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MOS开关电源原理

线(xian)性电源的动(dong)态(tai)(tai)响(xiang)应非常快，稳压性能(neng)好，只可惜其功(gong)率转(zhuan)(zhuan)换(huan)效率太低。要想提(ti)高效率，就必须使图 1-2中的功(gong)率调整(zheng)器件(jian)（即调整(zheng)管(guan)）处于开关上(shang)作状态(tai)(tai)，再对图1-2所(suo)示(shi)电路相应地(di)稍加改变即成(cheng)为开关型稳压电源。转(zhuan)(zhuan)变后的降(jiang)(jiang)压型开关电源原理图如图1-8所(suo)示(shi)。调整(zheng)管(guan)作为开关而言，导(dao)通时（压降(jiang)(jiang)小(xiao)）几乎(hu)不消耗能(neng)量(liang)(liang)，关断时漏电流很小(xiao)，也(ye)几乎(hu)不消耗能(neng)量(liang)(liang)，从而大大提(ti)高了转(zhuan)(zhuan)换(huan)效率，其功(gong)率转(zhuan)(zhuan)换(huan)效率可达80%以上(shang)。

在图1-8中，波动的直流电压U输入高频变换器（即开关管VT和碳化硅二极管VD），经高(gao)频(pin)(pin)变(bian)换器(qi)(qi)(qi)转变(bian)为高(gao)频(pin)(pin)(≥20kHz)脉(mai)(mai)冲(chong)方波(bo)(bo)电(dian)(dian)(dian)压(ya)(ya)(ya)，该脉(mai)(mai)冲(chong)j‘波(bo)(bo)电(dian)(dian)(dian)压(ya)(ya)(ya)通过输(shu)出(chu)滤(lv)波(bo)(bo)器(qi)(qi)(qi)（电(dian)(dian)(dian)感(gan)L和(he)电(dian)(dian)(dian)容c）变(bian)成平(ping)滑的(de)(de)直(zhi)流电(dian)(dian)(dian)压(ya)(ya)(ya)供给负载(zai)。高(gao)频(pin)(pin)变(bian)换器(qi)(qi)(qi)和(he)输(shu)出(chu)滤(lv)波(bo)(bo)器(qi)(qi)(qi)一起构成主回(hui)路，完成能量处理任务(wu)。而(er)稳定(ding)输(shu)出(chu)电(dian)(dian)(dian)压(ya)(ya)(ya)的(de)(de)任务(wu)是靠控制(zhi)(zhi)回(hui)路对(dui)主回(hui)路的(de)(de)控制(zhi)(zhi)作用(yong)来(lai)实现(xian)的(de)(de)。控制(zhi)(zhi)回(hui)路包括取(qu)样电(dian)(dian)(dian)压(ya)(ya)(ya)部分、基准(zhun)电(dian)(dian)(dian)压(ya)(ya)(ya)部分、比(bi)较放大(da)器(qi)(qi)(qi)（误差放大(da)器(qi)(qi)(qi)）、电(dian)(dian)(dian)压(ya)(ya)(ya)／脉(mai)(mai)冲(chong)转换器(qi)(qi)(qi)等(deng)。开(kai)关(guan)电(dian)(dian)(dian)源(yuan)稳定(ding)输(shu)出(chu)电(dian)(dian)(dian)压(ya)(ya)(ya)可(ke)以直(zhi)观理解为通过控制(zhi)(zhi)滤(lv)波(bo)(bo)电(dian)(dian)(dian)容的(de)(de)充(chong)、放点(dian)时间来(lai)实现(xian)。

具体的(de)(de)(de)MOS稳(wen)压(ya)(ya)(ya)过(guo)程为：MOS当(dang)开(kai)关电(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)负(fu)载(zai)电(dian)(dian)(dian)(dian)(dian)(dian)流增(zeng)大或输(shu)(shu)(shu)入电(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)U降低(di)时，输(shu)(shu)(shu)出(chu)(chu)电(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)U轻(qing)微下降，控制(zhi)回路(lu)就(jiu)使(shi)高(gao)频变(bian)换器(qi)输(shu)(shu)(shu)出(chu)(chu)的(de)(de)(de)脉冲方波(bo)的(de)(de)(de)宽度变(bian)宽，即给电(dian)(dian)(dian)(dian)(dian)(dian)容(rong)多充(chong)电(dian)(dian)(dian)(dian)(dian)(dian)点(dian)( 充(chong)电(dian)(dian)(dian)(dian)(dian)(dian)时间(jian)加长），少放点(dian)电(dian)(dian)(dian)(dian)(dian)(dian)（放电(dian)(dian)(dian)(dian)(dian)(dian)时间(jian)减短），从(cong)而(er)使(shi)电(dian)(dian)(dian)(dian)(dian)(dian)容(rong)C上的(de)(de)(de)电(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)（即输(shu)(shu)(shu)出(chu)(chu)电(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)）回升起到稳(wen)定输(shu)(shu)(shu)出(chu)(chu)电(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)的(de)(de)(de)作(zuo)用。反(fan)之(zhi)，、当(dang)外界因(yin)素引起输(shu)(shu)(shu)出(chu)(chu)电(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)偏高(gao)时，控制(zhi)电(dian)(dian)(dian)(dian)(dian)(dian)路(lu)使(shi)高(gao)频变(bian)换器(qi)输(shu)(shu)(shu)出(chu)(chu)脉冲方波(bo)的(de)(de)(de)宽度变(bian)窄，即给电(dian)(dian)(dian)(dian)(dian)(dian)容(rong)少充(chong)点(dian)电(dian)(dian)(dian)(dian)(dian)(dian)，从(cong)而(er)使(shi)电(dian)(dian)(dian)(dian)(dian)(dian)容(rong)c上的(de)(de)(de)电(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)同(tong)落，稳(wen)定输(shu)(shu)(shu)出(chu)(chu)电(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)。

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