Custom Toroidal Inductors by Plitron



Consult with Plitron engineers for more design and technical information. Typically, inductors are custom designed to customer specifications.The information below is intended to serve as a guide when specifying an inductor.

An inductor is a passive wound magnetic component that creates and stores a magnetic field when a current is passed through it. The stored energy is called inductance, and is rated in terms of ‘henries’. An expanding and collapsing magnetic field sets up a corresponding and proportionally opposing counter field that opposes any change in current. The effect of an inductor in a circuit is to oppose changes in current through it by developing a voltage across it proportional to the rate of change of the current. (See Also High Frequency Magnetics, and Chokes.)

Low Frequency Filter Applications

Plitron Toroidal Inductor Hysterisis CurveToroidal architecture brings many of the same advantages to inductors as it does for power transformers. Inductors are common in analog and signal processing applications. When used in conjunction with capacitors, they form an LC filter circuit, to remove DC fluctuations after rectification in power supplies. Hi-B electrical steels used in toroidal cores are classified as ‘square-loop’ materials, thus they are linear in operation and exhibit high saturation levels. However, the knee of the curve is abrupt and becomes non linear, and above that point can be driven into saturation – especially when used in DC filtering applications.

For This reason an air gap is commonly introduced into the magnetic circuit, which has the effect to ‘round’ the hysteresis loop, and allow the coil to operate without being driven into saturation. As introduction of a gap flattens the B-H loop of the material, so too does it lower the residual flux and the permeability.

A gapped core gains the ability to handle AC + DC flux components without saturating. However it is not an ideal solution as it degrades some of the specs and performance. Core gapping is a relatively expensive process, adding cost to the product. As expected, the core permeability is driven down, thus the inductor needs to grow in size, and additional turns are needed. This makes the inductor more expensive, larger, and increases the temperature rise. Stray magnetics in proximity of the gap increase by a large magnitude, and can easily interfere with other circuit components. The possibility of mechanical ‘hum’ increases with gap size and current.

Plitron’s Gapless Toroidal Cores for DC Inductors

Through original research, Plitron has developed a range of round-loop materials utilizing gapless toroidal cores, making them an ideal choice for toroidal inductors.

Gapless toroidal cores smooth out the hysteresis curve, and extend the linear operating portion.

They are often less expensive than gapped cores, and can resolve issues associated with the air gap.

Stray fields are lowered across the board, and remove any ‘hot-spots’ especially near the gap.

There is less likelihood of cross-talk and interference to other commencements. A continuously wound core contains no cut edges to vibrate, thus noise reduction is not an issue.


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