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在电(dian)路(lu)板上(shang)，我们经常会(hui)看到一个(ge)类(lei)似三(san)极管的元件---三(san)端(duan)稳压(ya)(ya)器。三(san)端(duan)稳压(ya)(ya)器常用(yong)在需要电(dian)压(ya)(ya)变(bian)换的地方。如18伏(fu)(fu)变(bian)12伏(fu)(fu)、12伏(fu)(fu)变(bian)5伏(fu)(fu)。

常(chang)见的(de)(de)(de)三(san)端(duan)稳压(ya)(ya)器有78系列(lie)(lie)的(de)(de)(de)7805、7808、7809、7812、7824等。78后(hou)面的(de)(de)(de)数字代(dai)(dai)表(biao)稳压(ya)(ya)器输(shu)(shu)(shu)(shu)出的(de)(de)(de)电压(ya)(ya)值。78系列(lie)(lie)的(de)(de)(de)稳压(ya)(ya)器输(shu)(shu)(shu)(shu)出都为正压(ya)(ya)。如(ru)7805代(dai)(dai)表(biao)输(shu)(shu)(shu)(shu)出正5伏(fu)、7812代(dai)(dai)表(biao)输(shu)(shu)(shu)(shu)出正12伏(fu)。另一(yi)种(zhong)输(shu)(shu)(shu)(shu)出负压(ya)(ya)的(de)(de)(de)三(san)端(duan)稳压(ya)(ya)器是79系列(lie)(lie)的(de)(de)(de)。如(ru)7905代(dai)(dai)表(biao)输(shu)(shu)(shu)(shu)出伏(fu)5伏(fu)电压(ya)(ya)、7912代(dai)(dai)表(biao)输(shu)(shu)(shu)(shu)出负12伏(fu)电压(ya)(ya)。

有的(de)三(san)端稳压(ya)器标注带字母(mu)，那(nei)(nei)是代表(biao)承受电流。如输出电流以78(或79)后(hou)面加字母(mu)来区(qu)分。L表(biao)示0.1;AM表(biao)示0.5A，无字母(mu)表(biao)示1.5A，如78L05表(biao)求5V 0.1A。常见的(de)三(san)端稳压(ya)器管脚排列一(yi)般(ban)是带字的(de)那(nei)(nei)面朝向我们时，左边的(de)第一(yi)个脚为(wei)输入正极，中间(jian)为(wei)负极，最右边为(wei)输出正极。

在(zai)三(san)端(duan)稳压(ya)(ya)(ya)器(qi)(qi)输(shu)(shu)(shu)(shu)(shu)入端(duan)与输(shu)(shu)(shu)(shu)(shu)出(chu)(chu)端(duan)都会(hui)有一个(ge)电(dian)(dian)(dian)解电(dian)(dian)(dian)容。使用三(san)端(duan)稳压(ya)(ya)(ya)器(qi)(qi)要注意输(shu)(shu)(shu)(shu)(shu)入与输(shu)(shu)(shu)(shu)(shu)出(chu)(chu)之(zhi)间的(de)(de)电(dian)(dian)(dian)压(ya)(ya)(ya)差不能过小。以7805为例，该三(san)端(duan)稳压(ya)(ya)(ya)器(qi)(qi)的(de)(de)固(gu)定输(shu)(shu)(shu)(shu)(shu)出(chu)(chu)电(dian)(dian)(dian)压(ya)(ya)(ya)是5V，而输(shu)(shu)(shu)(shu)(shu)入电(dian)(dian)(dian)压(ya)(ya)(ya)至少大(da)(da)于(yu)7V，这样输(shu)(shu)(shu)(shu)(shu)入/输(shu)(shu)(shu)(shu)(shu)出(chu)(chu)之(zhi)间有2-3V及以上的(de)(de)压(ya)(ya)(ya)差。使调整(zheng)管(guan)保(bao)证(zheng)工作(zuo)在(zai)放大(da)(da)区。但压(ya)(ya)(ya)差取得大(da)(da)时，又(you)会(hui)增加集成块的(de)(de)功耗(hao)，所以，两(liang)者应兼(jian)顾，即(ji)既(ji)保(bao)证(zheng)在(zai)最(zui)大(da)(da)负载电(dian)(dian)(dian)流时调整(zheng)管(guan)不进入饱和，又(you)不至于(yu)功耗(hao)偏大(da)(da)。另外一般在(zai)三(san)端(duan)稳压(ya)(ya)(ya)器(qi)(qi)的(de)(de)输(shu)(shu)(shu)(shu)(shu)入输(shu)(shu)(shu)(shu)(shu)出(chu)(chu)端(duan)接一个(ge)二极管(guan)，用来(lai)防止输(shu)(shu)(shu)(shu)(shu)入端(duan)短路时,输(shu)(shu)(shu)(shu)(shu)出(chu)(chu)端(duan)存(cun)储的(de)(de)电(dian)(dian)(dian)荷通过稳压(ya)(ya)(ya)器(qi)(qi),而损(sun)坏器(qi)(qi)件。

