DIY RF Inductors--The ABCs of inductors （4）

Published:2011/7/25 2:48:00 Author:Li xiao na From:SeekIC

By B. Kainka


Inductor calculations using software


A small Visual Basic (VB) program called LCFR has been written to make calculations for inductors and resonant circuits. The source and executable code for this program can be obtained free of charge from the Elektor Electronics website. The number is 030398-11, see this month’s Free Downloads. This program, whose user interface is shown in Figure 6, calculates the inductance of air-core inductors and inductors using cores with known AL values. In addition, it can determine the resonant frequency and inductive impedance R[_ of the inductor at resonance if a capacitance value is entered in addition to the inductance value.



The program consists of three parts that independently perform calculations, which for purely practical reasons are merged into a single user interface. Calculations for air-core inductors are made using the upper portion of the window, and magnetic-core calculations are made using the middle portion. At the bottom you can see the calculated resonant frequency and inductive impedance. If a new value is entered in any of the boxes, the results will change immediately. The most recently calculated inductance is automatically used for the calculations in the bottom section.

This program is ideal for quickly trying out’ new parameters. The fact that the inductance is shown to three decimal places should not be taken as an indication of the accuracy of the result. Instead, it is intended to allow calculations to be made for inductors covering a wide span of inductances, ranging from a few nanohenries (1 nH = 0.001 /JH) to many millihenries (1 mH = 1000/iH).

If you want to build a resonant circuit for a specific frequency, you can start by entering the capacitance, then calculating the inductance and finally determining the number of turns for a type given type of core or coil form. However, a less systematic approach often works better. You can simply select a type of inductor and then try several inductance and capacitance values until you find a satisfactory result. For instance, you may wish to determine which standard component values of fixed inductors and capacitors can be used to build a resonant circuit that will have a particular resonant frequency in a specific circuit. Here a trial-and-error approach often yields results faster than systematic calculation.

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