The new inductor core meets the industry’s needs for smaller, quieter, and more reliable power supplies

“Engineering composite magnetic cores allow Inductor manufacturers to integrate large inductors into small volumes. FlakeComposite’s new technology brings the core performance to a new level, and adds additional mechanical flexibility to support new ultra-thin devices.

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Author: Patrik Kalbermatten, KEMET

Engineering composite magnetic cores allow inductor manufacturers to integrate large inductors into small volumes. FlakeComposite’s new technology brings the core performance to a new level, and adds additional mechanical flexibility to support new ultra-thin devices.

Power inductors are key devices used to manage energy flow in switching converters, ensuring smooth power transmission and helping coordinate commutation. In order to keep the current flowing for long enough to make the circuit work correctly when the main switch is turned off, engineers need to choose a suitable inductance value to store enough energy.

Although in order to support continuous or discontinuous current mode (CCM or CDM) or resonant operation, the calculation of the inductance value will vary according to the type of converter, but for a given rated current, the inductance value is usually larger than the size . In addition, it is necessary to provide stable performance in the expected frequency range, and for applications such as automotive or aerospace, it is also necessary to provide temperature stability and increase the maximum operating temperature.

Engineering inductor reaches its limit

The properties of inductors are limited by the laws of physics. Careful design of the core material helps push these limits to the limit, thus providing the best combination of parameters for the engineer’s application. Commonly used magnetic core materials include manganese zinc (MnZn) and nickel zinc (NiZn) ferrites, as well as metal powder cores formed by specially formulated alloy particles (separated by insulating binders). Although it is difficult to solve power applications by increasing the magnetic core volume, thin-film inductors can also be manufactured by depositing cobalt-based alloys to achieve high permeability with good saturation performance.

Despite some shortcomings, ferrite cores have high permeability-NiZn materials are as high as about 300, while MnZn is even higher. These materials are often very brittle, so they are not suitable for embedding in PCBs or making thin inductors, such as planar lateral flux devices. In addition, they will experience sudden saturation, causing the inductance to roll off sharply as the DC bias increases.

As far as powder cores are concerned, popular alloys include iron silicon (FeSi) or sendust (FeSiAl), as well as other compositions including amorphous iron and permalloy. This type of distributed air gap magnetic core has a granular structure and its saturation characteristics are softer than ferrite inductors, so it is less sensitive to small offset DC bias. On the other hand, its magnetic permeability is usually about an order of magnitude smaller than that of ferrite, and its organic binder cannot withstand high operating temperatures.

The new sheet metal pressing technology can now produce distributed air gap magnetic core materials with permeability comparable to NiZn ferrite and soft saturation characteristics comparable to traditional powder cores. In addition, this new FlakeComposite core also has higher temperature stability, higher maximum operating temperature and mechanical flexibility. This increased flexibility brings not only the opportunity to create ultra-thin inductors, but also the ability to embed powerful inductors in the PCB to save space, and to explore opportunities to integrate new types of inductors (such as transverse flux inductors). ) Integrated with active devices in the next generation power conversion design.

Performance comparison

Figure 1 shows the comparison of the key permeability and saturation characteristics of FlakeComposite core materials and ferrite, powder and thin film cores.

Figure 1: FlakeComposite’s permeability is equivalent to ferrite, and has excellent saturation performance.

As we all know, ferrite materials will lose permeability at high frequency, high temperature or high DC bias current value, resulting in a rapid decrease in inductance value, thereby affecting performance. To ensure that FlakeComposite core inductors are at least as good as ferrite inductors, we need to compare frequency, temperature, and DC bias performance.

Figure 2 compares the dispersion of FlakeComposite and NiZn ferrite composite permeability. The graphs of the two materials show that the permeability decreases rapidly above about 6MHz, which indicates that FlakeComposite has the same or better performance as NiZn in switching converters with operating frequencies up to 1MHz.

Figure 2: For power applications with frequencies up to several MHz, FlakeComposite provides performance comparable to NiZn ferrite.

Comparing the magnetic saturation characteristics, FlakeComposite is softer than NiZn ferrite when it enters saturation, and has a lower temperature dependence, so it is of great benefit (Figure 3).

Figure 3: Compared with NiZn ferrite, FlakeComposite’s magnetic saturation curve is softer and has lower temperature dependence.

Figure 4 compares the DC bias performance of FlakeComposite with NiZn ferrite and traditional metal composite (powder). FlakeComposite combines the advantages of both types. It has excellent permeability comparable to NiZn under low bias, while maintaining higher permeability under high bias with the lowest temperature dependence.

Figure 4: When a high DC bias electric field is applied, the DC bias characteristics show that FlakeComposite has a higher magnetic permeability.

If the operating temperature of the inductor reaches the Curie temperature of the magnetic core material-at which temperature the magnetic core will lose its magnetism-the magnetic permeability of the magnetic core will drop rapidly, resulting in a rapid loss of inductance. As shown in Figure 5, the Curie temperature of FlakeComposite is also higher than that of typical NiZn or MnZn ferrites.

Figure 5: FlakeComposite has a higher Curie temperature, which ensures that the inductance value is maintained at a higher operating temperature.

The inductor becomes thinner and the footprint becomes smaller

In order to continuously reduce the footprint of power conversion modules such as point-of-load (PoL) converters, the industry has proposed new designs that integrate active and passive components. Unlike the traditional longitudinal flux mode previously used to construct thin inductors, the planar inductors used in these designs have been specifically designed to have a lateral flux mode. As the thickness of the inductor decreases, the transverse flux inductor exhibits increasingly superior inductance compared with the traditional longitudinal flux device. FlakeComposite’s mechanical properties can realize inductors with a thickness of 50μm to 2mm, so it is very suitable for manufacturing ultra-thin transverse flux inductors.

Inductors made of FlakeComposite are extremely thin but sturdy. In order to help save footprint, they can also achieve inherent alignment when embedded in PCBs, and can reduce inductance by up to 40% compared with traditional ferrite cores.器高。 Height.

Elastic high permeability material

In addition to being used in power inductors, FlakeComposite’s combination of magnetic and mechanical properties is also suitable for electromagnetic shielding applications including EMI suppression and shielding wireless transmission coils, thereby optimizing charging performance and protecting nearby Electronic devices. FlakeComposite technology is the core of Kemet’s Flex Suppressor® products, and it has been proven that such products can reduce electromagnetic noise in various applications.

Summarize

The new method of FlakeComposite can optimize the magnetic core performance of inductors and further expand the opportunities to realize the miniaturization of power conversion circuits in the future. Therefore, it will surpass the achievements of current ferrite core materials. FlakeComposite can provide similar permeability, as well as excellent saturation characteristics, DC bias performance and higher temperature performance, thereby realizing the design of ultra-thin power inductors and providing the required mechanical performance for PCB embedded inductors, thereby Realize real space saving.

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