三端稳压器(qi)的故障率不高，最(zui)常(chang)见的是管脚开焊。但在(zai)维修中常(chang)常(chang)是我们检测电(dian)压是否正常(chang)的一(yi)个检测点，所以(yi)很有必要对它进(jin)行了(le)解。

稳压管的(de)应用:

1、浪涌保护(hu)电(dian)(dian)(dian)(dian)(dian)(dian)路(lu):稳压(ya)管(guan)在准(zhun)确(que)的(de)电(dian)(dian)(dian)(dian)(dian)(dian)压(ya)下击(ji)穿,这就使得(de)它可作为(wei)限制(zhi)或保护(hu)之(zhi)元件来使用(yong),因为(wei)各种(zhong)电(dian)(dian)(dian)(dian)(dian)(dian)压(ya)的(de)稳压(ya)二极(ji)管(guan)都可以得(de)到,故对于(yu)这种(zhong)应(ying)用(yong)特别适(shi)宜(yi).图(tu)中的(de)稳压(ya)二极(ji)管(guan)D是作为(wei)过压(ya)保护(hu)器件.只(zhi)要电(dian)(dian)(dian)(dian)(dian)(dian)源电(dian)(dian)(dian)(dian)(dian)(dian)压(ya)VS超过二极(ji)管(guan)的(de)稳压(ya)值D就导通(tong),使继电(dian)(dian)(dian)(dian)(dian)(dian)器J吸(xi)合负载RL就与电(dian)(dian)(dian)(dian)(dian)(dian)源分开；

2、电(dian)(dian)(dian)视机(ji)里的过(guo)压保(bao)护电(dian)(dian)(dian)路:EC是(shi)电(dian)(dian)(dian)视机(ji)主(zhu)供电(dian)(dian)(dian)压,当EC电(dian)(dian)(dian)压过(guo)高(gao)时,D导(dao)(dao)通(tong)(tong),三极管BG导(dao)(dao)通(tong)(tong),其(qi)集电(dian)(dian)(dian)极电(dian)(dian)(dian)位将由原(yuan)来(lai)的高(gao)电(dian)(dian)(dian)平(5V)变为低电(dian)(dian)(dian)平,通(tong)(tong)过(guo)待(dai)机(ji)控制线的控制使电(dian)(dian)(dian)视机(ji)进入待(dai)机(ji)保(bao)护状态(tai)；

3、电(dian)弧抑(yi)制电(dian)路:在(zai)电(dian)感线(xian)圈(quan)上(shang)并联接入(ru)一只合适的稳压二(er)极管(guan)(也(ye)(ye)可接入(ru)一只普通二(er)极管(guan)原理一样)的话(hua),当(dang)线(xian)圈(quan)在(zai)导通状态切断(duan)时,由于其电(dian)磁能释放(fang)所产生的高压就被二(er)极管(guan)所吸(xi)收,所以当(dang)开(kai)关断(duan)开(kai)时,开(kai)关的电(dian)弧也(ye)(ye)就被消除了.这(zhei)个应用电(dian)路在(zai)工业上(shang)用得(de)比较多(duo),如(ru)一些较大功率(lv)的电(dian)磁吸(xi)控(kong)制电(dian)路就用到它；

4、串联(lian)型(xing)稳(wen)压(ya)(ya)电(dian)(dian)路(lu)(lu):在此电(dian)(dian)路(lu)(lu)中,串联(lian)稳(wen)压(ya)(ya)管(guan)BG的基极被(bei)稳(wen)压(ya)(ya)二极管(guan)D钳定(ding)(ding)在13V,那么其发(fa)射极就(jiu)输(shu)出恒(heng)定(ding)(ding)的12V电(dian)(dian)压(ya)(ya)了.这个电(dian)(dian)路(lu)(lu)在很多场合下都有应用(yong)；

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