IGBT Modules - Technologies, Driver and Application (Second Edition) - page 252

6 I
6.6 Influencing the switchingbehaviour
6.6.1 Gate resistor
The classical way to influence the switching behaviour of an IGBT is by selecting the
gate resistor in the voltage-controlled driver stages. Depending on gate control, as can
be seen in
this can be the same or different for the on and off switching
In the latter case, the turn-on gate resistor is denominated with R
and for
turning off withR
Fig. 6.36
Gate resistors in different configurationswith the use of BJTs
By varying the gate resistor the turn-on behaviour can be strongly influenced as was
shown in
This essentially changes the commutation behaviour of the
associated freewheeling diode (FWD), which in turn reacts on the IGBT turn-on
characteristics. Theoretically, the IGBT could be switched on with an R
of 0
if this
would not be stopped by the limitations of the FWD. Currently, only FWD based on
silicon carbide SiC are sufficiently robust to make a design possible without a gate
resistor to turn on the IGBT. However, here too, more or less strong oscillations are to
be expected.
The variant b) is not recommended for a bipolar booster stage, as a base-emitter breakdown of the transistor
mayoccur under certain circumstances. This leads to increased losses in the transistor T
and slows down the
switching process for the IGBT. AlternativelyMOSFETs can beused instead of a bipolar stage or any of the other
variants or gate resistors arrangements.
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