(yu)瞬间电(dian)(dian)(dian)流大，加RT1（热敏电(dian)(dian)(dian)阻）就能有效的(de)防止浪涌电(dian)(dian)(dian)流。因瞬时(shi)能量全消耗(hao)在RT1电(dian)(dian)(dian)阻上，一定时(shi)间后温(wen)度升高后RT1阻值(zhi)减小（RT1是负温(wen)系(xi)数元件），这时(shi)它消耗(hao)的(de)能量非常小，后级电(dian)(dian)(dian)路(lu)(lu)可正常工(gong)作。

③、整流滤波电路：交(jiao)流电压(ya)经BRG1整流后，经C5滤波后得(de)到较(jiao)为纯净(jing)的(de)直流电压(ya)。若C5容量(liang)变小，输(shu)出的(de)交(jiao)流纹(wen)波将增(zeng)大。

2、DC输入滤波电路原理：

①、输(shu)入(ru)滤波电路：C1、L1、C2组成的双π型滤波网(wang)络主(zhu)要是对(dui)输(shu)入(ru)电源的电磁(ci)噪声及杂(za)波信号进(jin)行(xing)抑制，防(fang)止对(dui)电源干扰，同(tong)时也(ye)防(fang)止电源本身(shen)产生的高频杂(za)波对(dui)电网(wang)干扰。C3、C4为安规(gui)电容，L2、L3为差模(mo)电感。

②、R1、R2、R3、Z1、C6、Q1、Z2、R4、R5、Q2、RT1、C7组成抗浪涌电(dian)(dian)路(lu)(lu)。在起(qi)机的(de)(de)(de)瞬间(jian)，由于(yu)C6的(de)(de)(de)存在Q2不(bu)导(dao)通，电(dian)(dian)流经RT1构成回路(lu)(lu)。当(dang)C6上的(de)(de)(de)电(dian)(dian)压充(chong)至Z1的(de)(de)(de)稳压值时Q2导(dao)通。如(ru)果(guo)C8漏电(dian)(dian)或后级电(dian)(dian)路(lu)(lu)短路(lu)(lu)现象(xiang)，在起(qi)机的(de)(de)(de)瞬间(jian)电(dian)(dian)流在RT1上产生(sheng)的(de)(de)(de)压降(jiang)增(zeng)大，Q1导(dao)通使Q2没(mei)有栅极电(dian)(dian)压不(bu)导(dao)通，RT1将会在很短的(de)(de)(de)时间(jian)烧毁(hui)，以保护后级电(dian)(dian)路(lu)(lu)。

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)成缓冲器，和(he)开(kai)(kai)关(guan)MOS管(guan)(guan)(guan)(guan)并(bing)接，使开(kai)(kai)关(guan)管(guan)(guan)(guan)(guan)电(dian)(dian)压(ya)(ya)(ya)应力减少(shao)，EMI减少(shao)，不发生二次(ci)击(ji)穿。在(zai)开(kai)(kai)关(guan)管(guan)(guan)(guan)(guan)Q1关(guan)断时(shi)(shi)，变(bian)压(ya)(ya)(ya)器的(de)(de)(de)(de)原边线(xian)圈(quan)易产生尖(jian)峰(feng)电(dian)(dian)压(ya)(ya)(ya)和(he)尖(jian)峰(feng)电(dian)(dian)流，这(zhei)些元件组(zu)合一(yi)起(qi)，能(neng)很好地吸(xi)收(shou)尖(jian)峰(feng)电(dian)(dian)压(ya)(ya)(ya)和(he)电(dian)(dian)流。从(cong)R3测得(de)的(de)(de)(de)(de)电(dian)(dian)流峰(feng)值信号参与当(dang)(dang)前(qian)(qian)工(gong)(gong)作(zuo)周波(bo)的(de)(de)(de)(de)占空比(bi)(bi)控制(zhi)(zhi)，因此是当(dang)(dang)前(qian)(qian)工(gong)(gong)作(zuo)周波(bo)的(de)(de)(de)(de)电(dian)(dian)流限制(zhi)(zhi)。当(dang)(dang)R5上的(de)(de)(de)(de)电(dian)(dian)压(ya)(ya)(ya)达到1V时(shi)(shi)，UC3842停止工(gong)(gong)作(zuo)，开(kai)(kai)关(guan)管(guan)(guan)(guan)(guan)Q1立(li)即关(guan)断。R1和(he)Q1中的(de)(de)(de)(de)结电(dian)(dian)容CGS、CGD一(yi)起(qi)组(zu)成RC网络，电(dian)(dian)容的(de)(de)(de)(de)充(chong)放电(dian)(dian)直接影响着开(kai)(kai)关(guan)管(guan)(guan)(guan)(guan)的(de)(de)(de)(de)开(kai)(kai)关(guan)速(su)度(du)。R1过(guo)(guo)小(xiao)，易引起(qi)振荡，电(dian)(dian)磁干扰也会(hui)(hui)很大(da)；R1过(guo)(guo)大(da)，会(hui)(hui)降低开(kai)(kai)关(guan)管(guan)(guan)(guan)(guan)的(de)(de)(de)(de)开(kai)(kai)关(guan)速(su)度(du)。Z1通常将MOS管(guan)(guan)(guan)(guan)的(de)(de)(de)(de)GS电(dian)(dian)压(ya)(ya)(ya)限制(zhi)(zhi)在(zai)18V以下(xia)，从(cong)而保护(hu)了MOS管(guan)(guan)(guan)(guan)。Q1的(de)(de)(de)(de)栅极(ji)受控电(dian)(dian)压(ya)(ya)(ya)为锯(ju)形波(bo)，当(dang)(dang)其(qi)占空比(bi)(bi)越大(da)时(shi)(shi)，Q1导通时(shi)(shi)间(jian)越长(zhang)，变(bian)压(ya)(ya)(ya)器所储存的(de)(de)(de)(de)能(neng)量也就越多；当(dang)(dang)Q1截(jie)止时(shi)(shi)，变(bian)压(ya)(ya)(ya)器通过(guo)(guo)D1、D2、R5、R4、C3释(shi)放能(neng)量，同时(shi)(shi)也达到了磁场复位(wei)的(de)(de)(de)(de)目的(de)(de)(de)(de)，为变(bian)压(ya)(ya)(ya)器的(de)(de)(de)(de)下(xia)一(yi)次(ci)存储、传递能(neng)量做(zuo)好了准备。IC根据输出电(dian)(dian)压(ya)(ya)(ya)和(he)电(dian)(dian)流时(shi)(shi)刻调整着⑥脚(jiao)锯(ju)形波(bo)占空比(bi)(bi)的(de)(de)(de)(de)大(da)小(xiao)，从(cong)而稳定了整机的(de)(de)(de)(de)输出电(dian)(dian)流和(he)电(dian)(dian)压(ya)(ya)(ya)。C4和(he)R6为尖(jian)峰(feng)电(dian)(dian)压(ya)(ya)(ya)吸(xi)收(shou)回路。

