Soft Ferrite Cores - Speedofer
102
1 Soft Ferrite Cores Mr. Probal Mukherjee, Head, Technical, Speedofer Components Pvt. Ltd. Plot No: 101 & 102, Toy City, Ecotech – III, Greater Noida – 201306, Uttar Pradesh, India. [email protected] , +919830876431 www.speedofer.com
Transcript of Soft Ferrite Cores - Speedofer
1
Soft Ferrite Cores
Mr. Probal Mukherjee, Head, Technical, Speedofer Components Pvt. Ltd.
Plot No: 101 & 102, Toy City,
Ecotech – III, Greater Noida – 201306,
Uttar Pradesh, India.
[email protected], +919830876431
www.speedofer.com
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Contents
3: Manganese Zinc Soft Ferrite Materials, Chemistry, Production Process, Electromagnetics
Properties, Nomenclature and Specifications
17: Basic Electrical Technology, Inductive Components, Magnetic Circuits, Reluctance, Core
Factors
30: Power Ferrite materials- characteristics & applications
41: Ferrites Applications
51: Basic Statistical Computations, Sampling, Tolerance Settings, Rejection Estimation, AQL
Prediction
59: Standardization of Ferrite Cores As Related to Their Applications
77: ISO9001 Consideration for Soft Ferrite Product Development
84: Ferrite Materials – Characteristics & applications in Current Transformers in Energy-meters
91: Ferrite Cores in Lighting
97: LED Lighting
100: Author’s Bio-data www.speedofer.com
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Manganese Zinc Soft Ferrite Materials,
Chemistry, Production Process,
Electromagnetics Properties,
Nomenclature and Specifications
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Composition & Preparation of Ferrite Materials
1
2
3
1
2
3 Sintering (1200°C~1600°C) or solidifying the shapes
Ferrite Cores Manufacturing Process Flow
Powder Processing & Composition
Pressing to the desired size & shape
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Electromagnetic Properties of Ferrite Materials
1500 to 15000 at room temperature
350 to 550mT at 25°C
250 to 450mT at 100°C
Specified over 25kHs to 1MHz,
50mT to 300mT, 25°C to 120°C
Relative at 1MHz for Permeability
>5000
Normalized Impedance peak within
1MHz
100 to 160°C for High Permeability
>200°C for Power Ferrites
Relative
Permeability
Saturation Flux
Density
Large Signal Losses
(Power Ferrites)
Small Signal Losses
(High-Permeability)
Frequency
Response
Curie Temperature
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Saturation and B-H Loop of a Ferrite Material
Bs is the saturation flux density, Br the remnance flux density and Hc the coercive field. The B-H loop
contracts with temperature with the saturation flux density reducing as shown.
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Initial Permeability of Ferrite Materials
Ferrite materials are temperature sensitive and the magnetic properties vanish at the Curie
temperature Tc. The ferrite material regains its magnetic properties once the temperature falls below
Tc.
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Amplitude Permeability of a Ferrite Material
Amplitude permeability denoted as ma of a ferrite material is the slope of the B-H loop at large signal
as shown. This is a measure of the linearity of inductance at the operating point. The amplitude
permeability may have a dual value (either m11 or m12 ) at flux density B1 but has a unique value m2
at flux density B2.
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Core Loss versus Temperature of Ferrite Materials
The safe operating point is in the negative slope region and the limit is the SPM temperature. Hence
material 3 may be operated best at 100oC but materials 1 and 2 at 50oC. Material 1 has lower loss
than material 2 even though both have the same SPM temperature.
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Core Loss versus Frequency & Flux Density of Power Ferrite Materials
The core loss density pv (kW/m3) of a power ferrite material for a frequency f (kHz) and peak
sinusoidal flux density B (mT) at a temperature T (oC) is given by the Steinmetz equation:
pv = C(T) * fa(T) * Bb(T)
both a(T) and b(T) are temperature dependant and C(T) is given as:
C(T) = c0 – c1*T + c2*T2 c0, c1, c2 > 0
and the SPM temperature TSPM = c1/(2*c2)
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Performance Factor of Power Ferrite Materials
The Performance Factor (PF) of a Power Ferrite Material is the product of flux density and
frequency at a given core loss and temperature. The maximum operating frequency of the material
at the given condition is the frequency corresponding to the peak of the Performance Factor curve.
For a choice of frequency, temperature and core loss density, the material with a higher
Performance Factor should be chosen for design economy.
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High Permeability Ferrite Materials- Loss Tangent, Complex Permeability
Ferrite materials having permeability mi >5000 are generally called high permeability. The losses in
these materials (also known as small-signal loss) is expressed as the tangent of the phasor angle d
between the voltage and current, hence tand. The product of tand and permeability is called the
imaginary part of permeability mi’ and together with the real part mi, is known as Complex
Permeability.
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Normalized Impedance of Ferrite Materials
The small signal loss of a ferrite material is generally expressed as tand/mi
The other applicable property is the Normalized Impedance zn (W/mm):
Zn = 8*p2*f*10-7*[mi2 + mi’
2]1/2
f is the frequency in kHz.
All the properties of high permeability ferrites are expressed as Frequency Response to select the
correct material for the frequency of application.
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Small Signal Distortion in Ferrites and Hysteresis Material Constant hB
The slope of tand against flux density B for small signal application, B<10 mT Is called the Hysteresis
Material Constant and is denoted as hB (10-6/mT). A transformer with ferrite core introduces distortion
in the signal which is a function of the Hysteresis Material Constant of the ferrite material.
The selection of a ferrite material in telecom application depends on its Hysteresis Material Constant.
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Temperature Coefficient of Permeability of Ferrite Materials
The permeability of all ferrite materials vary with temperature. A typical curve is shown. In many
applications, such variation may cause problems in the actual application if it is too large. For
instance, wide permeability variation with temperature in the ring cores in CFL , causes flickering.
Hence this variation is specified as Temperature Coefficient of Permeability of the ferrite material.
The Coefficient may be expressed as
a = Dm/DT (/oK)
Generally it is specified as
aF = Dm/ (m1*DT) (10-6/oK)
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Density & Resistivity of Ferrite Materials
All the magnetic properties as Saturation Flux Density, Permeability Loss Tangent etc. depend on
the density of the sintered ferrite.
The sintered density is also related to the dimensions of the core by the shrinkage factor of the base
ferrite powder. Hence it is customary to provide the Density (kg/m3 of g/cc) for the ferrite material
after sintering.
