Device based modelling of high current bipolar transistors for the detailed simulation of converter circuits

• Main Author: Prest, Rory Bruce
• Published: 2014
• Subjects: Bipolar transistors; Bipolar integrated circuits; Junction transistors
• Online Access: http://hdl.handle.net/10210/9511

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.