4、推挽式功率变换电路：

Q1和Q2将轮流(liu)导通(tong)。

5、有驱动变压器的功率变换电路：

T2为(wei)驱(qu)动变压(ya)器，T1为(wei)开关(guan)变压(ya)器，TR1为(wei)电流环。

四、输出整流滤波电路

1、正激式整流电路：

T1为(wei)开关变压器(qi)，其初极(ji)(ji)(ji)和次极(ji)(ji)(ji)的(de)相位同相。D1为(wei)整流(liu)二(er)极(ji)(ji)(ji)管，D2为(wei)续流(liu)二(er)极(ji)(ji)(ji)管，R1、C1、R2、C2为(wei)削尖峰电路。L1为(wei)续流(liu)电感(gan)，C4、L2、C5组成(cheng)π型滤(lv)波器(qi)。

2、反激式整流电路：

T1为(wei)(wei)(wei)开关变压器，其(qi)初极(ji)和次极(ji)的相位相反。D1为(wei)(wei)(wei)整流二极(ji)管，R1、C1为(wei)(wei)(wei)削(xue)尖峰(feng)电(dian)路(lu)。L1为(wei)(wei)(wei)续(xu)流电(dian)感，R2为(wei)(wei)(wei)假负载(zai)，C4、L2、C5组成π型滤波器。

3、同步整流电路：

工作(zuo)原(yuan)理：当(dang)变压器次级(ji)上端为(wei)正时，电(dian)(dian)流(liu)经C2、R5、R6、R7使(shi)Q2导(dao)通，电(dian)(dian)路(lu)(lu)构成(cheng)(cheng)回路(lu)(lu)，Q2为(wei)整流(liu)管(guan)。Q1栅极由(you)于处(chu)于反偏(pian)而截止。当(dang)变压器次级(ji)下端为(wei)正时，电(dian)(dian)流(liu)经C3、R4、R2使(shi)Q1导(dao)通，Q1为(wei)续流(liu)管(guan)。Q2栅极由(you)于处(chu)于反偏(pian)而截止。L2为(wei)续流(liu)电(dian)(dian)感，C6、L1、C7组成(cheng)(cheng)π型(xing)滤波器。R1、C1、R9、C4为(wei)削尖峰电(dian)(dian)路(lu)(lu)。

五、稳(wen)压环(huan)路原理

1、反馈电路原理图：

2、工作原理：

当输出(chu)(chu)U0升高，经取样(yang)电(dian)阻(zu)R7、R8、R10、VR1分(fen)压(ya)后(hou)，U1③脚(jiao)(jiao)电(dian)压(ya)升高，当其超过U1②脚(jiao)(jiao)基准电(dian)压(ya)后(hou)U1①脚(jiao)(jiao)输出(chu)(chu)高电(dian)平(ping)，使(shi)Q1导(dao)(dao)通(tong)(tong)，光耦OT1发光二(er)极(ji)管(guan)发光，光电(dian)三(san)极(ji)管(guan)导(dao)(dao)通(tong)(tong)，UC3842①脚(jiao)(jiao)电(dian)位(wei)相应变(bian)(bian)低(di)(di)(di)(di)，从而改变(bian)(bian)U1⑥脚(jiao)(jiao)输出(chu)(chu)占空比(bi)减小，U0降低(di)(di)(di)(di)。当输出(chu)(chu)U0降低(di)(di)(di)(di)时，U1③脚(jiao)(jiao)电(dian)压(ya)降低(di)(di)(di)(di)，当其低(di)(di)(di)(di)过U1②脚(jiao)(jiao)基准电(dian)压(ya)后(hou)U1①脚(jiao)(jiao)输出(chu)(chu)低(di)(di)(di)(di)电(dian)平(ping)，Q1不(bu)导(dao)(dao)通(tong)(tong)，光耦OT1发光二(er)极(ji)管(guan)不(bu)发光，光电(dian)三(san)极(ji)管(guan)不(bu)导(dao)(dao)通(tong)(tong)，UC3842①脚(jiao)(jiao)电(dian)位(wei)升高，从而改变(bian)(bian)U1⑥脚(jiao)(jiao)输出(chu)(chu)占空比(bi)增大(da)，U0降低(di)(di)(di)(di)。周而复始，从而使(shi)输出(chu)(chu)电(dian)压(ya)保持稳定(ding)。调节(jie)VR1可改变(bian)(bian)输出(chu)(chu)电(dian)压(ya)值(zhi)。

