简单直流降压电路图

直流降压原理
降压斩波电路

斩波电(dian)路(lu)的典型用途之一(yi)是拖(tuo)动(dong)直流电(dian)动(dong)机，也可带蓄电(dian)池负(fu)载，两(liang)种情况下负(fu)载中均会出(chu)现(xian)反电(dian)动(dong)势，如下图中Em所示

工作原理(li)，两个阶(jie)段

简单直流降压电路原理图

如下图所示，LM317输出电(dian)流(liu)为1.5A，输出电(dian)压(ya)可(ke)在1.25－37V之间连续调节，其输出电(dian)压(ya)由两只外(wai)接电(dian)阻R1、RP1决定，输出端(duan)和调整端(duan)之间的电(dian)压(ya)差为1.25V，这个(ge)电(dian)压(ya)将产生几(ji)毫安的电(dian)流(liu)，经R1、RP1到(dao)(dao)地(di)，在RP1上分得的电(dian)压(ya)加到(dao)(dao)调整端(duan)，通过改变RP1就能改变输出电(dian)压(ya)。

注意(yi)，为了得(de)到稳定(ding)的输(shu)出电压，流经R1的电流小(xiao)于3.5mA。LM317在不加散热(re)(re)器时(shi)最大(da)功(gong)耗(hao)为2W，200×200×4mm3散热(re)(re)板时(shi)其最大(da)功(gong)耗(hao)可达15W。VD1(IN4002)为保护二极管，防止稳压器输(shu)出端短路(lu)而损坏IC，VD2(IN4002)用于防止输(shu)入短路(lu)而损坏集成电路(lu)。

简(jian)单直(zhi)流降(jiang)压电路图(tu)-48V输入12V输出直(zhi)流降(jiang)压电路

48V输入12V输出的(de)直流降压电路如下(xia)图所示：

简单直流降压电路图详解（一）

直流(liu)(liu)稳(wen)(wen)(wen)压(ya)电(dian)源是一种将220V工频交流(liu)(liu)电(dian)转换(huan)成(cheng)(cheng)稳(wen)(wen)(wen)压(ya)输出的直流(liu)(liu)电(dian)的装(zhuang)置，它需要变压(ya)、整流(liu)(liu)、滤波、稳(wen)(wen)(wen)压(ya)四个环节才能(neng)完成(cheng)(cheng)。一般由电(dian)源变压(ya)器、整流(liu)(liu)滤波电(dian)路及稳(wen)(wen)(wen)压(ya)电(dian)路所(suo)组成(cheng)(cheng)，基(ji)本框图如(ru)下(xia)：

直流稳压电源的原理框图和(he)波形(xing)变换(huan)图

1、降压部分

电(dian)源变(bian)压(ya)(ya)(ya)(ya)器(qi)(qi)(qi)是降(jiang)压(ya)(ya)(ya)(ya)变(bian)压(ya)(ya)(ya)(ya)器(qi)(qi)(qi)，它的(de)作用是将220V的(de)交流电(dian)压(ya)(ya)(ya)(ya)变(bian)换成整流滤波电(dian)路所(suo)需(xu)要的(de)交流电(dian)压(ya)(ya)(ya)(ya)Ui。变(bian)压(ya)(ya)(ya)(ya)器(qi)(qi)(qi)的(de)变(bian)比(bi)由变(bian)压(ya)(ya)(ya)(ya)器(qi)(qi)(qi)的(de)副边(bian)按比(bi)例确定，变(bian)压(ya)(ya)(ya)(ya)器(qi)(qi)(qi)副边(bian)与原边(bian)的(de)功率(lv)比(bi)为P2/P1=n，式中n是变(bian)压(ya)(ya)(ya)(ya)器(qi)(qi)(qi)的(de)效(xiao)率(lv)。

2、整流部分

该设计采用单相桥(qiao)式整流(liu)电(dian)路。其由四只二极管组(zu)成，其构成原(yuan)则就是保证在变压器(qi)副(fu)边电(dian)压u的(de)整个周(zhou)期内(nei)，负载上(shang)的(de)电(dian)压和(he)电(dian)流(liu)方向始终不变。为(wei)达到这(zhei)一目的(de)，需要(yao)在Uz的(de)正、负半周(zhou)内(nei)正确引(yin)导流(liu)向负载的(de)电(dian)流(liu)，使其方向不变，设变压器(qi)副(fu)边两端分(fen)别(bie)为(wei)a和(he)

b，则a为“+”b为“一”时(shi)应(ying)(ying)有(you)电流(liu)流(liu)出a点(dian)，a为“一”b为“+”时(shi)应(ying)(ying)有(you)电流(liu)流(liu)入a点(dian)；相反，a为“+”b为“一”时(shi)应(ying)(ying)有(you)电流(liu)流(liu)入b点(dian)，因而a和b点(dian)均应(ying)(ying)接两(liang)只(zhi)二极管，以引导电流(liu)，具(ju)体电路原理如下图所示。

