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单片开(kai)关电源的基本原理

信(xin)息来源：本站(zhan)　日(ri)期：2017-05-20　

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单(dan)片开关电源的基本原理(li)

单片MOS开关电源的(de)典(dian)型应(ying)用(yong)电(dian)(dian)(dian)路如图1-13所(suo)示。由于单(dan)端反(fan)激式(shi)(shi)开关(guan)电(dian)(dian)(dian)源电(dian)(dian)(dian)路简(jian)单(dan)、所(suo)用(yong)元件少，输出与(yu)输人间有(you)电(dian)(dian)(dian)气(qi)隔(ge)离，能方便地(di)实现多(duo)路输出，开关(guan)管(guan)驱动简(jian)单(dan)，所(suo)以该(gai)电(dian)(dian)(dian)源便采(cai)用(yong)了单(dan)端反(fan)激式(shi)(shi)拓(tuo)扑(pu)结构(gou)。由图1-13可知，高(gao)频(pin)变(bian)压(ya)(ya)器(qi)初级(ji)绕(rao)(rao)组(zu)NP的(de)极(ji)性(xing)与(yu)次级(ji)绕(rao)(rao)组(zu)反(fan)馈绕(rao)(rao)组(zu)NF的(de)极(ji)性(xing)相(xiang)反(fan)。当导(dao)通时，次级(ji)整(zheng)流(liu)管(guan)VD2截(jie)止(zhi)，此(ci)时电(dian)(dian)(dian)能以磁能量形式(shi)(shi)存储(chu)(chu)在(zai)(zai)初级(ji)绕(rao)(rao)组(zu)中(zhong)；当截(jie)止(zhi)时，VD2导(dao)通，能量传(chuan)输给(ji)次级(ji)。高(gao)频(pin)变(bian)压(ya)(ya)器(qi)在(zai)(zai)电(dian)(dian)(dian)路中(zhong)兼有(you)能量存储(chu)(chu)、隔(ge)离输出和电(dian)(dian)(dian)压(ya)(ya)变(bian)换三大(da)功(gong)能。在(zai)(zai)图l-13中(zhong)，BR整(zheng)流(liu)桥，CIN为(wei)输入端滤波(bo)电(dian)(dian)(dian)容，为(wei)输出滤波(bo)电(dian)(dian)(dian)容。交(jiao)流(liu)电(dian)(dian)(dian)压(ya)(ya)UAC经(jing)过整(zheng)流(liu)滤波(bo)后得到直(zhi)流(liu)高(gao)压(ya)(ya)U1,经(jing)高(gao)频(pin)变(bian)压(ya)(ya)器(qi)的(de)初级(ji)绕(rao)(rao)组(zu)加(jia)(jia)至的(de)漏(lou)极(ji)上(shang)(shang)(shang)。在(zai)(zai)MOS关(guan)断瞬间，高(gao)频(pin)变(bian)压(ya)(ya)器(qi)的(de)漏(lou)感会(hui)产生(sheng)尖峰电(dian)(dian)(dian)压(ya)(ya)。另(ling)外(wai)，其在(zai)(zai)初级(ji)饶组(zu)上(shang)(shang)(shang)还会(hui)产生(sheng)感应(ying)电(dian)(dian)(dian)压(ya)(ya)（其反(fan)向电(dian)(dian)(dian)动势）uoR，两者(zhe)叠(die)加(jia)(jia)在(zai)(zai)直(zhi)流(liu)输入电(dian)(dian)(dian)压(ya)(ya)Ul上(shang)(shang)(shang)，加(jia)(jia)至内(nei)MOSFET的(de)漏(lou)极(ji)上(shang)(shang)(shang)，因此(ci)，必须在(zai)(zai)漏(lou)极(ji)增位(wei)保护电(dian)(dian)(dian)路。钳位(wei)保护电(dian)(dian)(dian)路由瞬态电(dian)(dian)(dian)压(ya)(ya)抑制器(qi)或稳(wen)压(ya)(ya)二极(ji)管(guan)VXz,阻塞

二极管VD1组成，VD1宜采用超快恢复二极管。当MOS导通(tong)时，变压(ya)器的(de)(de)初级极性(xing)为上(shang)正下(xia)负，从而导致VD1截(jie)止，因而钳(qian)位保护电路(lu)不起作用(yong)。在(zai)MOS截(jie)止瞬(shun)间，变压(ya)器的(de)(de)初级极性(xing)则(ze)变为F_负下(xia)正，此时尖峰电压(ya)就被VDZ1吸收掉。

该电源的稳压原理简述如下：反馈绕组电压经过整流滤波后获得反馈电压，经光耦合器中的光敏三极管给TOPSwitch的控制端提供偏压。CT是控制端c的旁路电容。设稳压二极管vDZ2的稳定电压为Uz2，限流电阻lt．两端的压降为uR．光耦合器由LED发光二极管的正向压降为uF则输出电压UO可表示为Uo=Un+Z2+UR当由于某种原因（如交流电压升高或负载变轻）致使Uo升高时，因Uz2不变，则uF就随之升高，使LED的工作电流，增大，再通过光耦合器使的控制端电流LC增大，但因输出占空比D与lc量反比，故D减小，这就迫使UO降低，从而达到了稳压目的。反之，同样起到(dao)稳压作用。由此可见，反馈电路是通过调占空比(bi)，使(shi)输出电压趋于稳定的。