反馈(kui)环路是影响开关电源稳(wen)定性的重要电路。如反馈(kui)电阻电容错、漏、虚(xu)焊(han)等，会产生自激振荡，故障现(xian)象为：波形异常，空(kong)、满载振荡，输出电压不稳(wen)定等。

六、开关式稳压电源的基本工作原理

开(kai)(kai)(kai)关(guan)式(shi)稳(wen)(wen)压(ya)(ya)电(dian)源(yuan)接控(kong)制方式(shi)分为(wei)调宽式(shi)和调频式(shi)两种(zhong)，在实际(ji)的应用(yong)中，调宽式(shi)使用(yong)得较(jiao)多(duo)，在目前开(kai)(kai)(kai)发(fa)和使用(yong)的开(kai)(kai)(kai)关(guan)电(dian)源(yuan)集成电(dian)路中，绝(jue)大(da)多(duo)数(shu)也为(wei)脉(mai)宽调制型(xing)。因此下面就主要介绍调宽式(shi)开(kai)(kai)(kai)关(guan)稳(wen)(wen)压(ya)(ya)电(dian)源(yuan)。

调(diao)宽(kuan)式开(kai)关稳压(ya)电源的基本原理可参见下图(tu)。

对于单极(ji)性矩形脉(mai)冲来说，其直(zhi)流(liu)平(ping)(ping)均(jun)电(dian)压(ya)Uo取决于矩形脉(mai)冲的宽度，脉(mai)冲越宽，其直(zhi)流(liu)平(ping)(ping)均(jun)电(dian)压(ya)值就越高(gao)。直(zhi)流(liu)平(ping)(ping)均(jun)电(dian)压(ya)Ｕ。可(ke)由公式(shi)计算，

即Uo=Um×T1/T

式中Um为矩(ju)形(xing)脉(mai)(mai)冲最大电压值；T为矩(ju)形(xing)脉(mai)(mai)冲周(zhou)期；T1为矩(ju)形(xing)脉(mai)(mai)冲宽度(du)。

从上式(shi)可(ke)以看出，当(dang)Um 与(yu)T 不变时(shi)，直流平均电(dian)压(ya)(ya)(ya)Uo 将与(yu)脉冲宽(kuan)度T1 成正比。这样(yang)，只(zhi)要我(wo)们设法使脉冲宽(kuan)度随稳压(ya)(ya)(ya)电(dian)源输出电(dian)压(ya)(ya)(ya)的增高(gao)而变窄(zhai)，就可(ke)以达(da)到稳定电(dian)压(ya)(ya)(ya)的目的。

七、开关式稳压电源的原理电路

1、基本电路

图二 开(kai)关电源(yuan)基本电路框图

开关式(shi)稳压电源的基(ji)本电路框(kuang)图如(ru)图二所示。

交流(liu)电(dian)(dian)(dian)压(ya)(ya)经(jing)整流(liu)电(dian)(dian)(dian)路及(ji)滤波电(dian)(dian)(dian)路整流(liu)滤波后，变成含有一定脉(mai)动成份的(de)(de)直(zhi)流(liu)电(dian)(dian)(dian)压(ya)(ya)，该(gai)电(dian)(dian)(dian)压(ya)(ya)进(jin)人高频变换器被转换成所需(xu)电(dian)(dian)(dian)压(ya)(ya)值的(de)(de)方波，最后再将这(zhei)个方波电(dian)(dian)(dian)压(ya)(ya)经(jing)整流(liu)滤波变为所需(xu)要的(de)(de)直(zhi)流(liu)电(dian)(dian)(dian)压(ya)(ya)。

控(kong)制电路(lu)为一脉冲(chong)宽度调(diao)制器(qi)，它主要由取样器(qi)、比较器(qi)、振荡器(qi)、脉宽调(diao)制及基准电压等电路(lu)构成(cheng)。这部分电路(lu)目前已集(ji)成(cheng)化，制成(cheng)了各(ge)种开(kai)关(guan)电源用集(ji)成(cheng)电路(lu)。控(kong)制电路(lu)用来调(diao)整高(gao)频(pin)开(kai)关(guan)元件的(de)开(kai)关(guan)时间比例(li)，以达到稳定(ding)输出电压的(de)目的(de)。

２、单端反激式开关电源

单端反激式(shi)开(kai)关电源的(de)典型电路(lu)如图三所示。电路(lu)中(zhong)所谓(wei)的(de)单端是指(zhi)高频变换器(qi)的(de)磁芯仅工作在磁滞回线的(de)一(yi)侧(ce)。所谓(wei)的(de)反激，是指(zhi)当开(kai)关管(guan)VT1 导通时(shi)，高频变压(ya)器(qi)Ｔ初级绕组的(de)感应电压(ya)为上正下负，整(zheng)流二极管(guan)VD1处(chu)于(yu)截止(zhi)状态(tai)，在初级绕组中(zhong)储存(cun)能量。当开(kai)关管(guan)VT1截止(zhi)时(shi)，变压(ya)器(qi)Ｔ初级绕组中(zhong)存(cun)储的(de)能量，通过次级绕组及(ji)VD1 整(zheng)流和电容Ｃ滤波后向负载(zai)输出(chu)。

