High-voltage-rated
insulated-gate bipolar transistors (IGBTs) are commercially
available up to 6.5 kV. Such voltage ratings are attractive
for pulsed power and high-voltage switch-mode converter
applications. However, as the IGBT voltage ratings increase, the
rate of current rise and fall are generally reduced. This tradeoff is
difficult to avoid as IGBTs must maintain a low resistance in the
epitaxial or drift region layer. For high-voltage-rated IGBTs with
thick drift regions to support the reverse voltage, the required
high carrier concentrations are injected at turn on and removed
at turn off, which slows the switching speed. An option for faster
switching is to series multiple, lower voltage-rated IGBTs. An
IGBT-stack prototype with six, 1200 V rated IGBTs in series has
been experimentally tested. The six-series IGBT stack consists
of individual, optically isolated, gate drivers and aluminum
cooling plates for forced air cooling which results in a compact
package. Each IGBT is overvoltage protected by transient voltage
suppressors. The turn-on current rise time of the six-series IGBT
stack and a single 6.5 kV rated IGBT has been experimentally
measured in a pulsed resistive-load, capacitor discharge circuit.
The IGBT stack has also been compared to two IGBT modules
in series, each rated at 3.3 kV, in a boost circuit application
switching at 9 kHz and producing an output of 5 kV. The six-series
IGBT stack results in improved turn-on switching speed, and
significantly higher power boost converter efficiency due to a
reduced current tail during turn off. The experimental test
parameters and the results of the comparison tests are discussed
in the following paper.