Inductor

Inductor Design

Eldho Jacob (13MQ81)

INTRODUCTION Inductors are used in almost all Power Electronic

Applications Typical Classification

AC applications DC applications Filtering Smoothing (limiting di/dt) Components of resonance circuits

In Some Applications Inductors are Custom Designed In High Frequency Applications, Specific inductors are

available from Manufacturers. Passive Components(Inductors & Capacitors) account

for 80% of Weight and Cost of a Converter

PROCEDURE Design of Magnetic Elements are considered too

complicated Sometimes many iterations are required to meet the specs Many thump-rules are to be followed Typical Design Process:

Determine the value of Inductance Select Appropriate Core Material based on application and

frequency Determine the Core Cross Sectional Area to handle the required

power Determine the required Air-gap and Number of Turns Determine the Wire Gauge Measure Inductance, Resistance and Power Dissipation Design Heat Sinks if required

DC-DC CONVERTER Major Application of Inductors is in DC-DC

Converters The Trend is to keep Switching Frequency

higher to reduce the Inductor and Capacitor Sizes

At higher frequency Core loss and Conduction losses increases

Inductor Usually serves the Purpose of Energy Storage or Filter

Sometimes Isolation is required and coupled Inductances are used

Example Design: Flyback Converter

Q1 is usually available in IC form with pwm generation and feedback control and current limit features

Specifications:


EE Core of suitable size is selected based on Bmax and LM


Primary Winding Turns (n1) can be calculated from AL Value Specified in Core Datasheet. (LM = AL x N2)

Secondary Turns (n2) is now calculated from Turns Ratio Suitable Airgap prevents core saturation, but Reduces

Inductance Value. Proper Wire Gauges are selected based on maximum Primary

and Secondary Current. In this example: Primary : 28 AWG Secondary : 19 AWG

Core Loss and Copper Loss are calculated and Proper Heat Sinks are decided

Care Must be taken in PCB Routing/ Wiring as EE Cores doesn’t provide full shielding.

Core Types Depending on Application Different Core Types

are available Iron-based materials

Usually for large and High Power applications Laminated to reduce Eddy Current Losses E and I Shapes are common

Ferrites For High Frequency Applications E Core, PQ Core, RM Core etc (based on shape)

Standard Inductors and Transformers For Small Power Applications, Standard Values with

specified Current Ratings are available

Major Manufacturers are Coilcraft TDK/Epcos Cramer Coil Pulse inc etc

Their Websites provide useful tools for selection of components

Documents

Inductor