1.5.8 RC IGBTs
IGBTs, especially in applications with inductive load, require a parallel freewheeling
diode to protect them from over-voltages that occur and/or to provide a commutation
path for the current. If now an IGBT is developed that has both the necessary structures
of an IGBT and, parallel to that, the structure of a diode implemented, this is called a
reverse conducting (RC) IGBT.
AnRC IGBTdoes not involve simply the external parallel connectionof two independent
semiconductor components, but their realisation within the semiconductor. Because of
the coordination of the integrated diodes, this type of IGBT initially became established
in resonant applications such as inductive heating of household hotplates. For hard-
switched applications, like those in frequency inverters, the diodesmust be executed in
amuchmore robust way. The coordination of the diodes for this type of applicationwas
optimised accordingly for selectedRC IGBTs.
In terms of engineering process, an RC IGBT is realised by joining part of the n-doped
backside emitter of thediodewith the p-dopedbackside emitter of the IGBT.
Several manufacturers offer RC IGBTs, including ABB, who make a bi-mode insulated
gate transistor (BIGT), Infineon Technologies, with two variants for resonant (RC IGBT)
and hard-switching (RC-D IGBT) applications, andMitsubishi Electric (RC IGBT).
Example of the combination of a diode and IGBT structure, which leads to the
RC IGBT (not to scale)
1.5.9 Integrated additional functions
Other functions can be realisedwithin an IGBT in addition to the basic function, which is
to switch currents. Theseother functions are typically:
Measurement of current
Measurement of temperature
With integrated current measurement, some of the emitter current of the IGBT is
directed separately via an auxiliary connection. In terms of magnitude, this current is