Siliziumkarbid-Transistoren für Audioverstärker der Klasse-D

The sound of music has always fascinated mankind. In contrast Aristotels’ time, visiting a concert is more than mere entertainment in the normal course of life – nowadays, it is a splendid performance, turned into an emotional moment by light and audio engineering. To meet the arising demands, the audio engineering must utilise a so-called public address system (PA system) consisting of an array of single amplifiers, to drive loudspeakers. Each amplifier requires high performance in terms of energy efficiency and audio quality. In order to achieve the desired power level, a PA system may consist of over 100 single amplifiers. The intricacy of wiring as well as the physical effort to build up a PA system increase rapidly with the number of amplifiers. Although the complexity of a PA system could be reduced using switch-mode class D amplifiers, in the majority of cases linear class H amplifiers are used. These linear amplifiers are less efficient but provide excellent audio quality due to low harmonic distortion. A switch-mode class D amplifier works efficiently but generates harmonic distortion to a greater extent. Currently, this harmonic distortion is generally reduced by complex feedback topologies requiring major time and effort during the designing process of the amplifier.
This thesis investigates the benefit of silicon carbide (SiC) transistors for the power stage of a class-D amplifier, since harmonic distortion is also caused by the power stage devices. The fast-switching SiC-transistors may partially resolve the root of the poorer sound quality by minimising the harmonic distortion of the power stage. Further advantages also arise; e.g. concerning output power and efficiency. In this work, four class D power stages are developed and characterised. Detailed analysis of the audio quality reveals interesting aspects relating to existing class D amplifier theory. The outcome, particularly with regard to output power and efficiency, may be transferred to other switch-mode applications in power electronics. Beyond that, the relationship between the transistor’s semiconductor-characteristics and the source of harmonic distortion is investigated in detail for the first time. The results are outlined in each chapter beginning with ’Einfluss der Transistor-Charakteristika auf..’.
The use of silicon carbide power devices would open new prospects in many aspects of class D amplifier performance. This work examines these aspects with respect to audio quality, output power and efficiency.