LED灯驱动电源电路图

根(gen)据驱(qu)动电(dian)(dian)(dian)(dian)(dian)路(lu)(lu)的(de)(de)输出特性，白(bai)(bai)光(guang)(guang)(guang)LED闪光(guang)(guang)(guang)灯(deng)的(de)(de)驱(qu)动电(dian)(dian)(dian)(dian)(dian)路(lu)(lu)可(ke)(ke)分(fen)为恒(heng)压型(xing)(xing)(xing)和恒(heng)流(liu)(liu)(liu)(liu)型(xing)(xing)(xing)；按(an)电(dian)(dian)(dian)(dian)(dian)路(lu)(lu)工作原理，可(ke)(ke)以分(fen)为电(dian)(dian)(dian)(dian)(dian)感升压电(dian)(dian)(dian)(dian)(dian)路(lu)(lu)和电(dian)(dian)(dian)(dian)(dian)荷泵电(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。白(bai)(bai)光(guang)(guang)(guang)LED是电(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)驱(qu)动型(xing)(xing)(xing)器件，其亮(liang)度(du)与电(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)成比例关(guan)系(xi)。在恒(heng)压型(xing)(xing)(xing)驱(qu)动电(dian)(dian)(dian)(dian)(dian)路(lu)(lu)中，往往有一个电(dian)(dian)(dian)(dian)(dian)阻(zu)与白(bai)(bai)光(guang)(guang)(guang)LED串联，用(yong)来设(she)置产生预(yu)期白(bai)(bai)光(guang)(guang)(guang)LED正向电(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)所需(xu)的(de)(de)电(dian)(dian)(dian)(dian)(dian)压。这种方式有一个缺(que)点，即白(bai)(bai)光(guang)(guang)(guang)LED正向电(dian)(dian)(dian)(dian)(dian)压的(de)(de)任何变化(hua)都会导致白(bai)(bai)光(guang)(guang)(guang)LED电(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)的(de)(de)变化(hua)，从(cong)而无法(fa)保(bao)(bao)证流(liu)(liu)(liu)(liu)过白(bai)(bai)光(guang)(guang)(guang)LED的(de)(de)电(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)等于预(yu)设(she)置值，也就(jiu)无法(fa)确保(bao)(bao)白(bai)(bai)光(guang)(guang)(guang)LED的(de)(de)亮(liang)度(du)恒(heng)定(ding)。而在恒(heng)流(liu)(liu)(liu)(liu)型(xing)(xing)(xing)驱(qu)动电(dian)(dian)(dian)(dian)(dian)路(lu)(lu)中，是通过检测串联在白(bai)(bai)光(guang)(guang)(guang)LED回路(lu)(lu)电(dian)(dian)(dian)(dian)(dian)阻(zu)的(de)(de)电(dian)(dian)(dian)(dian)(dian)压来保(bao)(bao)证流(liu)(liu)(liu)(liu)过白(bai)(bai)光(guang)(guang)(guang)LED的(de)(de)电(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)恒(heng)定(ding)的(de)(de)。这种方式可(ke)(ke)以消除由(you)正向电(dian)(dian)(dian)(dian)(dian)压变化(hua)而产生的(de)(de)电(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)变化(hua)，因(yin)此白(bai)(bai)光(guang)(guang)(guang)LED可(ke)(ke)产生相对恒(heng)定(ding)的(de)(de)亮(liang)度(du)。

由(you)于移动电(dian)话的(de)锂(li)离子电(dian)池的(de)工作(zuo)电(dian)压(ya)范围一(yi)般(ban)为(wei)3.*.2V，而(er)白光(guang)(guang)(guang)LED的(de)正向电(dian)压(ya)一(yi)般(ban)为(wei)3～4V，且白光(guang)(guang)(guang)LED闪光(guang)(guang)(guang)灯(deng)一(yi)般(ban)为(wei)多个白光(guang)(guang)(guang)LED串、并联(lian)在一(yi)起，以(yi)(yi)(yi)(yi)提(ti)供闪光(guang)(guang)(guang)功能(neng)所需(xu)的(de)光(guang)(guang)(guang)通量，所以(yi)(yi)(yi)(yi)在低电(dian)压(ya)输入(ru)、高(gao)电(dian)压(ya)输出的(de)时候，必须(xu)采(cai)(cai)用(yong)升(sheng)压(ya)电(dian)路将(jiang)电(dian)压(ya)升(sheng)高(gao)以(yi)(yi)(yi)(yi)驱动白光(guang)(guang)(guang)LED。驱动白光(guang)(guang)(guang)LED闪光(guang)(guang)(guang)灯(deng)时一(yi)般(ban)采(cai)(cai)用(yong)两种(zhong)(zhong)方(fang)式升(sheng)压(ya)，一(yi)种(zhong)(zhong)是(shi)采(cai)(cai)用(yong)以(yi)(yi)(yi)(yi)电(dian)感(gan)为(wei)储(chu)能(neng)元件的(de)升(sheng)压(ya)式变换器，另一(yi)种(zhong)(zhong)是(shi)采(cai)(cai)用(yong)以(yi)(yi)(yi)(yi)电(dian)容为(wei)储(chu)能(neng)元件的(de)电(dian)荷泵。采(cai)(cai)用(yong)以(yi)(yi)(yi)(yi)电(dian)感(gan)为(wei)储(chu)能(neng)元件的(de)升(sheng)压(ya)变换器的(de)优点是(shi)效率相对较高(gao)。

