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MOSFET (Si/SiC) Forum Discussions

User19230
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First question asked
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Hello,

The switching parameters of IGBTs are characterized by a double-pulse test with an inductive load. The switching times (Tdon, Tr, Tdoff and Tf) are defined in relation with the collector current (Ice).
For the MOSFETs (such as SiC MOSFETs), a resistive load is used for the test. The switching times are defined in relation with the drain source voltage (Vds).

My questions are:
Why do we prefer an inductive load for IGBTs? Why the switching times are not measured in relation with the collector voltage (Vce) ?
Why do we always use a resitive load for SiC MOSFET? Can the switching times be defined by the drain current (Ids) or they need to be defined by the drain voltage (Vds) ?

For the context: I need to determine the minimum dead time for two power converters, one made of SiC MOSFETs and the second one made of IGBTs.

Thanks in advance
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electricuwe
Moderator
Moderator 5 sign-ins 25 replies posted 10 solutions authored
Moderator
Hello Gabriel,

to understand this application an device background is needed.

The main application of IGBT are inverters consisting of halfbridges for drives or for feeding renewable energy into the grid. In this case the load -seen in the µs timeframe- is an inductive load, either the motor stray inductance or a filter inductance. The IGBT, regardless of the voltage class, is well suited for this applications as it is usually combined with a decent separate freewheeling diode.

The applications of Mosfets are much more diverse. Many Mosfets are used as single switches without the need to have a fast antiparallel diode. Si-Mosfets for low voltage (up to 200 V) do have intrinsic body diode capable of fast commuation as well. But Si-Mosfets for higher voltages have a very poor body diode and are usually not applicable in halfbridge circuits working with inductive load.


SiC-Mosfets in the whole voltage range either have a usable bodydiode (as our CoolSiC-Mosfet) or are combined with separate freewheeling diodes (as most SiC-Mosfets from competition). In both cases the devices are suitable for operation in halfbridges working on inductive loads and hence can now enter typical IGBT applications.

A recommendation for setting and verifying the deadtime in IGBT designs you can find here: https://www.infineon.com/dgdl/Infineon-Deadtime_calculation_for_IGBT_modules-ApplicationNotes-v01_00...

Most of this is applicable to SiC-Mosfet designs as well. Due to lower switching losses Inverters with SiC-Mosfets can be operated with higher switching frequency compared to IGBT inverters. To avoid detrimental effects on output voltage waveform or behavior in a control loop, the deadtime should not be bigger than appox. 1% of the switching frequency periode. To achieve this strong drivers with low tolerance and variation of propagation delay are required.

Best regards,
electricuwe

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electricuwe
Moderator
Moderator 5 sign-ins 25 replies posted 10 solutions authored
Moderator
Hello Gabriel,

to understand this application an device background is needed.

The main application of IGBT are inverters consisting of halfbridges for drives or for feeding renewable energy into the grid. In this case the load -seen in the µs timeframe- is an inductive load, either the motor stray inductance or a filter inductance. The IGBT, regardless of the voltage class, is well suited for this applications as it is usually combined with a decent separate freewheeling diode.

The applications of Mosfets are much more diverse. Many Mosfets are used as single switches without the need to have a fast antiparallel diode. Si-Mosfets for low voltage (up to 200 V) do have intrinsic body diode capable of fast commuation as well. But Si-Mosfets for higher voltages have a very poor body diode and are usually not applicable in halfbridge circuits working with inductive load.


SiC-Mosfets in the whole voltage range either have a usable bodydiode (as our CoolSiC-Mosfet) or are combined with separate freewheeling diodes (as most SiC-Mosfets from competition). In both cases the devices are suitable for operation in halfbridges working on inductive loads and hence can now enter typical IGBT applications.

A recommendation for setting and verifying the deadtime in IGBT designs you can find here: https://www.infineon.com/dgdl/Infineon-Deadtime_calculation_for_IGBT_modules-ApplicationNotes-v01_00...

Most of this is applicable to SiC-Mosfet designs as well. Due to lower switching losses Inverters with SiC-Mosfets can be operated with higher switching frequency compared to IGBT inverters. To avoid detrimental effects on output voltage waveform or behavior in a control loop, the deadtime should not be bigger than appox. 1% of the switching frequency periode. To achieve this strong drivers with low tolerance and variation of propagation delay are required.

Best regards,
electricuwe
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