单端反激式开(kai)关电(dian)源(yuan)是一(yi)种成本最(zui)低的(de)电(dian)源(yuan)电(dian)路，输(shu)(shu)出功(gong)率为20－100Ｗ，可以同时输(shu)(shu)出不同的(de)电(dian)压(ya)(ya)(ya)，且有较好(hao)的(de)电(dian)压(ya)(ya)(ya)调整(zheng)率。唯一(yi)的(de)缺点是输(shu)(shu)出的(de)纹波电(dian)压(ya)(ya)(ya)较大，外特性差，适用于(yu)相(xiang)对(dui)固定的(de)负(fu)载。

单端反(fan)激式开关电(dian)源使(shi)用(yong)的开关管VT1 承受的最大反(fan)向(xiang)电(dian)压是电(dian)路工作电(dian)压值的两倍，工作频率(lv)在20－200kHz之间。

３、单端正激式开关电源

单(dan)端正激式开(kai)关电(dian)(dian)(dian)(dian)源的典型电(dian)(dian)(dian)(dian)路如图四所(suo)示。这种电(dian)(dian)(dian)(dian)路在形式上与(yu)单(dan)端反(fan)激式电(dian)(dian)(dian)(dian)路相似，但工作情形不同(tong)。当开(kai)关管(guan)VT1导(dao)通时，VD2也导(dao)通，这时电(dian)(dian)(dian)(dian)网向负载传送(song)能量，滤波(bo)电(dian)(dian)(dian)(dian)感Ｌ储存(cun)能量；当开(kai)关管(guan)VT1截止时，电(dian)(dian)(dian)(dian)感Ｌ通过续流(liu)二极(ji)管(guan)VD3 继续向负载释放能量。

在(zai)电(dian)(dian)路(lu)(lu)中还设有钳位(wei)(wei)线圈与二极管(guan)(guan)VD2，它可以将开关管(guan)(guan)VT1的(de)最高电(dian)(dian)压(ya)(ya)限制在(zai)两倍电(dian)(dian)源电(dian)(dian)压(ya)(ya)之(zhi)间。为满足磁芯复(fu)位(wei)(wei)条件(jian)，即磁通建立和复(fu)位(wei)(wei)时间应(ying)相等，所以电(dian)(dian)路(lu)(lu)中脉冲的(de)占空(kong)比不能大(da)于５０％。由于这种电(dian)(dian)路(lu)(lu)在(zai)开关管(guan)(guan)VT1导(dao)通时，通过变(bian)压(ya)(ya)器向(xiang)负载(zai)传(chuan)送能量，所以输出功率范(fan)围(wei)大(da)，可输出50－200 Ｗ的(de)功率。电(dian)(dian)路(lu)(lu)使(shi)用的(de)变(bian)压(ya)(ya)器结构复(fu)杂，体(ti)积(ji)也较大(da)，正因为这个原因，这种电(dian)(dian)路(lu)(lu)的(de)实际应(ying)用较少。

４、自激式开关稳压电源

自(zi)激式(shi)开关稳压电源(yuan)的典(dian)型电路如图五(wu)所示。这是(shi)一种(zhong)利(li)用间歇振荡电路组成的开关电源(yuan)，也是(shi)目前广泛使用的基本电源(yuan)之(zhi)一。

当接(jie)入电(dian)(dian)(dian)源(yuan)后在R1给(ji)开(kai)(kai)关(guan)管VT1提(ti)(ti)供启动电(dian)(dian)(dian)流(liu)(liu)，使(shi)(shi)VT1开(kai)(kai)始(shi)导(dao)(dao)通(tong)，其集电(dian)(dian)(dian)极(ji)电(dian)(dian)(dian)流(liu)(liu)Ic在L1中(zhong)(zhong)线(xian)性增(zeng)长，在L2 中(zhong)(zhong)感(gan)应(ying)出(chu)使(shi)(shi)VT1 基(ji)极(ji)为正，发(fa)(fa)射极(ji)为负(fu)(fu)的(de)(de)正反(fan)馈电(dian)(dian)(dian)压(ya)(ya)(ya)，使(shi)(shi)VT1 很快(kuai)饱和(he)。与此(ci)同时，感(gan)应(ying)电(dian)(dian)(dian)压(ya)(ya)(ya)给(ji)C1充电(dian)(dian)(dian)，随着C1充电(dian)(dian)(dian)电(dian)(dian)(dian)压(ya)(ya)(ya)的(de)(de)增(zeng)高，VT1基(ji)极(ji)电(dian)(dian)(dian)位逐渐变(bian)低，致使(shi)(shi)VT1退出(chu)饱和(he)区，Ic 开(kai)(kai)始(shi)减小，在L2 中(zhong)(zhong)感(gan)应(ying)出(chu)使(shi)(shi)VT1 基(ji)极(ji)为负(fu)(fu)、发(fa)(fa)射极(ji)为正的(de)(de)电(dian)(dian)(dian)压(ya)(ya)(ya)，使(shi)(shi)VT1 迅(xun)速截(jie)止(zhi)，这时二极(ji)管VD1导(dao)(dao)通(tong)，高频(pin)变(bian)压(ya)(ya)(ya)器Ｔ初(chu)级(ji)绕(rao)组中(zhong)(zhong)的(de)(de)储能释放(fang)给(ji)负(fu)(fu)载(zai)。在VT1截(jie)止(zhi)时，L2中(zhong)(zhong)没有感(gan)应(ying)电(dian)(dian)(dian)压(ya)(ya)(ya)，直流(liu)(liu)供电(dian)(dian)(dian)输人电(dian)(dian)(dian)压(ya)(ya)(ya)又经R1给(ji)C1反(fan)向充电(dian)(dian)(dian)，逐渐提(ti)(ti)高VT1基(ji)极(ji)电(dian)(dian)(dian)位，使(shi)(shi)其重(zhong)新(xin)导(dao)(dao)通(tong)，再次翻转(zhuan)达(da)到饱和(he)状态，电(dian)(dian)(dian)路(lu)就这样重(zhong)复振荡下(xia)去。这里就像(xiang)单(dan)端反(fan)激式开(kai)(kai)关(guan)电(dian)(dian)(dian)源(yuan)那样，由变(bian)压(ya)(ya)(ya)器Ｔ的(de)(de)次级(ji)绕(rao)组向负(fu)(fu)载(zai)输出(chu)所需要(yao)的(de)(de)电(dian)(dian)(dian)压(ya)(ya)(ya)。

