IGBT Modules - Technologies, Driver and Application (Second Edition) - page 114

Fig. 2.43
Example of parallel connection of three IGBTs and diode chips
(plotted currents relate to thediodes)
Dynamic current sharing can be described in terms of the inductive design of the IGBT
module and the gate emitter connection. The influence of external factors, such as the
driver stage and cooling in relation to the parallel connection, will be dealt with in later
To achieve an even balance, i.e. to synchronise the turning on and turning off of IGBTs
and diodes, the DCB layout and bond layout must exclude preferential or
disadvantageous switching of the chips. This simply means keeping the parasitic
influences of the design as even as possible for all semiconductors connected in
parallel. This is achieved by connecting an auxiliary emitter, among other things. The
auxiliary emitter is created from themain emitter for all IGBTs connected in parallel. The
positioning of the electrical connection is crucial to the entire switching behaviour and
high short circuit capability of the IGBT module. This effect is known as positive and
negative emitter feedback. In certain circumstances, the chip top surfaces (emitter
potential) of the IGBTs and diodes connected in parallel are additionally connected
using a bond wire to achieve symmetry in the switching behaviour and prevent high
frequency oscillations. This is described inmore detail in chapte
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