1 / 8

Analysis of dv_dt Induced Spurious Turn-on of Mosfet

Analysis of dv_dt Induced Spurious Turn-on of Mosfet. Author: Yuming Bai,Deva Pattanayak,Alex Q. Huang. 胡庄主 2006_03_10 Delta SDC.

abie
Download Presentation

Analysis of dv_dt Induced Spurious Turn-on of Mosfet

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Analysis of dv_dt Induced Spurious Turn-on of Mosfet Author: Yuming Bai,Deva Pattanayak,Alex Q. Huang 胡庄主2006_03_10 Delta SDC

  2. 对高频的DC-DC转换器,功率MOSFET是一个关键的器件.快速的开关可以降低开关LOSS, 但是在MOS漏级上dv/dt也变得越来越高.然而,高的dv/dt可能导致在没有正常的门极触发信号时MOS开通,这样会产生更多的功耗.最常见的可能是由于寄生电容和电感引起的.本文研究了寄生现象对MOS假开通的影响.

  3. 假触发(spurious-trigger)现象发生在当漏极电压快速上升时.这种情况下MOSFET的等效电路如图1示.由于通常的解法会导致四阶的差分方程,本文通过忽略相关不太重要的寄生参数的影响来简化问题.其影响后文再述.基于20V-30V 层次的MOS来考虑寄生参数. 此处,Lg>>Ls; Cgs>>Ggd, Cgs>>Cds. 由于从节点G到地的阻抗比从节点S到地的阻抗要大得多,图1可以简化成如图2的电路.此处MOS被移走,既然其在误触发之前仍旧处在关断状态. 假设施加到D极的电压线性上升: Vin=Kt.则S域整个电流可表示为: 则通过电容Cgd的电流以及在节点S上的电压为:

  4. 电流Igd和电压Vs均对门极电压Vgs有影响.首先计算电流Igd对Vgs产生的影响,如图3示.节点S直接连接到地,电压Vs的影响稍后再考虑.为简化计算,将电流Igd分成两部分:Igd=Icgd_dc+Icgd_ac;分别代表固定的直流电流和及交流电流.Igd_dc=K*Cgd/s; Igd_ac=-K*Cgd*s/(s2+w02);从G到地的阻抗为:

  5. 电流Igd和电压Vs均对门极电压Vgs有影响. 现在计算节点S电压Vs(式5所示,正弦电压)对Vgs上升产生的影响.从节点S到G,Cgs提供了一个最小阻抗的路径.因此,可使用简化的电路,如图4,来计算由Vs产生的Vgs,在S域计算:

  6. 结论:在等式21中,第一部分K*Cgd*Rgs是参考文献3所提供的.第二部分显示了其它参数的影响.电感Lgd,Ls,Lg以及电容Cds导致了更高的Vgs.然而,电容Cgs会导致Vgs变小.图6比较了Vmax值,在加和不加第二部分的情况下.由于Cgs的影响,两者差别并不大.为了简化电路,以上分析作了不少假设.准确的Vgs可以通过Pspice的仿真得出.从仿真结果看,分析差会比仿真值小10%左右.尽管Cgs会使假开通电压变小,但是对large area的MOS来说,更可能具有假开通,因为此时Cgd在Vmax中起主要的作用.

  7. END

More Related