自激式(shi)开(kai)关(guan)(guan)电(dian)源(yuan)中的(de)开(kai)关(guan)(guan)管起着开(kai)关(guan)(guan)及振荡(dang)的(de)双重作从，也(ye)省去了(le)控制电(dian)路(lu)。电(dian)路(lu)中由(you)于负载(zai)位于变压器的(de)次(ci)级且工(gong)作在(zai)反激状态，具(ju)有输(shu)人和(he)输(shu)出相互隔离的(de)优点。这种电(dian)路(lu)不仅适(shi)用(yong)于大功(gong)率(lv)电(dian)源(yuan)，亦适(shi)用(yong)于小(xiao)功(gong)率(lv)电(dian)源(yuan)。

５、推挽式开关电源

推挽(wan)式开(kai)关电(dian)源的(de)(de)典型电(dian)路如图六(liu)所示。它(ta)属于双端(duan)式变换电(dian)路，高频变压(ya)器的(de)(de)磁芯工作在磁滞回线的(de)(de)两侧。电(dian)路使用两个(ge)开(kai)关管VT1和VT2，两个(ge)开(kai)关管在外(wai)激励方波(bo)(bo)信号的(de)(de)控制下交替的(de)(de)导(dao)通与截止(zhi)，在变压(ya)器Ｔ次(ci)级(ji)统(tong)组得(de)到方波(bo)(bo)电(dian)压(ya)，经整流滤波(bo)(bo)变为所需要(yao)的(de)(de)直流电(dian)压(ya)。

这种电(dian)路的优点(dian)是两(liang)个开(kai)关管容易驱动，主要(yao)缺点(dian)是开(kai)关管的耐压(ya)(ya)要(yao)达到两(liang)倍电(dian)路峰值电(dian)压(ya)(ya)。电(dian)路的输出功率较大，一(yi)般在100-500 Ｗ范围(wei)内(nei)。

６、降压式开关电源

降压(ya)(ya)式开关(guan)电(dian)(dian)(dian)源的典型电(dian)(dian)(dian)路如图七所(suo)示。当开关(guan)管VT1 导通时(shi)，二极管VD1 截止(zhi)(zhi)，输(shu)人的整流(liu)(liu)(liu)电(dian)(dian)(dian)压(ya)(ya)经(jing)VT1和L向Ｃ充(chong)电(dian)(dian)(dian)，这一(yi)电(dian)(dian)(dian)流(liu)(liu)(liu)使电(dian)(dian)(dian)感(gan)Ｌ中的储(chu)能(neng)增加(jia)(jia)。当开关(guan)管VT1截止(zhi)(zhi)时(shi)，电(dian)(dian)(dian)感(gan)Ｌ感(gan)应出(chu)左负(fu)右正的电(dian)(dian)(dian)压(ya)(ya)，经(jing)负(fu)载(zai)RL和续流(liu)(liu)(liu)二极管VD1释(shi)放(fang)电(dian)(dian)(dian)感(gan)Ｌ中存储(chu)的能(neng)量(liang)，维持输(shu)出(chu)直流(liu)(liu)(liu)电(dian)(dian)(dian)压(ya)(ya)不变。电(dian)(dian)(dian)路输(shu)出(chu)直流(liu)(liu)(liu)电(dian)(dian)(dian)压(ya)(ya)的高低由加(jia)(jia)在VT1基极上的脉冲(chong)宽度确定。

这种电路使用(yong)元件少，它(ta)同下面介绍的另(ling)外两种电路一样，只需要利用(yong)电感(gan)、电容和(he)二极管即可实现(xian)。

７、升压式开关电源

升压(ya)式(shi)开(kai)(kai)关电(dian)(dian)(dian)(dian)源(yuan)(yuan)的稳压(ya)电(dian)(dian)(dian)(dian)路(lu)如图八所(suo)示。当(dang)开(kai)(kai)关管 VT1 导(dao)通(tong)时，电(dian)(dian)(dian)(dian)感(gan)Ｌ储存能(neng)量。当(dang)开(kai)(kai)关管VT1 截止时，电(dian)(dian)(dian)(dian)感(gan)Ｌ感(gan)应出(chu)左负右(you)正的电(dian)(dian)(dian)(dian)压(ya)，该电(dian)(dian)(dian)(dian)压(ya)叠加(jia)在输(shu)人电(dian)(dian)(dian)(dian)压(ya)上，经二极管VD1向负载(zai)供电(dian)(dian)(dian)(dian)，使输(shu)出(chu)电(dian)(dian)(dian)(dian)压(ya)大于输(shu)人电(dian)(dian)(dian)(dian)压(ya)，形成升压(ya)式(shi)开(kai)(kai)关电(dian)(dian)(dian)(dian)源(yuan)(yuan)。

