IGBT chip. The TVS diode used in this example has a nominal value of U
However, as shown in
the effective collector-emitter voltage during the
clamping process is around 1050V because of the temperature dependence and
toleranceof theTVS diode plus theapplied gate-emitter voltage.
Effectiveness of collector-emitter clamping (ActiveClamping)
In the following anoverviewof TVS diodes used inActiveClamping circuitries is given.
STMicroelectronics, Vishay, etc.
1.5KE6.8xx - 1.5KE540xx
P6SMB220xx - P6SMB550xx
Examples of TVS diodes
18.104.22.168 Conditional ActiveClamping
Under certain conditions, the DC-bus voltage values may rise above the breakdown
voltage of the TVS or suppressor diode, but still be below the blocking voltage of the
IGBT. Applications include solar inverters, inwhich the panel voltage is usually higher in
winter than it is in summer. If this occurs when the inverter is not operating and
therefore able to dissipate the DC-bus voltage, the currents through the TVS diode of
the Active Clamping circuit can overload these diodes and other components in the
IGBT driver, with the final result being destruction of the IGBT driver. In these types of
applications, it may be necessary to leave out the Active Clamping altogether or
increase the TVS diode voltage, although the disadvantage of the latter is that it makes
theActiveClamping less effective.
In applications in which regeneration energy causes the DC-bus voltage to rise (e.g.
hybrid vehicles), it may be worthwhile modifying the Active Clamping circuit. The
purpose of modification is to ensure that the ActiveClamping circuit cannot be activated
when the IGBT is not triggered. In other words, the circuit must not be allowed to
function unless the IGBT is operating normally. In all other circumstances, the Active
Clampingmust remain turned off. Thismodification is achieved by inserting for instance
a switch S
into the clamping path, which is controlled jointly with the gate signal, as