利盈娱乐(中国)创新平台有限公司

开关损耗(hao)的简介

开(kai)关(guan)损(sun)(sun)耗(hao)(hao)包括(kuo)导通(tong)损(sun)(sun)耗(hao)(hao)和截(jie)(jie)止(zhi)(zhi)损(sun)(sun)耗(hao)(hao)。导通(tong)损(sun)(sun)耗(hao)(hao)指(zhi)功率管从(cong)截(jie)(jie)止(zhi)(zhi)到(dao)导通(tong)时,所产生(sheng)的功率损(sun)(sun)耗(hao)(hao)。截(jie)(jie)止(zhi)(zhi)损(sun)(sun)耗(hao)(hao)指(zhi)功率管从(cong)导通(tong)到(dao)截(jie)(jie)止(zhi)(zhi)时,所产生(sheng)的功率损(sun)(sun)耗(hao)(hao)。开(kai)关(guan)损(sun)(sun)耗(hao)(hao)（Switching-Loss）包括(kuo)开(kai)通(tong)损(sun)(sun)耗(hao)(hao)（Turn-on Loss）和关(guan)断损(sun)(sun)耗(hao)(hao)(Turn-of Loss)，常常在(zai)硬开(kai)关(guan)（Hard-Switching）和软开(kai)关(guan)（Soft-Switching）中讨论。所谓开(kai)(kai)通损(sun)(sun)耗(hao)（Turn-on Loss），是(shi)指非理想的开(kai)(kai)关(guan)(guan)管在(zai)开(kai)(kai)通时，开(kai)(kai)关(guan)(guan)管的电(dian)压(ya)不是(shi)立(li)即下降到零(ling)，而(er)是(shi)有一个(ge)下降时间，同时它的电(dian)流(liu)也(ye)(ye)不是(shi)立(li)即上升到负载电(dian)流(liu)，也(ye)(ye)有一个(ge)上升时间。在(zai)这段时间内，开(kai)(kai)关(guan)(guan)管的电(dian)流(liu)和电(dian)压(ya)有一个(ge)交叠区，会(hui)产(chan)生(sheng)(sheng)损(sun)(sun)耗(hao)，这个(ge)损(sun)(sun)耗(hao)即为(wei)开(kai)(kai)通损(sun)(sun)耗(hao)。以(yi)(yi)此类比，可(ke)以(yi)(yi)得出(chu)关(guan)(guan)断(duan)损(sun)(sun)耗(hao)产(chan)生(sheng)(sheng)的原因(yin)，这里不再赘述。开(kai)(kai)关(guan)(guan)损(sun)(sun)耗(hao)另一个(ge)意(yi)思是(shi)指在(zai)开(kai)(kai)关(guan)(guan)电(dian)源中，对(dui)大(da)的MOS管进(jin)行(xing)开(kai)(kai)关(guan)(guan)操作时，需要对(dui)寄生(sheng)(sheng)电(dian)容充(chong)放电(dian)，这样也(ye)(ye)会(hui)引(yin)起(qi)损(sun)(sun)耗(hao)。