单(dan)相桥式整流电路(lu)

如果桥式(shi)整(zheng)(zheng)流电路变压(ya)器副边中点接(jie)(jie)地，就应(ying)将两(liang)(liang)个(ge)负(fu)(fu)载(zai)电阻相(xiang)连(lian)接(jie)(jie)且连(lian)接(jie)(jie)中点接(jie)(jie)地。根据桥式(shi)整(zheng)(zheng)流电路的工(gong)作(zuo)原理，当a点为(wei)(wei)“+”b点为(wei)(wei)“一”时(shi)，Dl、D3导通，D2、D4截(jie)止(zhi)，U01=U2，U02=一U2；而当b点为(wei)(wei)“+”a点为(wei)(wei)“一”时(shi)，D2、D4导通，D1、D3截(jie)止(zhi)，U01=一U2，U02=U2，这样两(liang)(liang)个(ge)负(fu)(fu)载(zai)上就分别获得正、负(fu)(fu)电压(ya)。

若设(she)变压(ya)(ya)器(qi)副(fu)边(bian)(bian)电压(ya)(ya)u2=U2sinwt，U2为(wei)其有效值(zhi)。当(dang)u2为(wei)正半周时(shi)，电流(liu)(liu)由a点流(liu)(liu)出，经Dl、RL、D3流(liu)(liu)入b点，因而负载电阻RL上的(de)电压(ya)(ya)等于变压(ya)(ya)器(qi)副(fu)边(bian)(bian)电压(ya)(ya)，即(ji)uo=u2，D2和D4管承(cheng)受的(de)反(fan)向(xiang)电压(ya)(ya)为(wei)一u2。当(dang)u2为(wei)负半周时(shi)，电流(liu)(liu)由b点流(liu)(liu)出，经D2、RL、D4流(liu)(liu)入a点，负载电阻RL上的(de)电压(ya)(ya)等于一u2，即(ji)uo=一u2，D1、D3承(cheng)受的(de)反(fan)向(xiang)电压(ya)(ya)为(wei)u2。这(zhei)样，由于D1、D3和D2、D4两对二极(ji)管交(jiao)替导通，致(zhi)使负载电阻RL上在u2的(de)整个周期内都有电流(liu)(liu)通过(guo)，而且方向(xiang)不变，则输出电压(ya)(ya)uo=|U2sinwt|。

3、滤波电路

经过整流后的直流电幅值变化很(hen)大(da)，会影响(xiang)电路(lu)的工作性能。可(ke)利(li)用电容(rong)的“通交流，隔直流”的特性，在电路(lu)中(zhong)并(bing)(bing)人两个并(bing)(bing)联电容(rong)作为电容(rong)滤(lv)波器，滤(lv)去其中(zhong)的交流成(cheng)分。

电(dian)(dian)(dian)(dian)容(rong)(rong)滤(lv)波(bo)(bo)电(dian)(dian)(dian)(dian)路(lu)(lu)是最(zui)常见也是最(zui)简单的(de)滤(lv)波(bo)(bo)电(dian)(dian)(dian)(dian)路(lu)(lu)，在整流电(dian)(dian)(dian)(dian)路(lu)(lu)的(de)输出(chu)端（即负(fu)载电(dian)(dian)(dian)(dian)阻两端）并(bing)联一(yi)个(ge)电(dian)(dian)(dian)(dian)容(rong)(rong)即构成电(dian)(dian)(dian)(dian)容(rong)(rong)滤(lv)波(bo)(bo)电(dian)(dian)(dian)(dian)路(lu)(lu)。滤(lv)波(bo)(bo)电(dian)(dian)(dian)(dian)容(rong)(rong)容(rong)(rong)量较大，因此一(yi)般均采用(yong)电(dian)(dian)(dian)(dian)解(jie)电(dian)(dian)(dian)(dian)容(rong)(rong)，在接(jie)线(xian)时(shi)要注意电(dian)(dian)(dian)(dian)解(jie)电(dian)(dian)(dian)(dian)容(rong)(rong)的(de)正(zheng)负(fu)极(ji)。电(dian)(dian)(dian)(dian)容(rong)(rong)滤(lv)波(bo)(bo)电(dian)(dian)(dian)(dian)路(lu)(lu)利用(yong)电(dian)(dian)(dian)(dian)容(rong)(rong)的(de)充、放电(dian)(dian)(dian)(dian)作用(yong)，使(shi)输出(chu)电(dian)(dian)(dian)(dian)压趋(qu)于平滑(hua)。如果将两个(ge)滤(lv)波(bo)(bo)电(dian)(dian)(dian)(dian)容(rong)(rong)相(xiang)连接(jie)，且(qie)连接(jie)点接(jie)地，就可同(tong)时(shi)得到输出(chu)电(dian)(dian)(dian)(dian)压平滑(hua)的(de)正(zheng)负(fu)电(dian)(dian)(dian)(dian)源。

