Power inductors can be classified in several ways: by inductance value, by power or current rating, by type of application, by type of construction, by industry, by material and others. Choke and reactor are other names for power inductors. Inductors inhibit the flow of electrical current in A.C. or transient applications. Inductors are used in some A.C. circuits to reduce the voltage reaching the intended load. Inductors may be used to limit the amount of A.C. current flow. Since an inductor’s impedance increases with frequency, they are good for blocking (suppression) of high frequency electrical noise. Inductors are frequently used for electrical/electronic filtering purposes. You can find in tuning and most types of bandwidth filters. Saturable inductors can be used in signaling circuits to create time delays. Boost inductors, flyback inductors, and buck inductors are inductors used in some switching power supplies. Inductors are also used in switching power supplies to smooth out ripple voltage and ripple current.

Inductors store energy. Transformers are not intended to store energy (but do store some). Coupled inductors are used in some multi-output switching power supply designs to improve voltage regulation. In this case, the inductor is also acting as a transformer because there is transformer coupling occurring between the multiple outputs. A Flyback Transformer is technically an inductor. A coil winding is used to create a magnetic field thereby storing energy in the field. The stored energy is then released to the output. There is no direct (simultaneous) coupling of energy.

Types or inductor construction include bobbin wound, toroidal, air core (no core), tube wound, foil wound, wound with litz wire, encapsulated (potted), laminated, powdered core, and others. An Inductor’s core material is heavily influenced by the application’s frequency range. Line frequency applications usually use a laminated or tape wound silicon steel core stack. Low frequency audio applications may use laminated nickel-iron core stack or possibly powdered core materials. High frequency applications generally use a ferrite material.

Common Mode Chokes are used because many electrical devices may be connected to the same power lines (or power supply lines), substantial electrical noise can exist on these lines. Switch mode power supplies can generate a lot of high frequency noise which can travel over the power lines and interfere with the operation of computers and other electronic devices connected to the power lines. Electro-magnetic interference in the environment can induce or couple electrical noise into the power lines. Electrical noise which comes in one power line wire and returns to the noise source through the other power line wire is differential noise. Electrical noise which comes through one power line and returns to the noise source through some type of ground path is common mode noise..

Differential and common mode chokes (or inductors) are often placed between electrical (or electronic) equipment and the power lines supplying power to the electrical equipment. The chokes reduce electrical noise both entering and leaving a piece of electrical equipment. A common mode choke (or filter) is used to reduce common mode (electrical) noise. Common mode chokes can be designed to include some differential filtering thereby eliminating the need for a separate differential choke (or inductor) in some applications.
Toroids are the preferred core shape to use in common mode chokes. The continuous unbroken circular path maximizes magnetic coupling between windings thereby minimizing leakage inductance. "E" cores are the second most preferred core shapes for common mode chokes. The toroids are less costly than the "E" cores, but "E" core bobbins are easier and less costly to wind. Toroidal coils are usually more costly to mount into an assembly. An air gap can be easily placed between "E" core halves. A gapped core has more leakage inductance; hence "E" core structures are usually preferred when some differential filtering is desired from the common mode choke. Common mode chokes can be made from other core shapes but usually at higher cost. Their use occurs when a special characteristic is needed. For example, an "EFD" core may be used when a low profile is desired.

Selecting the optimum core material for common mode chokes is not easy. The frequency range of the electrical noise is the major factor. If only power frequency noise is expected (i.e. 60 Hz. harmonics), then laminated silicon steel may suffice. Laminated nickel iron or powdered iron or "sandust" type powder will do for lower audio range noise frequencies. Perhaps molypermalloy powders for the upper audio range (depending on noise levels). Ferrite materials are needed for noise frequencies above 20 kHz. Although the inductive value of ferrites diminishes rapidly above 1 megahertz, some ferrite materials are still suitable for common mode chokes because the resistive component helps maintain a sufficiently high impedance value.

Competitive Magnetics manufactures electronic transformers, Inductors, and Common Mode Chokes in a wide variety of materials and sizes with pin-thru, surface mount, and/or flying leads terminations. We also manufacture “tube wound” inductors and air core coils. Various standard types of “core with bobbin” structures (E, EP, EFD, PQ, POT, U and others), toroids, and some custom designs. Our maximum weight and power limitations are 40 pounds of weight and 2 kilowatts of power. We have experience with foil windings, litz wire windings, and perfect layering. For toroids, special winding techniques such as sector winding, progressive winding, bank winding, and progressive bank winding can be accomplished to satisfy your dielectric, creepage distance, capacitance, and leakage inductance requirements.