现在的(de)(de)(de)白(bai)光(guang)LED闪(shan)(shan)光(guang)灯驱(qu)动(dong)控(kong)制(zhi)器都集成(cheng)了(le)控(kong)制(zhi)电(dian)(dian)(dian)路(lu)(lu)(lu)(lu)和(he)(he)升(sheng)压开关管，但是(shi)(shi)电(dian)(dian)(dian)感(gan)和(he)(he)用(yong)(yong)于续流的(de)(de)(de)肖(xiao)特基二极管还是(shi)(shi)外接(jie)的(de)(de)(de)，这增加了(le)电(dian)(dian)(dian)路(lu)(lu)(lu)(lu)的(de)(de)(de)复杂(za)性、成(cheng)本和(he)(he)PCB面(mian)积。此(ci)外，由于闪(shan)(shan)光(guang)灯驱(qu)功电(dian)(dian)(dian)路(lu)(lu)(lu)(lu)、LED闪(shan)(shan)光(guang)灯显示屏(ping)、移(yi)动(dong)电(dian)(dian)(dian)话(hua)的(de)(de)(de)天线一般位于移(yi)动(dong)电(dian)(dian)(dian)话(hua)上端，与移(yi)动(dong)电(dian)(dian)(dian)话(hua)的(de)(de)(de)射频电(dian)(dian)(dian)路(lu)(lu)(lu)(lu)靠得(de)很(hen)近(jin)，所以有(you)效(xiao)防止驱(qu)动(dong)电(dian)(dian)(dian)路(lu)(lu)(lu)(lu)电(dian)(dian)(dian)感(gan)的(de)(de)(de)EMI干(gan)扰(rao)也(ye)是(shi)(shi)很(hen)重(zhong)要(yao)的(de)(de)(de)问题(ti)。图1是(shi)(shi)采用(yong)(yong)电(dian)(dian)(dian)感(gan)升(sheng)压变换(huan)器驱(qu)动(dong)标准(zhun)白(bai)光(guang)LED的(de)(de)(de)典型(xing)应(ying)用(yong)(yong)电(dian)(dian)(dian)路(lu)(lu)(lu)(lu)。电(dian)(dian)(dian)荷泵采用(yong)(yong)电(dian)(dian)(dian)容(rong)作储能元件(jian)，且不需要(yao)外接(jie)电(dian)(dian)(dian)感(gan)，因(yin)此(ci)不存在电(dian)(dian)(dian)磁(ci)干(gan)扰(rao)的(de)(de)(de)问题(ti)。此(ci)外，整个解决(jue)方案所占PCB的(de)(de)(de)面(mian)积也(ye)较(jiao)小，但相对来说效(xiao)率较(jiao)低。由于闪(shan)(shan)光(guang)灯工作时间非常短，持续时间一般为100～300ms，所以其效(xiao)率对电(dian)(dian)(dian)池使用(yong)(yong)时间的(de)(de)(de)影响不是(shi)(shi)太(tai)大(da)。图2是(shi)(shi)采用(yong)(yong)电(dian)(dian)(dian)荷泵驱(qu)动(dong)标准(zhun)白(bai)光(guang)LED的(de)(de)(de)应(ying)用(yong)(yong)电(dian)(dian)(dian)路(lu)(lu)(lu)(lu)。

图(tu)1 采(cai)用电感升(sheng)压变(bian)换器驱(qu)动标(biao)准白光LED

图2 采用电荷泵驱动标准白光LED的(de)应用电路(lu)

