Technical Information Site of Power Supply Design

2017.02.09 DC/DC

Overview of Selection of Inductors and Capacitors for DC/DC Converters

Selection of Inductors and Capacitors for DC/DC Converters

This section begins a new “Design Edition” relating to DC/DC converters. In this chapter, rather than discussing the entirety of DC/DC converter design, we focus on “Selection of Inductors and Capacitors for DC/DC Converters”, and in particular explain the methods for choosing the inductors and capacitors that are principal components of step-down DC/DC converters, and the selection of which has a major impact on performance and characteristics.

First, we review the basic operation of a step-down DC/DC converter and the accompanying flow of current. In order to select inductors and input and output capacitors, it is important to understand the flow of currents in the circuit and the current waveforms.

We present the procedure and calculation equations for selecting an inductor, and describe a selection example. We’ll begin by explaining the relation between an inductor and the inductor current.

With respect to output capacitors, we explain calculation methods and output ripple.

For input capacitors, we likewise describe calculation methods and describe the DC characteristics that must be considered when selecting a device.

Where overall design is concerned, details are provided in the data sheets and application nodes for power supply ICs. Here we will address some issues and practical knowledge that go somewhat beyond such standard materials.

<Selection of Inductors and Capacitors for DC/DC Converters>

  • Basic operation of step-down converters
  • Inductor selection
  • Output capacitor selection
  • Input capacitor selection
  • Summary

Key Points:

・When designing a DC/DC converter, selection of inductors and input and output capacitors is particularly important.

・It is important to understand the circuit operation and current paths, and the roles played by the various components.

PCB Layout and Selection of Peripheral Parts

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