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Explain some technical terms for magnetic component

Multilayer Inductor
An inductor constructed by layering the coil between layers of core material, the coil typically consists of a bare metal material( no insulation), this technology is sometimes referred to as "non-wirewound", the inductance value can be made larger by adding additional layers for a given sprial pattern.

Shielded Inductor
An inductor designed for its core to contain a majority of its magnetic field, some inductor designs are self shielding, examples these are magnetic core shapes which include toroidal, pot ocres and E-cores, magnetic core shapes such as slug cores and bobbins require the application of a magnetic sleeve or similar method to yield a shielded field will escape the core material, this even applicable for toroidal cores are lower core permeabilities will have higher fringing fields than will high permeability toroidal cores.

Epoxy coated Inductor
Inductors that have been coated with epoxy as opposed to haveing a molded case, shrink wrapped tubing or left with an open construction body, epoxy coated inductos typically have smooth edges and surfaces, the epoxy coat acts an insulation, both radial and axial styles can be found with epoxy coated surfaces.

Molded Inductor
An inductor whose case has been formed via a molding process, common molding processes include injection and transfer molding, molded inductors typically have well defined body dimensions which consist of smooth surfaces and sharper corners as compared to other case types such as epoxy costed and shrink wrape coatings.

Axial Inductor
An inductor constructed on a core with concentric leads on opposite end of the core, Axial inductors are available for both power applications and RF applications, and are available in many core materials including the basic phenolic, ferrite and powdered iron types, both rod and bobbin shapes are utilized, axial inductors are very suitable for tape and reel packaging for auto placement.

Radial Inductor
An inductor constructed an a core with leads exiting from the same side of the inductor body as to be mounted in the same plane, Radial inductors mist often refer to two leaded devices but technically include devices with more than two leads as well, some common core shapes include rod cores, bobbins and toroidal.

Color codes
Inductors cloors codes have been standardized, the color marks or brands represent the inductor's value and tolerance, following is a table that translates the colours and numbers.
color significant figures or decimal point multiplier inductance tolerance
Brown 1 10 +/-1%
Red 2 100 +/-2%
Orange 3 1000 +/-3%
Yellow 4 10,000 +/-4%
Green 5
Blue 6
Violet 7
Gray 8
White 9
Black 0 1 +/-20%
Silver 0.01 +/-10%
Gold 0.1

Toroidal Inductor
An inductor constructed by placing a winding on a core that was a donut shapes surface, toroidal coirs are available in many magnetic core materials with in the four basic types: ferrite,powered iron, alloy and high flux and tape wound,characteristics of toroidal inductors include: self shielding (closed magnetic path), effcient energy transfer, high coupling between windings and early saturation.

Distributed capacitance
In the construction of an inductor, each turn of wire or conductor acts as a capacitor plate, the combined effects of each turn can be represented as a single capacitance knows as the distributed capacitance,this capacitance is in parallel with the inductor, this parallel combination will resonate at some frequency with is called the self-resonant frequency(SRF), lower distributed capacitances for a given inductance value will result in a higher SRF value and vice versa.

The impedance of an inductor is the total resistance to the flow of current, including the AC and DC component, the DC component of the impedance is simply the DC resistance of the winding, the AC component of the impedance includes the inductor reactance, the following formula calcalates the inductive reactance of an ideal inductor to a sinusoidal AC signal.
Z=XL=2Pi fL
L is henries and f is hertz, this equation indicated that higher impedance levels are achieved by higher inductance valueds or at higher frequencies, skin effect and core lossed also add to the impedence of an inductor.

SRF(Self-resonant frequency)
The frequency at which the inductor's distributed capacitance resonateds with the inductance, it is at this frequency that the inductance is equal to the capacitance and they cancell each other, the inductore will act purely resistive with a high impedance at the SRF point,the distributed capacitance is caused by the turns of wire layered on top of each other and around the core, this capacitance is in parallel to the inductance ,at frequencies above the SRF, the capacitive reactance of the parallel combination will become the dominant component, also, the Q of the inductor is equal to zero at the SRF point since the inductive reactance is zero, the SRF is specified in MHz and is listed as a minimum value on product data sheets.

Saturation Current
The DC bias current flowing through the inductor which causes the inductance to drop by a specified amount from the initial zero DC bias inductance value , common specified inductance drop percentages include 10% and is useful to use the 10% inductance drop value for ferrite cores and 20% for powdered iron cores in energy storage applications, the cause of the inductance to drop due to the DC bias current is related to the magnetic flux density, beyond the maximum flux density point, the permeability of the core is reduced, thus, the inductance is caused to drop.

Rated current
The level of continuous DC current that can be passed through the inductor, this DC current level is based on a maximum temperature rise of the inductor at the maximum rated ambient temperature, the rated current is related to the inductor's ability to minimize the power losses in the winding by having a low DC resistance, it is also related to the inductor's ability to this power lost in the winding, thus, the rated current can be increased by reducing the DC resistance or increasing the inductor size, for low frequency current waveforms, the RMS current can be substitued for the DC rated current, the rated current is not related to the magnetic properties of the inductor. .

The unit of measurement for resistance and impedance, resistance is calculated by ohm's law. .

Q value
The Q value of an inductor is a measure of the relative losses in an inductor, the Q is also knows as the "quality factor" and is technically defined as the ratio of inductive reactance to effective resistance and is represented by Q=XL/R=2pifL/R
Since XL and R are functions of frequency, the test frequency must be given when specifying Q,XL typically increased with frequency at a faster rate than Re at lower frequencies, and vice versa at high frequencies, this results in a bell shaped curve for Q vs frequency, R is mainly comprised of the DC resistance of the wire, the core losses and skin effect of the wire, based on the above formula, it can be shown that the Q is zero at the self resonant frequency since the inductance is zero of the point. .

Number turns
The series impedance of a high frequency ferrite device can be increased by running two or more turns of the treated conductor through the ferrites core, magnetic theory predicts that the impedance of the device will increase with the square of the number of turns, however, due to the lossy and non-linear nature of EMI suppression ferrits,aferrite bead with wo turns will yield somewhat less than four times the impedance of an identical part wound with only one turn of the conductor.

DCR(DC resistance)
The resistance of the inductor winding measured with no alternating current, the DCR is most often minimized in the design of an iductor, the unit if measure is ohms,and it is usually specified as a maximum rating.

Inductance tolerance
Standard inductance tolerances are typically designated by a tolerance letter, standard inductance tolerance letters include:

Test frequency
The frequency at which inductors are tested for either inductane or Q or both,some test fequencies used widely in the industry include:
1KHz power inductors( wide value range)
79.6K inductors(above 10000uH to 100000uH
252K inductors(above 1000uH to 10000uH)
796K inductors( above 100uH to 1000uH)
2.52M inductors(above 10uH to 100uH)
7.96M inductors(above 1uH to 10uH)
25.2M inductors(above 0.1uH to 1uH)
50M inductors(above 0.01uH to 0.1uH)
Most of these test frequencies have been designated by military specifications, however there are some conflicting frequency assignments among the military specifications, there is present trend to assign test frequencies that match the user frequencies, this is particularly true for evry low values, these user frequencies do not match those listed above.

The property of a circuit element which tends to oppose any change in the current flowing through it, the inductance for a given inductor is influenced by the core material, core shape and size, the turns count and shape of the coil,inductors most often have their inductances expressed in microhenries(uH),the following table can be used to convert units of inductance to microhenries, thus,47mH would equal 47,000uH


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