The ferrite core need to be electrically insulated from its contacts. Hence the Resistivity (W*m) is
provided. This is measured at dc excitation on a unit cube by Ohm’s Law.
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Basic Electrical Technology,
Inductive Components,
Magnetic Circuits, Reluctance,
Core Factors
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Passive Electrical Components, Fields, Circuits
Passive Electrical Components either dissipate or store energy. The three Passive Electrical
Components are Resistor (denoted as R), Capacitor (denoted as C) and Inductor (denoted as L).
A Resistor dissipates energy as heat (or light), a Capacitor stores energy in electric form, an
Inductor stores energy in magnetic form.
Physically, all electromagnetic phenomenon are explained by the two types of fields, Electric and
Magnetic. A Capacitor is subject to an Electric field, an Inductor to a Magnetic field.
A Resistor when influenced by an Electric field or a time-varying Magnetic field, sets up a flow of
electric current which causes the energy dissipation in the Resistor. In most applications of
Electrical Engineering, fields are confined to and approximated by circuits and the Electric field is
replaced by its space integral Voltage (Volts) and the Magnetic field by its space integral Current
(Amperes). The three Passive Components are characterized by both their field and circuit
equations.
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Field Variables & Electromagnetic Properties of Materials
The basic field variables and their MKSA (Meter, Kilogram, Second, Ampere) units are:
• The Electric field intensity vector E in Volts/m
• The Magnetic field intensity vector H in Amperes/m
• The Electric flux density vector D in Coulombs/m2
• The Magnetic flux density vector B in Webers/m2 (Tesla)
• The Current density vector J in Amperes/m2
• The three electromagnetic properties of material are:
• The conductivity s in Mho/m (or the Resistivity r=1/s in Ohm-m)
• The field equation J = s E
• The permittivity e*e0 in Farads/m
• e0 = 8.85*10-12 Farads/m is the permittivity of free-space
• e is the relative permittivity of the material
• The field equation D = e e0 E
• The permeability m*m0 in Henrys/m
• m0 = 4*p*10-7 Henrys/m is the permeability of free-space
• m is the relative permeability of the material
• The field equation B = m m0 H
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Circuit Variables, Passives and Equations
The basic circuit variables and their MKSA units are:
• The Electric charge q in Coulombs
• The Magnetic flux f ; for N turns the flux-linkage y = N f in Webers
• The Electric potential v in Volts; the Electric current i in Amperes
• The Magnetic potential N i in Ampere-turns
• The frequency f in Hz and for sinusoidal time variation w = 2 p f
• The Resistance in Ohms; the Capacitance C in Farads
• The Inductance L in Henry and AL = L/N2 in Henry
• S denotes the area vector normal to field lines
• l the length vector tangential to field lines
The circuit and field variables are related by:
D = q/S B = f/S
E = v/l H = Ni/l
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Passives and Equations- Resistance
The basic equation : v = R i
The characteristic is shown in the figure.
The firm black line is the linear region that satisfies the
equation.
The dotted lines indicate the limits on voltage / current
that may be applied to the resistance.
The red line indicates short circuit by failure and the blue line indicates open circuit by
failure.
The Resistance is related to material property and dimensions by:
R = r l / S = l / (s S)
The Power dissipation in a Resistance is the product of its voltage and current.
P = v i = v2 / R = i2 R
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Passives and Equations- Capacitance
Equation Integral form
Equation Differential
form
The firm black line is the linear region and the red dotted line indicates dielectric breakdown, the
capacitor becomes a short-circuit.
The Capacitance is related to material property and dimensions by:
C = e e0 S / l and the energy stored is given by: C v2/ 2
The loss in a Capacitor is shown by an equivalent Resistance in parallel.
The loss factor D is given by:
D = 1 / (w R C)
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Passives and Equations- Inductance
Equation Integral form
Equation Differential form
The firm black line is the linear region and the red line indicates saturation, the inductor becomes
a short-circuit. But unlike the destructive breakdowns of Resistance and Capacitance, the
saturation of an Inductance is reversible.
The Inductance is related to material property and dimensions by:
AL = m m0 S / l and the energy stored is given by: L i2/ 2
For Core loss the loss factor D is given by:
D = w L / Rp Q = 1 / D
The loss in an Inductor is due to its
winding denoted by Resistor Rs in
series and in core denoted by Resistor Rp in parallel.
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Impedance, Admittance, Resonance
Impedance of a Passive component is the ratio of its voltage to its current. Generally it is denoted
as Z = v / i
The Impedance of a Resistor R is given as R;
The Impedance of an Inductor L is given as XL = w L ;
The Impedance of a Capacitor C is given as XC = 1 / (w C)
Admittance of a Passive component is the reciprocal of its impedance and is generally denoted as
Y = i / v
The Admittance of a Resistor R is given as G = 1 / R
The Admittance of an Inductor L is given as BL = 1 / (w L)
The Admittance of a Capacitor C is given as BC = w C
When passive components are connected in series as shown and XL = XC, the condition is called Series Resonance
When passive components are connected in parallel as shown and BL = BC, the condition is called Parallel Resonance
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The Ideal and the Practical Transformer
The Transformer is a four terminal Passive component unlike the two terminal Resistor, Inductor or Capacitor.
An Ideal Transformer is shown. The equations:
v2 = n v1 (voltage balance)
n i2 = i1 (ampere-turns balance)
Z2 = n2 Z1 (Impedance transformation)
Ferrite core transformers generally have low winding loss
and leakage flux.
The practical representation of Ferrite core transformers is
shown as a combination of an ideal transformer and two
passive components.
Lm is the magnetizing inductance for the core and Rc the
equivalent resistance for core loss.
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Magnetic Circuits, Reluctance
A Ferrite EE core pair is shown with its Winding and the
path of Magnetic flux F.
It is assumed that the core contains the entire flux and
there is no leakage flux that escapes from the core.
It is also assumed that there is no air-gap
between the two cores. Such a structure is called a closed
Magnetic Circuit and is represented as an equivalent
electric circuit as shown below.
The Magneto-motive Force (MMF) is NI where N is the
number of turns in the winding and I the current and this is
represented as an Electro-motive force.
The flux is shown as an equivalent electric current and the
core structure is divided into symmetrical parts along the
flux path. Each such segment is the electrical equivalent
of Resistance and for a Magnetic Circuit is known as
Reluctance.
