2RT0435T
Target Description and Application Manual
www.IGBT-Driver.com
Page 12
V
ce
monitoring / short-circuit protection
The basic V
ce
monitoring circuit implemented in
2RT0435T SCALE-2 Base Boards is illustrated in
Fig. 2. Both IGBT collector-emitter voltages are
measured with sense diodes. V
ce
is checked after
the response time (see Fig. 9) at turn-on to
detect a short circuit. If this voltage is higher than
the programmed threshold V
th
, the driver detects
a short circuit at the IGBT and signals it
immediately to the corresponding SOx output.
The corresponding IGBT is immediately switched
off. The IGBT is kept off (non-conducting) and
the fault is shown at pin SOx as long as the
blocking time is active.
The blocking time is applied independently to
each channel. It starts when V
ce
exceeds the
threshold of the V
ce
monitoring circuit.
Note:
The desaturation function is for short-
circuit detection only and cannot provide
overcurrent protection. However, overcurrent
detection has a lower time priority and can be
easily provided by the application.
Advanced Active Clamping
Active clamping is a technique designed to partially turn on the IGBT in case the collector-emitter voltage
exceeds a predefined threshold. The IGBT is then kept in linear operation. The basic circuit for active clamping
can be found in /5/.
Basic active clamping topologies implement a single feedback path from the IGBT’s collector through transient
voltage suppressor devices (TVS) to the IGBT gate. The 2RT0435T Base Boards support CONCEPT’s Advanced
Active Clamping based on this principle: when active clamping is activated, the turn-off MOSFET of the driver
is switched off in order to improve the effectiveness of the active clamping and to reduce the losses in the
TVS. This feature is mainly integrated in the secondary-side ASIC.
Fig. 9 Turn-on characteristic of an IGBT