自举电路,电压

自举电路

自(zi)(zi)(zi)举(ju)电(dian)路(lu)(lu)也叫升压(ya)电(dian)路(lu)(lu)，是利用自(zi)(zi)(zi)举(ju)升压(ya)二(er)极(ji)管，自(zi)(zi)(zi)举(ju)升压(ya)电(dian)容等电(dian)子元件，使电(dian)容放电(dian)电(dian)压(ya)和电(dian)源电(dian)压(ya)叠加，从而使电(dian)压(ya)升高，有的(de)电(dian)路(lu)(lu)升高的(de)电(dian)压(ya)能达到数倍电(dian)源电(dian)压(ya)。

自举电路原理

举个(ge)简单的(de)(de)(de)例子：有一(yi)个(ge)12V的(de)(de)(de)电(dian)(dian)(dian)路，电(dian)(dian)(dian)路中有一(yi)个(ge)场效(xiao)应(ying)管(guan)需要15V的(de)(de)(de)驱动电(dian)(dian)(dian)压(ya)(ya)(ya)，这(zhei)个(ge)电(dian)(dian)(dian)压(ya)(ya)(ya)怎(zen)么弄出(chu)来(lai)？就是(shi)用(yong)自举。通常(chang)用(yong)一(yi)个(ge)电(dian)(dian)(dian)容(rong)和(he)一(yi)个(ge)二极管(guan)，电(dian)(dian)(dian)容(rong)存储电(dian)(dian)(dian)荷，二极管(guan)防(fang)止电(dian)(dian)(dian)流倒灌，频(pin)率较(jiao)高的(de)(de)(de)时候，自举电(dian)(dian)(dian)路的(de)(de)(de)电(dian)(dian)(dian)压(ya)(ya)(ya)就是(shi)电(dian)(dian)(dian)路输入的(de)(de)(de)电(dian)(dian)(dian)压(ya)(ya)(ya)加上电(dian)(dian)(dian)容(rong)上的(de)(de)(de)电(dian)(dian)(dian)压(ya)(ya)(ya)，起到升压(ya)(ya)(ya)的(de)(de)(de)作用(yong)。

自(zi)举电(dian)(dian)路只是在(zai)实践中定的(de)(de)名称(cheng)，在(zai)理(li)论上(shang)没有这个概念。自(zi)举电(dian)(dian)路主要是在(zai)甲(jia)乙类单电(dian)(dian)源(yuan)互(hu)补对称(cheng)电(dian)(dian)路中使(shi)用较(jiao)为普遍。甲(jia)乙类单电(dian)(dian)源(yuan)互(hu)补对称(cheng)电(dian)(dian)路在(zai)理(li)论上(shang)可(ke)以(yi)使(shi)输(shu)出电(dian)(dian)压Vo达(da)到(dao)Vcc的(de)(de)一(yi)半(ban)，但(dan)在(zai)实际的(de)(de)测试中，输(shu)出电(dian)(dian)压远达(da)不到(dao)Vcc的(de)(de)一(yi)半(ban)。其中重要的(de)(de)原(yuan)因(yin)就需要一(yi)个高于Vcc的(de)(de)电(dian)(dian)压。所(suo)以(yi)采用自(zi)举电(dian)(dian)路来升压。

开关直流(liu)升压电路(即所谓的boost或者step-up电路)原理

the boost converter,或(huo)者(zhe)叫step-up converter，是(shi)一(yi)种(zhong)开关(guan)直(zhi)流(liu)升(sheng)压(ya)电路，它可以(yi)是(shi)输出(chu)电压(ya)比输入电压(ya)高。基本电路图见图21.

假(jia)定(ding)那个(ge)开关(三极管或(huo)者mos管)已经断(duan)开了很(hen)长时间，所有(you)的元件都处于理想(xiang)状态，电(dian)容电(dian)压(ya)等于输入(ru)电(dian)压(ya)。下面要分充电(dian)和放电(dian)两个(ge)部(bu)分来说(shuo)明这个(ge)电(dian)路。