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Reluctance Calculation of a Magnetic Circuit
The electrical equivalent gives: F/2 = Ni/(R1+R2+2R3+2R4+2R5)
Hence the equivalent Reluctance R = Ni/F = (R1+R2+2R3+2R4+2R5)/2
As L = y/i = NF/i = N2/R and hence AL = 1/R
For the kth segment having a cross-section Ak normal to flux path and
length lk along the flux path let the MMF be Nik. SkNik = Ni
Bk =F/Ak =m0mHk and Hk =Nik/lk gives the Reluctance of the kth segment
Rk = Nik/F = (1/m0m)*lk/Ak and R =SkNik/F= SkRk
Finally: AL = m0m SkAk/lk
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Calculation of Effective Core Factors
The total magnetic circuit is divided into regions of similar cross-sections as shown for the
example of a pair of E cores below (k=1,..5) and the effective magnetic length le , the
effective magnetic area Ae , and the effective magnetic volume Ve are defined from the
general formulas given above.
The effective core factors are thus not physical but a mathematical exercise which is agreed
by consensus of all Ferrite Manufacturers.
C1
k
lk
Ak
C2
k
lk
Ak )2
Ae
C1
C2le
C12
C2
Ve Ae leC1
3
C22
The minimum physical cross-section is given by:
Amin is used for voltage computation for Core loss measurement.www.speedofer.com
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Effective Core Factors for Gapped Cores
For gapped cores the geometry factors lk, Ak and hence
Ae, le are considered and computed similarly as for the
un-gapped core. The value of m is the material
permeability for the un-gapped case.
For the gapped case, m is replaced by me
which is called the effective permeability.
The value of me depends both on the gap
lg and the permeability of the material.
Generally, for lg/le <5%, the fringing flux may be
neglected and me is given as shown. For larger gaps,
one may use the approximation me = lg/le but it is safer
to determine me by actual measurement of AL and use
the formula.
Un-gapped cores have a residual air-gap at the mating surface in the range of 5 to 20 microns and
this must be entered in the formula for me.
The formula for AL reduces to:
AL (nH) = 0.4*p*me*Ae(mm2)/le(mm)
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Power Ferrite materials- characteristics
& applications
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Speedofer SFP4
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Temperature Characteristics of Power Ferrites
• For the thermal resistance line Rth1 and ambient of 50°C a stable operating point is possible for all the materials but for higher (thus cheaper) Rth2 only SFP41 can have a stable operating point.
• For a shift in ambient to 25°C SFP4 offers the best efficiency for the same thermal resistance line Rth1.
Loss-temperature curves and thermal resistance lines for
power ferrite materials at 200mT, 100kHz
0
100
200
300
400
500
600
700
20 40 60 80 100 120
Temperature oC
Po
wer
loss k
W/m
3 Epcos N87
Epcos N97
Epcos N95
Rth1
Rth1
Rth2
Speedofer SFP3
Speedofer SFP4
Speedofer SFP41
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Transimissible Power of Ferrite Transformer
Netrans AAjBfCIUP D
Circuit Topology
Frequency Flux Density
Current Density
Core Geometry
BfPtransˆ Performance Factor PF
The performance factor measured at constant core loss (300KW/m3) and temperature (100OC)
enables the comparison of the transmissible power of a transformer at constant heating
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Characteristics of gapped power ferrite materials
Gapping of ferrite shears the B-H curve. The coercive force Hc remains unchanged but the remnanceBr reduces. The inductor can store and transfer more energy as shown from the shaded areas above. Such inductors carry an average (dc) current.
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Characteristics of gapped power ferrite materials
The capability to support an average current (also known as DC bias capability) by a ferrite inductor increases with a gap as shown. The DC bias capability reduces with temperature and there are specially designed materials as SFP42 having high DC bias capability at high temperature.
0
20
40
60
80
100
120
1 10 100 1000 10000I dc (mA)
Pe
rce
nta
ge
in
du
cta
nce
Variation of inductance with average current for
core shape RM10 and Epcos material N87
Gapped
ferrite
0.5 mm
100oC
25oC
Ungap
ferrite
Pe
rce
nta
ge
in
du
cta
nce
0
20
40
60
80
100
120
0 0.3 0.6 0.9 1.2 1.5I dc (A)
Pe
rce
nta
ge
in
du
cta
nce
Inductance with average current for gapped
ferrite cores from Epcos materials at 100oC
N87
N92
RM10
0.5mm
gap
Inductance with average current for gapped
ferrite cores from Speedofer materials at 100°CVariation of Inductance with average current for
core shape RM10 and Speedofer material SFP4
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SFP4
SFN92
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Application of Speedofer power ferrite materials
SFP3 SFP4 SFP42, SFP4, SFP5, SFP41
SFP4 SFP4 SFP5, SFP41, SFP3 SFP42
Speedofer Material Grade
SFP3, SFP4, SFP41, SFP42
SFP3, SFP4, SFP42
SFP3, SFP4, SFP41, SFP5
SFP4, SFP5, SFP41
SFP3, SFP4
SFP4, SFP42
SFP3
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Application of Speedofer power ferrite materials
0
10000
20000
30000
40000
50000
60000
10 100 1000
N27
N72
N49
N92
N87
N97
Frequency kHz
PF
kH
z*m
T
Performance Factor for Epcos power ferrite materials at
500kW/m3 losses and SPM temperature of material
The Performance Factor takes into account the frequency, flux density, losses and operating
temperature of a converter. It is useful both for loss limited and saturation limited designs.
SFP3
SFP4
SFP3
SFP42
SFP4
SFP41
Performance Factor for Speedofer Power Ferrite Materials at
500kW/m3 losses and SPM temperature of material
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Core loss measurement equipment
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Gap and inductance factor for Speedofer power ferrites
0
100
200
300
400
500
600
0 2 4 6s [mm]
AL [
nH
]
AL measured
AL calculated
10
100
1000
0.1 1 10 lg s [mm]
lg A
L [
nH
]
AL measured
AL calculated
2/1
1
K
L
K
As
12 KsA K
L
The air gap s (mm) needed to achieve an inductance factor AL (nH) is given by the following
empirical method.
K1, K2 values are found by making a logarithmic curve fit to the actual measured data.
