Abstract
D.Ing. (Electrical & Electronic Engineering )
In recent years, bipolar transistors have become available with large current
ratings (300A-1DODA). The purpose 01 this study is to analyse the modelling 01
these devices, with a view to applying the results to detailed power electronic
circuit design (for example base drive and snubber circuits). In contrast to the
many curve-filling approaches existing in this field, a model which correctly
represents the physical mechanisms is desirable, in order to characterise the
device behaviour with a minimum number of parameters.
Existing modelling techniques, which have mostly been developed for low
current devices, are examined in detail to determine their validity for high current
8JTs. Alter a survey of the literature, the assumptions contained in the
lundamental first order theory are investigated, together with the most important
second order ellecls. This is followed by a detailed experimental investigation, to
establish the dominant mechanisms for both de and dynamic operation.
The behaviour 01 large power devices is dominated by conductivity modulation
01 the lightly doped collector region. This means that the Gummel-Poon model,
which is based on ellects in the base is not the most appropriate for high current
modelling. II also found that the the simple charge control equation can give
accurate results for dynamic modelling. The dynamic saturation region 01
operation is described by a simple model, based on the quantity 01 stored
charge. This is an improvement on the currently used Gummel-Poon models.
The findings are all incorporated into a new model, which is included in a
version of the SPICE network simulation program and then tested experimentally.
The importance 01 the reverse conduction mode 01 operation is discussed and
some techniques for modelling this region are presented, together with some
experimental results.
II is shown conclusively that the developed device based approach, models the
behaviour of the devices adequately for converter design purposes, over a wide
range of operating conditions.