The switching characteristics of the freewheeling diode are also affected by the gate resistance and limit the minimum value of the gate impedance. This means that the turn-on switching speed of the IGBT can only be increased to a level compatible with the reverse recovery characteristics of the freewheeling diode used. The reduction in gate resistance not only increases the overvoltage stress of the IGBT, but also increases the overvoltage limit of the freewheeling diode due to the increase in DIC/dt.
The figure below shows the typical dependence of the freewheeling diode reverse recovery current I RRM on diF/dt. diF/dt is determined by the given IGBT gate resistance RG(on). The reverse recovery current increases with the commutation speed diF/dt. An increase in I RRM also results in a higher freewheeling diode turn-off power loss.
Diode reverse recovery peak current vs.di/dt and RG (for example, SKM200GB128D) and soft recovery function
In the IGBT module, SEMIKRON uses a specially designed CAL (axial life controllable) diode with soft recovery. This makes the reverse peak current small, so that the on-current of the IGBT in the bridge is small.
Drive output stage
The driver output stage of the gate drive circuit is a typical design that uses two MOSFETs configured in a totem pole form. The gates of the two MOSFETs are driven by the same signal. When the signal is high, the N-channel MOSFET is turned on. When the signal is low, the P-channel MOSFET is turned on, resulting in a push-pull output configuration of two transistors. The output stage of the MOSFET can have one or two outputs. The table below shows the different solutions for symmetric or asymmetrical gate control.
Connect RG(on), RG(off)
The output stage has two outputs for simple, asymmetric gate control. This allows the gate resistance to be decomposed into two resistors RG(on) and RG(off) for turn-on and turn-off, respectively. In this way, the inevitable crossover current from VG+ to VG- generated during the switching of the driver MOSFET can be limited.
However, the main advantage is that this solution offers the possibility to individually optimize turn-on and turn-off for the pass-through, turn-off overvoltage spikes, and short-circuit characteristics.
SEMIKRON's drive solutions, such as the SKYPER® 32R or SKYPER® 32PROR, provide two outputs for easy asymmetric control.
Data sheets for the SEMIKRON drive solution are available on the Drive Electronics page of
If only one output is used for the gate resistance, asymmetric control can still be used.
In order to separately adjust the on and off characteristics, the resistor RG2 and a diode may be connected in series in parallel with the gate resistor RG1.
Increasing RG1 will extend the turn-off time of the IGBT. The peak overvoltage induced during turn-off will decrease.
Increasing RG2 will extend the turn-on time of the IGBT. The reverse peak current of the freewheeling diode will decrease.
When the MOSFET is switched, this configuration can cause a short circuit at the MOSFET level if delay is not considered.
There is only one output circuit for the gate resistor. The same resistor is used for turn-on and turn-off, so it is symmetric gate control.
When switching MOSFETs, this configuration can cause a short circuit at the MOSFET level if delay is not considered.
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