在白(bai)光(guang)LED驱(qu)动(dong)电(dian)(dian)路的(de)(de)设计中，有两个(ge)参数会影响设计方(fang)(fang)案的(de)(de)选择(ze)，一个(ge)是(shi)(shi)白(bai)光(guang)LED正(zheng)(zheng)向(xiang)电(dian)(dian)压(ya)(ya)，另一个(ge)是(shi)(shi)电(dian)(dian)源的(de)(de)工作电(dian)(dian)压(ya)(ya)。电(dian)(dian)感式升压(ya)(ya)变换器通常用于驱(qu)动(dong)串(chuan)联的(de)(de)白(bai)光(guang)LED，它能够(gou)产(chan)生充是(shi)(shi)的(de)(de)输(shu)出电(dian)(dian)压(ya)(ya)，以(yi)提供可被编程的(de)(de)驱(qu)动(dong)白(bai)光(guang)LED电(dian)(dian)流。采用这种(zhong)驱(qu)动(dong)方(fang)(fang)法(fa)时，因为(wei)无论正(zheng)(zheng)向(xiang)电(dian)(dian)压(ya)(ya)高低(di)，所(suo)有的(de)(de)白(bai)光(guang)LED都(dou)能获得相同的(de)(de)电(dian)(dian)流，又因为(wei)白(bai)光(guang)LED的(de)(de)亮(liang)度(du)(du)与流经(jing)白(bai)光(guang)LED的(de)(de)正(zheng)(zheng)向(xiang)电(dian)(dian)流成(cheng)正(zheng)(zheng)比，所(suo)以(yi)白(bai)光(guang)LED阵(zhen)列的(de)(de)亮(liang)度(du)(du)非常均(jun)衡、和谐。

电(dian)(dian)荷(he)泵(beng)(beng)(beng)可以产生值为输入电(dian)(dian)压整(zheng)数(shu)倍(bei)(bei)的(de)输出(chu)电(dian)(dian)压。若要(yao)提高(gao)其扩大倍(bei)(bei)数(shu)，需增加(jia)泵(beng)(beng)(beng)电(dian)(dian)容和开关电(dian)(dian)路，因此电(dian)(dian)荷(he)泵(beng)(beng)(beng)的(de)实际(ji)输出(chu)电(dian)(dian)压被(bei)限制为了2倍(bei)(bei)的(de)输入电(dian)(dian)压。虽(sui)然有些(xie)电(dian)(dian)荷(he)泵(beng)(beng)(beng)能够提供分数(shu)倍(bei)(bei)输出(chu)电(dian)(dian)压（1.5倍(bei)(bei)），但是需要(yao)2个(ge)泵(beng)(beng)(beng)电(dian)(dian)容。

因(yin)为(wei)2倍压是(shi)最方便(bian)的(de)升压倍数，考虑(lv)到白光(guang)(guang)LED典(dian)型的(de)正向电(dian)(dian)压，则电(dian)(dian)荷(he)泵方法主要用于驱动并联的(de)白光(guang)(guang)LED。因(yin)为(wei)每个(ge)并联支路的(de)白光(guang)(guang)LED必须独立控(kong)制，这必然会导(dao)致(zhi)白光(guang)(guang)LED阵列之间出现轻微的(de)亮度失谐，这种亮度失谐现象(xiang)在电(dian)(dian)荷(he)泵驱动方法中是(shi)不可避免的(de)。

与(yu)整数(shu)倍(bei)压(ya)(ya)电荷泵驱动方(fang)法相比，电感升(sheng)压(ya)(ya)变换(huan)器(qi)的(de)效率更(geng)高。改用(yong)分(fen)数(shu)倍(bei)压(ya)(ya)电荷泵虽然可以(yi)提(ti)高性能，但是其(qi)远不如(ru)(ru)电感升(sheng)压(ya)(ya)变换(huan)器(qi)设计(ji)(ji)方(fang)案。因为在(zai)电感升(sheng)压(ya)(ya)变换(huan)器(qi)设计(ji)(ji)中，白(bai)(bai)光LED是串联的(de)，所以(yi)升(sheng)压(ya)(ya)控制器(qi)与(yu)白(bai)(bai)光LED之间只需两条PCB走(zou)线。这在(zai)设计(ji)(ji)上(shang)是一(yi)(yi)个(ge)很重(zhong)要的(de)优势，例如(ru)(ru)，如(ru)(ru)果(guo)白(bai)(bai)光LED的(de)数(shu)量发生(sheng)了变化，或者单独安装在(zai)一(yi)(yi)个(ge)相机(ji)闪光模(mo)块上(shang)，则电感升(sheng)压(ya)(ya)变换(huan)器(qi)的(de)设计(ji)(ji)很容易适应这种变化，而采用(yong)电荷泵方(fang)案的(de)PCB必须(xu)完全重(zhong)新设计(ji)(ji)。

虽(sui)然电(dian)(dian)(dian)感升(sheng)压(ya)变(bian)(bian)换器(qi)设计(ji)的(de)引脚数量(liang)少，且(qie)允(yun)许(xu)使(shi)用比(bi)电(dian)(dian)(dian)荷泵设计(ji)更小的(de)封装(zhuang)，但是电(dian)(dian)(dian)感升(sheng)压(ya)变(bian)(bian)换器(qi)需要(yao)电(dian)(dian)(dian)感器(qi)，这会导致(zhi)占PCB的(de)总体面积(ji)变(bian)(bian)大、变(bian)(bian)厚。另外，与电(dian)(dian)(dian)荷泵设计(ji)中(zhong)的(de)泵电(dian)(dian)(dian)容对比(bi)，其外接(jie)电(dian)(dian)(dian)感器(qi)成本昂(ang)贵。另外，电(dian)(dian)(dian)感升(sheng)压(ya)变(bian)(bian)换器(qi)的(de)噪声通常(chang)比(bi)电(dian)(dian)(dian)荷泵高，因此(ci)为了限(xian)制或避免不同组件之间的(de)干(gan)扰，需要(yao)更精确的(de)设计(ji)。

LED驱动电源电路图分析

原理(li)分(fen)析：为了方便分(fen)析，我把它分(fen)成几个部(bu)分(fen)来讲(jiang)，尽(jin)量分(fen)的细一点来讲(jiang)，如下：

1：输入过压保护---主要(yao)是雷击(ji)或者市冲(chong)击(ji)带来的浪涌）

2：整流滤波电路---将交流（或者是(shi)直流）变成(cheng)直流的过程

3：箝位电路(lu)---------主要是吸收变(bian)压器(qi)工作(zuo)时产(chan)生的尖峰(feng)和反向电动势

4：IC工作过(guo)程--------主要是(shi)IC的(de)供电(dian)原理，变压器的(de)工作方式，电(dian)压变换(huan)过(guo)程。

5：输出整流---------将(jiang)交流再次变成平滑理想(xiang)的直流电压过程

6：恒流(liu)原(yuan)理(li)---------电(dian)路中稳定输出电(dian)流(liu)控制过程分析

1、 输入过压保护电路

首先(xian)电(dian)(dian)压从(cong)(cong)“+48V、GNG”两(liang)端进来通过(guo)一(yi)个R1的(de)电(dian)(dian)阻(zu)（这个电(dian)(dian)阻(zu)的(de)作用就是(shi)限(xian)流(liu)(liu)，当(dang)后面(mian)的(de)线(xian)路(lu)(lu)出(chu)现(xian)短路(lu)(lu)时(shi)，R1流(liu)(liu)过(guo)的(de)电(dian)(dian)流(liu)(liu)就会增大，随之两(liang)端压降跟着增大，当(dang)超过(guo)1W时(shi)就会自(zi)动断开，阻(zu)值增加至无穷大，从(cong)(cong)而达(da)到(dao)(dao)保(bao)护输入(ru)电(dian)(dian)路(lu)(lu)+48V不受到(dao)(dao)负载的(de)影(ying)响）限(xian)流(liu)(liu)后进入(ru)整流(liu)(liu)桥，另一(yi)方面(mian)R1与旁边的(de)MOV1构成(cheng)了(le)一(yi)个简单(dan)过(guo)压保(bao)护电(dian)(dian)路(lu)(lu)，MOV1是(shi)一(yi)个压敏元件，是(shi)利用具有非线(xian)性的(de)半导(dao)体材料制作的(de)而成(cheng)，其(qi)伏安(an)特性与稳压二极(ji)管差不多，正(zheng)常情况(kuang)显(xian)高(gao)阻(zu)抗状态，流(liu)(liu)过(guo)的(de)电(dian)(dian)流(liu)(liu)很少，当(dang)电(dian)(dian)压高(gao)到(dao)(dao)一(yi)定的(de)时(shi)候（这里主要是(shi)指尖峰浪涌，如打雷的(de)时(shi)候高(gao)脉冲串(chuan)通过(guo)市电(dian)(dian)串(chuan)入(ru)进来），压敏MOV1会显(xian)现(xian)短路(lu)(lu)状态，直接(jie)截取整个输入(ru)总电(dian)(dian)流(liu)(liu)，使后面(mian)的(de)电(dian)(dian)路(lu)(lu)停止工作，这时(shi)候，由于所有电(dian)(dian)流(liu)(liu)将流(liu)(liu)过(guo)R1和(he)MOV1，因R1只有1W的(de)功率，所以(yi)瞬间(jian)可以(yi)开路(lu)(lu)，从(cong)(cong)而保(bao)护了(le)整个电(dian)(dian)路(lu)(lu)不被损坏。

