Abstract
M.Ing. (Electrical & Electronic Engineering)
The technology of the use of electronic devices as power switches
is still being developed. Because of the increasing demand
for low mass and cost, the switching frequency must be as
high as possible. The limiting factor for the frequency is the
energy loss which is dissipated in the semiconductor crystal
during each switching-transient. If tllis switching loss can be
reduced, a higher frequency can be obtained. The switching
loss is due to the non-instantaneous switching process of the
semiconductor device. For the reduction of this switching
loss, the device must be switched as fast as possible via its
control-electrode. Further improvement can be obtained through
the use of snubber networks.
This thesis considers the bipolar high-voltage transistor as a
power switch. The unfavourable switching loci of the transistor-
switch is discussed in chapter 1. In chapter 2 the basedrive
during transistor turn-off is investigated, in order to
reduce the turn-off time.
The following chapters de;al with the use of snubber circuits,
which relieve the transistor during turn-on and turn-off. The
advantages, as well as the disadvantages and limitations of
snubbers are discussed. After the linear turn-off and turn-on
snubbers have been treated, the non-linear turn-on snubber,
which uses a saturable inductor, will be considered from an
experimental point of view. The results show that this snubber
is very effective in relieving the transistor during turn-on.
In chapter 7 the non-linear turn-off snubber is treated on an
experimental as well as on a mathematical bas e . Cri teria,
which must be satisfied for realisation of a practical nonlinear
capacitor, is also laid down.
Because of the fact that a first order snubber is always
loading the transistor during the complimentary switchin,]-transient,
chapter 8 deals with a second order snubber, which consists
of both a capacitor and an inductor.
Experimentally it was found that the turn-on time is reduced
with the use of a turn-on snubber, while the turn-off time is
increased with the use of a turn-off snubber. In chapter 9 the
physical behaviour of the switching processes is investigated,
after which the influences of the snubbers on the switching
times is explained qualitatively...