自举电路应用

1、利用(yong)自举电路提高电路增益

图2、图3所示的(de)(de)两电(dian)(dian)(dian)(dian)路(lu)都是利用自(zi)举(ju)电(dian)(dian)(dian)(dian)路(lu)提高电(dian)(dian)(dian)(dian)路(lu)增益(yi)的(de)(de)。先看图2，图中以T1为核(he)(he)心(xin)构成(cheng)共射(she)电(dian)(dian)(dian)(dian)路(lu)，以T2为核(he)(he)心(xin)构成(cheng)的(de)(de)是射(she)随(sui)器，C3为自(zi)举(ju)电(dian)(dian)(dian)(dian)容。该电(dian)(dian)(dian)(dian)路(lu)输出电(dian)(dian)(dian)(dian)压跟随(sui)N点(dian)的(de)(de)电(dian)(dian)(dian)(dian)位(wei)变化(hua)(hua)而(er)变化(hua)(hua)，通过C3的(de)(de)反馈(kui)将(jiang)输出电(dian)(dian)(dian)(dian)压反馈(kui)到M点(dian)，使M点(dian)的(de)(de)电(dian)(dian)(dian)(dian)位(wei)也跟随(sui)N点(dian)电(dian)(dian)(dian)(dian)位(wei)的(de)(de)电(dian)(dian)(dian)(dian)位(wei)变化(hua)(hua)而(er)变化(hua)(hua)，实现自(zi)举(ju)。

图2

同理可分析(xi)图3电(dian)(dian)路(lu)，图6中T1、T2的(de)(de)作(zuo)用(yong)(yong)与图5相同，C3仍(reng)为自(zi)举(ju)(ju)(ju)电(dian)(dian)容。该(gai)电(dian)(dian)路(lu)的(de)(de)输(shu)(shu)出电(dian)(dian)压(ya)跟(gen)随M点(dian)的(de)(de)电(dian)(dian)位(wei)变化而(er)(er)变化，通(tong)过(guo)C3的(de)(de)反馈作(zuo)用(yong)(yong)使(shi)N点(dian)的(de)(de)电(dian)(dian)位(wei)也跟(gen)随M点(dian)电(dian)(dian)位(wei)变化而(er)(er)变化，实现自(zi)举(ju)(ju)(ju)。自(zi)举(ju)(ju)(ju)的(de)(de)结果(guo)使(shi)Re2两端的(de)(de)电(dian)(dian)位(wei)很接近(jin)，因此(ci)流(liu)过(guo)Re2 的(de)(de)交流(liu)电(dian)(dian)流(liu)大(da)(da)(da)大(da)(da)(da)减少，相当于提(ti)高(gao)(gao)了Re2的(de)(de)交流(liu)等(deng)效阻(zu)抗(kang)，即提(ti)高(gao)(gao)了T1的(de)(de)集电(dian)(dian)极等(deng)效阻(zu)抗(kang)，从而(er)(er)使(shi)电(dian)(dian)路(lu)获得较高(gao)(gao)的(de)(de)增(zeng)(zeng)益。不(bu)难分析(xi)图3电(dian)(dian)路(lu)利用(yong)(yong)T2管产生自(zi)举(ju)(ju)(ju)作(zuo)用(yong)(yong)，不(bu)仅提(ti)高(gao)(gao)了电(dian)(dian)路(lu)的(de)(de)增(zeng)(zeng)益，而(er)(er)且(qie)也使(shi)电(dian)(dian)路(lu)的(de)(de)输(shu)(shu)出电(dian)(dian)阻(zu)大(da)(da)(da)大(da)(da)(da)增(zeng)(zeng)加，所(suo)以适用(yong)(yong)于后(hou)级(ji)放大(da)(da)(da)电(dian)(dian)路(lu)输(shu)(shu)入(ru)阻(zu)抗(kang)较高(gao)(gao)的(de)(de)场合。

图3

2.利(li)用(yong)自举电路解决交、直(zhi)流(liu)参数设置(zhi)

如图(tu)4电(dian)路(lu)是一个(ge)利用自举(ju)电(dian)路(lu)解决驻(zhu)极体话(hua)(hua)筒与放大器的(de)交、直(zhi)(zhi)流(liu)参数合理配置(zhi)的(de)例子。驻(zhu)极体话(hua)(hua)筒由于具有音质好、输出平坦、阻抗低而价格(ge)又便宜的(de)特点，应用范围(wei)已(yi)越来越广泛了(le)。但(dan)驻(zhu)极体话(hua)(hua)简工(gong)作时，要求提供(gong)一个(ge)直(zhi)(zhi)流(liu)偏置(zhi)电(dian)流(liu)和偏置(zhi)电(dian)压。