８、反转式开关电源

反(fan)转式开关电(dian)(dian)源(yuan)的典型电(dian)(dian)路(lu)(lu)如图九(jiu)所示。这种电(dian)(dian)路(lu)(lu)又称为升(sheng)降压式开关电(dian)(dian)源(yuan)。无论开关管VT1之(zhi)前的脉动(dong)直流电(dian)(dian)压高于或低于输出端的稳定电(dian)(dian)压，电(dian)(dian)路(lu)(lu)均(jun)能正常工(gong)作。

当开(kai)关管 VT1 导通(tong)(tong)时(shi)，电(dian)(dian)感L 储(chu)存能量，二(er)极(ji)管VD1 截止(zhi)，负载(zai)RL靠电(dian)(dian)容(rong)C上次的充电(dian)(dian)电(dian)(dian)荷供(gong)电(dian)(dian)。当开(kai)关管VT1截止(zhi)时(shi)，电(dian)(dian)感Ｌ中(zhong)的电(dian)(dian)流继续流通(tong)(tong)，并感应出上负下正的电(dian)(dian)压，经二(er)极(ji)管VD1向负载(zai)供(gong)电(dian)(dian)，同(tong)时(shi)给电(dian)(dian)容(rong)Ｃ充电(dian)(dian)。

以上介绍了脉冲宽度调制(zhi)(zhi)式开(kai)关稳(wen)压电(dian)(dian)(dian)源的基本工作原理和各种(zhong)电(dian)(dian)(dian)路(lu)类型，在(zai)实际(ji)应(ying)用中，会有各种(zhong)各样(yang)的实际(ji)控制(zhi)(zhi)电(dian)(dian)(dian)路(lu)，但无论怎样(yang)，也都是(shi)在(zai)这些基础上发展出(chu)来的。

八、短路保护电路

1、在输(shu)出端短路的情况下，PWM控制(zhi)电(dian)路能够(gou)把输(shu)出电(dian)流(liu)限制(zhi)在一个安全范围内，它可以用多(duo)种方法来(lai)实现限流(liu)电(dian)路，当(dang)功率限流(liu)在短路时(shi)不起作用时(shi)，只有(you)另增设一部(bu)分电(dian)路。

2、短(duan)(duan)路(lu)保护(hu)电(dian)路(lu)通常有两种，下(xia)图是小功率短(duan)(duan)路(lu)保护(hu)电(dian)路(lu)，其原理简述如下(xia)：

当(dang)(dang)输出(chu)电(dian)(dian)路(lu)短(duan)(duan)路(lu)，输出(chu)电(dian)(dian)压消失，光(guang)耦OT1不(bu)导通，UC3842①脚(jiao)电(dian)(dian)压上(shang)升至5V左右，R1与R2的分压超过(guo)TL431基准，使(shi)之导通，UC3842⑦脚(jiao)VCC电(dian)(dian)位被拉(la)低，IC停止(zhi)工作(zuo)。UC3842停止(zhi)工作(zuo)后①脚(jiao)电(dian)(dian)位消失，TL431不(bu)导通UC3842⑦脚(jiao)电(dian)(dian)位上(shang)升，UC3842重新(xin)启动(dong)(dong)，周而复(fu)始。当(dang)(dang)短(duan)(duan)路(lu)现象消失后，电(dian)(dian)路(lu)可以自(zi)动(dong)(dong)恢复(fu)成正常工作(zuo)状(zhuang)态。

3、下(xia)图是(shi)中(zhong)功率短路保(bao)护电路，其原理简述如下(xia)：

当(dang)(dang)输出短(duan)路(lu)，UC3842①脚电压(ya)上升,U1③脚电位高(gao)于②脚时，比较器翻转①脚输出高(gao)电位，给C1充(chong)电，当(dang)(dang)C1两端电压(ya)超过⑤脚基准电压(ya)时U1⑦脚输出低电位，UC3842①脚低于1V，UCC3842停止工作(zuo)，输出电压(ya)为0V，周而复始，当(dang)(dang)短(duan)路(lu)消失后电路(lu)正(zheng)常工作(zuo)。R2、C1是充(chong)放电时间常数(shu)，阻值不对时短(duan)路(lu)保护(hu)不起(qi)作(zuo)用。

4、下图是常见(jian)的限流、短(duan)路保护(hu)电路。其工作原理简述如下：

当输(shu)出电(dian)路短路或过流，变压器原边(bian)电(dian)流增(zeng)(zeng)大，R3两端电(dian)压降(jiang)增(zeng)(zeng)大，③脚电(dian)压升高(gao)，UC3842⑥脚输(shu)出占空比逐渐增(zeng)(zeng)大，③脚电(dian)压超过1V时，UC3842关闭无输(shu)出。

5、下(xia)图(tu)是用电(dian)流互感器(qi)取样(yang)电(dian)流的保护电(dian)路(lu)(lu)，有(you)着功耗小，但(dan)成(cheng)本(ben)高和电(dian)路(lu)(lu)较为复杂，其工作原理简述如(ru)下(xia)：

