开关电源,电流,浪涌电流

开关电源概述

开关(guan)电(dian)(dian)(dian)(dian)源(yuan)又(you)称交换(huan)(huan)式(shi)电(dian)(dian)(dian)(dian)源(yuan)、开关(guan)变换(huan)(huan)器(qi)，是(shi)一(yi)种高频化(hua)电(dian)(dian)(dian)(dian)能转换(huan)(huan)装(zhuang)置，是(shi)电(dian)(dian)(dian)(dian)源(yuan)供(gong)应器(qi)的(de)(de)(de)一(yi)种。其功能是(shi)将(jiang)一(yi)个(ge)位准的(de)(de)(de)电(dian)(dian)(dian)(dian)压(ya)，透过不(bu)同形式(shi)的(de)(de)(de)架构转换(huan)(huan)为用户端所需求的(de)(de)(de)电(dian)(dian)(dian)(dian)压(ya)或电(dian)(dian)(dian)(dian)流(liu)(liu)。开关(guan)电(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)输入多半是(shi)交流(liu)(liu)电(dian)(dian)(dian)(dian)源(yuan)（例如(ru)市(shi)电(dian)(dian)(dian)(dian)）或是(shi)直(zhi)流(liu)(liu)电(dian)(dian)(dian)(dian)源(yuan)，而输出多半是(shi)需要直(zhi)流(liu)(liu)电(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)设(she)备，例如(ru)个(ge)人电(dian)(dian)(dian)(dian)脑，而开关(guan)电(dian)(dian)(dian)(dian)源(yuan)就进行两者(zhe)之间电(dian)(dian)(dian)(dian)压(ya)及电(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)转换(huan)(huan)。

开(kai)关(guan)(guan)(guan)电(dian)(dian)(dian)源(yuan)不同于线性电(dian)(dian)(dian)源(yuan)，开(kai)关(guan)(guan)(guan)电(dian)(dian)(dian)源(yuan)利用的切换(huan)晶体管(guan)(guan)多(duo)半是(shi)在(zai)(zai)全(quan)开(kai)模(mo)式（饱和区(qu)）及全(quan)闭(bi)模(mo)式（截止区(qu)）之间切换(huan)，这两(liang)个模(mo)式都有低耗(hao)(hao)散(san)的特(te)点，切换(huan)之间的转(zhuan)换(huan)会(hui)有较高(gao)(gao)的耗(hao)(hao)散(san)，但时间很(hen)短，因此比(bi)较节省能源(yuan)，产(chan)生废热(re)较少。理想(xiang)上，开(kai)关(guan)(guan)(guan)电(dian)(dian)(dian)源(yuan)本身(shen)(shen)是(shi)不会(hui)消(xiao)耗(hao)(hao)电(dian)(dian)(dian)能的。电(dian)(dian)(dian)压(ya)稳压(ya)是(shi)透过(guo)调整晶体管(guan)(guan)导(dao)通及断路的时间来达(da)到。相反的，线性电(dian)(dian)(dian)源(yuan)在(zai)(zai)产(chan)生输出电(dian)(dian)(dian)压(ya)的过(guo)程中，晶体管(guan)(guan)工作(zuo)在(zai)(zai)放(fang)大(da)区(qu)，本身(shen)(shen)也(ye)会(hui)消(xiao)耗(hao)(hao)电(dian)(dian)(dian)能。开(kai)关(guan)(guan)(guan)电(dian)(dian)(dian)源(yuan)的高(gao)(gao)转(zhuan)换(huan)效率(lv)是(shi)其一大(da)优点，而且因为开(kai)关(guan)(guan)(guan)电(dian)(dian)(dian)源(yuan)工作(zuo)频(pin)率(lv)高(gao)(gao)，可以使用小尺寸(cun)、轻重量的变压(ya)器，因此开(kai)关(guan)(guan)(guan)电(dian)(dian)(dian)源(yuan)也(ye)会(hui)比(bi)线性电(dian)(dian)(dian)源(yuan)的尺寸(cun)要小，重量也(ye)会(hui)比(bi)较轻。

