Understanding Ferrite Inductor Calculations: A Comprehensive Guide

The art of inductor calculation has been a crucial aspect of electrical engineering, particularly in the design and development of electronic circuits. One such important parameter is the self-inductance of an inductor, which can be calculated using various formulas. In this article, we will delve into the world of ferrite inductor calculations and explore the formulae used to determine its self-inductance.

The Self-Inductance Coefficient (kS)

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The self-inductance coefficient (kS) is a dimensionless correction factor that accounts for the difference between the self-inductance of a round-wire loop and that of a single-turn current sheet. According to David Knight's article, the value of kS can be calculated using the formula:

10.4

This formula takes into account the coil diameter (Dc) in centimeters measured between wire centers and the number of turns (N).

The Mutual Inductance Coefficient (kM)

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Another important coefficient is the mutual inductance coefficient (kM), which represents the difference in total mutual inductance between a set of round-wire loops and that of a set of current-sheet loops. David Knight's article also provides a formula for calculating kM:

10.18

This formula incorporates the same variables as mentioned above, including Dc and N.

The Round-Wire Corrections

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Edward Bennett Rosa, an American physicist, developed the round-wire corrections in the late 19th century. These corrections are essential when dealing with coils made of thin wire with many closely spaced turns. The correction formula is given by:

(10.1)

This equation is a good approximation for round wire coils with multiple closely spaced turns.

Current Sheets and Solenoidal Current

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A current sheet refers to a coil wound with very thin tape wire, with no gaps between adjacent turns. This type of coil is often referred to as a solenoidal current sheet. For calculating the inductance (LS) of such coils, David Knight's article recommends using Weaver's numerical methods.

Single-Layer Inductor Design

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In terms of design, a single-layer inductor consists of a coil with a specific diameter (Dc), length (l), pitch (p), wire diameter (d), and wire insulation diameter (di). The picture above illustrates the various components of this type of inductor.

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Ferrite inductor calculations require careful attention to detail, particularly when considering the self-inductance coefficient (kS) and mutual inductance coefficient (kM). By understanding these formulae and incorporating the round-wire corrections, you can ensure accurate calculations for your electronic circuit designs. Additionally, familiarizing yourself with current sheet theory and solenoidal currents will help you better comprehend the intricacies of inductor design.

Ferrite inductor calculator