======================MAGNETIC_CORES======================

                      B      = uH
                      V      = N*A*delta_B/delta_time
                      enegry = C*V^2/2 =i^2*L/2

                                 ^  B
                                  /_\
                                   |    ________    B  = u*H    H*L =N*I
                                   | _--   _--
                                   |/    /          V  = N*delta_Phi/delta_time
                                   /    /
                                  /|   /            L  = N*delta_Phi/delta_I
                         ________/_|__/_________\ H 
                                /  | /          /   Phi =B*Area   u =u_0*u_r
                      Phi = Flux
                      B   = Flux density
                      H   = Magnetic field
                      u   = permeablity
                      m_r = 2000-> 6000 machine materials

------------------------------------------------------------------------------------- 
             
                                            ^
STARTUP MAGENITZATION                      /_\ B FIELD      B_SAT
                                            |
                                            |  ######################
                                            |#         N #
                                            # ...... N. #
                                           #.       N. #
                                          #.| *****N. #
                                         #. *     N. #
                                        #. *|    *. #
                           COERCIVITY  #. * |   N. #     H FIELD
                       _______________#._*___N_*_.#_____________|\
                                     #. *   | *. #              |/
                                    #. *    |*. #
                                   #. *     *. #
                                  #. ****** . #
                                 #........  |#    N STARTUP MAGENITZATION
                                #           #     * MINIMUM MAGENITZATION
                               #           #|     . MIDDLE  MAGENITZATION
                         ################## |     # MAXIMUM MAGENITZATION
                                            |
                     

----------------------------------------------------------------------------

                                              ^
                                             /_\ B FIELD      B_SAT
FREQUENCY EFFECTS                             |
                                             *| #######################
                                         *    #         #    * *
                                        *    #|        #    *
                                       *    # |       #    *
                                      *    #  |      #    *
                                     *    #   |     #    *  H FIELD
                           ______________#____|____#_______________|\
                                   *    #     |   #    *           |/
                                  *    #      |  #    *
                                 *    #       | #    *
                                *    #        |#    * 6000HZ
                               *    #         #    *
                              *    #         #|   *
                      ######################  |*
                                              |
                                              |

----------------------------------------------------------------------------

                         ^
AIR GAP                 /_\ B FIELD
                         |
                         |           #    #  #  #  *#   *
                         |      #                *
                         |                     *
                         |                  *
                         |   #             *
                         |                *
                         |               *
                         |  #           *
                         |             *
                         |            *        # NORMAL
                         | #         *         # AIR GAP
                         |          *
                         |         *
                         |        *
                         |       *
                         |#     *
                         |     *
                         |    *
                         |   *                          H FIELD
                         |#____________________________________|\
                                                               |/
air-gap is useful     It can be. The shape of the air-gap can be important as well. 
                      Some devices are built with a 'stepped air-gap'. This causes the magnetic field in the vicinity of the
                      gap to concentrate near the narrower portion of the gap (which has a lower reluctance). 
                      This portion of the device will saturate before that near the longer gap. The
                      device will exhibit an initial higher inductance until a portion of the material saturates, 
                      when the device will exhibit a 'step' to a lower value. Thus for low values of
                      DC excitation the device will exhibit an inductance higher than for larger values of DC, 
                      creating what is called a 'swinging choke', useful in some filter applications.
                      One can use a 'wedge' shaped air gap to create a more smoothly varying inductance with DC excitation. 
                      But of course these changes will also occur with instantaneous excitation as well.
                      
                      
                      Why is there a gap or 'hole' in the middle of a typical B-H curve? 
                      It represents a loss component, however. Most magnetic materials will retain some
                      magnetization after being 'magnetized' and the excitation is removed. 
                      There will be some residual flux present. This must be overcome to return to a benign, zero flux state.
                      