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Low Profile Cores: Standard Shapes
Design Criteria low profile cores:
a) A > 2B
b) C > B
d) A > C
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Relative Transmissible power in large cores
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Ferrites Applications
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Basics of Ferrites for EMI Applications
Rwinding RS, core XLS, core
LFilter
Input Output
) 22
SS RLZ w The impedance of the EMI ferrite must be as high as possible
in the frequency range of the interference
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Definition of the Normalized Impedance ZN
0
5
10
15
20
25
30
35
0.01 0.1 1 10
f [MHz]
ZN [
W/m
m]
0
2000
4000
6000
8000
10000
12000
0.01 0.1 1 10
f [MHz]
µ',
µ''
22
0
2
2
2
0
2
2
0 2 SS
e
e
e
eS
e
eS f
l
AN
l
AN
l
ANZ mmmpmmwmmw
LS RS ZN
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Principal of a Current Compensated Choke
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Coating of Ring Cores
Epoxy Galxyl (Parylene)
Main application Ring cores greater than R 9.5 Ring cores smaller or
equal than R 9.5
Coating thickness < 0.4 mm 0.012 mm or 0.025mm
Break through voltage > 1.0 kV (R9.5, 10)
> 1.5 kV (R12.5 up to R20)
> 2.0 kV (>R20
> 1 kV (Standard value)
Mechanical properties High firmness Smooth surface
Max. temperature (short
time)
approx. 180°C approx. 130°C
Advantage Small influence on the AL-
value
Very thin coating
thickness
UL-Certification UL 94 V-0 UL 94 V-0
Ordering code B64290-L B65290-P
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EMI suppression in three phase system
The schematic of a three phase EMI suppression common-mode choke is shown below.
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Magnetomotive force H and flux density B in three phase system
The three phase conductors are shown in the three conventional colors red, yellow and blue.
The currents in the respective phases are I r, Iy and Ib. In perfect balance system:
Ir Iy Ib 0 at every instant
Hence there is no MMF developed in the ferrite core. Only when a common mode current I c
flows in two phases then the MMF is developed.
Ir Iy Ib Ic Ic 2 Ic
MMF N 2 Ic In this case N=1 turn
The magnetomotive force H and flux density B in the core are given as
H2 Ic
leB m0 me H
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Zero sequence current in three phase system
This B will cause heating in the core depending on the frequency and magnitude of the
common mode current and the ambient temperature and cooling of the ferrite. Hence the
heating can occur only in the event of common mode disturbance.
But in many practical cases due to unbalance in the system (supply or/ and load)
Ir Iy Ib In
In is called the zero sequence current and this occurs even without a common mode
disturbance. This will cause an MMF and hence a H field and flux density B as given by
HIn
leB m0 me
In
le
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Conclusions
This B causes heating in the ferrite irrespective of common mode current. If the zero sequence
current is restricted to power frequency (50/60 Hz) losses in the ferrite core shall be negligible.
But i n many converter applications the zero sequence current may consist of high frequency
harmonics and this shall cause a constant heating of the ferrite. Stacking more ferrites may not
help because the exciting current shall remain same and hence H and B. Increasing the size
and hence l e will reduce the flux density but this will need more space and the magnetic
coupling will also be reduced.
Suggestions: 1) Check and control the zero sequence current--only customer can do this.
2) Increase the diameter of the ring core --if space permits and the leakage flux
is not too much.
3) High perm materials have excessive losses in large signal mode and the
losses generally increase with temperature. Use of power material as N87
will reduce the losses at the same flux density and the losses will also
decrease with temperature. N87 has a normalized impedance curve nearly
parallel to N30 with a lower inductance (AL). Stacking of cores will multiply
the inductance with reduced loss and hence heating.
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Small signal distortion in ferrites and hB
wt
v(t)
input signal
output signal
for tand=0
output signal for
tand=constant
output signal for
tand=f(B)
Signal distortion and hB
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Basic Statistical Computations,
Sampling, Tolerance Settings,
Rejection Estimation, AQL Prediction
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Passive Electrical Components are always mass produced on automatic or semi-automatic
lines. The target of any such production line is to have no manual interference once it has
been set for a particular type of product (usually denoted by a Part Number).
In actual practice, a method of Statistical Quality Control (SQC) is adopted whereby samples
of the parts (either at the semi-finished or at the finished stage) are taken from the line at pre-
determined intervals and checked for the desired properties as set by the validated design.
For ferrite core production, SQC is practiced at the Pressing stage on the green cores (semi-
finished parts); after the Sintering stage on the sintered cores (semi-finished parts); and after
the Finishing (Grinding / Gapping / Lapping / De-burring) stage on the finished parts.
Similar SQC is also adopted for Ferrite Powder production.
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Quality Control of Electronic Components
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In the mass production of Passive Electronic Components, it is not generally possible to have
a 100% check on the semi-finished and finished parts to maintain productivity and achieve
economy.
But it must be noted that these components are to be used in electronic products that are
always subject to 100% performance test for warranty.
Hence the SQC process must be reliable to guarantee the performance of the entire
population based on the test done on the sample parts.
If the sampling is imperfect and the lot passes through it becomes a Customer’s Risk with
ensuing Quality Claims and loss of the manufacturer’s goodwill.
If the lot is held back owing to dubious sampling it becomes a Producer’s Risk adding to extra
cost of re-work, derogation or rejection. In both cases it is the manufacturer who is affected.
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Importance of Sampling
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To ensure a fool-proof sampling, certain plans as the IEC 410, are adopted. Depending on the
parameter, complexity and time of measurement, the normal or the reduced sampling plan is
taken.
For ferrite cores, dimensions, AL are subject to normal sampling and core loss, hysteresis loss,
saturation / DC bias, temperature coefficient etc are subject to reduced sampling.
It must be noted that all sampling plans are based on a Normal (Gaussian) probability
distribution of the parameter and calls for authentic unbiased sampling from the entire
population.
This implies that for on-line sampling the frequency (time-interval) for sampling must be properly
maintained.
For off-line sampling, the samples must be drawn from the entire time-span and machine-span
of the population, as applicable.
54
Sampling Plans
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Attributive Sampling is done by Go-NoGo gauges for checks on physical deformity, visual
inspection for physical irregularities, measurement related to material property as core loss, hB, DC-
bias, aF etc. The pass bands for such properties are usually customer approved and validated at
the design stage.
Attributive Sampling may use the normal or the reduced plan.