在理想情况下，变压(ya)器(qi)副边无(wu)损耗，二极管导通电(dian)(dian)(dian)(dian)压(ya)为零，所以电(dian)(dian)(dian)(dian)容(rong)(rong)两端(duan)电(dian)(dian)(dian)(dian)压(ya)相等。而当其上升到峰值(zhi)后开始(shi)(shi)下降(jiang)(jiang)，电(dian)(dian)(dian)(dian)容(rong)(rong)便通过(guo)负(fu)载(zai)电(dian)(dian)(dian)(dian)阻放(fang)电(dian)(dian)(dian)(dian)，其电(dian)(dian)(dian)(dian)压(ya)也开始(shi)(shi)下降(jiang)(jiang)，趋势与(yu)电(dian)(dian)(dian)(dian)容(rong)(rong)两端(duan)电(dian)(dian)(dian)(dian)压(ya)基本相同。但是由于电(dian)(dian)(dian)(dian)容(rong)(rong)按指数规律放(fang)电(dian)(dian)(dian)(dian)，所以当其下降(jiang)(jiang)到一定数值(zhi)后，电(dian)(dian)(dian)(dian)容(rong)(rong)将继(ji)续通过(guo)负(fu)载(zai)放(fang)电(dian)(dian)(dian)(dian)，电(dian)(dian)(dian)(dian)容(rong)(rong)两端(duan)电(dian)(dian)(dian)(dian)压(ya)按指数规律缓慢下降(jiang)(jiang)。

简单直流降压电路图详解（二）

将220V交(jiao)流(liu)电转换(huan)为低压(ya)直流(liu)的常规方法(fa)是(shi)采用变压(ya)器降压(ya)后再整流(liu)滤(lv)波，但(dan)是(shi)当产品(pin)受体积和成(cheng)本等因素的限制时，最简(jian)单实用的方法(fa)就是(shi)采用电容降压(ya)方式(shi)。

一、电路原理

电(dian)(dian)容(rong)降压(ya)式简易电(dian)(dian)源的(de)基本电(dian)(dian)路如图(tu)1，C1为降压(ya)电(dian)(dian)容(rong)器(qi)，VD2为半波整流(liu)二极管，VD1在市电(dian)(dian)的(de)负半周(zhou)时(shi)(shi)给C1提供(gong)放电(dian)(dian)回(hui)路，VD3是稳压(ya)二极管，R1为关断(duan)电(dian)(dian)源后C1的(de)电(dian)(dian)荷(he)泄放电(dian)(dian)阻。在实际应用(yong)时(shi)(shi)常常采用(yong)的(de)是图(tu)2的(de)所(suo)(suo)示的(de)电(dian)(dian)路。当(dang)需要(yao)向负载提供(gong)较大的(de)电(dian)(dian)流(liu)时(shi)(shi),可采用(yong)图(tu)3所(suo)(suo)示的(de)桥式整流(liu)电(dian)(dian)路。

整流(liu)后未经稳压的(de)(de)直流(liu)电(dian)压一般会高于30伏，并且会随负载电(dian)流(liu)的(de)(de)变化发生很大的(de)(de)波(bo)动,这是(shi)因为此(ci)类电(dian)源内(nei)阻(zu)很大的(de)(de)缘(yuan)故所致,故不适合大电(dian)流(liu)供电(dian)的(de)(de)应用(yong)场合。

二、器件选择(ze)