                     
----------------------------------------------------------------------------

Measuring B-H curve  R2 senses the current in the primary (The magnetizing force) - 
                     R1 and C1 act as a crude integrator, 
                     
                     
                     
                                                  1:N          100K         ___
                          ______________________ o   o_______/\  /\  /\____| Y |
                        _|_                      \   /         \/  \/   _| |___|
                       /_  \                   _  | |  _                 |
                      // \  \                 / \/   \/ \    MEASURE B  _|_
                      \   \//                 \_/\   /\_/               ___
                       \___/                   _  | |  _                 |
                        _|_                   / \/   \/ \                | 3uF
                        ///   MEASURE H       \_/\   /\_/                |
                                        ___       | |                    |
                          __/\  /\  /\_| X |_____/   \___________________|
                        _|_   \/  \/   |___|                            _|_
                        ///     5                                       ///
                     
                     
                                               _  _  _         _  _  _
                             ___              / \/ \/ \ L1    / \/ \/ \ L2                  1:N      ___
                            |   |_/\  /\  /\__| () () |_______| () () |__/\  /\  /\________o   o____|   |
                            |___|   \/  \/                |                \/  \/ R2       \   /    |___|
                                       R1        _  _  _  |     LE                       _  | |  _
                                                / \/ \/ \ |                             / \/   \/ \
                                              __| () () |_|                             \_/\   /\_/
                                             |     LM                                    _  | |  _
                                             |                                          / \/   \/ \
                                             |                                          \_/\   /\_/
                             ___             |                                              | |      ___
                            |   |____________|_____________________________________________/   \____|   |
                            |___|                                                                   |___|
                     
                     
                     
                     Lm is the required magnetizing inductance.
                     measuring both lead resistances, and primary inductance with
                     the secondary both open (magnetizing inductance) and shorted (leakage
                     inductance L1 + L2*N^2).
----------------------------------------------------------------------------

                      
                                 Lp_Leak      Lsec_Leak
                                  _  _  _      _  _  _       RL*(Np/Ns)^2
                        __  Rp   / \/ \/ \    / \/ \/ \  Rs     __
                       |  |_  /\_| () () |____| () () |_  /\___|  |_
                       |__| \/   |       |  |  _  _  _  \/   | |__| |
                                _|_   Rc /  | / \/ \/ \     _|_     / 
                             Cp ___ core \  |_| () () |  Cs ___     \
                        __       |  loss /   K*Lprime |      |  __  /
                       |  |______|_______|____________|______|_|  |_|     
                       |__|                                    |__|
                                  L    
                      
                      
                      Ip*Np     Is*Ns
                      Vp/Np     Vs/Ns
                      Rp        winding resistance primary
                      Lp        winding reactance  primary
                      Rs        winding resistance secondary
                      Ls        winding reactance  secondary
                      Rc        core heating
                      LK*Lp     magnetic current

----------------------------------------------------------------------------


FERRITE CHARACTERISTICS.
                                         Saturation
                                                          Moment                                                   Saturation      
                 Saturation   Curie     in Bohr                           First-Order      Magneto-
                  Moment      Temp      Magnetons  X-ray     Lattice      Anisotropy       striction
Ferrite           in Gauss     in ~C    n_B       Density     Constant     Constant K1     Lambda_eX106
NiFe2O4           3400        585       2.3       5.38       8.34           Ñ0.06          Ñ22
Ni0.8Zn0.2Fe2O4   4600        460       3.5       -          -              -              Ñ        Ñ18.5
Ni0.5Zn0.5Fe2O4   5800        360       4.8       Ñ          Ñ                             Ñ15.0
Ni0.5Zn0.5Fe2O4   5500        290       5.0       Ñ           -             Ñ              Ñ8.3
Ni0.3Zn0.5Fe2O4   2600        85        4.0       Ñ           Ñ0.004             Ñ1.0
MnFe2O4           5200        300       0         5.00         8.50         Ñ0.04          Ñ14
Mn0.5Zn0,
Fe204                         100       6.0       Ñ            Ñ            Ñ0.004         Ñ
FeFe2O4           6000        585       4.1       5.24         8.39         Ñ0.135         +41
CoFe2O4           5000        520       3.8       5.20         8.38         Ñ2000          Ñ250
CuFeoO4           1700        455       1.3       5 35         8.24          Ñ             Ñ
                                                                                  8.68
Li0.5Fe2.5O4      3900        670       2.6       4 75         8.33          Ñ              -
MgFe204           1400        440       1.1       4.52         8.36          Ñ    0.05      Ñ
MgA1FeO4           Ñ           Ñ        0.3       Ñ            Ñ
NiAl0.25Fe1.75O4  1300        506       1.30      Ñ            8.31          Ñ     Ñ
NiAl_0.45Fe_1.55O4 900        465       0.61      Ñ            8.28          Ñ     Ñ
NiAl_0.62Fe_1.38O4 0          360       0         Ñ            8.25          Ñ     Ñ
NiAlFeO4         900          198       0.64     5.00          8.20          Ñ     Ñ
-----------------------------------------------------------------------------------


