IGBT是什么(2)

IGBT模块主要作为功率开关，如在斩波电路或者变频器中的应用。在这些应用中，续流二极管(FWD)是必不可少的，因为大多数情况负载为感性，IGBT关断后，负载会持续通过电流。通过配置合适的二极管，该电流通路被允许。当IGBT再次开启时，相连的二极管充满载流子，起初相当于短路。存储的电荷QRR必须清除以阻断电压，表现在负载电流上叠加了一个额外电流，称为二极管反向恢复电流Irr。反向恢复电流大小取决于正向电流IF、换流速度di/dt、结温及工作电压。
关断IGBT会产生电流变化，寄生电感中的电流变化速度di/dt又会导致一个电压尖峰。转载请注明出处 http://www.igbt8.com IGBT集电极与栅极之间的寄生电容CGC也被称为米勒电容，具有很强的非线性行为。米勒效应就是集电极-发射极电压VCE通过米勒电容反馈到栅极，意味着变化的VCE相当于一个内部电流源，电流大小为i_G =C_GC(V_CE) x dv/dt。但是，CGC不是恒定的，随着VCE的变化而变化，CGC最强的变化发生在较低的VCE时。
This explains that during turning on (starting with: VCE high, VGE zero or negative) with constant gate charging current a linear increase of the gate voltage results. With falling collector-emitter voltage VCE the gate bias current is used for increasing the charge of CGC and the gate voltage remains constant. Later, when the collector-emitter voltage has come down, CGC becomes larger as much that also at reduced slope of VCE still all the bias supplied gate current is used up. Only when finally the current needed for charging becomes smaller than the bias supplied current, the gate voltage rises again. At this point the collector-emitter voltage has reached the saturation voltage VCEsat.
At turning off (starting with: VCE low, VGE positive or greater than the threshold voltage Vth) the gate voltage first decreases nearly linearly (at constant gate discharge current). With still low collector-emitter voltage VCE and with only moderate increase there is a strongest change (decrease) of CGC. Decrease of a capacitance at constant charge, increases the voltage. As there is a bias source which is drawing current out of the gate, the gate-emitter voltage remains constant. Subsequently VCE increases and most of the gate discharge current is used up for iG = CGC(VCE) x dv/dt; the gate voltage further remains constant. The change over process finally is finished when VCE roughly reaches the DC-link voltage. Now a further decrease of the gate voltage is possible.
By the Miller-effect the gate current during turn-on or turn-off is used for first changing the charge of CGC. This is why charging up or down the gate is slowed down. It should be mentioned that.
由于米勒效应，栅极电流在开通或者关断时首先被用来改变CGC的充电电荷。这就是为什么栅极的充放电速度降低。CGC和VCE的变化通过有效的门极电流消耗来自我调节，意味着更大的门极串联电阻，所有的事件需要持续较长的时间，即开通或管段时间更长。转载请注明出处 http://www.igbt8.com