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三端稳压管好坏判断
三端稳压管

三端稳压(ya)(ya)管(guan)是(shi)(shi)一(yi)(yi)种直(zhi)到临界反(fan)向击(ji)穿(chuan)电(dian)压(ya)(ya)前都具有(you)很高(gao)电(dian)阻的半导(dao)体器件。稳压(ya)(ya)管(guan)在反(fan)向击(ji)穿(chuan)时，在一(yi)(yi)定(ding)的电(dian)流(liu)范围(wei)内(nei)（或者说(shuo)在一(yi)(yi)定(ding)功率损耗(hao)范围(wei)内(nei)），端电(dian)压(ya)(ya)几乎不变，表现(xian)出(chu)(chu)稳压(ya)(ya)特性，因(yin)而(er)广泛应用于(yu)稳压(ya)(ya)电(dian)源与限幅(fu)电(dian)路之中。三端稳压(ya)(ya)管(guan)，主要有(you)两种，一(yi)(yi)种输出(chu)(chu)电(dian)压(ya)(ya)是(shi)(shi)固(gu)(gu)定(ding)的，称为固(gu)(gu)定(ding)输出(chu)(chu)三端稳压(ya)(ya)管(guan)，另(ling)一(yi)(yi)种输出(chu)(chu)电(dian)压(ya)(ya)是(shi)(shi)可调的，称为可调输出(chu)(chu)三端稳压(ya)(ya)管(guan)。

电(dian)(dian)(dian)子产品一(yi)(yi)般三(san)(san)端(duan)稳压(ya)(ya)(ya)集(ji)成(cheng)电(dian)(dian)(dian)路(lu)有(you)(you)一(yi)(yi)个正电(dian)(dian)(dian)压(ya)(ya)(ya)输(shu)(shu)出(chu)78xx系列(lie)(lie)79x系列(lie)(lie)和(he)(he)负电(dian)(dian)(dian)压(ya)(ya)(ya)输(shu)(shu)出(chu)。因此,公义,三(san)(san)端(duan)集(ji)成(cheng)电(dian)(dian)(dian)路(lu)是(shi)指电(dian)(dian)(dian)压(ya)(ya)(ya)调整器和(he)(he)集(ji)成(cheng)电(dian)(dian)(dian)路(lu)和(he)(he)三(san)(san)针输(shu)(shu)出(chu),输(shu)(shu)入,接地端(duan)和(he)(he)输(shu)(shu)出(chu)端(duan)。它看起来像普通三(san)(san)极(ji)管(guan)、TO-220标准封装,有(you)(you)9013-92封装的。用78/79系列(lie)(lie)三(san)(san)端(duan)稳压(ya)(ya)(ya)集(ji)成(cheng)电(dian)(dian)(dian)路(lu)形成(cheng)几个外围组件所需(xu)的稳压(ya)(ya)(ya)电(dian)(dian)(dian)源,内(nei)部电(dian)(dian)(dian)路(lu)和(he)(he)过流、过热和(he)(he)调整管(guan)保护(hu)电(dian)(dian)(dian)路(lu),而(er)且价格便宜。这一(yi)(yi)系列(lie)(lie)的集(ji)成(cheng)稳压(ya)(ya)(ya)集(ji)成(cheng)电(dian)(dian)(dian)路(lu)模(mo)型在78或(huo)79的数字代表(biao)三(san)(san)端(duan)集(ji)成(cheng)稳压(ya)(ya)(ya)电(dian)(dian)(dian)路(lu)的输(shu)(shu)出(chu)电(dian)(dian)(dian)压(ya)(ya)(ya),如7806表(biao)示输(shu)(shu)出(chu)电(dian)(dian)(dian)压(ya)(ya)(ya)6v,79099v输(shu)(shu)出(chu)电(dian)(dian)(dian)压(ya)(ya)(ya)是(shi)负的。

