Single Conversion stage AMplifier - SICAM

Abstract

This Ph.D. thesis presents a thorough analysis of the so called SICAM - SIngle Converter stage AMplifier approach to building direct energy conversion audio power amplifiers. The mainstream approach for building isolated audio power amplifiers today consists of isolated DC power supply and Class D amplifier, which essentially represents a two stage solution, where each of the components can be viewed as separate and independent part. The proposed SICAM solution strives for direct energy conversion from the mains to the audio output, by dedicating the operation of the components one to another and integrating their functions, so that the final audio power amplifier represents a single-stage topology with higher efficiency, lower volume, less board space, lower component count and subsequently lower cost. The SICAM approach is both applicable to non-isolated and isolated audio power amplifiers, but the problems encountered in these two cases are different. Non-isolated SICAM solutions are intended for both AC mains-connected and battery-powered devices. In non-isolated mains-connected SICAMs the main idea is to simplify the power supply or even provide integrated power factor correction (PFC) functions, while still maintaining low component stress and good audio performance by generally decreasing the input voltage level to the Class D audio power amplifier. On the other hand, nonisolated battery-powered SICAMs have to cope with the ever changing battery voltage and provide output voltage levels which are both lower and higher than the battery voltage, while still being simple and single-stage energy conversion solutions. In isolated SICAMs the isolation transformer adjusts the voltage level on the secondary side to the desired level, so the main challenges here are decreasing the size of the magnetic core and reducing the number and size of bulky reactive components as much as possible. The main focus of this thesis is directed towards the isolated SICAMs and especially the so called isolated SICAM with non-modulated transformer voltages. The latter is found to be the most interesting isolated SICAM solution for the modern multichannel audio power amplification systems, since all of the output stages corresponding to the different audio channels can reuse the same input stage and transformer core. While the proposed approach tends to be very simple from topological perspective and allows for reduction of reactive component count, the commutation of the load current in the output bridge and the bridge itself are much more complicated than their Class D predecessors. The main contribution of the thesis can be found in the thorough analysis of the present topologies for isolated SICAMs, as well as the numerous structural improvements and several newly proposed control methods for alleviating the problem of load current commutation and high-performance control of the whole SICAM. Another significant contribution is the presentation of several interesting topologies and associated control principles in the field of non-isolated SICAMs for mains-connected and portable audio amplifiers