MOS管在开关应用过程中的问题

公司网络、数(shu)据及无线基站产(chan)品(pin)各(ge)单板(ban)都(dou)采用通(tong)过简单的(de)(de)(de)改(gai)变RC充电(dian)回路(lu)(lu)中R和C值，产(chan)生一个渐变的(de)(de)(de)电(dian)压控制一个在一定电(dian)压下导(dao)通(tong)的(de)(de)(de)开关MOS管(guan)(guan)(guan)(guan)(guan)，来导(dao)通(tong)输入直流(liu)(liu)-48V电(dian)压进(jin)而减少热插拔(ba)过程(cheng)的(de)(de)(de)浪涌电(dian)流(liu)(liu)。但(dan)是(shi)因为对于MOS管(guan)(guan)(guan)(guan)(guan)本身内(nei)部结构(gou)、开关过程(cheng)和损耗了(le)解不(bu)全面，造(zao)成(cheng)了(le)大批MOS管(guan)(guan)(guan)(guan)(guan)失(shi)(shi)效(xiao)(xiao)(xiao)的(de)(de)(de)案例(li)。笔者通(tong)过对公司各(ge)产(chan)品(pin)直流(liu)(liu)-48V缓启动(dong)(dong)电(dian)路(lu)(lu)MOS管(guan)(guan)(guan)(guan)(guan)失(shi)(shi)效(xiao)(xiao)(xiao)情况分析(xi)和统(tong)计(ji)(ji)发现(xian)，MOS管(guan)(guan)(guan)(guan)(guan)的(de)(de)(de)失(shi)(shi)效(xiao)(xiao)(xiao)在公司各(ge)产(chan)品(pin)事业部都(dou)有发生，失(shi)(shi)效(xiao)(xiao)(xiao)问题(ti)数(shu)量比较多，但(dan)失(shi)(shi)效(xiao)(xiao)(xiao)原因却(que)比较单一，都(dou)是(shi)由于短时过功(gong)率烧毁(hui)。失(shi)(shi)效(xiao)(xiao)(xiao)案例(li)中同(tong)时也(ye)提(ti)出了(le)改(gai)善对策，需要我们改(gai)进(jin)目前-48 V DC缓启动(dong)(dong)电(dian)路(lu)(lu)的(de)(de)(de)驱(qu)动(dong)(dong)设计(ji)(ji)减少MOS管(guan)(guan)(guan)(guan)(guan)开关过程(cheng)的(de)(de)(de)损耗，避免MOS管(guan)(guan)(guan)(guan)(guan)失(shi)(shi)效(xiao)(xiao)(xiao)问题(ti)的(de)(de)(de)再(zai)次(ci)发生。

MOS管的开关损耗

1、 栅极电荷QG

在MOS管中，栅极(ji)电(dian)(dian)荷(he)(he)决(jue)定于栅极(ji)氧化层的(de)厚(hou)度(du)及其它与(yu)裸片布线(xian)有关的(de)物(wu)理参(can)数，它可以(yi)表示为驱动电(dian)(dian)流值与(yu)开通时(shi)间之积或(huo)栅极(ji)电(dian)(dian)容值与(yu)栅极(ji)电(dian)(dian)压之积。现在大部分MOS管的(de)栅极(ji)电(dian)(dian)荷(he)(he)QG值从几(ji)十纳库仑到一、两(liang)百纳库仑。如图所(suo)示，是栅(zha)(zha)(zha)(zha)(zha)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)和栅(zha)(zha)(zha)(zha)(zha)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)之(zhi)间(jian)的(de)关系，从(cong)中(zhong)可以(yi)(yi)看到栅(zha)(zha)(zha)(zha)(zha)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)的(de)非线(xian)(xian)性(xing)(xing)(xing)特性(xing)(xing)(xing)。这条曲线(xian)(xian)的(de)斜率(lv)可用来估计(ji)栅(zha)(zha)(zha)(zha)(zha)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容Cgs的(de)数(shu)值。曲线(xian)(xian)的(de)第一段是线(xian)(xian)性(xing)(xing)(xing)的(de)，QGS是使栅(zha)(zha)(zha)(zha)(zha)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)从(cong)0升(sheng)到门限值所(suo)需电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)，此时漏(lou)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流出现，漏(lou)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)开始下(xia)降(jiang)(jiang);此段栅(zha)(zha)(zha)(zha)(zha)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容Cgs就是Cgs。曲线(xian)(xian)的(de)第二段是水(shui)平的(de)，栅(zha)(zha)(zha)(zha)(zha)极(ji)(ji)(ji)(ji)到漏(lou)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)QGD是漏(lou)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)下(xia)降(jiang)(jiang)时克服(fu)“Miller”效(xiao)应所(suo)需电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)，所(suo)以(yi)(yi)栅(zha)(zha)(zha)(zha)(zha)极(ji)(ji)(ji)(ji)到漏(lou)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)QGD也(ye)称为(wei)“Miller”电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)。此时栅(zha)(zha)(zha)(zha)(zha)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)不变(bian)、栅(zha)(zha)(zha)(zha)(zha)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)积(ji)聚而漏(lou)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)急聚下(xia)降(jiang)(jiang)。这一段的(de)栅(zha)(zha)(zha)(zha)(zha)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容是Cgs加上Cgd的(de)影响(xiang)(通常称为(wei)Miller效(xiao)应)。通过观察栅(zha)(zha)(zha)(zha)(zha)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)UGS和栅(zha)(zha)(zha)(zha)(zha)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)QG之(zhi)间(jian)的(de)关系可以(yi)(yi)看出，寄生的(de)栅(zha)(zha)(zha)(zha)(zha)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)QG值虽(sui)然很小，但是在MOS管导通过程中(zhong)可分为(wei)明显的(de)3个阶段;同时，由于受栅(zha)(zha)(zha)(zha)(zha)极(ji)(ji)(ji)(ji)到漏(lou)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)QGD即“Miller”电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)的(de)影响(xiang)使栅(zha)(zha)(zha)(zha)(zha)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)产生了(le)非线(xian)(xian)性(xing)(xing)(xing)特性(xing)(xing)(xing)，也(ye)影响(xiang)了(le)栅(zha)(zha)(zha)(zha)(zha)极(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)压(ya)(ya)(ya)UGS的(de)线(xian)(xian)性(xing)(xing)(xing)升(sheng)高。