2、 整流滤波电路

当+48V电(dian)(dian)压进入整流(liu)(liu)桥D1时，输出一(yi)个上(shang)正下(xia)负的(de)(de)(de)直(zhi)(zhi)流(liu)(liu)电(dian)(dian)压（这里我要说明一(yi)下(xia)，如(ru)果+48V是(shi)(shi)交流(liu)(liu)的(de)(de)(de)那(nei)么直(zhi)(zhi)接(jie)整流(liu)(liu)，如(ru)果+48V电(dian)(dian)源本(ben)身也是(shi)(shi)直(zhi)(zhi)流(liu)(liu)的(de)(de)(de)，那(nei)整流(liu)(liu)桥的(de)(de)(de)作用就(jiu)是(shi)(shi)对(dui)输入起(qi)到的(de)(de)(de)是(shi)(shi)极性保护作用，无(wu)论输入是(shi)(shi)上(shang)正下(xia)负还是(shi)(shi)上(shang)负下(xia)正都(dou)不会(hui)损坏(huai)驱动电(dian)(dian)源）通过C1\C2\L1进行滤波，这是(shi)(shi)一(yi)个LC Π型滤波电(dian)(dian)路，目(mu)的(de)(de)(de)是(shi)(shi)将整流(liu)(liu)后(hou)的(de)(de)(de)电(dian)(dian)压波形平滑的(de)(de)(de)直(zhi)(zhi)流(liu)(liu)电(dian)(dian)。

3、 箝位吸收电路

这个(ge)(ge)(ge)(ge)箝(qian)路(lu)(lu)电(dian)(dian)(dian)路(lu)(lu)存在(zai)(zai)的(de)(de)理由其实就是(shi)(shi)(shi)保护IC里(li)面的(de)(de)MOS管(guan)，其过(guo)程为－－整(zheng)流(liu)滤波以(yi)后的(de)(de)电(dian)(dian)(dian)压分成2路(lu)(lu)，一路(lu)(lu)通(tong)过(guo)变(bian)压器(qi)(qi)绕组后进(jin)(jin)入(ru)IC TK5401的(de)(de)第7、8脚，这个(ge)(ge)(ge)(ge)我(wo)们等下在(zai)(zai)后面来讲，先看箝(qian)位(wei)(wei)这一路(lu)(lu)，这路(lu)(lu)是(shi)(shi)(shi)通(tong)过(guo)R1、C3、D2然后也(ye)连到7、8脚，这个(ge)(ge)(ge)(ge)R1、C3、D2就组成了一个(ge)(ge)(ge)(ge)简单的(de)(de)箝(qian)位(wei)(wei)电(dian)(dian)(dian)路(lu)(lu)，主要功能就是(shi)(shi)(shi)用(yong)来吸(xi)收尖(jian)峰和浪涌(yong)的(de)(de)，这和刚才输入(ru)那个(ge)(ge)(ge)(ge)MOV1是(shi)(shi)(shi)不一样的(de)(de)，MOV1主要是(shi)(shi)(shi)防止打雷或者市电(dian)(dian)(dian)冲击起到保护作用(yong)，这个(ge)(ge)(ge)(ge)箝(qian)位(wei)(wei)它的(de)(de)功能是(shi)(shi)(shi)吸(xi)收变(bian)压器(qi)(qi)T1绕组两端的(de)(de)反(fan)向(xiang)电(dian)(dian)(dian)动(dong)势(shi)，以(yi)消(xiao)除自激振荡，说(shuo)白了就是(shi)(shi)(shi)快(kuai)速(su)(su)复(fu)位(wei)(wei)的(de)(de)意思，为变(bian)压器(qi)(qi)进(jin)(jin)入(ru)下一个(ge)(ge)(ge)(ge)周(zhou)(zhou)期做好准备，因为如果(guo)变(bian)压器(qi)(qi)得不到复(fu)位(wei)(wei)就会饱和，这样就会失去感抗，这个(ge)(ge)(ge)(ge)R1和C3就组成了一个(ge)(ge)(ge)(ge)RC充放(fang)电(dian)(dian)(dian)回路(lu)(lu)，用(yong)来反(fan)向(xiang)积累的(de)(de)电(dian)(dian)(dian)动(dong)势(shi)，D2主要是(shi)(shi)(shi)隔离(li)作用(yong)，就在(zai)(zai)变(bian)压器(qi)(qi)在(zai)(zai)正半周(zhou)(zhou)的(de)(de)时(shi)候(hou)（就是(shi)(shi)(shi)感应电(dian)(dian)(dian)动(dong)势(shi)为上正下负时(shi)）使整(zheng)过(guo)环路(lu)(lu)处于(yu)断开状(zhuang)(zhuang)态(tai)，而等变(bian)压器(qi)(qi)进(jin)(jin)入(ru)负半周(zhou)(zhou)时(shi)，给(ji)(ji)箝(qian)位(wei)(wei)电(dian)(dian)(dian)路(lu)(lu)提供(gong)通(tong)路(lu)(lu)，快(kuai)速(su)(su)将电(dian)(dian)(dian)动(dong)势(shi)环路(lu)(lu)处于(yu)断开状(zhuang)(zhuang)态(tai)，而等变(bian)压器(qi)(qi)进(jin)(jin)入(ru)负半周(zhou)(zhou)时(shi)，给(ji)(ji)箝(qian)位(wei)(wei)电(dian)(dian)(dian)路(lu)(lu)提供(gong)通(tong)路(lu)(lu)，快(kuai)速(su)(su)将电(dian)(dian)(dian)动(dong)势(shi)释放(fang)，从而达到保护IC里(li)头(tou)的(de)(de)MOS管(guan)不被尖(jian)峰击穿而损坏。

