IGBT Modules - Technologies, Driver and Application (Second Edition) - page 284

6 I
Fig. 6.66
Datasheet extract of TVS diodes in the SMBJ5V0(C)A – SMBJ170(C)A series
If the gate is clamped against the positive supply voltage
it must be ensured that the
leakage or blocking current I
of the diode used still has low values at high
temperatures. If the blocking current is too high the power supply of the driver is loaded
unnecessarily and the blocking current boosts the gate voltage (while the IGBT is in the
turned off state). If the driver stage has a high impedance connection to GND in this
state, this may reduces the nominal gap to the threshold voltage U
of the IGBT.
Under unfavourable conditions, parasitic turn-on of the IGBTmay occur.
Fig. 6.67
Circuit symbol and I/U diagram of bidirectional TVS diodes
Schottky diodes, with their very low forward voltage in comparison to pn-diodes, are
ideally suited to this task, as this forward voltage has to be added to the voltage value of
the supply voltage. When pn-diodes are used, clamping voltages of at least 17V occur,
The buffer capacitor(s) usually serve(s) as the reference point for the supply voltage in gate clamping. If a
booster stage is placed between the actual driver and the gate, thebuffer capacitors of the booster stage become
the referencepoint.
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