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Inductance Calculator for DC/DC Converters

Inductor Selection Tool for DC/DC Converter

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What is EMI/EMC?

EMI stands for Electromagnetic Interference also known as Radio Frequency Interference (RFI). It is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction. The disturbance may degrade the performance of the circuit or even stop it from functioning.

EMI – electromagnetic interference can arise from many sources, being either man made or natural. Categorization of EMI is by the way it was created:

Man-made Electromagnetic interference: Generally arises from other electronics circuits, although some Electromagnetic interference can arise from switching of large currents, etc.

Naturally occurring Electromagnetic interference: Arise from many sources like cosmic noise as well as lightning and other atmospheric types of noise.

There are many ways in which the electromagnetic interference can be coupled from the noise source to the victim. Understanding which coupling method brings the interference to the victim is key to being able to address the issue.

Four EMI Coupling Mechanisms:

Radiative Coupling – When an unwanted signal is transferred from source equipment to victim equipment by radiation through space, It is referred as Radiative Coupling.

Inductive Coupling – The source and the victim are coupled by a magnetic field. The level of disturbance depends on the current variations (di/dt) and the mutual coupling inductance.

Conducted Coupling – When there is a conduction route along which the signals can travel. This may be along power cables or other inter-connection wires. The conduction may be in one of two modes:

Capacitive Coupling – The level of disturbance depends on the voltage variations (dv/dt) and the value of the coupling capacitance between the disturber and the victim.

Common mode: This type of EMI coupling occurs when the noise appears in the same phase on the two conductors, e.g. out and return for signals, or +ve and -ve for power cables.

Differential mode: This occurs when the noise is out of phase on the two conductors.

Category of EMI by its Time Duration

Impulse noise:   This kind of EMI may be man-made or naturally type. Lightning, ESD, and switching systems all contribute to impulse noise.

Continuous interference:  This kind of EMI generally arises from a source such as a circuit that is emitting a continuous signal. However background noise, which is continuous may be created in a number of ways, either man-made or naturally.

Category of EMI by its Bandwidth

Narrowband EMI –  Typically this form of EMI is likely to be a single carrier source – possibly generated by an oscillator of some form. Another form of narrowband EMI is the spurious signals caused by intermodulation and other forms of distortion in a transmitter such as a mobile phone of Wi-Fi router. These spurious signals will appear at different points in the spectrum and may cause interference to another user of the radio spectrum. As such these spurious signals must be kept within tight limits.

Broadband EMI  –  There are many forms of broadband noise which can be experienced. It can arise from a great variety of sources. Man-made broadband interference can arise from sources such as arc welders where a spark is continuously generated. Naturally occurring broadband noise can be experienced from the Sun – it can cause sun-outs for satellite television systems when the Sun appears behind the satellite and noise can mask the wanted satellite signal. Fortunately these episodes only last for a few minutes.

Common Sources of EMI

DC/DC Converters

Switching ICs

Inductive Load

Multiple Clock Frequencies

Useful link 

Noise Filters

Inductance Calculation for Buck Converters

Inductor Selection for DC/DC Convertors

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What is an Inductor?

Inductor is an electrical component that stores energy in the form of magnetic field.

An inductor is a passive electrical component that opposes sudden changes in current. Inductors are also known as coils or chokes.

The inductor can be made through conducting wire as a coil. Inductors slow down current surges or spikes by temporarily storing energy in an electro-magnetic field and then releasing it back into the circuit.

The inductance of an Inductor is highly dependable on multiple factors, such as number of turns of wire, the spacing between the turns, no of layers of turns, type of core materials, its magnetic permeability, size, shape etc.

The electrical symbol for an inductor is L

The measurement unit of an inductor is Henry [H].

It blocks any changes in current flowing through it.

How does an Inductor work?

Difference between two terminologies, Magnetic Field and Magnetic Flux.

During the Current flow through the conductor, a magnetic field is generated. These two things are linearly proportional. Therefore, if the current is increased, so the magnetic field will also increase. This magnetic field is measured in the SI unit, Tesla (T). Now, what is Magnetic Flux? Well, it is the measurement or quantity of the magnetic field which passes through a specified area. Magnetic Flux also has a unit in SI standard, it is Weber.

So, as of now, there is a magnetic field across inductors, produced by the current flowing through it.

To understand further, understanding of Faraday’s law of inductance is required. As per Faraday’s law of inductance, the generated EMF is proportional to the rate of change of the magnetic flux.

VL = N (dΦ / dt)

where N is the number of turns and Φ is the amount of flux

Construction of an Inductor

One generic, standard inductor construction and working can be demonstrated as a copper wire wrapped tightly across a core material. In the below image, copper wire is closely wrapped across a core material, making it a two terminal passive inductor.

When the current flow through the wire, the electromagnetic field will develop across the conductor and electromotive force or EMF will generate depending upon the rate of change of the magnetic flux. So, the flux linkage will be Nɸ.

What is the Self Resonant Frequency of an inductor?

The self resonant frequency of an inductor is the frequency at which the parasitic capacitance of the inductor resonates with the ideal inductance of the inductor resulting in an extremely high impedance.  The parasitics of an inductor vary based on the type of inductor – wire wound inductor, multi-layer inductor, conductive film inductor etc.

Use of Inductor

Inductors are used in tuning circuits

Inductors are used as filters

Inductors used for energy storage

Types of Inductors

Inductors for Noise Filtering

SMD Ferrite Beads for Noise Filtering

THT Ferrite Beads for noise attenuation

Rod Core Inductor for EMI Filtering

High Current SMD Ferrite beads for noise Filtering

Common Mode Chokes

SMD Common Mode Chokes

High Current SMD Common Mode Chokes

Line Filters

Current Compensated Chokes

High Frequency Choke Coils

Inductors for Energy Storage

Radial Inductors

Toroidal Inductors

Multilayer SMD Inductors

Wirewound Inductors

Tiny Inductors

Resin Shield Inductors

Shielded Inductors

High Current Inductors

Moulded Inductors

Dual Inductors for Buck-Boost or SEPIC converters

Application Notes

MTAN17819 - Inductor Selection Guide for Buck Converters

Inductor Selection Tool

Online Inductor Selector

Cross Reference Tool

For more details, visit https://magnoteknik.com/inductor/