2、MOS管的极间电容

MOS管(guan)(guan)其(qi)内(nei)部(bu)极间(jian)(jian)电(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)主要有(you)Cgs、Cgd和Cds。并且Cgs>>Cds>>Cgd。其(qi)中Cgs为栅(zha)源电(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)、Cgd为栅(zha)漏电(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)，它们是由Mos结(jie)构的绝缘层形成的;Cds为漏源电(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)，由PN结(jie)构成。MOS管(guan)(guan)极间(jian)(jian)电(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)等效电(dian)(dian)(dian)(dian)路如图(tu)2所示。MOS管(guan)(guan)管(guan)(guan)的极间(jian)(jian)电(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)栅(zha)漏电(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)Cgd、栅(zha)源电(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)Cgs、漏源电(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)(rong)Cds可以由以下公(gong)式确(que)定：

Cgd=Crss

Cgs=Ciss-Crss

Cds=Coss-Crss

公式中(zhong)Ciss、Coss、和Crss分别(bie)是MOS管(guan)的输入(ru)电容(rong)、输出电容(rong)和反馈电容(rong)。它(ta)们的数值(zhi)可以(yi)在MOS管(guan)的手册上查(cha)到。

通(tong)过观察MOS管(guan)极(ji)(ji)间(jian)电(dian)(dian)(dian)(dian)容(rong)(rong)(rong)和寄生栅极(ji)(ji)电(dian)(dian)(dian)(dian)荷QG，可以看到(dao)(dao)，MOS管(guan)极(ji)(ji)间(jian)电(dian)(dian)(dian)(dian)容(rong)(rong)(rong)是由其导电(dian)(dian)(dian)(dian)沟道结构及工艺决定，固有的。由于存在(zai)(zai)反馈电(dian)(dian)(dian)(dian)容(rong)(rong)(rong)及栅极(ji)(ji)到(dao)(dao)漏极(ji)(ji)电(dian)(dian)(dian)(dian)荷QGD，QGD的大(da)部分(fen)用来减(jian)小UDS从关断电(dian)(dian)(dian)(dian)压到(dao)(dao)UGS(th)产(chan)生的“Miller”效(xiao)应(ying)，此时Vds尚未达(da)到(dao)(dao)Vsat。对曲(qu)线水平段所(suo)对应(ying)的电(dian)(dian)(dian)(dian)容(rong)(rong)(rong)Cgs充电(dian)(dian)(dian)(dian)所(suo)花费(fei)的时间(jian)越长，Vgs维持在(zai)(zai)一(yi)个恒定电(dian)(dian)(dian)(dian)压上的时间(jian)也(ye)(ye)就越长，MOS管(guan)达(da)到(dao)(dao)饱(bao)和状态所(suo)需的时间(jian)也(ye)(ye)就越长。这种情(qing)况相应(ying)的MOS管(guan)的能量损耗也(ye)(ye)越大(da)，产(chan)生的热量越多、效(xiao)率越低。

