Electronic systems are becoming smaller, while operating under an increasing range of electrical conditions. This makes magnetic component selection a critical aspect of circuit design, particularly when current regulation, filtering, electromagnetic interference, and space considerations need to be taken into account simultaneously.

Of the magnetic components used in electronic design, Drum Core Inductors and Common mode choke components represent two different approaches to addressing electrical characteristics using magnetic structures.

Drum Core Inductors and Component Construction

Drum core inductors, sometimes called bobbin core inductors, are constructed around a cylindrical core with wire wrapped around the core. The physical configuration can be made in various configurations based upon the demands of the application.

Drum Core Inductors can be made with either axial or radial lead configurations. Shielded and unshielded versions are also available, allowing designers to consider the effects to the magnetic component and surrounding circuitry during selection.

The choice of configurations is not purely a matter of preference. Available PCB space, current, magnetic characteristics, operating frequency and electromagnetic environment can all dictate the choice.

Electrical Characteristics Matter Beyond Inductance

When considering an inductor, the given inductance is not the only characteristic that influences its behavior, which must be taken into account when selecting components for a circuit.

The current rating, DC resistance, tolerances, core material, temperature rise, and operating frequency are parameters engineers might want to consider as well. The inductor’s characteristics may change depending on the load.

Therefore, two inductors with the same nominal inductance may exhibit different characteristics in a circuit.

The inductance value, core material, and winding geometry determine the characteristics of the inductor.

Common Mode Choke and Noise Control

A Common mode choke is constructed with a different magnetic configuration. This kind of choke usually has multiple windings on a common magnetic core and is intended to provide impedance to undesired common-mode noise.

Common-mode noise can occur when undesirable higher frequency electrical signals carry on the conductors in the same direction. Controlling of such undesired signals in the electronic equipment is an essential part of electromagnetic compatibility design.

Therefore, common mode chokes are widely considered in the filtering networks where conducted EMI or RFI should be addressed.

Component’s performance depends on such factors as inductance, impedance, frequency, winding resistance, current conditions, magnetic core properties, and construction details.

Frequency Changes the Design Equation

Magnetic components do not behave identically across every frequency range. Core materials have their own magnetic characteristics, while winding construction can influence parasitic effects at higher frequencies.

This becomes particularly relevant when components are used around switching circuits.

At higher frequencies, engineers may need to consider factors beyond the nominal inductance value, including frequency-dependent impedance, core losses, winding resistance, and parasitic capacitance.

For a Common mode choke, the frequency range over which noise suppression is required can influence the magnetic design and winding arrangement.

Similarly, Drum Core Inductors may require different construction approaches depending on the intended operating conditions.

Mechanical Requirements Can Influence Magnetic Design

Electronic component choice can also be dictated by the physical environment in which the component must operate.

PCB footprint, component height, lead orientation, mounting method, spacing, and enclosure dimensions, among others, can all be factors in choosing an inductor or choke.

A radial-lead component may be preferable in a particular board arrangement, whereas an axial configuration may be required in another. Shielded constructions should also be considered where interaction with nearby circuitry is an important design factor.

These mechanical aspects are often dictated at the same time as the electrical specifications, and not necessarily after a magnetic component has been selected.

Customization in Magnetic Components

Not every electronic design fits a single standard component specification.

Magnetic component manufacturers might be able to create a part from a customer's electrical specs, drawings, bills of materials or existing component design. Specifications might include inductance, dimensions, winding configuration, lead arrangements, shielding, current characteristics and more.

CET Technology's published product information shows that their drum/bobbin-core inductors are available in standard and custom inductances with different lead and shielding options.

Such customization can be useful if an existing component will not suffice with a design's electrical or mechanical constraints.

The Relationship Between Inductors and EMI Filtering

Inductors and chokes can appear in different sections of an electronic system, but their magnetic behavior can be part of a broader power and signal-management strategy.

An inductor can contribute to current control and filtering within a circuit, while a common-mode choke is specifically structured to provide impedance against common-mode noise.

CET Technology describes its Common Mode Choke as a magnetic component intended to filter high-frequency common-mode noise while allowing differential-mode signals and lower-frequency currents to pass with relatively low loss.

The distinction is important because choosing a component based only on the word “inductor” does not necessarily mean that it will provide the same filtering behavior as a purpose-designed common-mode choke.

Component Selection Should Start With the System

A good choice of magnetic components is best done with knowledge of the electrical and mechanical requirements of the whole system.

The evaluation for Drum Core Inductors may include inductance, current, saturation, resistance, frequency, dimensions, and shielding.

However, for a Common mode choke, designers may look at common-mode impedance, differential characteristics, frequency response, the way windings are arranged, and the properties of undesired noise.

In this way, magnetic component specifications match the conditions they will have to work under.

The Role of Magnetic Components in Electronic Design

Transformers, inductors, and chokes are essential elements in any electronic system. From the outside, they may seem simple, but their internal construction of core and windings is based on complex electrical laws. Transformers, inductors, and chokes are electrical components whose characteristics are determined by the interaction between core material, winding construction, frequency, current, temperature, and geometry.

Drum Core Inductors provide a solution for electrical and mechanical design challenges posed by a wide range of applications and consist of a core and windings. Common mode choke constructions highlight the versatility of these components and provide some insight into the electrical and mechanical design challenges posed by a wide range of applications.

As modern electronic equipment becomes more integrated and compact, magnetic components will continue to evolve to meet the electrical needs of modern low-profile electronic systems and address the broader engineering requirements of the system in which they are installed.

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