若(ruo)(ruo)电源(yuan)的高(gao)效率、体积及重量是(shi)考虑重点时(shi)，开关电源(yuan)比(bi)线性电源(yuan)要(yao)好。不过开关电源(yuan)比(bi)较复杂(za)，内部晶体管会(hui)频繁切换(huan)，若(ruo)(ruo)切换(huan)电流尚加以(yi)处理，可能会(hui)产生噪声(sheng)及电磁(ci)干扰影响其他设备，而且若(ruo)(ruo)开关电源(yuan)没(mei)有特别设计(ji)，其电源(yuan)功率因(yin)数(shu)可能不高(gao)。

浪涌电流概述

通常(chang)在(zai)开(kai)关电(dian)(dian)(dian)(dian)(dian)(dian)源起动(dong)时(shi)，可能(neng)需要输(shu)入(ru)(ru)端(duan)的(de)主(zhu)电(dian)(dian)(dian)(dian)(dian)(dian)网提供(gong)短时(shi)的(de)大电(dian)(dian)(dian)(dian)(dian)(dian)流(liu)脉冲，这种电(dian)(dian)(dian)(dian)(dian)(dian)流(liu)脉冲通常(chang)被(bei)称为“输(shu)入(ru)(ru)浪涌电(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(inrush current)”。输(shu)入(ru)(ru)浪涌电(dian)(dian)(dian)(dian)(dian)(dian)流(liu)首先给主(zhu)电(dian)(dian)(dian)(dian)(dian)(dian)网中的(de)断(duan)(duan)路器(qi)（main circuit breaker）和其(qi)(qi)它(ta)熔断(duan)(duan)器(qi)的(de)选择造成了麻烦(fan)：断(duan)(duan)路器(qi)一方面要保证在(zai)过载时(shi)熔断(duan)(duan)，起到保护作用；另一方面又(you)必须在(zai)输(shu)入(ru)(ru)浪涌电(dian)(dian)(dian)(dian)(dian)(dian)流(liu)出现时(shi)不(bu)能(neng)熔断(duan)(duan)，避免误动(dong)作。其(qi)(qi)次，输(shu)入(ru)(ru)浪涌电(dian)(dian)(dian)(dian)(dian)(dian)流(liu)会产生(sheng)输(shu)入(ru)(ru)电(dian)(dian)(dian)(dian)(dian)(dian)压波形塌(ta)陷(xian)，使供(gong)电(dian)(dian)(dian)(dian)(dian)(dian)质量变差，进而影(ying)响(xiang)其(qi)(qi)它(ta)用电(dian)(dian)(dian)(dian)(dian)(dian)设备(bei)的(de)工作。

出现输入浪涌电流的原因

如图1所(suo)示的开关电(dian)(dian)源中，输入电(dian)(dian)压(ya)首(shou)先(xian)经过(guo)干扰滤波，再通过(guo)桥式(shi)整流(liu)器(qi)变成直流(liu)，然后通过(guo)一个(ge)很(hen)大的电(dian)(dian)解电(dian)(dian)容(rong)器(qi)进行波形(xing)平(ping)滑，之后才能进入真(zhen)正的直流(liu)/直流(liu)转换器(qi)。输入浪(lang)涌电(dian)(dian)流(liu)就是在对这(zhei)个(ge)电(dian)(dian)解电(dian)(dian)容(rong)器(qi)进行初(chu)始充电(dian)(dian)时(shi)产(chan)生的，它的大小(xiao)取决于起(qi)动上(shang)电(dian)(dian)时(shi)输入电(dian)(dian)压(ya)的幅(fu)值(zhi)以及由桥式(shi)整流(liu)器(qi)和电(dian)(dian)解电(dian)(dian)容(rong)器(qi)所(suo)形(xing)成回路的总(zong)电(dian)(dian)阻。如果恰好在交流(liu)输入电(dian)(dian)压(ya)的峰值(zhi)点起(qi)动时(shi)，就会出现峰值(zhi)输入浪(lang)涌电(dian)(dian)流(liu)。

图1 开关电(dian)源输入端简(jian)图

5种抑制冲击电流的方法解析

（一）

最常用(yong)的输(shu)入浪涌电(dian)流(liu)限(xian)(xian)制方法：串联负温(wen)度系(xi)数热敏限(xian)(xian)流(liu)电(dian)阻(zu)器(ntc)

