How to select an inductor-Coilmaster Electronics

How To Select An Inductor
Inductors
Inductors, also called a coil or reactor, are passive two-terminal components which have
different function, such as for filtering, timing and power electronics applications. Power
Inductor (SMD / Pin type of inductor) store energy in the form of magnetic fields as long
as a current is flowing. The unit of inductance is Henry (H). Moreover, the inductor can
be approximated as an open circuit for AC signals and as a short circuit for DC
signals.
The inductance value will affect by several factors, the most common one is like below,
the size of the coil area, the number of turns in the coil, coil length and the most
important one the material of the core. Coilmaster Electronics have strong engineer team,
most of our engineers could design / amend the core material to fulfilled customer’s
demand. The inductor have several types, some SMD inductor / Leaded inductor
normally have a magnetic core made of iron or ferrite inside the coil, which serves to
increase the magnetic field and thus the inductance. On the other hand, inductors with a
magnetic core have losses such as hysteresis and eddy currents
Normally, when selecting an inductor, several parameters that are important to keep in
mind. Self-Resonant Frequency (SRF) , Q factor, DC Resistance (DCR) and Saturation
Current. We will try to explain each factors as below.
• Q factor, all called a Quality Factor, refers to the ratio of an inductor’s reactance to
effective resistance. This value is frequency dependent and test frequency is often
specified in datasheets. Q factor impacts the sharpness of the center frequency in an
LC circuit. Usually, a high value of Q factor is preferred. Moreover, according to the
formula, Q=wL/R, the high Q air core inductors often have large diameters and many
turns.
• Self-Resonant Frequency (SRF), the inductor will have no function beyond specific
frequency, this frequency is called self-resonant frequency (SRF). The inductor has
low distributed capacitance between terminal electrodes or the turns of a
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wire-wound conductor, and its inductance with such distributed capacitance
resonates at a certain frequency. Therefore, when selection of SMD inductor/ high
current inductor/ shielded SMD inductor or pin type inductor for RF circuits, the
higher value of SRF (self-resonant frequency) should be chosen. The SRF value
should exceed the operating frequency of the circuit. As the inductance is zero at
the self-resonant frequency, the Q factor is zero also.
• Saturation Current refers to the DC current which causes the inductance to drop by
a specified value, normally the percentage of decreasing will be from 5% to 30%
compare to original inductance value. The inductance drops because at that current
which the core is completely filled with magnetic flux and it can't take any more.
While saturation current is related to the magnetic properties of the inductor, rated
current is related to physical properties, and it describes the maximum DC current
that can be passed in an inductor.
• DC Resistance (DCR) refers to the resistance inherent in the metal conductor of the
inductor, and it can be modeled as a resistor in series with the inductor. DC resistance
is an important parameter in DC-DC converters design as the resistance leads to I2R
losses thus reducing the efficiency.
• Tolerance is the variation in the inductance value of an actual inductor compared to
the specified value in the data sheet. This could result in unwanted shift in frequency
selection of an RF filter.
INDUCTOR TYPES
Some engineers will use the inductor for blocking or decoupling higher frequencies, it is
called as “choke”. There are different types of inductors based on materials used in cores
and construction. The most common type is Ferrite core inductor, Iron powder
inductor(molded inductor / high current inductor), Toroidal inductor (Leaded inductor/Pin
type inductor), Axial inductor, Semi-shielded inductor (Cost effective solution product).
I. Air Core Inductor / RF Inductors / Spring Air Core Inductors
Air-core inductors also called RF Inductor, Spring Air Core Inductor, it do not use any
magnetic core, the air-core inductor have biggest advantage, have a high Q factor value
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and low losses. On the other hand, as the air core inductor, to gain the same value of
inductance result in the bigger size. The air core inductor are mainly used in high
frequency applications such as resonant circuits where low inductance values are
sufficient.
Part Selection: Coilmaster SS series
II. Ferrite Core Inductor
Ferrite core inductors are made of a ferromagnetic material which has high permeability.
These inductors have much wilder inductance range compare to other types of SMD
inductor. And the advantage of ferrite core inductor is low losses. Ferrite core inductor
are used in noise filters, high quality transformers and DC-DC converters
Part Selection: Coilmaster MW series
III. Iron Core Inductor
Iron core inductors(molded inductor / high current inductor) can have very high saturate
current. Molded SMD inductor / High current inductor can handle very high power but
are limited in high frequency capacity, usually be used in low frequency applications such
as audio equipment, DC-DC converter. Coilmaster Electronics have complete production
line in field of high current power inductors could use to design in power supply
inductor, SMD high current inductors, high saturate current inductor, high power
inductor, surface mount inductor, or other circuit which may require a high saturate
current inductors.
Part Selection: Coilmaster SEP series
IV. Toroidal / Leaded / Pin type Inductor
When inductors are wound around a ring or circular toroid, they are referred to as toroidal
inductors. The Toroidal / Leaded / Pin type Inductor possess the higher inductance and Q
factor than an inductor with straight core. Toroidal / Leaded / Pin type Inductor structure
is suitable for large current, high inductance or high Q factor applications. These inductors
are used in DC-DC switching voltage regulators, medical and refrigeration equipment,
telecommunication circuits and more. Coilmaster Electronics could offer customize item
to meet customer’s requirement. Since we have strong background at ferrite core, we
could adjust the core material and winding condition.
Part Selection: Coilmaster TC series
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V. Axial Leaded Inductor
Axial lead inductor are wound on a cylindrical bobbin and can be either axial
leaded or radial leaded, different size are available, such as 0204,0307,0410,0510.
The lager or customized one is also available at Coilmaster. Axial lead inductor
(RF Inductors) are mostly used for printed circuit boards (PCBs). They vary
widely in terms of power rating, operating frequencies, size and other parameters.
Part Selection: Coilmaster AL series
VI. Ferrite Beads
Ferrite Beads are passive components that use to remove high frequency electromagnetic
interference (EMI) noise from a circuit. It is a specific type of electronic choke. Ferrite
beads are used as inductors to form a passive low-pass filter. Normally, Ferrite beads are
placed in series with the signal source. When select the ferrite beads, it is preferred to
have low values of DCR (dc resistance). However, some application will need high
impedance value over some defined frequency range to suppress the noise.
Part Selection: Coilmaster SMB series
Need further support, please visit our website
www.coilmaster.com.tw
Or send the mail to us : info@coilmaster.com.tw
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