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Inductors & Inductance Calculations |
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 Inductors
are passive devices used in electronic circuits to store energy in the form of a magnetic field. They are the
compliment of capacitors, which store energy in the form of an
electric field. An ideal inductor is the equivalent of a short circuit (0 ohms) for direct currents (DC), and
presents an opposing force (reactance) to alternating currents (AC) that depends on the frequency of the current.
The reactance (opposition to current flow) of an inductor is proportional to the frequency of the current flowing
through it. Inductors are sometimes referred to as "coils" because most inductors are physically constructed of
coiled sections of wire.The property of inductance that opposes current flow is exploited for the purpose of preventing signals with a higher frequency component from passing while allowing signals of lower frequency components to pass. This is why inductors are sometimes referred to as "chokes," since they effectively choke off higher frequencies. A common application of a choke is in a radio amplifier biasing circuit where the collector of a transistor needs to be supplied with a DC voltage without allowing the RF (radio frequency) signal from conducting back into the DC supply.   When
used in series (left) or
parallel (right) with its circuit compliment, a capacitor, the
inductor-capacitor combination forms a circuit that resonates at a particular frequency that depends on the values
of each component. In the series circuit, the impedance to current flow at the resonant frequency is zero with
ideal components. In parallel circuits (right), the impedance to current flow is infinite with ideal components. Real-world
inductors made of physical components exhibit more than just a pure inductance when present in an AC circuit.
A common circuit simulator model is shown to the right. It includes the actual ideal inductor with a parallel
resistive component that responds to alternating current. The DC resistive component is in series with the ideal
inductor, and a capacitor is connected across the entire assembly and represents the capacitance present due to
the proximity of the coil windings.Equations (formulas) for combining inductors in series and parallel are given below. Additional equations are given for inductors of various configurations. The HamWaves.com website has a very sophisticated calculator for coil inductance that allows you to enter the conductor diameter.
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,
resistive
component, an equivalent circuit can be defined with a resistor in parallel with the inductor. This
equation is valid only a a single frequency, "f," and must be calculated for each frequency of
interest.
