Power Inductor Selection Criteria for Switched Mode Power Supplies

Abstract

Today’s SMPS must meet the demands for high power, small size, high switching frequency and high efficiency. With the increasing demand for high power and high frequency switch mode power supplies, manufacturers face the challenge of developing high current, low loss and cost effective power inductors. Selection of appropriate power inductors is a vital step in the successful design of a switched mode power supply. The selection process can be confusing if physical inductors are not well understood. Application requirements from the market mean these power inductors must be capable of working in high DC bias current as well as high frequency ripple current with minimal heat generation, yet without sacrificing inductance. Because circuits are switching at higher frequency and handling more current in tighter printed circuit board space, electromagnetic interference (EMI) cannot be ignored. This paper covers basic circuit equations to provide a starting point for the selection process. Two most important applications of power inductors – energy storage and EMI suppression are discussed in detail. Selecting an appropriate inductor depends on understanding perfect inductors in addition to the actual characteristics of physical inductors.