Iron Powder Cores
MPP Cores
Sendust Cores
High Flux Cores
Flat Transformers


MPP, Sendust, High Flux Cores

MPP, Sendust, Kool Mu, High Flux are part of the powder core family and are similar to Iron Powder cores. They are used as inductor, choke and filters. The choice of one type of powder material over another often depends on the following:

1) DC Bias Current through the inductor
2) Ambient Operating Temperature and acceptable temperature rise. Ambient temperature of over 100 deg C is now quite common.
3) Size constraint and mounting methods ( through hole or surface mount )
4) Costs : iron Powder being the cheapest and MPP, the most expansive.
5) Electrical stability of the core with temperature changes
6) Availability of the core material.

With powder cores, high permeability material is ground or atomized into powder. The permeability of the cores will depend on the particle size and density of the high permeability materials. Adjustment of the particle size and density of this material leads to different permeability of the cores. The smaller the particle size, the lower the permeability and better DC bias characteristics, but at a higher cost. The individual powder particles are insulated from one another, allowing the cores to have inherently distributed air gaps for energy storage in an inductor.

This distributed air gap property ensures that the energy are stored evenly through the core. This makes the core have a better temperature stability.

MPP (Molypermalloy Powder Cores)
Composition: Mo-Ni-Fe

MPP cores has the lowest overall core loss and best temperature stability. Typically, inductance variance is under 1% up to 140 deg C. MPP cores are available in initial permeabilities (µi) of 26, 60, 125, 160, 173, 200, and 550. MPP offers high resistivity, low hysteresis and eddy current losses, and very good inductance stability under DC bias and AC conditions. Under AC excitation, inductance change is under 2% (very stable) for µi=125 cores at AC flux density of over 2000 gauss. It does not saturate easily at high DC magnetization or DC bias condition.The saturation flux density of MPP core is approximately 8000 gauss ( 800 mT)

Compared to other materials, MPP cores are the costliest, but highest quality in terms of core loss and stability. For application involving DC bias condition, use the following guidelines. To get less than 20% decrease in initial permeability under DC bias condition:- For µi= 60 cores, max. DC bias < 50 oersted; µi=125, max. DC bias < 30 oersted; µi=160, max. DC bias <20 oersted.

Unique Features:

  1. Lowest core loss among all the powder materials. Low hysterisis loss resulting in low signal distortion and low residual loss.
  2. Best temperature stability. Under 1%.
  3. The maximum saturation flux density is 8000 gauss (0.8 tesla)
  4. Inductance tolerance: + - 8%. (3% from 500 Hz to 200 kHz)
  5. Most commonly used in aerospace, military, medical and high temperature application.
  6. Most readily available as compared to high flux and sendust.

Applications :
High Q filters, loading coils, resonant circuits, RFI filters for frequencies below 300 kHz, transformers, chokes, differential mode filters, and DC biased output filters.

High Flux Cores
Composition: Ni-Fe

High Flux cores is composed of compacted 50% nickel and 50% iron alloy powder. The base material is similar to the regular nickel iron lamination in tape wound cores. High Flux cores have higher energy storage capabilities, and higher saturation flux density. Their saturation flux density is around 15,000 gauss ( 1500 MT), about the same as iron powder cores. High Flux cores offers slightly lower core loss than Sendust. However, High Flux's core loss is quite a bit higher than MPP cores. High Flux cores are most commonly used in application where the DC bias current is high. However, it is not as readily available as MPP or Sendust, and are limited in its permeability choices or size selections.

Applications :

1) In Line Noise filters where the inductor must support large AC voltages without saturation.

2) Switching Regulators Inductors to handle large amount of DC bias current

3) Pulse Transformers and Flyback Transformers as its residual flux density is near to zero gauss. With the saturation flux density of 15K gauss, the usable flux density ( from zero to 15K gauss) is ideally suited for unipolar drive applications such as pulse transformer and flyback transformers.

Composition: Al-Si-Fe

Sendust Powdered Cores (also known as Koolmu Cores) with its distributed air gap are made from a ferrous alloy powder. The base material is approximately 85% iron, 6% aluminum and 9% silicon. Sendust powders are made by atomization the base alloy melt. The powders are insulated and then pressed into various core shapes (toroidal or E-Cores) under very high pressure.

Sendust cores have very low core loss and good temperature stability. In high frequency applications, sendust cores offer up to 80% reduction in core loss over iron powder cores. Hence, Sendust cores significantly lower the temperature rise. Sendust cores also exhibits very low magnetostriction coefficient, and it is therefore suitable for applications requiring low audible noise. Sendust cores has a saturation flux density of 10,000 gauss.

Sendust cores are available in initial permeabilities (Ui) of 60 and 125. Sendust core offer minimal change in permeability or inductance (under 3% for ui=125) under AC excitation. Temperature stability is very good at the high end. Inductance change is less than 3% from ambient to 125 deg C. However, as the temperature decreases to 65 deg C, its inductance decreases by about 15% for µi=125. Also note that as temperature increases, sendust exhibits a decrease in inductance versus an increase in inductance for all the other powder materials. This could be a good choice for temperature compensation, when used with other materials in a composite core structure.

Sendust cores cost less than MPPs or high fluxes, but slightly more expensive than iron powder cores. For application involving DC bias conditions, use the following guidelines. To get under 20% decrease in initial permeability under DC bias condition:

For µi= 60 cores, max. DC bias < 40 oersted; µi=125, max. DC bias < 15 oersted.

Unique Features:

  1. Lower core loss than Iron Powder.
  2. Low magnetostriction coefficient, low audible noise.
  3. Good temperature stability. Under 4% from -15 'C to 125 'C
  4. Maximum flux density: 10,000 gauss (1.0 tesla)
  5. Inductance tolerance: ▒ 8%.


  1. Switching Regulator Inductors: Sendust Cores are well-suited for high energy storage/filter inductors used in switch mode power supplies. The 10,000 gauss saturation level of sendust cores provides a higher energy storage capability than standard MPP cores or a gapped ferrite cores of the same size and permeability. Sendust cores are a better choice than powdered iron if there are significant ripples to be filtered. However, Sendust Cores are a little more expensive than iron powder cores.
  2. In-Line Noise Filters: Sendust cores are ideal for in-line noise filters where the inductor must support large ac voltage without core saturation occurring. Line filters using Sendust cores can be smaller in size, requiring fewer turns than by using ferrite cores.
  3. Pulse Transformers, Fly-Back Transformers: The high flux density and low core loss make Sendust cores excellent for unidirectional drive applications such as pulse transformers and flyback transformers

MPP, Sendust, and High Flux toroidal cores can be purchased using CWS ByteMark on line shopping. Please click on the following links for on line shopping.

1) MPP
2) Sendust
3) High Flux.

They are available in many popular sizes and permeabilities ranging from 60 to 125 Ái. Also, Sendust E-cores are available in AL value ranging from 10 nH/N2 to 210 NH/N2 with core sizes with inside diameter ranging from 0.110/2.79 mm to .785/19.94 mm and outside diameter ranging from 0.500/12.7 mm to 3.0/77.5 mm. Please check with factory for other sizes and permeabilities here.

Core Finish
The MPP, Sendust and High Flux cores are uniformly coated with a special epoxy finish. This finish provides a tough chemical resistance and high dielectric protection for the cores.

Core coatings are tested to a minimum voltage breakdown of 500 volts.

Click here for cross reference chart.

Return to Top of Page