Ferrite Mix Selection Guidelines
Quite often we are asked which mix is best for a certain application or frequency range and there is a lot of misinformation on the internet and elsewhere regarding the selection of proper mix for a given application.
There are two basic ferrite material groups: (1) Those having a permeability range from 20 to 850 µ are of the Nickel Zinc (NiZn) class (mix 43, 52, 61), and (2) those having initial permeabilities above 850 µ are usually of the Manganese Zinc (MnZn) class (Mix 31, 75, 77).
The NiZn ferrite cores (mix 43, 52, 61) have low permeability, exhibit high volume resistivity, moderate temperature stability and high ‘Q’ factors for the 500 KHz to 100 MHz frequency range. They are well suited for low power, high inductance resonant circuits. Their low permeability factors also make them useful for wide band transformer applications. Nickel-zinc ferrites have a higher resistivity and are used at frequencies from 2 MHz to several hundred megahertz. The exception is common mode inductors where the impedance of NiZn material is recommended from 70 MHz to several hundred GHz.
The MnZn ferrite cores (Mix 31, 75, 77) have high permeabilities above 800 µ, have fairly low volume resistivity and moderate saturation flux density. They offer high ‘Q’ factors for the 1 KHz to 1 MHz frequency range. Cores from this group of materials are widely used for switched mode power conversion transformers operating in the 20 KHz to 100 KHz frequency range. These cores are also very useful for the attenuation of unwanted RF noise signals in the frequency range of 2 MHz to 250 MHz. Manganese-zinc ferrites are generally used in inductor applications where the operating frequency is less than 5 MHz. The exception is common mode inductors where the impedance of MnZn material makes it the best choice up to 70 MHz
What’s Different between Mixes?
The “Mix” is the chemical formula of the iron oxide. Ferrite is a ceramic consisting of iron oxide and generally either of two types:
- Manganese-zinc (MnZn) available as Mix #31, #75 and #77 (and others) – work well for common mode chokes
- Nickel-Zinc (NiZn) available as Mix #43, #52, #61, (and others) – generally preferred material for baluns/ununs
Palomar Engineers uses mix 31, 43, 52, 61, 75 and 77(73 replacement) for most applications from RFI/EMI common mode suppression, multi-ratio toroid baluns and ununs and sleeve baluns for line isolation. Each mix number has a measurable permeability and suggested frequency range for certain applications.
The table below gives our recommended applications for various mixes and effective frequency ranges
|Mix #||Material||Initial Permeability||RFI/EMI Common Mode Suppression Range||Tuned Circuits – Coil
||Wide Band Transformer|
|31 (1)||MnZn||1500||1-300 MHz||< 30 MHz||1:1 only, <250 MHz|
|43 (2)||NiZn||800||25-300 MHz||< 30 MHz||3-60 MHz|
|52 (6)||NiZn||250||200-1000 MHz||< 30 MHz||1-60 MHz|
|61 (3)||NiZn||125||200-2000 MHz||<25 MHz||1-300 MHz|
150 KHz – 30 MHz*
*Optimized for 150Khz – 10 MHz, effective to 30 MHz
|< 5 MHz||.1-20 MHz|
|77 (5)||MnZn||2000||.1-50 MHz||.01-5 MHz||<10 MHz|
(1) Mix 31 excellent for 1-10 MHz common mode suppression, then about same as 43 up to 250 MHz, NOT recommended for multi-ratio impedance transformers (baluns/ununs) due to material characteristics and power handling capability – ok for ham radio 1:1 feed line choke applications. Mix 31 is available in TOROIDS, SLIP ON BEADS, and SNAP ON SPLIT BEADS
(4) Mix 75 is a high permeability MnZn ferrite intended for a range of broadband and pulse transformer applications and common-mode inductor designs. Excellent for common mode suppression on AM broadcast frequencies from 500 KHz-1.8 MHz. Also very useful for medical instrument transducer isolation, inverter assemblies, inductive motors and control units. Mix 75 is available in TOROIDS, and SNAP ON SPLIT BEADS
- Optimized to solve low-frequency EMI issues between 200 kHz and 30 MHz
- Suppresses common-mode noise up to 30 MHz
- Replaces expensive line filters to mitigate conducted noise
- Split cores closely resemble solid cores, allowing seamless transitions from test to production
- Automotive: Inverter assemblies, inductive motors
- Consumer Electronics: Power supplies, peripheral cables
- Medical: Transducer isolation, human-machine interfaces
- White Goods: Control units, motors
(5) Mix 77 very useful for RFI/EMI suppression of AM broadcast and 160 meter frequencies, 160 meter to-40 meter impedance transformers (baluns/ununs). Mix 77 is available in TOROIDS
(6) The Jerry Sevick, W2FMI broadband transformers (baluns/ununs) used a permeability of 250 (Mix 52) and the F240-52 ring toroids are ideal for replicating his designs.
