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Efficient use of electrical
power is a goal shared in every
area of electrical engineering
and electronics. Wind and
solar have come to provide a
significant part of our daily
energy needs, placing the
focus on power electronics
components able to switch
hundreds of volts and amps
at a high degree of efficiency
before this green power can
be fed into the grid. We refer
to state-of-the-art power
switches, IGBTs and SiC-
FETs, and how to supply the
respective gate drivers with
voltage in the most effective
possible way.
These semiconductor technologies
are to be found today not only in
wind and solar power inverters, but
across the board in power electronics,
ranging from motor control to welding
equipment, induction furnaces and
vacuum generators to e-mobility and
more.
Developers only had bipolar power
transistors available to them in the
early stages of the power electronics;
these were suitable for reverse
voltages of up to 500V and could
switch currents of 100 amps and more;
this might be a perfectly respectable
level of performance, but it comes at
the cost of very high control currents
- usually ten to twenty percent of
collector current - to keep switching
losses from relatively sharp edges in
limits.
The first power MOSFETs (metal oxide
field effect transistors) to be developed
solved this problem. A MOSFET gate
is insulated by design, only requiring
negligibly small currents to charge
and discharge the gate capacitor. This
development significantly reduced
power losses from gate control.
Obviously, there were still two
sources of loss as known from bipolar
semiconductors:
1. Switching losses from limited edge
steepness during switching cycles
2. ON losses while the semiconductor
is in its ON state
ON losses are intrinsic to the technical
specification of MOSFETs and are
therefore largely fixed; switching
losses on the other hand depend
on control quality, which may be be
improved in the development phase
by suitable circuit designs.
IGBTs combine the
advantages of MOSFETs
and bipolar transistors
The disadvantage of higher ON
losses on the drain-source path
Switching hundreds of volts
and amps without loss
Reinhard Zimmermann, RECOM Power GmbH
56 l New-Tech Magazine Europe