TDK Distributed Air Gaps in Ferrite Cores

An air gap increases the magnetic resistance in the magnetic circuit.
24 Nov 17

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EPCOS have created an all new distributed air gap featured in ferrite cores. They have centre post gapping that increased the magnetic resistance in the circuit as the gap delays core saturation. The gapping also increases the power handling capability making the core inductance independent of material permeability. There are a number of benefits to the new distributed air gaps. There is a significantly increased power density with up to 70% reduction in leakage field losses. The gap enables use of a larger winding area by reducing fringing flux meaning low winding losses compared to a single large air gap. This means there is then a reduction of core size by one class thanks to the lower winding losses which would then enable copper saving overall.

Core Types

EPCOS offers six different core types, commonly used in the design of power chokes and flyback converters. The distributed air gaps are available or may be manufactured for the following core and sizes: E Core, EQ Core, ER Core, ETD Core, PM Core, PQ Core

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Technical Background

An air gap increases the magnetic resistance in the magnetic circuit. Magnetic saturation will then only occur at higher field strengths and reduces the slope of the B-H loop. The air gap is required to increase the power handling capability and makes the core inductance independent of the material permeability. However, the bigger the air gap, the higher the fringing flux the spreads around it, e.g. into the copper winding. This phenomenon leads to higher losses. EPCOS is able to offer a technical solution designing a product that would significantly reduce the fringing flux that effects this in order to reduce electromagnetic emissions and heating.

Simulation with Ferrite cores E 55/28/25

The fundamental effect of having gaps of different sizes and location is to change the losses in the adjacent winding. The magnitude of this effect does depend on the fringing flux which enters the winding. The overall gap remains identical, only the location and individual size per gap are changed.

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The overall comparison between a single air gap and several smaller distributed air gaps shows that:
• The average of the square of the local flux density, B² average (relevant for winding losses) decreases as the number of smaller air gaps increases.
• Evenly distributed and spaced air gaps are more efficient than an uneven distribution
• The best performance/ cost compromise is to use three evenly distributed air gaps.
EPCOS distributed air gaps cores are realized with nonmagnetic spacers glued in between the ferrite slugs. The required priority for distributed air gaps is the AL Value.


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