RFI/EMI Suppression Mix Selection
Note Mix 77 has replaced Mix 73 in the diagram below.
Download Fair-Rite Material Specifications Sheet for 31, 43, 52, 61, 75, 77 – CLICK HERE
For RFI/EMI suppression remember to select the mix which includes the INTERFERING signal frequency. E.g. if AM broadcast is affecting your 7 Mhz ham receiver, choose mix 77 or 75 which is effective at AM broadcast frequency RFI choking. If your 160 meter signal is affecting your DSL or computer try mix 77 (F240-77) on the power line to the effected device as well as the signal source as the AC line often acts as an “antenna” at these frequencies picking up common mode current.
Download Fair-Rite MSDS Safety Sheet for 31, 43, 52, 61, 75, 77 – CLICK HERE
RFI/EMI Suppression Comparison of Mix 75 and Mix 31 for under 5 MHz:
What is ferrite?
Ferrite is a class of ceramic material with useful electromagnetic properties and an interesting history (see below). Ferrite is rigid and brittle. Like other ceramics, ferrite can chip and break if handled roughly. Luckily it is not as fragile as porcelain and often such chips and cracks will be merely cosmetic. Ferrite varies from silver gray to black in color. The electromagnetic properties of ferrite materials can be affected by operating conditions such as temperature, pressure, field strength, frequency and time.
There are basically two varieties of ferrite: soft and hard. This is not a tactile quality but rather a magnetic characteristic. ‘Soft ferrite’ does not retain significant magnetization whereas ‘hard ferrite’ magnetization is considered permanent. Fair-Rite ferrite materials are of the ‘soft’ variety.
Ferrite has a cubic crystalline structure with the chemical formula MO.Fe2O3 where Fe2O3 is iron oxide and MO refers to a combination of two or more divalent metal (i.e: zinc, nickel, manganese and copper) oxides. The addition of such metal oxides in various amounts allows the creation of many different materials whose properties can be tailored for a variety of uses.
Ferrite components are pressed from a powdered precursor and then sintered (fired) in a kiln. The mechanical and electromagnetic properties of the ferrite are heavily affected by the sintering process which is time-temperature-atmosphere dependent.
Ferrite shrinks when sintered. Depending on the specific ferrite, this shrinkage can range from 10% to 17% in each dimension. Thus the unfired component’s volume may be as much as 60% larger than the sintered value. Maintaining correct dimensional tolerances as well as the prevention of cracking and warpage related to this shrinkage are fundamental concerns of the manufacturing process.
A Short History of Ferrites
The history of ferrites (magnetic oxides) began centuries before the birth of Christ with the discovery of stones that would attract iron. The most plentiful deposits of these stones were found in the district of Magnesia in Asia Minor, hence the mineral’s name became magnetite (Fe3O4).
Much later, the first application of magnetite was as ‘Lodestones‘ used by early navigators to locate magnetic North. In 1600 William Gilbert published De Magnete, the first scientific study of magnetism. In 1819 Hans Christian Oersted observed that an electric current in a wire affected a magnetic compass needle. With further contributions by Faraday, Maxwell, Hertz and many others, the new science of electromagnetism developed.
Naturally occurring magnetite is a weak ‘hard’ ferrite. ‘Hard’ ferrites possess a magnetism which is essentially permanent. In time, man-made ‘hard’ ferrites with superior properties were developed but producing an analogous ‘soft’ magnetic material in the laboratory proved elusive.
During the 1930’s research on ‘soft’ ferrites continued, primarily in Japan and the Netherlands. However, it was not until 1945 that J. L. Snoek of the Phillips Research Laboratories in the Netherlands succeeded in producing a ‘soft’ ferrite for commercial applications. Originally manufactured in a few select shapes and sizes, primarily for inductor and antenna applications, ‘soft’ ferrite has proliferated into countless sizes and shapes for a multitude of uses. Ferrites are used predominately in three areas of electronics: low level applications, power applications, and Electro-Magnetic Interference (EMI) suppression.
Above History from Fair-rite.com