Inductor Manufacturers

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About Inductors

Inductors are a type of passive electrical devices that are used to store energy from magnetic fields and release it when needed. Together with chokes and capacitors, inductors have helped to reduce the size of electrical devices by providing a compact way to store power.

Inductance measures the quantity of magnetic flux that is produced by the current flowing through a coil. It is measured in units of Henries denoted by 'H'. Its value increases with the amount of current flowing and the number of loops in the coil.

Switched-mode inductors are used to store energy for power supplies. The inductor is operated for a certain fraction of the switching frequency and not energized for the rest of the cycle. This ratio of energy transfer specifies the value of input and voltage ratios. They are used as reactors in electrical power transmission systems to depress the voltage and confine the fault current.

Inductors are bigger and weigh more than similar devices, so solid state networks use only small inductors while using gyrator circuits for higher requirements.

How Inductors Work

The inductor has as a coil of copper conductors wound around a central core. When current is passed through the coil a magnetic flux is created around the coil due to the properties of electromotive force. The resistance increases when a core is placed in the coil and this increases the inductance by hundreds of times. The core can be made of different materials but cores made of ferrite produce the maximum inductance. The current to voltage lag is 90° but with the use of resistive substance a resistive and inductive circuit is formed, the phase angle lag becomes smaller and is based on the frequency that is constant.

Inductance is the circuit's resistance to change in current. Inductance tolerance is the amount of variation that is permitted within the nominal value. The frequency for which the distributed capacitance starts resonating with the inductance and canceling the capacitance is called the self resonant frequency or SRF. At SRF, the inductor works as a high impedance, resistive element. Quality factor (Q value) is the measure of relative losses of the inductor and is expressed as capacitive resistance divided by the equivalent serial resistance.

Types of Inductors

Inductors are classified by the type of core and the winding. Kinds of inductors are: coupled inductors, multi-layer chip inductors, wirewound ceramic core inductors, molded chip inductors, power inductors, shielded power inductors, molded inductors, conformal coated inductors, and wide band chokes.

• Coupled inductors: In these types of inductors, the magnetic flux of one inductor is linked to another conductor. These are used in special applications where mutual inductance is required like in transformers.
• Multi layer inductors: In this type, the coil is wound in multiple layers with insulation between each layer. This provides very high inductance.
• Ceramic core inductors: The core is made of a ceramic, which is a dielectric material and this type F conductor has high linearity, low hystersis and low distortion.
• Molded inductors: These are low value inductors used in printed circuit boards. Usually bar or cylindrical in shape, they have windings on a core and the whole assembly is molded in plastic or ceramic insulation. Terminations are given at the ends and they come in two types: through mount and surface mount.

Other types are variations of the above types. Shielded types are shielded to avoid EMI and RFI.

Types of Inductor Cores

The core is one of the most important parts of the inductor. The winding wire has very little resistance since it is made of conducting material and it keeps the electrons flowing. Copper wire and other conductors have a conductivity of almost 99.8% and the little inherent resistance of copper does not hinder the free flow of electrons. With the introduction of a core, resistance is introduced in the circuit and the current now builds up in the windings until the resistance of the core is overcome. This buildup is stored as magnetic energy in the core. Depending on the core resistance, the buildup soon reaches the magnetic saturation level and it can be released when required.

The number of turns in the winding and the core material determines the capacity of the inductor. Cores made of dielectric material like ceramics, wood, paper, etc. provide small amounts of stored energy while cores made of ferrite substances have a much higher resistance and the power that can be released is very high.

Major types of cores are:

• Air core: These inductors do not have any metallic core. This type of core has the maximum linearity and the smallest distortion. But for large values of inductance, longer coils are needed and the inductor size becomes very large.
• Solid Ferrite cores: These types provide the maximum resistance but they are not stable at higher values of inductance and the magnetic saturation is quickly reached. Ferrite materials are given designations like 33, 43, J/75, etc. Grade 33 is manganese zinc and used for the 1KHz to 1Mhz range in loop stick antenna rods. Grade 43 nickel zinc has a high quality factor and is used as medium wave inductors in wide band transformers. Grade 77 is used in wide band transformers, power converters, EMI and acoustic filters and is used in the 0.001 to 1MHz band.
• Powdered Ferrite cores: Powdered ferrite cores have greater linearity and distortion with predictable power curves. The core density is much greater and can be controlled by the compaction process. The ferrite material is given different grades like 0, 1, 12, 13, 15, 26, and so on. Grade 0 can be used for frequencies up to 200 Mhz and the amount of inductance varies with the winding method. Grade 1 uses Carbonyl C and has good resistance, grade 12 is made of synthetic oxide, has a good quality factor and moderate stability in the range of 50 to 100 MHz, grade 26 is made of iron that is reduced by hydrogen and is used in DC chokes and EMI filters.
• Steel core: Cores made of iron nickel alloys are used when the requirements call for low resistance and high inductance. They are better then air cores. While selecting steel cores, it is necessary to note the power rating, as denser cores avoid problems of magnetic saturation. By using thin metal sheets that are suitably insulated, eddy currents are eliminated. Very thin air gaps need to be provided in the core to remove non-linear effects.
• Toroid cores: Toroidal inductors have donut shaped cores with close packed wire winding. Very thin sheets of ferrite or steel are held closely together. Circular cross sections are the most efficient but square or rectangular sections are also used. Common types are Ferrite Toroid Cores and Powdered Iron Toroid Cores.
  • Iron Powder cores: These are made of Carbonyl HP, hydrogen reduced, Carbonyl GS6, Carbonyl C, powdered iron W, synthetic oxide, etc. They have a high to moderate Q factor with good linearity and stability. They are used in DC chokes, EMI filters and other applications.
  • Ferrite Toroid cores: They have the maximum permeability and a good residual flux density. The loss factor is less than other core types.

Color Coding

Small capacity molded inductors are given a color code for easy identification when they are mounted in circuits. Four-color bands are given in circles around the inductor. The bands are called 1st band, 2nd band, the third band is the multiplier and the fourth band indicates the tolerance. Colors used are: black, brown, red, orange, yellow, green, blue, violet, gray, white, no color, gold and silver. Colors in the first and second band have a specific value of inductance, the third band is a multiplier and the fourth band stands for the +- inductance tolerance like 1%, 2%, 3%, 20%, etc.

Applications of Inductors

• Blocking out noise, unwanted frequencies and reducing hum in radio broadcasting stations and equipment - When used in conjunction with capacitors
• DC filtering - When used as chokes in power supplies to remove hum and other types of fluctuations from the DC output
• Removing radio frequency (RF) interference - When used as filters
• Small and compact transformers with 400-Hz cycle AC current frequency for aircraft - When utilizing their coupled magnetic flux

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