三端稳压器的引脚识别与好坏判断方法

(1)引脚识别

三(san)端(duan)(duan)(duan)(duan)稳压器的封装(zhuang)有金(jin)属封装(zhuang)和塑料封装(zhuang)两种，外(wai)形如同(tong)一只大功率晶体管，引脚的排列如图(tu)9-30所示。不同(tong)系(xi)(xi)列的稳压器，其(qi)各脚的作(zuo)用不同(tong)。其(qi)中(zhong)最(zui)常(chang)用的W78××系(xi)(xi)列稳压器，为(wei)(wei)输(shu)(shu)入端(duan)(duan)(duan)(duan)(I)，为(wei)(wei)输(shu)(shu)出(chu)端(duan)(duan)(duan)(duan)(O)，为(wei)(wei)公共(gong)端(duan)(duan)(duan)(duan)(COM);W79××系(xi)(xi)列则(ze)是为(wei)(wei)公共(gong)端(duan)(duan)(duan)(duan)，为(wei)(wei)输(shu)(shu)出(chu)端(duan)(duan)(duan)(duan)，为(wei)(wei)输(shu)(shu)入端(duan)(duan)(duan)(duan);常(chang)用的可(ke)调(diao)(diao)(diao)三(san)端(duan)(duan)(duan)(duan)稳压器LM317T，外(wai)形如W78××，其(qi)为(wei)(wei)可(ke)调(diao)(diao)(diao)端(duan)(duan)(duan)(duan)，为(wei)(wei)输(shu)(shu)入端(duan)(duan)(duan)(duan)，为(wei)(wei)输(shu)(shu)出(chu)端(duan)(duan)(duan)(duan)。端(duan)(duan)(duan)(duan)输(shu)(shu)出(chu)电(dian)压值由端(duan)(duan)(duan)(duan)电(dian)压变(bian)化调(diao)(diao)(diao)节。

(2)性能鉴别

对(dui)78××和(he)79××系列三端稳(wen)压(ya)器，鉴别其(qi)好坏可(ke)使(shi)用(yong)万用(yong)表 R × 100挡，分别检测(ce)其(qi)输(shu)入(ru)端与输(shu)出端的(de)(de)(de)正、反向电阻(zu)值。正常(chang)时，阻(zu)值相(xiang)差(cha)在(zai)数(shu)千(qian)欧以上;若阻(zu)值相(xiang)差(cha)很小(xiao)或近似为零，说明其(qi)已(yi)损坏。表9-14、表9-15为最常(chang)用(yong)的(de)(de)(de)78××和(he)79××21种三端稳(wen)压(ya)器的(de)(de)(de)实测(ce)各(ge)引脚非在(zai)路电阻(zu)值，供检测(ce)时参考。

表9-14 78××三端稳压器各(ge)引脚非在路电阻值(kΩ )

表9-15 79××三端稳压器各引脚非在路电阻值(kΩ )

使用注意事项

(1)分清3个引出脚

三端(duan)(duan)(duan)集成(cheng)(cheng)稳(wen)压(ya)(ya)(ya)器(qi)的(de)输(shu)(shu)入、输(shu)(shu)出(chu)(chu)和接(jie)(jie)地端(duan)(duan)(duan)装错时(shi)(shi)很容(rong)易损坏(huai)(huai)，需特(te)别注意(yi)。在(zai)安装时(shi)(shi)一定要焊接(jie)(jie)良(liang)好，否则会(hui)导(dao)致输(shu)(shu)出(chu)(chu)电压(ya)(ya)(ya)的(de)波动，易损坏(huai)(huai)输(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)上的(de)其他电路，也可能损坏(huai)(huai)集成(cheng)(cheng)稳(wen)压(ya)(ya)(ya)器(qi)本(ben)身。在(zai)拆装集成(cheng)(cheng)稳(wen)压(ya)(ya)(ya)器(qi)时(shi)(shi)要先断开(kai)电源。输(shu)(shu)出(chu)(chu)电压(ya)(ya)(ya)大于6V的(de)三端(duan)(duan)(duan)集成(cheng)(cheng)稳(wen)压(ya)(ya)(ya)器(qi)的(de)输(shu)(shu)入、输(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)最好接(jie)(jie)一保(bao)护二(er)极管，可防止输(shu)(shu)入电压(ya)(ya)(ya)突然(ran)降(jiang)低时(shi)(shi)，输(shu)(shu)出(chu)(chu)电容(rong)对输(shu)(shu)出(chu)(chu)端(duan)(duan)(duan)放电引起三端(duan)(duan)(duan)集成(cheng)(cheng)稳(wen)压(ya)(ya)(ya)器(qi)的(de)损坏(huai)(huai)。