图4

市场(chang)上销售的(de)话(hua)筒(tong)参(can)数(shu)的(de)离(li)散性较(jiao)大(da)，其(qi)偏置电压一般在1.5V~10V之(zhi)间，工作电流常在0.1mA~1mA。在电路设计时(shi)，其(qi)偏置电阻(zu)与(yu)电源之(zhi)间有时(shi)较(jiao)难协调(diao)，为(wei)满足话(hua)筒(tong)对(dui)输(shu)出阻(zu)抗的(de)要(yao)求而将偏置电阻(zu)取大(da)时(shi)，势必要(yao)求Vcc要(yao)相应地(di)提高，如果(guo)将偏置电阻(zu)取小些，虽然可以(yi)满足对(dui)Vcc的(de)要(yao)求，但话(hua)筒(tong)的(de)输(shu)出阻(zu)抗又(you)难以(yi)匹(pi)配。

为(wei)解决这(zhei)一(yi)问题可采用(yong)(yong)图7电(dian)(dian)(dian)路(lu)(lu)(lu)，在这(zhei)一(yi)电(dian)(dian)(dian)路(lu)(lu)(lu)中偏置电(dian)(dian)(dian)阻（R1+R2）仅(jin)取2kQ，所以电(dian)(dian)(dian)源电(dian)(dian)(dian)压(ya)Vcc几(ji)乎全部降(jiang)在话(hua)筒(tong)(tong)(tong)上，为(wei)驻极体话(hua)筒(tong)(tong)(tong)提(ti)供较大的(de)(de)偏置电(dian)(dian)(dian)压(ya)，满足(zu)了(le)话(hua)筒(tong)(tong)(tong)参数离散(san)性的(de)(de)要求。只要电(dian)(dian)(dian)源电(dian)(dian)(dian)压(ya)Vcc大于(yu)话(hua)简(jian)工作电(dian)(dian)(dian)压(ya)1V就能使它很(hen)好工作。为(wei)了(le)满足(zu)话(hua)筒(tong)(tong)(tong)对输出阻抗的(de)(de)匹配的(de)(de)要求，该(gai)电(dian)(dian)(dian)路(lu)(lu)(lu)采用(yong)(yong)了(le)自(zi)(zi)举(ju)电(dian)(dian)(dian)路(lu)(lu)(lu)，C3为(wei)自(zi)(zi)举(ju)电(dian)(dian)(dian)容，由于(yu)C3的(de)(de)存在，使R1电(dian)(dian)(dian)阻下(xia)端的(de)(de)电(dian)(dian)(dian)位(wei)(wei)跟随R1.上端的(de)(de)电(dian)(dian)(dian)位(wei)(wei)变化而变化，即实现自(zi)(zi)举(ju)。R1两端的(de)(de)电(dian)(dian)(dian)位(wei)(wei)差(cha)值(zhi)很(hen)小(xiao)即意味着(zhe)R1的(de)(de)等效阻抗被大大地提(ti)高了(le)，从而实现与(yu)驻极体话(hua)简(jian)输出阻抗的(de)(de)良好匹配。此外(wai)，该(gai)电(dian)(dian)(dian)路(lu)(lu)(lu)具有一(yi)定的(de)(de)电(dian)(dian)(dian)压(ya)增(zeng)益，还(hai)可以减轻后(hou)级电(dian)(dian)(dian)路(lu)(lu)(lu)的(de)(de)负担。

自举电路如何把电压逐一升高

+5V_ALWP电压通过D32的1脚对C710、C722、C715、C719开始充电，充电完毕后电路状(zhuang)态如上图(tu)显示(shi)（二(er)极(ji)管压降忽略不(bu)计）。

此时的(de)+15V_ALWP，实际电压为(wei)5V

1、由于(yu)电(dian)(dian)(dian)(dian)容(rong)的(de)(de)两(liang)端电(dian)(dian)(dian)(dian)压不能(neng)突变，此时C715两(liang)端的(de)(de)电(dian)(dian)(dian)(dian)位为左(zuo)边5V，右边10V（C715的(de)(de)电(dian)(dian)(dian)(dian)压依然是10V-5V=5V），然后(hou)电(dian)(dian)(dian)(dian)流(liu)经过D35的(de)(de)2引脚，对C719电(dian)(dian)(dian)(dian)容(rong)充电(dian)(dian)(dian)(dian)，充电(dian)(dian)(dian)(dian)后(hou)C719的(de)(de)电(dian)(dian)(dian)(dian)压升(sheng)到10V。

