Tutorial #1 - Electromagnetic Compatibility of Switched-Mode Power Supplies

The tutorial/workshop "Electromagnetic Compatibility of Switched-Mode Power Supplies" is subdivided into several sections. Starting with a brief overview of legal regulations, like CE mark and Declaration of Conformity, a selection of emission and immunity standards is presented. This includes the description of test set-ups, for example for measuring conducted emissions using conventional or STFFT based test receivers and their detector circuits, as well as test parameters, like frequency ranges, based on European and International standards. Than four coupling mechanisms (impedance, capacitive, magnetic and radiated) are discussed, based on components and PCB structures. Subsequently basic countermeasures are proposed and evaluated according meaningful applicability to switched-mode power supplies. The section signals and characteristics explains common-mode and differential-mode interferences as well as the Fourier Transform in detail with a number of waveforms, like rectangular, triangular and trapezoidal waveforms, which are typically for switched-mode power supplies. In particular switching transients are discussed against the background of wide band gap devices like GaN transistors. One large section discusses the origin of electromagnetic interferences referring to the previous sections. This section addresses some widely used circuits, their operating modes, like continuous conduction mode, discontinuous conduction mode and boundary conduction mode, and also parasitics of passive components, using high frequency equivalent circuits of capacitors, inductors and transformers, and parasitics of active components, like junction capacitances and terminal inductances. A large number of examples is presented in form of results of measurements, simulations or calculations. The second half of the tutorial/workshop deals with EMC design of switched-mode power supplies, also evaluating efficiency and control issues. This section is subdivided into a number of subsections. Firstly the power factor correction is briefly presented. A large subsection addresses EMC filters, which is subdivided into pre filters and post filters. The filter structure is discussed according common-mode and differential-mode attenuation and source and load impedance. Problem solving approaches of the gap between measurements according standards and filter effectiveness are presented. Additionally an outlook to active EMI filters is given. Also design aspects of magnetic components are discussed. Followed by suitable components, which presents for example the impact of start of winding of a magnetic component, suitable circuits with soft-switching principles are compared to hard-switching circuits. After that shielding basics are presented, in particular the impact of holes for cooling purposes on electromagnetic shielding effectiveness. Finally PCB layout structures are evaluated and recommendations are presented. These investigations also address grounding, one of the most discussed topics in PCB design among engineers, as well as component placing and component selection, e. g. based on integrated circuit pin out and return current paths. Most aspects are explained by measured, simulated or calculated examples. Many examples are discussed against the background of electromagnetic compatibility as well as their impact on efficiency, lifetime and costs of the power supply. The tutorial contains on the one hand practical examples and uses on the other hand the basic physics of Maxwell for a principle understanding. Many principles can be transferred to other electronic circuits.