If the sampling fails the stipulated Acceptance Limit, the lot has to be either reworked, or
derogated or outright rejected.
Proper records of Attributive sampling ought to be kept for DFMEA and PFMEA purpose and for
technical customer negotiation, product costing.
Quantitative sampling refers to continuous parameters as dimensions, AL which have upper and
lower tolerance limits.
The result of any such sampling sums up in the Mean (Average) and the Standard Deviation.
These two are denoted by the Greek letters m and s respectively and they need be recorded
regularly.
Also to be recorded is the Range, that is the difference between the highest and lowest
measured value of a sample parameter.
55
Attributive and Quantitative Sampling
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The Capability of a Machine that produces parts with a Range R and Standard Deviation s is
given as:
Cp = R / (3*s)
The Capability of a Process that produces parts having a Tolerance Upper Limit U, a Tolerance
Lower Limit L , an observed Mean m and Standard Deviation s is given as:
Cpk = Min [ ( U-m), (m-L) ] / (3*s)
The Accepted Quality Level (AQL) of the parts produced by the process is the estimate of the
percent parts that would fall beyond the tolerance limits U and L.
The AQL is related to the Process Capability Cpk by the Normal Distribution curve.
A plot of AQL versus Cpk is shown in next slide.
56
Machine & Process Capabilities, AQL
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For a Cpk of 1.0 an AQL of 0.15% is achieved.
A Cpk of 1.67 gives an AQL below 1 ppm.
57
AQL and Cpk
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These are Core Loss, DC Bias, hB specifications for a core set.
The measurement are done on reduced sampling basis.
The following points should be noted at the sample preparation stage itself.
If there is a choice of a specific kiln for productivity reasons, all sampling should be done on that
kiln.
Else, the process validation may be tried in different kilns for the best result.
The measured value should be recorded with the kiln settings in all cases.
The customer test condition (and test coil if available) should be used for all measurement.
The estimated limits on specification are done as:
Upper Limit = Mean + 3*sigma
Lower Limit = Mean – 3*sigma
The limits should be cross-checked with cores sintered likewise having core factors (Ae, le) close to the core under test.
58
Specification Settings- Parameters with Reduced Sampling
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59
Standardization of Ferrite Cores As
Related to Their Applications
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60
Major Applications of Ferrite Cores
Power Conversion – Switch Mode Power Supplies, Inverters
Telecommunication – Filters, Splitters, Antennas, Receiver Front-end Transformers
EMI Suppression – Common Mode Chokes, Cable Shields, Absorbers
Energy Meters – Cores for Current Transformers
Magnetic Sensors -- Proximity Switches, Position Sensors, Keyless Entry Switches, Hall
probes
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61
General requirement: Dimensions of Ferrite cores
Dimensions of Ferrite cores are critical to any application:
Fitment in coil-formers
Fitment in PCB (planar cores)
Placement of final inductive product in PCB / assembly
Smooth operation in SMD lines
Uninterrupted operation of pick & place automated lines
Exact positioning of sensors
Desired ratio of dimension to wavelength for high frequency applications
Magnetic properties depend on dimensions
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62
Standardization of Ferrite cores : Dimensions
IEC 62317 – Ferrite core – Dimensions classifies the various types of cores and provides drawings and tables of their dimensions with their tolerances.
A manufacturer of ferrite cores claiming concurrence to IEC has to follow the nomenclature and dimensions along with the specified tolerances listed in the above standard.
This ensures clarity for the designer and producer using these ferrite cores.
The standard is divided in fourteen parts as in the table below.
Part 1 2 3 4 5 6 7
Core General Pot Pot-half RM EP ETD ER
Part 8 9 10 11 12 13 14
Core E Planar PM EC Ring PQ EFD
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Standardization of Ferrite cores : Dimensions
Dimensional drawing of an
ETD core (IEC 62317-Part 6)
Definition of all geometrical parameters of an RM core
(IEC 62317-Part 1)
A (mm) B (mm) C (mm) D (mm) E (mm) F (mm)
min max min max min max min max min max min max
43.0 45.0 22.1 22.5 14.4 15.2 16.1 16.9 32.5 34.1 14.4 15.2
The table of dimensions with tolerances for ETD44 is shown below (IEC 62317-Part 6).
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General requirement: Surface irregularities
Problems associated with surface irregularities in Ferrite cores
Cracks : Reduces mechanical strength, Distorts magnetic flux path, Might result in breakage at high temperature
Chips and Ragged Edges : Congestion of ferrite dust on PCB tracks, Reduction of effective magnetic cross-section
Flashes and Pull-outs : Interference in the winding space, Insulation damage of winding
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Standardization of Surface irregularities
IEC 60424 – Ferrite cores –Guide on the limit of surface irregularities define the limits on chips,
ragged edges, cracks, pull-outs and flashes on ferrite core surfaces. The standard is divided into
five parts as below.
Part 1 2 3 4 5
Core type General RM ETD, E Ring Planar*
Chips are generally defined as percentage of mating surface of the core. (Tables of chips in mm2
for standard core shapes are also listed).
Ragged edges are limited to a percentage of perimeter of the surface.
Cracks are generally defined as percentage of the thickness of the core.
Pull-outs are generally defined as percentage of the respective surface area.
Flashes generally have no limit but critical areas are listed which should have no flashes.
* Planar cores are defined by their dimensions in IEC62317-Part 9 Annex A.
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Standardization of Surface irregularities
IEC 60424 recommends visual inspection of ferrite cores at normal magnification. The standard gives an illustrative table for area and length reference for visual inspection—partly shown below.
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General requirement- Mechanical strength
A Ferrite core must necessarily have the required mechanical strength:
To be transportable to the customer.
To be suitable for assembly in a coil-former either manually or in an automated pick-and-
place line.
To withstand the stresses developed during gluing/potting after final assembly as an
inductive/sensor part.
To withstand the vibration requirement of the end user—for instance AEC Q200.
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Standardization of Mechanical strength
As the requirement of mechanical strength of a Ferrite core would depend on the application and vary from one end user to another, IEC 61631 specifies the Test method for mechanical strengthwithout any limits.
Tests for Compression W, M and I; for tension T and tests for canti-liver strength E are defined in the standard. The E, M and T tests are shown.
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Effective core parameters and their calculations
The inductance of any component depends on its shape and size (dimensions). The two key geometrical parameters are the effective path length of magnetic flux (le) and the effective cross-section of the magnetic flux (Ae).