3 、MOS管的导通过程

MOS管(guan)极间(jian)(jian)电容是影响开关时间(jian)(jian)的主(zhu)要因素。由于(yu)受极问(wen)电容的影响，MOS管(guan)的导通过程可分(fen)为(wei)如下(xia)几(ji)个阶段，如图所示(shi)：

1)t0～t1期(qi)间：驱(qu)动电压(ya)从零上升，经rG对图(tu)3 MOSFET等效结构中(zhong)G端(duan)输入电容Ciss充电，电压(ya)按(an)虚(xu)线上升(开路脉冲)，Ciss越(yue)小，则电压(ya)上升的越(yue)快;

2)t1～t2期(qi)间：t1瞬时(shi)，MOS管(guan)(guan)的(de)栅源(yuan)电(dian)(dian)(dian)(dian)压(ya)达到开(kai)启(qi)电(dian)(dian)(dian)(dian)压(ya)UGS(th)，漏极(ji)电(dian)(dian)(dian)(dian)流开(kai)始上升;由于漏源(yuan)等效的(de)输出电(dian)(dian)(dian)(dian)容Coss会对MOS管(guan)(guan)容性放(fang)电(dian)(dian)(dian)(dian)，漏极(ji)电(dian)(dian)(dian)(dian)流ID上升，漏源(yuan)电(dian)(dian)(dian)(dian)压(ya)下降;同时(shi)受(shou)反馈电(dian)(dian)(dian)(dian)容Crss的(de)影响(xiang)G驱(qu)动电(dian)(dian)(dian)(dian)压(ya)Vgs的(de)上升速(su)率特别(bie)平(ping)缓(huan)，(低于开(kai)路脉冲);

3)t2～t3期间：t2瞬间，漏极电(dian)(dian)(dian)流ID已经达到稳态幅值(zhi)，但Coss的电(dian)(dian)(dian)压尚大，电(dian)(dian)(dian)流还(hai)会上冲;

4)t3～t4期间：t3瞬时，Coss在漏极峰值(zhi)电流(liu)放电下，漏极电压(ya)迅速下降，受反馈(kui)电容Crss的(de)影响G驱动(dong)电压(ya)略有回落，维持漏极电流(liu)所(suo)需的(de)驱动(dong)电压(ya)值(zhi)，保持平衡;

5)t4之后：t4瞬时，Coss的电荷放完，漏源(yuan)电压近似为零，并保持不变;反馈消失。Vgs升高到开路脉冲，进(jin)入(ru)稳态导(dao)通(tong)期。

由此(ci)MOS管(guan)开(kai)通过(guo)程可(ke)看，漏(lou)极电(dian)(dian)流(liu)在QG波形的(de)(de)QGD阶段(duan)出现(xian)，由于(yu)受(shou)极间电(dian)(dian)容(rong)的(de)(de)影响，VDS电(dian)(dian)压失去了(le)线性的(de)(de)过(guo)程，所以一方面(mian)在漏(lou)极电(dian)(dian)流(liu)出现(xian)的(de)(de)过(guo)程，该(gai)段(duan)漏(lou)极电(dian)(dian)压依然很高(gao)，漏(lou)极电(dian)(dian)流(liu)上(shang)升的(de)(de)速度是漏(lou)极电(dian)(dian)压下降速度的(de)(de)几倍，这就造成了(le)MOS管(guan)功(gong)率损(sun)(sun)耗的(de)(de)增加。另一方面(mian)开(kai)关导(dao)通时(shi)，由于(yu)受(shou)受(shou) “Miller”电(dian)(dian)荷(he)的(de)(de)影响，电(dian)(dian)容(rong)Cgs充电(dian)(dian)需花费较长时(shi)间，Vgs长时(shi)间上(shang)升速率特(te)别(bie)平(ping)缓，(低于(yu)开(kai)路脉(mai)冲)，这种情况造成MOS管(guan)的(de)(de)损(sun)(sun)耗很大并产生大量热量、降低了(le)开(kai)关效(xiao)率。

