IGBT Modules - Technologies, Driver and Application (Second Edition) - page 325

too high
di , it may come to a destruction of the diode commutating off.With the use of
SiC Schottky diodes, however, the IGBT could in principle turn on with it maximum
, i.e. a gate resistor R
of 0
Fig. 7.20
Arrangement of a switch consisting of two Si IGBT and twelve SiC Schottky
If an IGBTmodule is equipped with SiCSchottky diodes, the following aspects need to
be considered in theapplication:
Currently SiC Schottky diodes are offered commercially only up to a current
rating of 15A (status: 2009). This means that IGBT modules with current
ratings of several hundred amps will have to have many SiC diode chips
connected in parallel
. Themore chips are used, themore difficult is
it to equalise the internal parallel set-up. Due to parasitic effects it may come to
oscillations, particularly with high switching speeds i.e. a small gate resistor of
the associated IGBT.
Due to parasitic capacitive effects, SiC Schottky diodes do not show the ideal
value of 0A for the recovery peak, but instead a value higher than 0A.
However, this value is constant over the entire temperature region. Thus,
conversely to the ideal component, therewill be switching losses.
For cost reasons the nominal current rating of the SiCSchottky diodes is often
chosen lower than the nominal current rating of the IGBTs. It is implied here
that the application will operate primarily with a positive power factor cos
which means that the IGBTs will take more load than the diodes.
shows such an example in which the diodes compared to the IGBTs are only
rated for 60% of the nominal current. In applications, however, with a high
content of regenerative current or with DC/DC converters the diode current
rating should be identical to that of the IGBTs. In addition, note that when SiC
Schottky diodes are implemented this often aims at operation with high
switching speeds.With the lower switching losses of the diode compared to the
IGBT the usable currents of both components match each other at high
switching speeds.
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