输出电(dian)路短路或电(dian)流过(guo)大，TR1次级线圈感应的电(dian)压(ya)就(jiu)越高，当UC3842③脚超过(guo)1伏，UC3842停止工作，周而复(fu)始，当短路或过(guo)载消(xiao)失(shi)，电(dian)路自行恢复(fu)。

九、输出端限流保护

上图(tu)是常见(jian)的输(shu)出(chu)端限流(liu)保(bao)护(hu)电(dian)路，其工作原(yuan)理简(jian)述(shu)如上图(tu)：当输(shu)出(chu)电(dian)流(liu)过(guo)大时，RS（锰铜(tong)丝）两端电(dian)压(ya)上升(sheng)，U1③脚电(dian)压(ya)高于②脚基准电(dian)压(ya)，U1①脚输(shu)出(chu)高电(dian)压(ya)，Q1导通，光耦(ou)发生光电(dian)效应，UC3842①脚电(dian)压(ya)降(jiang)低，输(shu)出(chu)电(dian)压(ya)降(jiang)低，从而(er)达到输(shu)出(chu)过(guo)载限流(liu)的目(mu)的。

十、输出过压保护电路的原理

输(shu)出(chu)过(guo)(guo)(guo)压(ya)(ya)(ya)(ya)保护电(dian)路(lu)的作(zuo)用是：当(dang)输(shu)出(chu)电(dian)压(ya)(ya)(ya)(ya)超过(guo)(guo)(guo)设计值时，把输(shu)出(chu)电(dian)压(ya)(ya)(ya)(ya)限(xian)定在一(yi)安全值的范围内。当(dang)开关电(dian)源内部稳(wen)压(ya)(ya)(ya)(ya)环路(lu)出(chu)现(xian)故障或者由于(yu)用户操(cao)作(zuo)不当(dang)引起输(shu)出(chu)过(guo)(guo)(guo)压(ya)(ya)(ya)(ya)现(xian)象时，过(guo)(guo)(guo)压(ya)(ya)(ya)(ya)保护电(dian)路(lu)进(jin)行保护以防止损坏后级用电(dian)设备(bei)。应用最(zui)为普遍(bian)的过(guo)(guo)(guo)压(ya)(ya)(ya)(ya)保护电(dian)路(lu)有如下几种：

1、可控硅触发保护电路：

如(ru)上图，当(dang)Uo1输(shu)出升高，稳(wen)压(ya)管（Z3）击(ji)穿导(dao)通(tong)，可(ke)控(kong)硅(gui)(gui)（SCR1）的控(kong)制端得到(dao)触(chu)发(fa)(fa)电(dian)(dian)压(ya)，因此可(ke)控(kong)硅(gui)(gui)导(dao)通(tong)。Uo2电(dian)(dian)压(ya)对地短路(lu)，过流保(bao)护(hu)电(dian)(dian)路(lu)或短路(lu)保(bao)护(hu)电(dian)(dian)路(lu)就会工作，停止整个电(dian)(dian)源(yuan)电(dian)(dian)路(lu)的工作。当(dang)输(shu)出过压(ya)现象排除，可(ke)控(kong)硅(gui)(gui)的控(kong)制端触(chu)发(fa)(fa)电(dian)(dian)压(ya)通(tong)过R对地泄放，可(ke)控(kong)硅(gui)(gui)恢(hui)复断(duan)开状态。

2、光电耦合保护电路：

如上图，当Uo有(you)过压现象时，稳(wen)压管击穿导(dao)通(tong)，经(jing)光(guang)(guang)耦（OT2）R6到地产生电流(liu)流(liu)过，光(guang)(guang)电耦合器(qi)的(de)(de)发(fa)光(guang)(guang)二极(ji)管发(fa)光(guang)(guang)，从(cong)而(er)使(shi)光(guang)(guang)电耦合器(qi)的(de)(de)光(guang)(guang)敏三极(ji)管导(dao)通(tong)。Q1基极(ji)得(de)电导(dao)通(tong)，3842的(de)(de)③脚电降低，使(shi)IC关闭(bi)，停止整(zheng)个电源的(de)(de)工作(zuo)，Uo为零，周(zhou)而(er)复始(shi)，。

3、输出限压保护电路：

输(shu)(shu)出(chu)限压(ya)(ya)保护电(dian)(dian)(dian)路如下图(tu)，当输(shu)(shu)出(chu)电(dian)(dian)(dian)压(ya)(ya)升(sheng)高，稳(wen)压(ya)(ya)管导(dao)(dao)通光耦导(dao)(dao)通，Q1基极有驱动电(dian)(dian)(dian)压(ya)(ya)而(er)道通，UC3842③电(dian)(dian)(dian)压(ya)(ya)升(sheng)高，输(shu)(shu)出(chu)降低，稳(wen)压(ya)(ya)管不(bu)导(dao)(dao)通，UC3842③电(dian)(dian)(dian)压(ya)(ya)降低，输(shu)(shu)出(chu)电(dian)(dian)(dian)压(ya)(ya)升(sheng)高。周(zhou)而(er)复始，输(shu)(shu)出(chu)电(dian)(dian)(dian)压(ya)(ya)将稳(wen)定(ding)在一(yi)范围内（取决于稳(wen)压(ya)(ya)管的稳(wen)压(ya)(ya)值）。

