DMR 91 - MnZn Ferrite Material with High Flux Density and Low Power Loss for Power Applications


Xu Zhao, Yang-Zhong Du, Su-Ping Wang and Milivoj Secan at Hengdian Group DMEGC Magnetics Co.

Manganese zinc soft ferrite materials are generally divided into two groups:

  • High-permeability materials that are used at low frequencies Power ferrite materials that are used at high frequencies and exhibit low power losses
  • Power ferrite materials are widely used at high frequency applications as cores for pulse transformers, switching mode power supply transformers etc. Ferrite producers typically provide following data about power materials to help designers and developers choose right material:

    µi – Initial permeability is the limiting value of the amplitude permeability when the magnetic field strength is limited to zero. It is measured on magnetically closed toroidal core at very low magnetic field strength and depends on temperature and frequency.
    Bs - Saturation flux density point where magnetization of material reaches its maximum value. This point is measured at a specific magnetic field H and specific temperature.
    Br - Remanence is residual flux density remaining in material previously magnetized to the saturation when H decreases to zero.
    Pv - Specific power loss of material is dependent of the magnetic flux density and frequency, and is specified in Watts per core volume.
    Hc - Magnetic coercivity is the value of magnetic field strength at which the magnetic flux density of material, which was previously magnetized to saturation, decreases to zero.

In the late 80’s of last century, TDK made available power material PC40 which served as an introduction to the third generation of soft ferrite power material. This material was a prelude of high Bs and Low power loss materials for many producers that launched similar materials afterwards.

In September 2004, it was again TDK who introduced a new high Bs and low power loss material PC90, which once again launched material development across the industry. However, ten years later, there has been no progress on this road as power material design still proves to be quite a difficult task.

DMEGC has taken on the challenge to make further improvements  in power ferrite materials that will allow higher operating flux under high temperature conditions. As a result DMEGC has developed new power material, which is called DMR91. This material is based on existing material DMR90, but with further improvements to the Bs and Power losses. With DMR91 material, DMEGC now has in portfolio ferrite material that improves Bs value of DMR90, while maintaining Power losses of DMR44 at high temperatures.

From Table 1, we can see an overall improvement in performance of DMR91 material, with Bs value at 100°C increased to 460mT, but also Residual Magnetic Flux Density is maintained at considerable level. ∆B at 100°C (Bs -Br) is above 390mT, so the core anti-saturation capacity is also enhanced.

Table 1: shows comparison of DMEGC’s power materials


Table 1 also shows how DMR91 has improved power loss value of DMR90 at almost all temperature points, and actually keeps on the same level of 300mW/cm3 at 100°C, as DMR44 material.


Figure 1: Bs-T curves for DMR40/DMR44/DMR90/DMR91

Figure 1 shows Bs-T curves for different power materials, the highest value of DMR91 is seen from this figure.


Figure 2: Power loss T curves for DMR40/DMR44/DMR90/DMR91

Figure 2 shows Power loss versus temperature for different power materials. The lowest point of DMR91 is close to 100°C, making it on par with DMR44 and especially suitable for applications where high operating temperature is expected.

At the beginning of development of new material, our first goal was to further increase Bs value of DMR90. To achieve this, we began increasing the content of Fe2O3 to the powder mixture. While this approach improves Bs, it simultaneously increases power losses, measured at room temperature as well as 120°C. So next step was taken to flatten the power loss curve and we have achieved this by adding the correct amount of Co2O3 to the powder mixture.


Figure 3: Power Loss vs. Flux Density for DMR91 with Frequency as Parameter

Conclusion

With DMR91 power material, DMEGC has made next step in High Flux Density and Low Power Loss applications, offering designers chance to reduce footprint of their components where space is an issue.

One of the goals we kept in mind while developing this material was cost factor. Although providing better performance, DMEGC is able  to maintain the same material cost level with DMR91 as with DMR90 material.

 

 

 

 

More information: Hengdian Group DMEGC Magnetics Co.    Source: Bodo's Power Systems, May 2015