IEC 60205 –Calculation of the effective parameters of magnetic piece parts --defines the formulas for determining Ae and le of different core types.
Different sections give the formulas for U, E, ETD/ER, Pot, RM, EP, PM, PQ, EFD, planar cores.
The effective parameters are also listed along with dimensions in IEC 62317 which also lists recommended dimensions for coil-formers.
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IEC 60205 --Calculation of effective parameters
The total magnetic circuit is divided into regions of similar cross-sections as shown for the
example of a pair of E cores below (k=1,..5) and the effective magnetic length le , the effective
magnetic area Ae , and the effective magnetic volume Ve are defined from the general formulas.
C2
k
lk
Ak )2
C1
k
lk
Ak
Ae
C1
C2
le
C12
C2
Ve Ae leC1
3
C22
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71
Inductance factor and its tolerance
The inductance factor AL of a magnetic circuit is its inductance per squared turn (reciprocal of the reluctance).
For a gapped core set AL depends on the effective parameters, the length of the gap and the relative permeability of the ferrite core material (AL may depend on temperature for too low gap lengths).
Designers and end users demand a specified tolerance on AL for any ferrite core set for an acceptable Quality level.
IEC 62358 –Ferrite Cores—Standard Inductance Factor (AL) and its Tolerancerecommends so for all gapped geometries of E, ETD, ER, EP, RM, Pot, PQ and Planar cores for an AQL of 0.25%.
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Measuring methods for Ferrite cores
Ferrite cores must satisfy certain electro-magnetic performance criteria in the various applications discussed.
To quantify these criteria, specific measurement of electro-magnetic properties, related to the applications, are needed.
IEC 62044–Cores made of Soft Magnetic Materials-Measuring Methods aim at standardizing these measurements to provide a consensus between the manufacturers of ferrite cores and the users. IEC 62044 is in three parts.
Part Scope Applications
1 Generic Specification
2 Magnetic properties at
low excitation level
(small signal)
Filters, Antennas, Front-end Transformers, EMI
Suppression, Sensors (general),
Energy-meters (external CT driven)
3 Magnetic properties at
high excitation level
(large signal)
Power Conversion, Splitters, Special sensors,
Whole current meters, Common-mode chokes
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Small and large signal measurements
Small Signal
Parameters
Applications Large Signal
Parameters
Applications
Inductance All
Initial Permeability
Telecom, EMI, Sensors
Amplitude Permeability
Power conversion
Loss Tangent Core loss
Hysteresis loss
TelecomSaturation /
DC bias
Power Conversion,
Common mode
chokes, Splitters,
Whole current
meters, Sensors
THD
Temperature
coefficient
Telecom, Sensors
Curie temperature All
Frequency
response
Telecom, EMI
Normalized Z EMI
Conductivity gp Telecom
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Soft Ferrite Material Classification
IEC 61332 – Soft Ferrite Material Classification is a standard with the view to:
Guide a designer to select the most applicable ferrite material for his application
Assist customers to compare the performance of ferrite materials of different suppliers
Provide a uniform benchmark for suppliers to publicize their ferrite materials
Help users tabulate ferrite materials of different suppliers for cross-reference
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IEC 61332 – Soft Ferrite Material Classification
IEC 61332 provides classification on three subjects as below. A ferrite manufacturer may indicate more than one class where a material may fall, if so desired.
Class Main Application Application
Temperature
Parameters
SP Signal Processing
(small signal)
25oC Frequency, Initial permeability, Loss
tangent, Curie
Temperature
IS EMI Suppression
(small signal)
25oC Frequency, Initial permeability,
Normalized impedance, Curie
Temperature
PW Power
Conversion (large
signal)
100oC Frequency, Initial permeability,
Performance Factor*, Core loss density,
Amplitude Permeability
* Performance Factor (PF) of a material is the plot of the product of peak flux density and
frequency at constant loss density and temperature versus frequency.
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IEC Classification of Speedofer ferrite materials
Small Signal Speedofer
Material
IEC-61332
Classification
Large Signal
Speedofer MaterialIEC-61332
SFA05 SP9, IS6a SFP3 PW1b
SFN4 SP6, IS5a SFP4 PW2b
SFA07 SP10b, IS8a SFP4 PW3a
SFA07 SP10a, IS8a SFP42 PW4a
SFA10 SP11a, IS8a SFP5 PW4a
SFA43 SP9, IS6a SFP41 PW4a
SFA05 SP9, IS5b
SFA12 SP12a, IS9a
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ISO9001 Consideration for Soft Ferrite
Product Development
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78
Customer Enquiry
Any Product Development begins with a Customer Enquiry.
A detailed enquiry helps the Product Development Process.
Sales / Marketing should be responsible for generating a clear and detailed enquiry before
passing on to Product Development Engineers.
A typical format for enquiry is attached. In case the customer misses out any point, it
should be the job of Sales / Marketing to collect the necessary information and complete the
enquiry.
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79
Semi-finished Specifications for Ferrite Core
Soft Ferrite cores have certain generic specifications related to the basic ferrite material.
Core loss, Saturation , hB, tand, aF, zn, m-T, ma are all material related specifications and are
not dependent on the final AL value or gap.
In some cases (DC bias, Saturation, aF) these are measured as generic property for a pre-
selected gap.
Based on these measurement done on a reduced sampling basis a sinter lot may be
released for finishing operation.
These are called Semi-finished Specifications.
Generally these measurement are made with standard test coils and condition.
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Finished Specifications for Ferrite Core
Semi-finished Specifications thus apply to a ferrite cores having a particular geometry and material.
Such cores may have different AL values depending on the gap. The test coils and condition may depend on customer.
These are called Finished Specifications.
The Finished Specifications are generally customer specific.
In case the customer the customer has a special requirement, a customer specific Semi-Finished Specification will also be needed.
These must be clarified at the enquiry stage itself with the customer.
Sales/Marketing must obtain all customer specific test coils.
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Datasheet and Customer Approval
To avoid misunderstanding with customer it is best to have a tentative specification approved
by him at the beginning.
This approval is to be obtained in a format called Datasheet.
Product Development must formulate the Datasheet and forward it to Sales/Marketing for
getting customer approval.
The product price is to be offered based on the Datasheet.
On receipt of an approved Datasheet only a product is to be developed.
The Datasheet must mention all applicable Finished and Semi-Finished Specifications and test
conditions in a format.