4、输出过压锁死电路：

图(tu)A的(de)工(gong)作(zuo)原(yuan)理是(shi)，当输出电(dian)(dian)压(ya)Uo升高(gao)(gao)(gao)，稳压(ya)管导(dao)通，光耦(ou)导(dao)通，Q2基极(ji)(ji)得电(dian)(dian)导(dao)通，由于Q2的(de)导(dao)通Q1基极(ji)(ji)电(dian)(dian)压(ya)降低也导(dao)通，Vcc电(dian)(dian)压(ya)经(jing)R1、Q1、R2使Q2始(shi)终导(dao)通，UC3842③脚始(shi)终是(shi)高(gao)(gao)(gao)电(dian)(dian)平(ping)(ping)(ping)而停(ting)止工(gong)作(zuo)。在图(tu)B中(zhong)，UO升高(gao)(gao)(gao)U1③脚电(dian)(dian)压(ya)升高(gao)(gao)(gao)，①脚输出高(gao)(gao)(gao)电(dian)(dian)平(ping)(ping)(ping)，由于D1、R1的(de)存在，U1①脚始(shi)终输出高(gao)(gao)(gao)电(dian)(dian)平(ping)(ping)(ping)Q1始(shi)终导(dao)通，UC3842①脚始(shi)终是(shi)低电(dian)(dian)平(ping)(ping)(ping)而停(ting)止工(gong)作(zuo)。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(shu)入(ru)电(dian)(dian)(dian)(dian)压(ya)(ya)经L1、L2、L3等组(zu)成的(de)EMI滤波(bo)器，BRG1整(zheng)(zheng)(zheng)流一(yi)(yi)路(lu)(lu)送PFC电(dian)(dian)(dian)(dian)感，另(ling)(ling)一(yi)(yi)路(lu)(lu)经R1、R2分(fen)压(ya)(ya)后送入(ru)PFC控制(zhi)器作(zuo)为输(shu)入(ru)电(dian)(dian)(dian)(dian)压(ya)(ya)的(de)取样(yang)，用以调整(zheng)(zheng)(zheng)控制(zhi)信(xin)号(hao)的(de)占(zhan)空比，即改(gai)变(bian)Q1的(de)导通和关(guan)断(duan)时(shi)间，稳(wen)定PFC输(shu)出(chu)电(dian)(dian)(dian)(dian)压(ya)(ya)。L4是PFC电(dian)(dian)(dian)(dian)感，它在Q1导通时(shi)储存能量(liang)，在Q1关(guan)断(duan)时(shi)施放能量(liang)。D1是启(qi)动二(er)极管(guan)。D2是PFC整(zheng)(zheng)(zheng)流二(er)极管(guan)，C6、C7滤波(bo)。PFC电(dian)(dian)(dian)(dian)压(ya)(ya)一(yi)(yi)路(lu)(lu)送后级(ji)电(dian)(dian)(dian)(dian)路(lu)(lu)，另(ling)(ling)一(yi)(yi)路(lu)(lu)经R3、R4分(fen)压(ya)(ya)后送入(ru)PFC控制(zhi)器作(zuo)为PFC输(shu)出(chu)电(dian)(dian)(dian)(dian)压(ya)(ya)的(de)取样(yang)，用以调整(zheng)(zheng)(zheng)控制(zhi)信(xin)号(hao)的(de)占(zhan)空比，稳(wen)定PFC输(shu)出(chu)电(dian)(dian)(dian)(dian)压(ya)(ya)。

十二、输入过欠压保护

1、原理图：

2、工作原理：

AC输(shu)(shu)入(ru)和DC输(shu)(shu)入(ru)的(de)开关(guan)电(dian)(dian)(dian)源的(de)输(shu)(shu)入(ru)过欠压(ya)(ya)(ya)保护原理(li)大致相同。保护电(dian)(dian)(dian)路(lu)(lu)的(de)取样(yang)电(dian)(dian)(dian)压(ya)(ya)(ya)均来自输(shu)(shu)入(ru)滤波后(hou)的(de)电(dian)(dian)(dian)压(ya)(ya)(ya)。取样(yang)电(dian)(dian)(dian)压(ya)(ya)(ya)分为两路(lu)(lu)，一路(lu)(lu)经R1、R2、R3、R4分压(ya)(ya)(ya)后(hou)输(shu)(shu)入(ru)比(bi)(bi)较(jiao)器3脚，如(ru)取样(yang)电(dian)(dian)(dian)压(ya)(ya)(ya)高于2脚基准(zhun)电(dian)(dian)(dian)压(ya)(ya)(ya)，比(bi)(bi)较(jiao)器1脚输(shu)(shu)出(chu)高电(dian)(dian)(dian)平(ping)去控(kong)制(zhi)(zhi)主控(kong)制(zhi)(zhi)器使其(qi)(qi)关(guan)断，电(dian)(dian)(dian)源无(wu)输(shu)(shu)出(chu)。另一路(lu)(lu)经R7、R8、R9、R10分压(ya)(ya)(ya)后(hou)输(shu)(shu)入(ru)比(bi)(bi)较(jiao)器6脚，如(ru)取样(yang)电(dian)(dian)(dian)压(ya)(ya)(ya)低于5脚基准(zhun)电(dian)(dian)(dian)压(ya)(ya)(ya)，比(bi)(bi)较(jiao)器7脚输(shu)(shu)出(chu)高电(dian)(dian)(dian)平(ping)去控(kong)制(zhi)(zhi)主控(kong)制(zhi)(zhi)器使其(qi)(qi)关(guan)断，电(dian)(dian)(dian)源无(wu)输(shu)(shu)出(chu)。

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