1.电(dian)(dian)(dian)(dian)路设计时，应先测定负载电(dian)(dian)(dian)(dian)流(liu)的(de)(de)(de)准确值，然后参考示例来选(xuan)择(ze)降(jiang)压(ya)电(dian)(dian)(dian)(dian)容器的(de)(de)(de)容量。因为(wei)通过(guo)(guo)降(jiang)压(ya)电(dian)(dian)(dian)(dian)容C1向负载提供的(de)(de)(de)电(dian)(dian)(dian)(dian)流(liu)Io，实际上是(shi)流(liu)过(guo)(guo)C1的(de)(de)(de)充(chong)放(fang)电(dian)(dian)(dian)(dian)电(dian)(dian)(dian)(dian)流(liu)Ic。C1容量越大，容抗Xc越小，则流(liu)经(jing)C1的(de)(de)(de)充(chong)、放(fang)电(dian)(dian)(dian)(dian)电(dian)(dian)(dian)(dian)流(liu)越大。当负载电(dian)(dian)(dian)(dian)流(liu)Io小于C1的(de)(de)(de)充(chong)放(fang)电(dian)(dian)(dian)(dian)电(dian)(dian)(dian)(dian)流(liu)时，多余(yu)的(de)(de)(de)电(dian)(dian)(dian)(dian)流(liu)就(jiu)会流(liu)过(guo)(guo)稳(wen)压(ya)管，若(ruo)稳(wen)压(ya)管的(de)(de)(de)最(zui)大允(yun)许电(dian)(dian)(dian)(dian)流(liu)Idmax小于Ic-Io时易造成稳(wen)压(ya)管烧毁。

2.为(wei)保(bao)证(zheng)C1可靠工作(zuo),其耐压选择应(ying)大于(yu)两倍的电源电压。

3.泄放电阻R1的选择(ze)必(bi)须保证在要求(qiu)的时间内(nei)泄放掉C1上(shang)的电荷(he)。

简单直流降压电路图详解（三）

DC-DC变换(huan)器(qi)的基本(ben)电路有升压变换(huan)器(qi)、降压变换(huan)器(qi)、升降压变换(huan)器(qi)三种。

降压(ya)变换器原理图如图1所示，当开关闭合时(shi)(shi)，加在电感(gan)两端的电压(ya)为（Vi-Vo），此时(shi)(shi)电感(gan)由电压(ya)（Vi-Vo）励磁，电感(gan)增加的磁通为：（Vi-Vo）*Ton。

当开(kai)关断(duan)开(kai)时，由于输出电流(liu)的连续，二极管(guan)VD变为导(dao)通(tong)，电感削磁，电感减少的磁通(tong)为：（Vo）*Toff。

当开(kai)(kai)关(guan)闭合与开(kai)(kai)关(guan)断开(kai)(kai)的状态达(da)到平(ping)衡时(shi)，（Vi-Vo）*Ton=（Vo）*Toff，由于占空(kong)比D《1，所(suo)以Vi》Vo，实现降压功能。

降压(ya)变换器原理图

升压(ya)变换器(qi)原理图如下图所(suo)示，当开关闭合时，输入电(dian)压(ya)加在(zai)电(dian)感(gan)(gan)上，此时电(dian)感(gan)(gan)由电(dian)压(ya)（Vi）励磁(ci)，电(dian)感(gan)(gan)增加的磁(ci)通为：（Vi）*Ton。

当开关断开时，由于输(shu)出(chu)电流的(de)连续，二极管VD变为导通，电感削磁(ci)，电感减少的(de)磁(ci)通为：（Vo-Vi）*Toff。

当开关(guan)(guan)闭合与(yu)开关(guan)(guan)断开的状态达到(dao)平衡时，（Vi）*Ton=（Vo-Vi）*Toff，由于占空比D《1，所以Vi。

升压变换器原理图(tu)

升降压(ya)变换器(qi)、入出极性相反原理如(ru)下图(tu)，当开关闭合时，此(ci)时电(dian)感(gan)(gan)(gan)由电(dian)压(ya)（Vi）励磁(ci)，电(dian)感(gan)(gan)(gan)增加的(de)磁(ci)通为(wei)：（Vi）*Ton;当开关断(duan)(duan)开时，电(dian)感(gan)(gan)(gan)削磁(ci)，电(dian)感(gan)(gan)(gan)减(jian)少的(de)磁(ci)通为(wei)：（Vo）*Toff。当开关闭合与开关断(duan)(duan)开的(de)状(zhuang)态达(da)到平衡时，增加的(de)磁(ci)通等于减(jian)少的(de)磁(ci)通，（Vi）*Ton=（Vo）*Toff，根据(ju)Ton比Toff值不同，可(ke)能Vi《Vo，也可(ke)能Vi》Vo。

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