4、 IC工作原理

这(zhei)(zhei)里面的(de)(de)(de)(de)(de)(de)变(bian)(bian)压器，根据它(ta)(ta)的(de)(de)(de)(de)(de)(de)同(tong)名(ming)端判断(duan)为反(fan)激(ji)式(shi)(shi)工作方式(shi)(shi)，就(jiu)(jiu)是(shi)(shi)变(bian)(bian)压器的(de)(de)(de)(de)(de)(de)初级和(he)次级的(de)(de)(de)(de)(de)(de)相位是(shi)(shi)相反(fan)的(de)(de)(de)(de)(de)(de)，在(zai)同(tong)一时(shi)间(jian)，两者相关(guan)180度，目前也有(you)正激(ji)式(shi)(shi)的(de)(de)(de)(de)(de)(de)，那(nei)就(jiu)(jiu)是(shi)(shi)同(tong)频同(tong)相，这(zhei)(zhei)个(ge)(ge)(ge)将来有(you)机会了(le)我(wo)(wo)(wo)再和(he)大家具体分享；我(wo)(wo)(wo)们还(hai)是(shi)(shi)回到这(zhei)(zhei)个(ge)(ge)(ge)IC问题上面来，这(zhei)(zhei)个(ge)(ge)(ge)IC有(you)8个(ge)(ge)(ge)脚(jiao)，这(zhei)(zhei)里我(wo)(wo)(wo)边讲(jiang)边介绍它(ta)(ta)引脚(jiao)的(de)(de)(de)(de)(de)(de)功能，我(wo)(wo)(wo)们接(jie)(jie)着刚刚那(nei)个(ge)(ge)(ge)说的(de)(de)(de)(de)(de)(de)那(nei)个(ge)(ge)(ge)整流滤波(bo)后通(tong)(tong)(tong)过变(bian)(bian)压器绕组然(ran)后进到IC的(de)(de)(de)(de)(de)(de)7、8脚(jiao)，这(zhei)(zhei)个(ge)(ge)(ge)7、8脚(jiao)就(jiu)(jiu)是(shi)(shi)IC里面MOS管(guan)的(de)(de)(de)(de)(de)(de)“D极(ji)”也叫漏(lou)极(ji)（相当于以(yi)前NPN三极(ji)管(guan)或者开(kai)关(guan)管(guan)的(de)(de)(de)(de)(de)(de)集(ji)电极(ji)），另外接(jie)(jie)地(di)的(de)(de)(de)(de)(de)(de)是(shi)(shi)“S极(ji)”也叫源极(ji)，整过电源电压的(de)(de)(de)(de)(de)(de)变(bian)(bian)换都由D极(ji)”和(he)S极(ji)两个(ge)(ge)(ge)引脚(jiao)的(de)(de)(de)(de)(de)(de)接(jie)(jie)通(tong)(tong)(tong)和(he)断(duan)开(kai)来实(shi)现(xian)，就(jiu)(jiu)是(shi)(shi)它(ta)(ta)们工作时(shi)会一直处在(zai)接(jie)(jie)通(tong)(tong)(tong)和(he)不接(jie)(jie)通(tong)(tong)(tong)状态，反(fan)复的(de)(de)(de)(de)(de)(de)接(jie)(jie)通(tong)(tong)(tong)和(he)断(duan)开(kai)使变(bian)(bian)压器实(shi)现(xian)在(zai)电－－磁－电的(de)(de)(de)(de)(de)(de)变(bian)(bian)换，至(zhi)于它(ta)(ta)是(shi)(shi)怎么进行接(jie)(jie)通(tong)(tong)(tong)和(he)不接(jie)(jie)通(tong)(tong)(tong)的(de)(de)(de)(de)(de)(de)？这(zhei)(zhei)个(ge)(ge)(ge)频率又是(shi)(shi)多少？