损耗来源

通(tong)过(guo)对MOS管(guan)(guan)特性(xing)(xing)的(de)(de)(de)(de)分析可以(yi)看出，MOS管(guan)(guan)并(bing)不是单纯的(de)(de)(de)(de)电(dian)(dian)(dian)压控制(zhi)(zhi)器件。它的(de)(de)(de)(de)开(kai)启(qi)和开(kai)关(guan)(guan)速度(du)(du)与电(dian)(dian)(dian)流(liu)有关(guan)(guan)，它取决于(yu)(yu)驱动(dong)电(dian)(dian)(dian)路是否能够在(zai)它需要(yao)(yao)时(shi)提供(gong)(gong)足(zu)够的(de)(de)(de)(de)电(dian)(dian)(dian)流(liu)，使电(dian)(dian)(dian)容Cgs快速充(chong)(chong)电(dian)(dian)(dian)。由(you)于(yu)(yu)在(zai)第(di)(di)二段(duan)时(shi)，受(shou)“Miller”电(dian)(dian)(dian)荷(he)及(ji)极间电(dian)(dian)(dian)容的(de)(de)(de)(de)影响(xiang)，电(dian)(dian)(dian)容充(chong)(chong)电(dian)(dian)(dian)需要(yao)(yao)较长时(shi)间，造成MOS管(guan)(guan)开(kai)关(guan)(guan)损耗(hao)增加(jia)，产生大量的(de)(de)(de)(de)热量。同(tong)(tong)时(shi)由(you)于(yu)(yu)VDS电(dian)(dian)(dian)压失去了线性(xing)(xing)的(de)(de)(de)(de)过(guo)程(cheng)，开(kai)关(guan)(guan)导(dao)通(tong)时(shi)漏(lou)极电(dian)(dian)(dian)流(liu)上(shang)升的(de)(de)(de)(de)速度(du)(du)是漏(lou)极电(dian)(dian)(dian)压下降速度(du)(du)的(de)(de)(de)(de)几倍，这(zhei)将(jiang)造成功率(lv)损耗(hao)增加(jia)。在(zai)这(zhei)整个过(guo)程(cheng)中，MOSF管(guan)(guan)的(de)(de)(de)(de)开(kai)关(guan)(guan)损耗(hao)和功率(lv)损耗(hao)都增加(jia)，这(zhei)就(jiu)很(hen)容易(yi)造成MOS管(guan)(guan)的(de)(de)(de)(de)烧(shao)毁(hui)。所以(yi)在(zai)第(di)(di)二段(duan)迫切要(yao)(yao)求(qiu)栅(zha)极驱动(dong)能够提供(gong)(gong)足(zu)够的(de)(de)(de)(de)电(dian)(dian)(dian)流(liu)，在(zai)短时(shi)间内为第(di)(di)二段(duan)曲(qu)线对应(ying)的(de)(de)(de)(de)栅(zha)极电(dian)(dian)(dian)容Cgs充(chong)(chong)电(dian)(dian)(dian)，使MOS管(guan)(guan)迅速地开(kai)启(qi)。同(tong)(tong)时(shi)，要(yao)(yao)提供(gong)(gong)一个合理的(de)(de)(de)(de) Vgs最佳平台电(dian)(dian)(dian)压(也就(jiu)是总的(de)(de)(de)(de)QG)，在(zai)此过(guo)程(cheng)控制(zhi)(zhi)VDS电(dian)(dian)(dian)压的(de)(de)(de)(de)线性(xing)(xing)度(du)(du)，使电(dian)(dian)(dian)流(liu)的(de)(de)(de)(de)变化(hua)(hua)和漏(lou)极电(dian)(dian)(dian)压变化(hua)(hua)率(lv)相等，减少功率(lv)损耗(hao)。利(li)用MOS管(guan)(guan)及(ji)分立器件实现(xian)-48 V电(dian)(dian)(dian)源缓启(qi)动(dong)需要(yao)(yao)优化(hua)(hua)电(dian)(dian)(dian)路设计，既要(yao)(yao)提供(gong)(gong)栅(zha)极电(dian)(dian)(dian)流(liu)，又要(yao)(yao)控制(zhi)(zhi)好漏(lou)源电(dian)(dian)(dian)压的(de)(de)(de)(de)线性(xing)(xing)度(du)(du)，从而控制(zhi)(zhi)漏(lou)极冲击(ji)电(dian)(dian)(dian)流(liu)，以(yi)减少MOS管(guan)(guan)的(de)(de)(de)(de)损耗(hao)。

