IGBT Modules - Technologies, Driver and Application (Second Edition) - page 292

6 I
6.8.1 Minimumpulsesuppression
Minimum pulse suppression is designed to prevent switch-on or switch-off pulses below
a certain length from turning the semiconductor on or off. These very short pulses only
cause losses in the power electronics component and its environment, due to the
change of charge of coupling capacitances, and do not usually contribute to supplying
current to a load. Also, if minimum switch-on times are not observed, undesired dynamic
effects may occur, which can destroy the power electronics component under certain
conditions (chapte
DSP and microcontrollers generate the control signals of the gate driver. If minimum
switch-on times are observed at the programming stage, extra provisions in the
hardware for minimum pulse suppression are superfluous. This is not always regarded
as reliable. In devices in high power applications, for example, the best possible
hardware protection is required. Magnetic coupling into the control wires and software
errors can cause voltage transients. If these are higher than the threshold voltage of the
driver input circuit, thegatedriver will turn on, which is undesirable.
Minimum pulse suppression prevents power electronics components from turning on
briefly when this is not wanted. Therefore, this includes not only the IGBT under
consideration, but also its freewheeling diode. For the gate driver, thismeans that turn-
on and turn-off pulses, which are shorter than the minimum turn-on times of the power
electronics component, must be suppressed. The easiest method of minimum pulse
suppression in the gate driver is the Schmitt Trigger with an additional low-pass filter at
the input. Sensible settings for t
are between 100ns and 800ns and can be longer for
componentswith higher voltages such as 3.3kV to6.5kV.
It should be remembered that the transition time tolerance usually increases as the
minimum pulse suppression times become longer. The transition time tolerance
depends heavily on the tolerances of the other components, particularly the capacitors.
Fig. 6.75
Exampleof minimumpulse suppressionwith a non-invertingSchmitt Trigger
6.8.2 Dead-timegenerationandhalf-bridge interlocking
An ideal switch turns on and off infinitely quickly, but a real switch does not. This causes
overlap times in half-bridge topologies in which one switch is already turned on and the
other has not yet turned off (chapter
. As a result, a cross current flowing through
the power electronics components generates additional losses, shortens the lifetime of
the components and may cause electromagnetic disturbance. This must be prevented.
As with minimum pulse suppression, it can be done by the supervising control.
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