Hitachi IGBT Module Application Manual
st
energy passing through the snubber
circuit and being refluxed. This allows overvoltage suppression. However, in reality, the snubber circuit also
has wiring inductance L
sn
which may cause overvoltages. How can L
st
and L
sn
be reduced? The answer is
to choose the right components and to lay them out appropriately.
Figure 22. Equivalent Circuit (transient state)
5.2.3 Snubber Circuit Current and Voltage Waveforms
Referring to Figure 21 above, consider the current and voltage waveforms in the circuit when the IGBT
is turned OFF. Figure 23 represents the IGBT module’s turn-OFF current and voltage waveforms and clearly
shows that use of a snubber circuit inhibits surge voltage stemming from wiring inductance L
st
to
E
o
+
∆
V
f
.
Figure 23. IGBT Module Current and Voltage Waveforms with Snubber Circuit
20