减少MOS管损耗的方法

减小开关(guan)损(sun)耗(hao)一(yi)方面(mian)要尽可能地制造出具有理想开关(guan)特性的器件(jian),另一(yi)方面(mian)利用(yong)新的线(xian)路(lu)技术改变器件(jian)开关(guan)时期的波形(xing),如(ru):晶体管缓(huan)冲电路(lu),谐振电路(lu),和软开关(guan)技术等。

(1)晶体管缓(huan)冲(chong)电路(即加吸收网络技术)

早期电(dian)源多采(cai)(cai)用(yong)此线路技术。采(cai)(cai)用(yong)此电(dian)路, 功(gong)率(lv)(lv)损(sun)(sun)耗(hao)(hao)(hao)(hao)虽有(you)所减小,但(dan)仍不是很(hen)理想。①减少导(dao)通(tong)损(sun)(sun)耗(hao)(hao)(hao)(hao)在变压器次级线圈后面(mian)加(jia)饱和电(dian)感(gan), 加(jia)反(fan)(fan)向恢复时(shi)间(jian)快(kuai)的二极管,利(li)用(yong)饱和电(dian)感(gan)阻(zu)碍电(dian)流变化的特性, 限制(zhi)电(dian)流上(shang)升的速(su)率(lv)(lv),使电(dian)流与(yu)电(dian)压的波形尽(jin)可(ke)能(neng)小地重(zhong)叠。②减少截止损(sun)(sun)耗(hao)(hao)(hao)(hao)加(jia)R 、C 吸(xi)收网络, 推迟变压器反(fan)(fan)激(ji)(ji)电(dian)压发生(sheng)(sheng)时(shi)间(jian), 最(zui)好在电(dian)流为0时(shi)产生(sheng)(sheng)反(fan)(fan)激(ji)(ji)电(dian)压,此时(shi)功(gong)率(lv)(lv)损(sun)(sun)耗(hao)(hao)(hao)(hao)为0。该电(dian)路利(li)用(yong)电(dian)容(rong)上(shang)电(dian)压不能(neng)突变的特性,推迟反(fan)(fan)激(ji)(ji)电(dian)压发生(sheng)(sheng)时(shi)间(jian)。为了增加(jia)可(ke)靠性,也(ye)可(ke)在功(gong)率(lv)(lv)管上(shang)加(jia)R 、C 。但(dan)是此电(dian)路有(you)明显(xian)缺(que)点:因(yin)为电(dian)阻(zu)的存在,导(dao)致(zhi)吸(xi)收网络有(you)损(sun)(sun)耗(hao)(hao)(hao)(hao) 。

(2)谐振电路(lu)

该电(dian)(dian)路只(zhi)改(gai)变(bian)(bian)开(kai)关瞬(shun)间电(dian)(dian)流波形,不(bu)改(gai)变(bian)(bian)导通时电(dian)(dian)流波形。只(zhi)要(yao)选择(ze)好合(he)适(shi)的(de)L 、C ,结(jie)(jie)合(he)二(er)极管结(jie)(jie)电(dian)(dian)容和变(bian)(bian)压(ya)器漏感, 就(jiu)能保证电(dian)(dian)压(ya)为0时,开(kai)关管导通或截止。因此, 采用谐振技术(shu)可使开(kai)关损耗很小。所以, SWITCHTEC 电(dian)(dian)源开(kai)关频(pin)率可以做到术(shu)结(jie)(jie)构380kHz的(de)高频(pin)率。

(3)软开关技术

该电(dian)(dian)路(lu)是在全桥逆(ni)变电(dian)(dian)路(lu)中加入电(dian)(dian)容和(he)二(er)极管(guan)。二(er)极管(guan)在开关(guan)管(guan)导通时起钳位作(zuo)用, 并构成泻(xie)(xie)放(fang)回(hui)路(lu), 泻(xie)(xie)放(fang)电(dian)(dian)流。电(dian)(dian)容在反激电(dian)(dian)压作(zuo)用下, 电(dian)(dian)容被充电(dian)(dian), 电(dian)(dian)压不(bu)能突然(ran)增加, 当电(dian)(dian)压比较大的时侯, 电(dian)(dian)流已经为0。

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