STEWARD, represented in Australia by RFI Industries , has released toroids for common mode and differential mode filtering. They meet the EMI/RFI filtering needs of switch mode power supplies.
Many switch mode power supplies generate noise at high frequencies. This noise can and will disturb many types of electronic equipment. In most cases a common mode filter is needed, a toroid using a higher permeability soft ferrite material. For Steward those materials would be 35 for 5k perm and 40 for 10k perm. In special cases a common mode filter in series with a differential mode filter will be required.
Selection of the material grade is very important. Steward recommends if the high frequency noise is below 1.5MHz the 40 material should be used. If the noise is above 1.5MHz the 35 material would be a better choice.
For even higher frequency noise filters or for some basic power transformers the power 63 material is available.