(2)正确选择输入电压范围

三(san)端集成稳压(ya)器内部(bu)的(de)(de)二极(ji)管、三(san)极(ji)管均有一定的(de)(de)耐压(ya)值，因(yin)此整流器输(shu)(shu)出电压(ya)的(de)(de)最大值不能大于集成稳压(ya)器的(de)(de)最大允许(xu)输(shu)(shu)入(ru)电压(ya)值。7805(7905)～7818(7918)的(de)(de)最大输(shu)(shu)入(ru)电压(ya)为35V，7824(7924)的(de)(de)最大输(shu)(shu)入(ru)电压(ya)为 40V。由于三(san)端集成稳压(ya)器有一个(ge)使用最小(xiao)压(ya)差(cha)(约为2V)的(de)(de)限制，一般应使其保持在6V左右。

(3)保证散热良好

对于用三端(duan)(duan)集(ji)成(cheng)(cheng)稳(wen)(wen)压器(qi)组成(cheng)(cheng)的大(da)(da)功率(lv)稳(wen)(wen)压电源，应在(zai)三端(duan)(duan)集(ji)成(cheng)(cheng)稳(wen)(wen)压器(qi)上(shang)安装足够(gou)大(da)(da)的散(san)热器(qi)。当散(san)热器(qi)的面(mian)积不(bu)够(gou)大(da)(da)，而(er)内部调(diao)整管的结温(wen)达(da)到保护动作点附近时，集(ji)成(cheng)(cheng)稳(wen)(wen)压器(qi)的稳(wen)(wen)压性能将(jiang)变差(cha)。

(4)并联运用

如果需要较大(da)的(de)(de)稳(wen)(wen)(wen)压(ya)(ya)(ya)(ya)电(dian)(dian)流(liu)输(shu)(shu)出，而单只(zhi)集成(cheng)稳(wen)(wen)(wen)压(ya)(ya)(ya)(ya)器的(de)(de)输(shu)(shu)出电(dian)(dian)流(liu)又不够时(shi)，可采(cai)用同(tong)型号稳(wen)(wen)(wen)压(ya)(ya)(ya)(ya)器并联(lian)(lian)输(shu)(shu)出的(de)(de)方(fang)法。这时(shi)的(de)(de)最大(da)输(shu)(shu)出电(dian)(dian)流(liu)为(wei)(wei)nIomax。式中(zhong)n 为(wei)(wei)并联(lian)(lian)稳(wen)(wen)(wen)压(ya)(ya)(ya)(ya)器的(de)(de)个数(shu)(shu)，Iomax为(wei)(wei)单个稳(wen)(wen)(wen)压(ya)(ya)(ya)(ya)器的(de)(de)最大(da)输(shu)(shu)出电(dian)(dian)流(liu)。稳(wen)(wen)(wen)压(ya)(ya)(ya)(ya)器并联(lian)(lian)运(yun)行时(shi)需注意两点：一是并联(lian)(lian)使用的(de)(de)集成(cheng)稳(wen)(wen)(wen)压(ya)(ya)(ya)(ya)电(dian)(dian)路应采(cai)用同(tong)一厂(chang)家、同(tong)一型号(包(bao)括后缀(zhui))的(de)(de)产品，以(yi)保(bao)证集成(cheng)稳(wen)(wen)(wen)压(ya)(ya)(ya)(ya)器参(can)数(shu)(shu)的(de)(de)一致(zhi)性;二(er)是最好在输(shu)(shu)出总电(dian)(dian)流(liu)上留(liu)有20%的(de)(de)余(yu)量，这样可以(yi)避免(mian)因个别集成(cheng)稳(wen)(wen)(wen)压(ya)(ya)(ya)(ya)器失(shi)效(xiao)而造成(cheng)其他(ta)集成(cheng)稳(wen)(wen)(wen)压(ya)(ya)(ya)(ya)器的(de)(de)连锁烧(shao)毁。

三端稳压管型号对照表

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