图2 串联NTC限制开机浪涌电流

串(chuan)联负温(wen)(wen)度(du)系数热敏限流(liu)电阻(zu)(zu)器(qi)(qi)ntc无疑是目前(qian)为止最简单(dan)的抑(yi)制输入浪(lang)涌电流(liu)的方法。因为ntc电阻(zu)(zu)器(qi)(qi)会(hui)随温(wen)(wen)度(du)升高而降低。在开关电源起动时，ntc电阻(zu)(zu)器(qi)(qi)处于(yu)常(chang)温(wen)(wen)，有(you)很高的电阻(zu)(zu)，可以有(you)效(xiao)地限制电流(liu)；而在电源起动之后(hou)，ntc电阻(zu)(zu)器(qi)(qi)会(hui)由于(yu)自(zi)身(shen)散(san)热而迅速(su)升温(wen)(wen)至(zhi)约(yue)110oc，电阻(zu)(zu)值则减少(shao)到(dao)室温(wen)(wen)时的约(yue)十五分之一，减少(shao)了(le)开关电源正(zheng)常(chang)工作时的功率损耗。

优点：

电路简单实用、成本低

缺(que)点(dian)：

1. ntc电(dian)(dian)阻器(qi)的(de)限流效果受(shou)环境温度影(ying)响较大：如果在低(di)温（零(ling)下）起(qi)(qi)动(dong)时，电(dian)(dian)阻过(guo)大，充电(dian)(dian)电(dian)(dian)流过(guo)小(xiao)，开(kai)关电(dian)(dian)源可能无法起(qi)(qi)动(dong)；如果在高温起(qi)(qi)动(dong)，电(dian)(dian)阻器(qi)的(de)阻值(zhi)过(guo)小(xiao)，则可能达不到限制输(shu)入浪涌电(dian)(dian)流的(de)效果。

2. 限流效果(guo)在短暂的输入主电(dian)网(wang)中(zhong)断（约几百毫秒(miao)数量级）时只能部分地达到(dao)。在这个短暂的中(zhong)断期间(jian)，电(dian)解(jie)电(dian)容器已被放(fang)电(dian)，而ntc电(dian)阻(zu)器的温度仍很(hen)(hen)高，阻(zu)值很(hen)(hen)小(xiao)，在需要电(dian)源马上重新起动时，ntc无法有效地实现限流作用。

3. ntc电阻器(qi)的功率(lv)(lv)损耗降低了开关电源的转换(huan)效(xiao)率(lv)(lv)。

（二）

在做微小功率(lv)的开(kai)关电源时，直(zhi)接使用功率(lv)电阻限制(zhi)浪涌电流。

图3 直(zhi)接(jie)串联(lian)功率(lv)电阻限制浪涌(yong)电流（只适合微小功率(lv)开关电源）

优点：

电路简单、成(cheng)本(ben)低、对(dui)浪(lang)涌(yong)电流的(de)的(de)限制(zhi)方面几乎(hu)不受高低温的(de)影响

缺点：

只适合微小功率开关电源

对效率影响(xiang)很大

（三）

NTC热敏电(dian)阻(zu)与(yu)普通(tong)功率电(dian)阻(zu)并联的方式来限(xian)制(zhi)浪涌电(dian)流(liu)

图4 NTC热(re)敏电阻与功率电阻并联(lian)的方(fang)式来抑(yi)制开机浪涌电流

常温起机(ji)时(shi)，功率电阻(zu)与热敏(min)电阻(zu)并联后(hou)的阻(zu)值(zhi)来限制浪(lang)(lang)涌电流，在低温起机(ji)时(shi)NTC热敏(min)电阻(zu)的阻(zu)值(zhi)急(ji)剧升高(gao)但功率电阻(zu)阻(zu)值(zhi)基本是不变的能保证低温启动，不过在高(gao)温实验时(shi)浪(lang)(lang)涌电路也很大。

