1 Electronics, Department of Electrical Engineering, Technical University of Denmark2 Department of Electrical Engineering, Technical University of Denmark
Switch-mode power electronics is disturbing other electronic circuits by emission of electromagnetic waves and signals. To allow transmission of information, a set of regulatory rules (electromagnetic compatibility (EMC)) were created to limit this disturbance. To fulfill those rules in power electronics, shielding and filtering is required, which is limiting the size reduction. The motivation for this project was to find alternative ways to avoid trouble with interference of switch-mode power electronics and transmission and receiver circuits. An especial focus is given to audio power amplifiers. After a historical overview and description of interaction between power electronics and electromagnetic compatibility (chapter 1), the thesis will first show the impact of the high frequency signals on the audio performance of switch-mode audio power amplifiers (chapter 2). Therefore the work of others will be put into perspective and self-oscillating amplifiers will be compared with external synchronized topologies. After that, solutions to the problem, which are widespread in industry will be given and explained (chapter 3). The challenges and advantages will be described. The improvement of the described problem where four different approaches: • Multi Carrier Modulation (MCM) • Active Electromagnetic Cancellation (AEC) • Current Driven Power Stages (CDP) • Radio Frequency Power Electronics (RF SMPS) Multi Carrier Modulation (chapter 4) is using more than one external carrier and generating multiple PWM signals. Those are combined by a logic circuit to one pulse coded information stream. The average of this stream is proportional to the modulated signal, while the spectral peaks of the switching frequencies are half compared to state-of-the art pulse width modulation (PWM). Active Electromagnetic Cancellation (chapter 5) has been known as active filtering in power electronics. It has been applied to switch mode audio power amplifiers. The specialty for the later will be described and a design is shown, decreasing the undesired spectrum by 15 dB. A different approach to tackle the problem is given by an alternative power stage in Current driven Power Stages (chapter 6). A focus of this approach is to minimize the biggest components, the inductors, in the filters of switchmode power electronics. This approach results in a size reduction of the filters by around 84 %. A very promising approach to remove the interference of power electronics circuits and telecommunication circuits is to stay away from the frequencies used for information transmission. Even though the electromagnetic spectrum is used without any exceptions, the situation can be optimized for audio applications. This is done by using switching frequencies beyond the communication frequencies and will be described in Radio Frequency Power Electronics (chapter 7).