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usually 10kHz to 50kHz for IGBTs and
somewhat more than 50kHz in SiC-
FETs – and steep edges put constant
stress on insulation components in
the system. Voltage peaks can cause
surges that strain the insulation in a
transducer to its limits, especially in
combination with “hidden” parasitic
capacitances and inductances in the
circuit. There is no magic formula
to calculate voltage peak levels and
therefore life expectancy of the system
to any degree of accuracy.
Measuring equipment can only help
to a very limited extent, as even the
relatively small capacitance in a high-
voltage oscilloscope probe will taint
range includes a complete range of
converters designed specifically for
supplying IGBT and SiC-FET drivers.
The converters have asymmetric
outputs at either +15V/-9 V (IGBT) or
+20V/-5V (SiC-FET) at input voltages
of 5V, 12V, 15V and 24V. The power
required also depends on switching
frequency – up to 1W is usually
sufficient for around 10 kHz, whereas
2W is required for 50kHz and more.
These products operate in power-
sharing mode where the rated power
can be distributed across the two
outputs.
Insulation
causes
additional
differences. Products in the RKZ
the result. An voltage spike measured
at 2kV, for example, could well be
double that without exposure to the
probe. There is no final guarantee,
and relying on measurement with a
converter on insulation that is already
tightly dimensioned risks the long-term
reliability of the product. Developers
therefore tend to allow sufficient
safety reserves and use converters
with the best possible insulation in
dimensioning fast power switches.
High-quality DC/DC
converters for IGBT and
FET SiC applications
The RECOM DC/DC converters
Fig. 2: Current/voltage AUC while switching on (diagrams above) and off (below) is a measure of
switching losses. SiC-FETs (top and bottom right) are more efficient than IGBTs by approximately
a factor of four due to the steeper switching edges – at 25°C ambient temperature and taking the
losses from one body diode into account
58 l New-Tech Magazine Europe