开始进行工作信号分析

A第一次变换的建立：就是第一个波形是怎么来的，当IC的7、8上电以后，电压另一方面通过IC的7、8脚连通的内部启动电路给IC供电，使用IC开始工作，此时IC将输出第1个方波脉冲传递给IC内部MOS管的“G极”也叫栅极，使D极和S极接通，这时D极和S级等电位，而S极又是接地的，也就等于把变压器的一端瞬间接地，从而产生回路，我们都知道变压器是感性元件，就是电流不能突变，所以它自身会产生感抗来阻止电流突变。从而按照线性的曲线进行变化，就像这个波形一样，它是慢慢上升，为了能够阻止它突然，它会产生一个与它相反的感应电压势来抑制它，这样一来，下面的绕组和次组绕组就会跟着产生电动势，从而产生电压，电—磁—电转换的机理也在于此，当然这是变压器和磁性材料本身具有的特性。

B第二次变换的建立：当变压器下面的绕组产生电动势以后（我们通常把它叫着正反馈供电绕组），通过D3整流，R3限流，再经C4滤波后分成二路进行供电，一路给IC的第2脚供电，另一路给光电耦合器件M10B供电，这个光耦我们讲稳压的时候再讲，当第2脚开 始供电时，IC内部的整个PWM供电控制系统将自动转到由正反馈绕组供电，使内部振荡电路继续工作，从而输出第2个脉冲控制信息，使MOS管开次开通，如此周而复始的使用MOS不断的处理开和关状态进而让变压器工作在电－磁－电的转换状态。这里我提到了PWM供电控制系统和内部振荡电路，可能让大家有觉得有些含糊，我会把它们单独抽出来最好是用分立元件来描述它们的信号流程和工作原理，这样可能就形象，通俗易懂一些，那时候再融入到这个电路里面来理解可能就不会抽象了，现在的电路都是集成电路了，内部的信息流程就不太好形象化，让我们只知道它的功能，不知道它的进程，这样总是不能够加深对它的理解，我个认为最好是用分立元件来分析它。

5、输出整流电路

变(bian)压器工作以后(hou)，次级就(jiu)(jiu)会输(shu)出(chu)一个电压通(tong)过(guo)D4整流，C8和(he)L1进行(xing)滤波，然(ran)后(hou)给LED灯(deng)进行(xing)供电，这里(li)的L1除了能(neng)够滤波，还有续(xu)流的作用，就(jiu)(jiu)是保持输(shu)出(chu)电流的一致性，正(zheng)是利用电感中(zhong)的电流不能(neng)突然(ran)这一特性。

