Toroidal Inductor : Construction, Working, Colour Codes & Its Applications

Inductors are the most significant components in the electrical domain. As compared to other types of inductors, toroidal inductor plays a key role in various industrial & commercial equipment because these inductors are well known due to their specific levels of current carrying capacity & inductance. So at present, many industries are depending on toroid inductors to meet international standards that need minimum electromagnetic fields within consumer goods manufacturing. In many electronic devices, these inductors are used to restrict the emissions of the magnetic field which can have very severe health effects on consumers. So to overcome these emissions, electronic manufacturers have to utilize premium quality toroid materials. This article discusses an overview of a Toroidal Inductor –working with applications.

What is Toroidal Inductor?

An insulated coil wounded on a ring-shaped magnetic core which is made with different materials like ferrite, powdered iron, etc is known as a toroid inductor. These inductors have more inductance for each turn & they can carry extra current as compared to solenoids with the same material & size. So, these are mostly used where large inductances are necessary. The toroidal inductor symbol is shown below. There are different types of toroidal inductors like Standard toroid, SMD power, High-temperature, Coupled toroid, Common mode toroid inductors, etc.

Toroidal Inductor Symbol
Toroidal Inductor Symbol

Toroidal Inductor Construction

Toroidal inductors are constructed with a doughnut or circular ring-shaped magnetic core which is wounded with a length of copper wire. These rings are made with different ferromagnetic materials like silicon steel, ferrite, laminated iron, iron powder, or nickel. This type of inductor has high coupling results between winding & early saturation.

Toroidal Inductor
Toroidal Inductor

This construction provides the minimum loss within magnetic flux which assists in avoiding coupling magnetic flux by other devices. This inductor has high inductance values & maximum energy-transmitting efficiency at low-frequency applications.

Working Principle

A toroid inductor simply works similarly to any other inductor utilized to increase frequencies to the necessary levels. A toroid inductor twists to induce a higher frequency. These are economical & more efficient to use as compared to solenoids.

When current is supplied throughout the toroid inductor then it generates a magnetic field around it. So the generated magnetic field strength mainly depends on the flow of the current value.


The magnetic field’s flux also relies on the number of twists that are perpendicular to the flow of the current direction. This flux changes at the same speed when the change within the current flows throughout the inductor. As the flux connects to the coil, then it induces an electromotive force in the coil in a reverse direction of applied voltage.

Toroidal Inductor Color Code

At present, toroidal cores are accessible as coated & uncoated to use in a variety of applications. The coated cores provide a smoother corner radius as well as a winding surface. In these cores, a coating is useful to provide additional edge coverage, edge protection & an insulation function.

Toroidal Inductor Color Code
 Toroidal Inductor Color Code

There are different color coatings are used in Toroidal cores like Epoxy paint and Parylene coating. Epoxy paint is available in different colors like blue, gray & green with CFR. Epoxy coating is approved by UL and is used mainly for coating the toroidal cores.

  • Parylene coating is mainly used for little Toroidal core rings that have a low-thickness coating & high dielectric strength.
  • Toroidal cores coating causes the initial permeability to drop based on the size of the core. So, this may also occur whenever the Toroidal cores are subjected to high permeability & higher winding forces.
    There are many benefits of using color-coated toroidal cores.
  • These cores are well-matched with various kinds of coatings like epoxy, parylene & powder coatings for increasing winding easily & also improving voltage breakdown.
  • The temperature range of Epoxy coatings to work is up to 200 degrees Celsius.
  • The coating gives protection for the edges & also an insulation function to the cores.
  • The toroid coating is required to generate an insulation barrier between wire & toroidal cores for avoiding a short circuit.
  • The color coating doesn’t affect the toroid’s AL value.
  • A toroidal core with an epoxy coating provides many benefits like strength, durability, moisture resistance, chemical resistance & strong dielectric properties.

Toroidal Inductor Magnetic Field

The toroidal inductor magnetic field is calculated by using the following formula.

B = (μ0 N I/2 π r)


‘ I’ denotes the amount of the flow of current throughout the toroidal.
‘r’ is the average radius of the toroid.
‘ n’ is the no. of turns for each unit length.
N = 2rn is the toroid’s average number of turns for each unit length.

Advantages and Disadvantages

The advantages of toroidal inductors include the following.

  • These inductors are lightweight.
    A toroidal inductor is more compact as compared to other shaped cores because they are made with fewer materials.
  • Toroid inductors generate high inductance because the closed-loop core has a strong magnetic field & they emit very low electromagnetic interference.
  • These are much quieter as compared to other typical inductors due to the lack of an air gap.
  • Toroid inductor has a closed-loop core, so it will have a high magnetic field, higher inductance & Q factor.
  • The windings are fairly short & wounded in a closed magnetic field, so it will increase electrical performance, efficiency & reduce distortion & fringing effects.
  • Because of the equilibrium of a toroid, small magnetic flux will escape from the core is low. So, this inductor is very efficient & radiates less EMI (electromagnetic interference) to nearby circuits.

The disadvantages of toroidal inductors include the following.

  • The toroidal core causes problems occasionally either during actual operation & testing.
  • It is very difficult to wind by machine.
  • In these inductors, attaining insulation is more complicated & also very hard to have a magnetic gap in between windings.
  • Toroids are harder to wind and also to tune. However, they are more efficient at producing needed inductances. For the same inductance as a regular solenoid, a toroid requires fewer turns and can be made smaller in size.


The applications of toroidal inductors include the following.

  • These inductors are used in different industries from the telecom industry to healthcare.
  • Toroid inductors are applicable in telecommunications, medical devices, industrial controls, musical instruments, ballasts, electronic brakes, refrigeration equipment, electronic clutches, aerospace & nuclear fields, amplifiers & air conditioner equipment.
  • These are utilized in different electronic circuits like inverters, power supplies, and amplifiers and also in electrical equipment like computers, radios, TVs & audio systems.
  • These are used in achieving energy efficiency when low frequencies need inductance.
  • These are used in SMPS or Switch mode power supplies, EMI (Electromagnetic Interference) sensitive circuits, and Filter applications.

Thus, this is an overview of a toroidal inductor and there are various kinds of inductors available that are used in different industries. The selection of these inductors mainly depends on different features like the size of the case, dimension, DC resistance, tolerance, nominal inductance, packaging type & current rating. All these features play a key role while choosing the exact toroid inductor for your specific application. Here is a question for you, what is an air core inductor?