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Enquiry Classification for Ferrite Cores
Customer Enquiries may be classified as three types.
Type A: Either an existing product or that requires no change or new introduction in semi-finished specification but just a minor change in gap to achieve the desired finished specification within AQL. Product Development and Marketing may directly quote against such enquiries.
Type B: The customer drawing matches an existing drawing but the material properties (semi-finished specifications) do not match any existing product. Alternatively, the semi-finished specifications also match but meeting the desired AL tolerance within AQL may need process verification. In all such cases Product Development / Marketing must obtain clearance from Process Engineering before quoting for such enquiries.
Type C: The customer drawing does not match any existing tooling. Product Development / Marketing must get an estimate for tool and clearance from Process Engineering to quote.
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Contract Review / Order Acceptance/ Design Validation
Orders against Type A enquiries may be accepted without any Design Validation and Datasheet
approval by customer. (Customer test coils if needed must be collected in all cases).
For Type B, Sales / Marketing must obtain initial approval of Datasheet to begin Design Validation by Product Development and Process Engineering. Based on the Validation, the final revised Datasheet has to be approved by customer for production.
For Type C, Tool Engineering must prepare a detailed drawing showing all chamfers, radii for customer approval. On drawing approval by customer, the tool has to be procured for Design Validation by Product Development and Process Engineering. Based on the Validation, the final revised Datasheet has to be approved by customer for production.
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84
Ferrite Materials - Characteristics
& applications in Current Transformers
in Energy-meters
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85
Ferrites in Energy-meter applications
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Ferrite ring cores have been accepted as current transducers in static Energy-Meters.
The ferrite ring core is used as the core material of single-turn bar primary current transformer
carrying the primary load current with adequate secondary turns.
The secondary current of the transformer is used as a proportional input to the processor of
the Energy-meter thus providing a Galvanic isolation between primary and secondary.
The current transformer is also potted in resin making it tamper-proof.
86
Errors in current transformers
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A current transformer has two sources of error which affect its performance in Energy-meters.
Ratio error: Ideally the ratio of secondary current to primary is 1/Ns where Ns is the secondary
turns but losses in the transformer core introduces a deviation. The losses at power
frequency in ferrites being negligible the ratio error in current transformers with ferrite cores is
well within the limit of 0.5% for Class 0.5 meters, the most accurate class.
Phase error: Ideally the secondary current is exactly in phase opposition to the primary
current but owing to the finite permeability of the core material there is a deviation. The
phase error is inversely proportional to permeability of the ferrite material. Typical phase error
requirement is 30 minutes.
87
Current transformer types
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A current transformer in Energy-meter may carry the total load current in its primary. Then it is
called a whole-current meter.
Alternatively, the current transformer may carry a fraction of the load current which is the
secondary of an external current transformer. Then it is called an external CT driven meter.
For a whole-current meter for placement on a live conductor the current transformer has to
fulfil the DC superposition test where a half-wave rectified current is injected in primary (circuit
in next slide) and the reading of the Meter under test has to be within 3% error from the
standard meter. The core material for this test has to have a high saturation flux density. This
is in addition to the ratio and phase error requirement.
For placement on neutral conductor and for external CT driven meter the DC superposition
test is not needed and the ratio and phase error requirement is enough.
88
Current transformers in energy meters
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89
DC superposition test of current transformer
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90
Ferrite materials for ring cores in current transformers for energy-meters
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Speedofer Material SFA07Speedofer Material SFN41
91
Ferrite Cores in Lighting
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92
Schematic of a Lighting Converter
In a lighting converter as shown below the current depends on the saturation flux density and the
permeability of the ferrite ring core and the regenerative switching voltage is derived from the B-H
loop of the ferrite material.
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H in A/m
B in
mT
Contraction of the B-H loop of a ferrite material from 25oC to 100oC
DB25DB100
93
Contraction of B-H loop at high temperature
The B-H loop of all ferrite materials contract at high temperature as shown in the curves and
vanishes above the Curie temperature. Thus the regenerative switching voltage reduces with
increasing temperature causing possible failure.
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Ring core ferrite material characteristics
Desired characteristics for circuit performance of the ring core ferrite material in a lighting
converter are listed below.
High permeability to reduce the number of turns needed to drive the core to saturation in
each half-cycle.
Sufficient expanse of the B-H loop for regenerative switching action at the maximum
operating temperature.
A Curie temperature well above the maximum operating condition.
A comparison between Speedofer material SFA05 and typical competition is shown below.
Parameter Speedofer
SFA05
Competition1 Competition2
Permeability 5200 +/-25% 5000+/-25% 2000+/-25%
Saturation flux density Bs at 25oC 460 mT 400 mT 480 mT
Saturation flux density Bs at 100oC 320 mT 260 mT 380 mT
Remnance flux density Br at 25oC 150 mT 150 mT 180 mT
Remnance flux density Br at 100oC 135 mT 130 mT 100 mT
DB at 25oC 310 mT 250 mT 300 mT
DB at 100oC 185 mT 130 mT 280 mT
Curie Temperature > 160oC > 120oC > 220oC
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Ring Core permeability vs temperature curve
This is another important characteristic of the ring core for the CFL to function without flicker and
not to draw excessive high current.
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96
Gapped core ferrite material characteristics
The gapped core is used as a
part of the inductor (ac-choke) in
the converter and carries the
alternating load current. The
desired properties of the ferrite
core for circuit performance are
listed below. Low core losses at the operating
condition of frequency, flux density and temperature.
Stable inductance at all operating condition for constant frequency (controlled by gap).
Sufficiently high saturation flux
density at the operating
temperature to avoid malfunction
at high input voltages. Curie temperature well above the
maximum operating condition. Comparisons between Speedofer
SFP4 and competition is shown next.
Parameter Speedofer
SFP4
Compe-
tition1
Compe-
tition2
Bs at 25oC 490 mT 500 mT 480 mT
Bs at 100oC 390 mT 350 mT 380 mT
Curie temp. >210oC >220oC >220oC
0
200
400
600
800
0 20 40 60 80 100 120 140C
ore
Lo
ss k
Wm
³
Temperature °C
Speedofer Core Loss kWm³ Typical Compititor Core Loss kWm³
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LED Lighting
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98
Salient Features of LED Converters
LED Lighting circuits use different converter topologies—buck, boost, buck-boost
The conversion frequency generally varies from 50 kHz to 200 kHz
Line Switches are frequently used as the power semiconductor—typically at 66 / 132 kHz
The operating temperature is quite high, typically close to 100°C
The converter circuits need be compact with large area of heat dissipation
LED lighting is widely used in automotive sector where the converters are exposed to varying
ambient conditions
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Ferrite cores for LED Lighting
The choice of power ferrite material and core shapes for LED Lighting is governed by the
features shown in the previous slide.