2、在上述1发生的(de)同时(shi)，Y输出的(de)第(di)一(yi)次高(gao)电(dian)(dian)(dian)平5V也对C710充(chong)电(dian)(dian)(dian)。同样电(dian)(dian)(dian)容(rong)两端(duan)电(dian)(dian)(dian)压(ya)不能(neng)突变，所(suo)以C710两端(duan)的(de)电(dian)(dian)(dian)位为左边5V，右边10V（C710的(de)电(dian)(dian)(dian)压(ya)依然是10V-5V=5V）。然后电(dian)(dian)(dian)流(liu)经过D32的(de)2引(yin)脚对C732D电(dian)(dian)(dian)容(rong)充(chong)电(dian)(dian)(dian)（充(chong)电(dian)(dian)(dian)前C722的(de)电(dian)(dian)(dian)压(ya)为5V），充(chong)电(dian)(dian)(dian)后C722的(de)电(dian)(dian)(dian)压(ya)升到(dao)10V。

此时(shi)+15V_ALWP电压为(wei)10V。

1、由于(yu)电(dian)(dian)(dian)(dian)容的(de)(de)两端电(dian)(dian)(dian)(dian)压不能(neng)突变，此时C715两端的(de)(de)电(dian)(dian)(dian)(dian)位(wei)为(wei)左(zuo)边(bian)(bian)0V，右边(bian)(bian)5V（C715的(de)(de)电(dian)(dian)(dian)(dian)压依然(ran)是5V-0V=5V，保持5V电(dian)(dian)(dian)(dian)压），当C715电(dian)(dian)(dian)(dian)压为(wei)5V后，由于(yu)C722电(dian)(dian)(dian)(dian)压10V＞C715电(dian)(dian)(dian)(dian)压5V，C722会对(dui)(dui)C715充(chong)电(dian)(dian)(dian)(dian)。充(chong)电(dian)(dian)(dian)(dian)后C715=C722=7.5V。此时C715电(dian)(dian)(dian)(dian)压依然(ran)比C719电(dian)(dian)(dian)(dian)压低。是由于(yu)D35的(de)(de)2引脚(jiao)处的(de)(de)二极(ji)管反向截止，所以C719不能(neng)对(dui)(dui)C715充(chong)电(dian)(dian)(dian)(dian)，C719电(dian)(dian)(dian)(dian)压保持在10V。

2、在(zai)上述(shu)1发(fa)生的同时，Y输出的第(di)一次低电(dian)(dian)平(ping)0V也改变了C710左端的电(dian)(dian)压。同样电(dian)(dian)容两端电(dian)(dian)压不(bu)能(neng)突变，所(suo)以C710两端的电(dian)(dian)位为左边0V，右边5V（C710的电(dian)(dian)压依然是(shi)5V-0V=5V）。此时C710电(dian)(dian)压低，C722电(dian)(dian)压高（7.5V）。但是(shi)由于(yu)D35的2引脚(jiao)处的二极管反(fan)向截止(zhi)，所(suo)以C722不(bu)能(neng)对C710充电(dian)(dian)。C722电(dian)(dian)压保持在(zai)7.5V。

3、当(dang)Y再次(ci)输出(chu)高(gao)电(dian)(dian)(dian)平(ping)时(shi)，C722又被充(chong)电(dian)(dian)(dian)到(dao)10V。当(dang)Y变为(wei)低电(dian)(dian)(dian)平(ping)是C722（10V）对(dui)C715(7.5V)充(chong)电(dian)(dian)(dian)。C715=8.75V。当(dang)Y再次(ci)输出(chu)高(gao)电(dian)(dian)(dian)平(ping)时(shi)，此时(shi)C715两端的(de)电(dian)(dian)(dian)位为(wei)：左(zuo)边：5V,右(you)边：13.75V(5V+8.75V)，C715对(dui)C719充(chong)电(dian)(dian)(dian)，C719电(dian)(dian)(dian)压(ya)变为(wei)11.875V，C715由于对(dui)C719充(chong)电(dian)(dian)(dian)，电(dian)(dian)(dian)压(ya)变为(wei)11.875V。此时(shi)+15V_ALWP电(dian)(dian)(dian)压(ya)是11.875V。

4、经(jing)过数次(ci)高(gao)(gao)低电(dian)平(ping)变化后，C715两端(duan)电(dian)压(ya)(ya)慢慢升高(gao)(gao)，同(tong)时C715对C719充电(dian)，C719电(dian)压(ya)(ya)也(ye)慢慢升高(gao)(gao)，最终(zhong)C715会被(bei)充电(dian)到10V，不再(zai)(zai)升高(gao)(gao)。当Y引(yin)脚再(zai)(zai)次(ci)输出高(gao)(gao)电(dian)平(ping)5V时，C715的电(dian)位为：左边5V，右边15V(10V+5V).最终(zhong)+15V_ALWP电(dian)压(ya)(ya)稳定在15V。

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