6、恒流电路

它(ta)的(de)(de)(de)(de)工作(zuo)过程，最后(hou)(hou)讲(jiang)一(yi)下(xia)(xia)(xia)这(zhei)(zhei)是(shi)怎(zen)么(me)实(shi)现恒流(liu)(liu)的(de)(de)(de)(de)，顺便先讲(jiang)了一(yi)下(xia)(xia)(xia)这(zhei)(zhei)个IC的(de)(de)(de)(de)每(mei)个引(yin)脚(jiao)(jiao)(jiao)(jiao)功能，8脚(jiao)(jiao)(jiao)(jiao)为MOS输(shu)入端，6脚(jiao)(jiao)(jiao)(jiao)是(shi)空脚(jiao)(jiao)(jiao)(jiao)，5脚(jiao)(jiao)(jiao)(jiao)外(wai)(wai)接(jie)(jie)的(de)(de)(de)(de)电(dian)(dian)(dian)(dian)容(rong)(rong)是(shi)振(zhen)荡电(dian)(dian)(dian)(dian)容(rong)(rong)，它(ta)的(de)(de)(de)(de)容(rong)(rong)量直接(jie)(jie)决(jue)定了RC时(shi)(shi)(shi)间常(chang)(chang)数(shu)，就是(shi)充放(fang)电(dian)(dian)(dian)(dian)时(shi)(shi)(shi)间，一(yi)般充电(dian)(dian)(dian)(dian)MOS管是(shi)接(jie)(jie)通(tong)(tong)(tong)时(shi)(shi)(shi)间，放(fang)电(dian)(dian)(dian)(dian)是(shi)断(duan)开(kai)时(shi)(shi)(shi)间，第4脚(jiao)(jiao)(jiao)(jiao)是(shi)电(dian)(dian)(dian)(dian)压(ya)(ya)(ya)(ya)检(jian)测(ce)脚(jiao)(jiao)(jiao)(jiao)，通(tong)(tong)(tong)过对(dui)第4脚(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)电(dian)(dian)(dian)(dian)压(ya)(ya)(ya)(ya)值控制(zhi)输(shu)出脉(mai)(mai)冲的(de)(de)(de)(de)占空比(bi)，把(ba)引(yin)脚(jiao)(jiao)(jiao)(jiao)说完了就重(zhong)点讲(jiang)第4脚(jiao)(jiao)(jiao)(jiao)；第3脚(jiao)(jiao)(jiao)(jiao)接(jie)(jie)地端，第2脚(jiao)(jiao)(jiao)(jiao)是(shi)IC供电(dian)(dian)(dian)(dian)脚(jiao)(jiao)(jiao)(jiao)，第1脚(jiao)(jiao)(jiao)(jiao)外(wai)(wai)接(jie)(jie)的(de)(de)(de)(de)电(dian)(dian)(dian)(dian)阻和第5脚(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)电(dian)(dian)(dian)(dian)容(rong)(rong)组成了RC电(dian)(dian)(dian)(dian)路(lu)(lu)，给IC内(nei)部提(ti)供振(zhen)荡源，脉(mai)(mai)冲的(de)(de)(de)(de)充放(fang)电(dian)(dian)(dian)(dian)时(shi)(shi)(shi)间常(chang)(chang)直接(jie)(jie)由这(zhei)(zhei)个电(dian)(dian)(dian)(dian)阻和电(dian)(dian)(dian)(dian)容(rong)(rong)决(jue)定。我们现在来重(zhong)点讲(jiang)第4脚(jiao)(jiao)(jiao)(jiao)，大(da)家(jia)看4脚(jiao)(jiao)(jiao)(jiao)外(wai)(wai)接(jie)(jie)的(de)(de)(de)(de)光耦(ou)M101B接(jie)(jie)到(dao)那里(li)去(qu)了？另(ling)一(yi)端PC817是(shi)不是(shi)和输(shu)出电(dian)(dian)(dian)(dian)路(lu)(lu)R4两端相(xiang)(xiang)并(bing)联了，这(zhei)(zhei)个R7在这(zhei)(zhei)里(li)是(shi)起(qi)到(dao)检(jian)测(ce)电(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)作(zuo)用，根据电(dian)(dian)(dian)(dian)压(ya)(ya)(ya)(ya)＝电(dian)(dian)(dian)(dian)流(liu)(liu)*电(dian)(dian)(dian)(dian)阻的(de)(de)(de)(de)原理(li)，这(zhei)(zhei)个电(dian)(dian)(dian)(dian)流(liu)(liu)越大(da)，R4两端的(de)(de)(de)(de)电(dian)(dian)(dian)(dian)压(ya)(ya)(ya)(ya)就会(hui)(hui)(hui)越大(da)，这(zhei)(zhei)样(yang)说大(da)家(jia)应该明白吧？电(dian)(dian)(dian)(dian)压(ya)(ya)(ya)(ya)越大(da)，那么(me)并(bing)连到(dao)R4两端的(de)(de)(de)(de)PC817也会(hui)(hui)(hui)有电(dian)(dian)(dian)(dian)压(ya)(ya)(ya)(ya)并(bing)且开(kai)始导(dao)通(tong)(tong)(tong)，导(dao)通(tong)(tong)(tong)后(hou)(hou)副边(bian)的(de)(de)(de)(de)M101B也会(hui)(hui)(hui)跟着导(dao)通(tong)(tong)(tong)，就是(shi)它(ta)内(nei)阻下(xia)(xia)(xia)降，这(zhei)(zhei)样(yang)一(yi)来第4脚(jiao)(jiao)(jiao)(jiao)的(de)(de)(de)(de)电(dian)(dian)(dian)(dian)压(ya)(ya)(ya)(ya)就会(hui)(hui)(hui)上升，上升以后(hou)(hou)与IC里(li)面的(de)(de)(de)(de)基础电(dian)(dian)(dian)(dian)压(ya)(ya)(ya)(ya)相(xiang)(xiang)对(dui)比(bi)，然(ran)后(hou)(hou)会(hui)(hui)(hui)直接(jie)(jie)输(shu)出一(yi)个信号使MOS管提(ti)成关(guan)断(duan)，从而达到(dao)恒流(liu)(liu)目的(de)(de)(de)(de)。

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