Turn-off behaviour of a 450A/1.2kV Trench-FS IGBT with on-times of different
The results from
uggest that no general statement can be made
regarding the definition of the minimal on-time in the application. The recommendation
is, to explicitly measure the application in question and adjust the minimal on-time of
both the IGBT as well as the diode of the application. As a guideline for this adjustment,
use a minimal on-time of 5µs to 10µs as the lowest reference point. Sometimes the
IGBTmodule datasheets show notes regarding theminimal on-time of the freewheeling
which should be observedwhendesigning theapplication.
7.4 Dead-time (interlockdelay time)
As described in chapte
he IGBTs are continually turned on and off according to
a modulation pattern. If one takes the half-bridge configuration from
that the top IGBT T
and the bottom IGBT T
are alternately turned on and off. It is
important, however, that at no time both IGBTs are turned on together, not even for a
short time. This would lead to a shorted bridgewith the resulting consequence
. Also it
has to be noted that an IGBT cannot instantaneously turn from the conducting to the
blocking mode, but instead requires some time to clear all carriers from the drift zone.
Additionally, the gate drive signals generated by the controller are subject to a transition
delay before they arrive at the IGBT. Overall, the following points need to be noted
when turning off one IGBTand turning on its counterpar
The turn-off delay time t
as a function of the junction temperature T
load current I
, the DC-bus voltage U
, the gate turn-off voltage U
gate turn-off resistor R
If the bridge stays shorted for a sufficiently long time it may be recognised by other protection circuits (e.g.
saturation voltage U
monitor) and turned off. If the short circuit only occurs for a very brief time (which is
usually the case) which is below the time resolution of the existing protection feature, then the short circuit will
lead to increased losses and stress for the components. The resultmay be a premature failure.
Thedefinition of the switching times is donealong chapte
naccordancewith IEC 60747-9.