优(you)点(dian)：

简单实用、对于常温和低温起(qi)机(ji)时效果不错

缺点：

效率(lv)影响较(jiao)大

高(gao)温浪(lang)涌电流(liu)大

（四）

串(chuan)联固定(ding)电(dian)阻器配(pei)合晶(jing)闸管，来限制输入浪(lang)涌电(dian)流

图5 串联固定电(dian)阻器配合(he)晶(jing)闸管来限制开机浪涌(yong)电(dian)流

上(shang)电(dian)时(shi)，Vs截止，电(dian)流经过R1，R1起到(dao)限(xian)流作用，达到(dao)一定条件，VS导通(tong)，将R1断路(lu)。是效率损失(shi)大(da)大(da)降低。

优点：

功耗(hao)低

对浪涌电(dian)流的(de)(de)的(de)(de)限制(zhi)方面几乎(hu)不受(shou)高(gao)低温的(de)(de)影响

缺点：

体积大、成(cheng)本(ben)高(gao)

（五）

利用(yong)MOSFET开关管及延(yan)时(shi)网络电(dian)路(lu)进行浪(lang)涌电(dian)流抑(yi)制浪(lang)涌电(dian)流

图6 利用开关管延时(shi)电路进行浪涌(yong)电流抑(yi)制浪涌(yong)电流

电(dian)(dian)路工作(zuo)的(de)基(ji)本(ben)原理是(shi)：由(you)于(yu)(yu)DC-DC开(kai)(kai)关电(dian)(dian)源的(de)输入(ru)(ru)(ru)端接(jie)有容性(xing)滤(lv)波电(dian)(dian)路，当开(kai)(kai)机加电(dian)(dian)瞬(shun)间由(you)于(yu)(yu)需要为滤(lv)波电(dian)(dian)容C1、C2充电(dian)(dian)，所以瞬(shun)间产生较(jiao)大的(de)浪(lang)涌电(dian)(dian)流，此(ci)时在母线输入(ru)(ru)(ru)的(de)地线上介入(ru)(ru)(ru)的(de)MOSFET（VT1）的(de)漏(lou)原极之间并未导(dao)(dao)通，随着R2、R3、DZ1及CA1组成(cheng)的(de)延(yan)时电(dian)(dian)路给MOSFET（VT1）的(de)栅极加电(dian)(dian)，是(shi)MOSFET（VT1）的(de)漏(lou)源极逐渐导(dao)(dao)通，从而(er)有效减小了开(kai)(kai)机瞬(shun)间由(you)输入(ru)(ru)(ru)端的(de)容性(xing)滤(lv)波电(dian)(dian)路充电(dian)(dian)而(er)产生的(de)浪(lang)涌电(dian)(dian)流值。当电(dian)(dian)路进入(ru)(ru)(ru)稳定工作(zuo)状态下(xia)，其漏(lou)源极始终处于(yu)(yu)导(dao)(dao)通状态。

由于(yu)实(shi)际(ji)的开关电源产品产品设计中对于(yu)浪(lang)涌电流抑制不(bu)(bu)尽相同，可通(tong)过(guo)调节CA1的具体参数而(er)获得不(bu)(bu)同的浪(lang)涌电流抑制的结(jie)果。

优点：

功耗低

常(chang)温、低(di)温、高温对浪(lang)涌电流的限(xian)制效果都特(te)别(bie)好(hao)

缺点：

体积大

成本高(gao)

浪涌电流

浪涌电(dian)流(liu)(liu)(liu)(liu)指电(dian)源(yuan)接通瞬间，流(liu)(liu)(liu)(liu)入(ru)电(dian)源(yuan)设备的(de)峰值电(dian)流(liu)(liu)(liu)(liu)。由于输入(ru)滤(lv)波电(dian)容迅速充电(dian)，所以该峰值电(dian)流(liu)(liu)(liu)(liu)远远大于稳态输入(ru)电(dian)流(liu)(liu)(liu)(liu)。电(dian)源(yuan)应该限制AC开关、整流(liu)(liu)(liu)(liu)桥、保险(xian)丝、EMI滤(lv)波器件能承受(shou)的(de)浪涌水平。反复开关环(huan)路，AC输入(ru)电(dian)压(ya)不(bu)应损坏电(dian)源(yuan)或者导致保险(xian)丝烧断。浪涌电流也指由(you)于电路异常情况引起的使结温超过(guo)额定结温的不(bu)重复性(xing)最大正向过(guo)载电流。

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