hysteresis of core    Ph = Kh*f*Bm^x*V  hysteresis loss
                      Kh is a constant which depends on the chemical 
                      analysis of the
                            material and the heat treatment and mechanical 
                      treatment to which
                            it has been subjected
                           f is frequency in Hz
                           Bm is maximum flux density in webers / m^2 (Teslas)
                           V is the volume of the material in cubic meters
                      Pe = Ke*f^2*c^2*Bm^2*V  eddy current loss
                           Ke is a constant which depends on the resistivity of 
                      the material
                           f is frequency in Hz
                           c is lamination thickness in meters
                           Bm is maximum flus density in webers / m^2 (Teslas)
                           V is volume of the material in cubic inches.


eddy current          in  laminations and another comes fromhysteresis of  core.
                      Ph = Kh*f*Bm^x*V  hysteresis loss
                      Kh is a constant which depends on the chemical 
                      analysis of material and  heat treatment and mechanical 
                      treatment to which it has been subjected
                      f is frequency in Hz
                      Bm is maximum flux density in webers / m^2 (Teslas)
                      V is the volume of the material in cubic meters
                      Pe = Ke*f^2*c^2*Bm^2*V  eddy current loss
                      Ke is a constant which depends on the resistivity of 
                      the material
                      f is frequency in Hz
                      c is lamination thickness in meters
                      Bm is maximum flus density in webers / m^2 (Teslas)
                      V is volume of the material in cubic inches.
                      Let's first guess at the Bm....
                      Assume inductance of core is constant as  of
                      frequency (poor guess for iron but a start)  
                      Bm will inversely proportional to  frequency 
                      and proportional to voltage. 
                      So we can change the above equations to
                      Ph = Kh'*f  hysteresis loss
                      Pe = Ke'*f^2  eddy current loss
                      since everything else is constant.
                      Pc = Ph*135/60 + Pe*(135/60)^2   total core loss
                      If *ALL* the power were in the hysteresis, you'd get a 
                      loss of 3.6 W,
                      Now let's *GUESS* that half  power went into hysteresis 
                      and half intoeddy current losses, then you would have....
                      Pc = .8*135/60 + .8*(135/60)^2   total core loss
                         =  5.9 W !!!

MAGNETOSTRICTION         static strain delta_l/l produced by a directcurrent polarizing flux density B_0 is given by
                         delta_l/l = c*B_0^2
                         c being a material constant expressed in m^4/weber^2.
Curie temperature        temperature at which a material loses all of its magnetic properties. 
                         Conventional strip-wound cores and
                         powder cores generally have such high Curie temperatures (>450 degrees C) 
                         Manganese-zinc ferrites,  Curie temperatures (120 to 250 degrees C) of ferrites.
bifilar winding?         Two strands of wire, usually twisted together. 
                         The dual wire is then wound on the core
                         or bobbin to produce two equal and parallel
                         windings which take the place of one large single
                         strand.
relative costs           of tdifferent magnetic materials?
                         For  powder cores, iron powder ranges from  1x - 3x
                         KOOL Mµ -- " " 4x - 5x  
                         Hig  Flux    approx. 10x
                         MPP          approx. 12x
                         For ferrites,F,P,R,J materials,roughlequivalent (1y)
                         W material------------1.25-1.75y
                         H mate-----------1.50-2.00y
                         Ferrite cost is also a function of geometry:
                         Toroids -------------least
                         E cores--------------mid
                         Other shapes-------most
B-H loop?                (or Hysteresis)
                         defines  flux density of material, coercive force, 
                         amount of drive level required to saturate the core, 
                         and permeability
                         (ability to change magnetic lines of force).
                         B-H loop changes with frequency and drive level. 
Why air gap into cores   "tilts", or "shears" the B-H loop, 
                         making it possible to use core at higher H levels, 
                         thus preventing early saturation of core. 
                         Once a core saturates, permeability reduced, 
magnetostriction?        When magnetic material is magnetized,
                         small change in dimension occurs.
                         in order of several parts per million,
                         called "magnetostriction". For
                         applications like ultrasonic generators, 
                         mechanical motion produced by magnetic excitation
                         through magnetostriction is used to good advantage.
                         operating in audiblefrequency range,
                         an annoying audible hum is observed. 
                         For this reason, low magnetostrictive
                         materials such as Permalloy 80, METGLAS 2714A, KOOL
                         Mµ and MPP powder cores may be used
disaccommodation         occurring in ferrites, 
                         reduction of permeability with time 
                         after a core is demagnetized. 
                         demagnetization can be caused by heating 
                         above Curie point, by applying AC of diminishing
                         amplitude, or by  mechanically shocking the core.
                         In this phenomenon,  permeability increases
                         towards its original value, then starts to decrease
                         exponentially. If no extreme conditions are
                         expected in the application, permeability changes
                         will be small because most of the change has
                         occurred during the first few months after
                         manufacture of the core. High temperature
                         accelerates the decrease in permeability.
                         Disaccommodation is repeatable with each successive
                         demagnetization; thus, it is not the same as aging.
inductance ferrite       toroid decrease after winding and potting?
                         Ferrite materials are susceptible to mechanical stress
                         both from winding the core and from encapsulation. 
                         High permeability materials are affected. remedies:
                         (1)after winding, bake and/or temperature-cycle, 
                         (2)thin out the epoxy used for encapsulation or dope
                         with an inert material such as sand or ground mica,
                         (3) cushion with tape,(4) silicone (RTV) dip 
                         wound cores prior to potting.
actual core losses       in gappedstructures larger than calculated?
                         When calculating the core losses, it is
                         assumed that  structure is homogeneous. In
                         reality, when core halves are mated, there is
                         leakage flux (fringing flux) at mating
                         surfaces, and gap losses contribute to 
                         total losses. 
difference ferrites      between nickel-zinc and manganese-zinc ferrites?
                         MnZn materials have a high permeability,
                         NiZn ferrites have low permeability.
                         Manganese-zinc ferrites used less than 5MHz.
                         Nickel-zinc ferrites used at frequencies 
                         from 2MHz to several hundred megahertz. 
                         The exception to this rule of
                         thumb is common mode inductors where the impedance
                         of  MnZn materials makes it the best choice up to
                         70MHz  and NiZn is recommended from 70MHz to
                         several hundred GHz.
permeability important   in powermaterials?
                         Permeability is flux density, B, 
                         divided by drive level, H. 
                         Power materials are generally used
                         for high frequency transformer applications.
                         Generally, the important characteristics are high
                         flux density and low core losses. Permeability is
                         of less importance because of its variability over
                         an operating flux range.
Why only min AL          listed in catalog?
                         Permeability (and AL) varies with drive level. 
                         For power applications, no need to limit max AL.
                         minimum ALtranslates into maximum excitation current.
How know ferrite         hardware willfit on the core?
                         Cores are manufactured to standards t
                         Tolerancesassigned to  critical dimensions.
                         Generally, hardware fit should not be a problem.
tighter dime tolerances  in ferrites?
                         ANSWER: During the sintering operation, parts
                         shrink to their final dimensions. Different
                         material and processing techniques result in
                         variance in this linear shrinkage which can range
                         from 10 to 200f  the pressed dimensions (in
                         finished parts, this could range from 1-4%). Some
                         dimensions cannot be held to a tighter tolerance.
                         Dimensions that can be machined after firing can
                         certainly be held to tighter tolerances.
                         QUESTION: Can I get a custom ferrite part?
                         ANSWER: It is possible to get a custom part.
                         Volumes of less than 500 pieces can be readily
                         machined. Quantities over 20,000 are generally
                         pressed from custom-built tools. Adjusting the
                         heights of existing parts is a practical way to
                         minimize machining and tooling costs.
                         QUESTION: What is the proper clamping pressure in
                         ferrites?
                         ANSWER: Generally, a recommended figure is about
                         70,000 kg/m² (100 lbs./sq. in.) of mating surface.
                         For specific recommended pressures for RM, PQ, EP
                         and pot cores, consult MAGNETICS' Ferrite Catalog,
                         FC-601.
                         QUESTION: What is the best core shape?
                         ANSWER: There is no "best shape."  It depends on
                         the application, space constraints, temperature
                         limitations, winding capabilities, assembly, and a
                         number of  other factors; this means that
                         compromises must be made. For additional
                         information on this subject, consult the MAGNETICS
                         Ferrite Cores Catalog where geometry considerations
                         are covered in more detail. Brochure PS-01 also
                         covers this subject.
                         QUESTION: Why do manufacturers flat-grind ferrite
                         cores?
                         ANSWER: Cores are flat-ground because of the uneven
                         surface produced during the firing process. It is
                         important for mating surfaces to mate with a
                         minimum air gap to keep the gap losses to a minimum
                         and to achieve an optimum inductance.
                         QUESTION: Why do cores get lapped?  What is the
                         surface finish?
                         ANSWER: Lapping is an additional production process
                         used to decrease the effects of an air gap on mated
                         surfaces. It is typically done on mated cores with
                         material permeabilities of 5000 and greater in
                         order to achieve the maximum AL value for a given
                         material. A mirror-like finish is the result. The
                         typical surface finish for normally flat-ground
                         surfaces is 25 micro-inches (.635 microns) and for
                         lapped surfaces is 5 micro-inches (.127 microns).
                         Proper surface finish is not measured as a rule,
                         but is maintained by monitoring the AL.
                         QUESTION: Why is the ferrite gapped tolerance not
                         always ±3%?
                         ANSWER: Due to limitations of the machine
                         performing the gapping, the smaller the gap, the
                         harder it is to hold tight tolerances. As the AL
                         value increases, the gap gets smaller, hence the
                         tolerance gets larger. As  the gap gets smaller,
                         the mechanical tolerance becomes proportionately
                         larger, plus the influence of variation in the
                         material permeability becomes greater. Thus, a gap
                         specified by its AL value yields a tighter
                         tolerance than a gap specified by its physical
                         dimensions.
                         QUESTION: How do you glue ferrite cores?
                         ANSWER: Gluing should be done with thermosetting
                         resin adhesives, in particular the epoxy resins.
                         The available range is very large. Important
                         factors in the choice are the required temperature
                         and viscosity. The curing temperature must not be
                         above the maximum temperature to which the assembly
                         may be safely raised. As far as viscosity is
                         concerned, if it is too high, application is
                         difficult; if it is too low, the resin may run out
                         of a poorly-fitted joint or may be absorbed by the
                         porosity of the ferrite. Follow the manufacturer's
                         instructions for a particular resin. Take care not
                         to thermally shock ferrites; raising or lowering
                         the core temperature too rapidly is dangerous.
                         Ferrites will crack if changes in temperature
                         exceed 5-10 degrees C/min. In addition, care must
                         be taken to match the adhesives' coefficient of
                         thermal expansion (CTE) to that of the ferrite
                         material. Otherwise, the resin may expand or
                         contract more quickly than the bulk ferrite; the
                         result can be cracks that will degrade the core.
                         QUESTION: Why are ferrite toroid AL tolerances wide
                         and powder cores narrow?
                         ANSWER: Magnetic materials naturally have wide
                         variations in permeability. Putting an air gap in
                         the structure can have the effect of not only
                         reducing permeability but also dramatically
                         reducing this variation. Powder cores have a
                         distributed air gap; this results in a narrower
                         inductance tolerance. Ferrite toroids do not have a
                         distributed air gap and are thus subject to
                         variations caused by normal processing. For a
                         complete description of the ferrite manufacturing
                         process, consult the MMPA Soft Ferrite User's
                         Guide, Publication number MMPA SFG. Magnetic
                         Materials Producer's Association, 600 South Federal
                         Street, Suite 400, Chicago, IL 60605.
                         QUESTION: Can you tighten electrical tolerances on
                         ferrite toroids?
                         ANSWER: (see also question 33). While a production
                         batch of ferrite toroids may have a wide tolerance,
                         when required in rare instances, the cores can be
                         graded into narrower inductance bands at a premium.
                         Due to equipment limitations, this is not possible
                         on all sizes. Check the factory for specific
                         information and costs.
                         QUESTION: What is the MAGNETICS specification for
                         out of roundness for a ferrite toroid ?
                         ANSWER: Out of  roundness is controlled by
                         mandating that cores meet overall dimensional
                         tolerances for OD and ID while keeping enough cross
                         section to meet the specified AL. Refer to the
                         MAGNETICS Ferrite Catalog  FC-601 for toroid
                         physical dimension tolerances.
                         QUESTION: What is the difference between nylon and
                         polyester coatings for ferrite toroids?
                         ANSWER: They are similar. Nylon is thicker, and can
                         stand temperatures up to 155 degrees C. Polyester
                         is good to about 200 degrees C. Nylon finishes are
                         generally applied to cores ranging in OD from 9 mm
                         to 29 mm. Very large and very small cores are
                         coated with a polyester finish. Voltage breakdown
                         guarantee of nylon and polyester coatings is 500
                         volts. Nylon cushions better and is more resistant
                         to solvents. Both finishes are held to the same
                         electrical and mechanical specifications.
                         QUESTION: What about availability of any other core
                         coatings for ferrites?
                         ANSWER: Black lacquer is an inexpensive coating put
                         on merely for the purpose of providing a smooth
                         winding surface. It does not have any voltage
                         breakdown guarantee. Size range is 7.6 mm. to 15.8
                         mm. in outside diameter.  Parylene C is a vacuum
                         deposited coating providing good resistance to
                         moisture and organic solvents. Electrical
                         characteristics are superior to other coatings. The
                         size range is economically limited to outside
                         diameters of 14mm.or less.
                         QUESTION: How do you determine the proper core
                         size?
                         ANSWER: Two elements are useful in determining core
                         size: core window (winding area) and core
                         cross-sectional area. The product of these two
                         elements (area product, or WaAc) relates to the
                         power handling capability of a core. The larger the
                         WaAc, the higher the power able to be handled. As
                         operating frequency increases, the area product can
                         be reduced, thus reducing the core size. MAGNETICS
                         publishes the area products of all cores as a
                         useful design tool.
                         QUESTION: Can MAGNETICS press powder cores and
                         ferrite toroids in different heights?
                         ANSWER: Many cores can be pressed to different
                         heights. Dies are made so that the cavities can
                         accommodate these different heights. Each core size
                         is different, however. Consult the factory for
                         specific questions on the sizes of interest,
                         minimum quantities and price. One advantage this
                         offers is the ability to produce other core sizes
                         without the expense of additional tooling.
                         QUESTION: In powder cores, why is actual inductance
                         different from calculated?
                         ANSWER: MAGNETICS measures inductance in a Kelsall
                         Permeameter Cup. Actual wound inductance outside a
                         Kelsall Cup is greater than the value calculated
                         due to leakage flux and flux developed in the
                         winding. The difference depends on core size,
                         permeability, core finish thickness, wire size and
                         number of turns, in addition to the way windings
                         are put on the core. The difference is negligible
                         for turns greater than 500 and permeabilities 125µ
                         and higher. The following table is a guide to the
                         differences that one might experience:
                         No. of  Turns     Actual L     No. of  Turns
                         Actual L
                         1000              0%
                         100            +3.0%
                         500             +0.5%
                         50             +5.0%
                         300             +1.0%
                         25             +8.5%
                         The following formula can be used to approximate
                         the leakage flux to add to the expected inductance.
                         This formula was developed from historical data of
                         cores tested at MAGNETICS. Be aware that this will
                         only give an approximation based on evenly spaced
                         windings. You might expect as much as ±50%
                         deviation from this result.
                         where LLK= leakage inductance (mH)
                         N= number of turns
                         Ae= core cross-section  (cm2)
                         le= core magnetic path  (cm)
                         CONVERSION FACTORS:
                         MULTIPLY             BY                      TO
                         OBTAIN
                         Oersteds
                         2.0213                      ampere-turns/inch
                         Oersteds
                         0.79577                     ampere-turns/cm
                         Oersteds
                         79.577                        ampere-turns/m
                         Ampere-turns/cm
                         1.2566                             oersteds
                         Gausses
                         10-4                                 teslas
                         Micro-inches
                         0.0254                              microns
                         ePanorama.net - Ground Loops