The ferrite material must have low core loss at the typical frequencies of application and
operating temperatures.
The ferrite material must have high saturation flux density at the operating temperature to cater
for high input voltages.
The ferrite material should have a sufficiently high amplitude permeability for un-gapped
applications to reduce input current and hence winding loss.
The ferrite material must have sufficiently high Curie Point to cover all operating condition.
For Automotive application the ferrite material should have a flat loss-temperature curve to
cater for shifting ambient.
The ferrite core should have the best dissipation area and EFD, PQ , RM cores are preferred
for this reason.
PQ cores also have the best area product for the same footprint and have a near-closed
magnetic circuit to contain leakage flux.www.speedofer.com
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Author’s Bio-data
Academics & Professional Experience
B Tech. in Electronics and Electrical Communications Engineering from IIT – Kharagpur in 1975
Currently Technical Advisor to Speedofer Components Pvt. Ltd., Greater Noida – Uttar Pradesh, India from 2013
General Manager – Development in EPCOS India since 1998 to 2013
Had been self-employed as a Technical Consultant from 1987 to 1998 to a number of small-scale units in Kolkata and Dhaka
for manufacturing various electronic products.
Worked as Technical Manager in M/s Krugg Engineers Private Limited, Kolkata from 1982 to 1987
Worked as Development Manager in M/s Opto-Electronics Industries Private Limited, Kolkata from 1978 to 1982
Worked as Scientific Officer C in BARC, Trombay from 1975 to 1978 on the mathematical modeling and analysis of
Electromagnetic Fields
Notable achievements:
i) Design-in with Static Energy-meter manufacturers in India and development of ferrite material T36 as core material for
current transformers.
ii) Design-in with CFL manufacturers in India and introduction of ferrite material T65 as core material for the switching toroid in
CFLs.
iii) Design-in with server power supply manufacturers globally and development of ferrite material N95 as core material for
improved fractional load efficiency.
iv) Design-in with consumer electronic manufacturers for the development of ferrite material N51 as core material suitable for
low standby loss in converters.
Honors & Awards:
Member representing India at the Technical Committee 51 on Magnetic Components and Ferrite Materials of the International
Electro-technical Commission (IEC) since 2004
Convener of the Magnetic Components and Ferrite Materials Panel of the Sectional Committee LITD5 of the Bureau of Indian
Standards since 2008
Received the IEC 1906 Award in 2008 for contribution to TC 51 Project on the Limits of Surface Irregularities for Planar Cores
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Author’s Bio-data
Publications, Application-notes, Nomograms:
1) Ferrite Material N51 for Switch Mode Power Supplies, Epcos Components, May 2006 (co-author Mr. S. Goswami)
2) Ferrite Material T36 for Energy Meter-Current Transformer, Bodos Power Systems, July 2006 (co-author Mr. S. Goswami)
3) Innovative Power Ferrite Materials of Epcos-N51 & N95, Electronica, Munich, November 2006
4) Selection Criteria of Ferrite Material for Power Applications, Power Electronics Technology, Dallas, October 2007
5) Current Peaking and Energy-storage in Gapped Ferrite Core Magnetic Circuits with DC Bias used in SMPS, PCIM, Nuremberg, May 2008
6) New Power Ferrite Magnetic Material N93 with improved Saturation Flux-Density at high Temperature for extended DC- bias Capability in
Single-quadrant SMPS topologies,
CWIEME, Berlin, June 2008 (co-authors Mr. S. Goswami, Mr. J. Groger, Mr. M. Sevcik)
7) Effect of Duty-cycle on Losses, Efficiency and Throughput Power of Ferrite-core Transformers with Non-sinusoidal Flux, International
Conference on Ferrites, Chengdu, China, October 2008
8) Standardization of Ferrite-cores as related to their Applications, Seminar of LITD 5 Sectional Committee, Bureau of Indian Standards,
Bangalore, January 2009
9) Selection of a Ferrite Material to meet the Efficiency Requirement at Fractional-load in a SMPS Converter using Wound Ferrite-core
Component, CWIEME, Mumbai, November 2009
10) Guide to Selection of Ferrite-cores for Transformers in Welding Converters, Indian Institute of Welding, National Welding Seminar, Kolkata,
December 2009
11) Enhancement of Transmissible Power in Ferrite-core Transformers used in SMPS by Multiple-stacking of large Ferrite cores, Application
note, September 2009
12) Performance Analysis of Ferrites as compared to other Magnetic-materials in high Energy-chokes in Applications as UPS, Renewable
Energy Converters, Welding Inverters and Traction Converters, Application note, November, 2009
13) Computation of Losses in the Passive Components in Zero Current Switch (ZCS) and Zero Voltage Switch (ZVS) Topologies of Resonant
Converters, PCIM, Nuremberg, May 2011
14) Non-sinusoidal Core-loss Density in Epcos Power Ferrite Materials, Excel Nomogram for ready computation
15) Throughput Power and Efficiency in Ferrite-core Transformers of Epcos Power Ferrite Materials, Excel Nomogram for ready computation
16) Fractional Efficiency in SMPS Converters with Epcos Ferrite cores, Excel Nomogram for ready computation
17) Computation of Current, Inductance roll-off and Efficiency for Single-quadrant Converters using Epcos Ferrite cores with DC-bias, Excel
Nomogram for ready computation
18) Computation of Passive Component Values and Losses in ZCS and ZVS Resonant Converters, Excel Nomogram for ready computation
19) Loss Limited Synthesis of Chokes and Transformers in Power Converters with Rectangular and Circular Limb E Cores made of Power
Ferrite Materials. International Conference on Ferrites, Okinawa, Japan, April 2013
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Thank You
Mr. Probal Mukherjee, Head, Technical, Speedofer Components Pvt. Ltd.
Plot No: 101 & 102, Toy City,
Ecotech – III, Greater Noida – 201306,
Uttar Pradesh, India.
[email protected], +919830876431
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