How2Power.com - Magnetics Design for Switching Power Supplies, Section 1

Magnetics Design for Switching Power Supplies, Section 1

Focus:

This 10-page chapter provides an introduction to basic magnetic terms and concepts for switched-mode power supply (SMPS) designers. This background information is intended to help the power supply designer in the following ways: develop electrical circuit models of magnetic components, relate electrical circuit models to magnetic device structures, work together with magnetic experts, and achieve one's own expertise in magnetics design. The author discusses barriers that engineers have faced in learning magnetic design including archaic concepts and engineering practices, disparities between the CGS and SI systems of units, and designers' lack of comfort in working with time as a factor in magnetics equations such as flux density. Another source of difficulty stems from characterization of core losses using sinusoidal drive as opposed to square waves which would be appropriate for SMPS design. The chapter explains magnetic field principles such as Ampere's Law and the importance of conservation of energy. Transformation of axis for translating B-H characteristic into Fi vs. F and Integral Edt vs. I are discussed. Key magnetic parameters are defined in both SI and CGS systems and their conversion factors are given. Terms such as permeability, permeance, reluctance, and inductance are defined. Energy plane plots (Integral Edt vs. I) are presented for inductors, capacitors, and resistors with both sinusoidal voltage drive and rectangular voltage drive and the meaning of these waveforms is discussed. The terms transformer and inductor are defined to explain their roles in SMPS design and distinguish between the two in terms of energy storage. Core material limitations are discussed.

What you’ll learn: