201606_ferrites,_cmc,_and_power_transformer_(1)e

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Soft Ferrite SpecificationCMC、 Power Choke

and Transformer(A)Soft Ferrite(B)CMC(C)Power

Choke/TransformerBy Ray LaiJune 2016

Table of ContentA. Specifications of Soft Ferrites

A1. B-H Curve (Magnetizing Curve) A2. Key Specifications – Power/High Perm Materials A3. Differences between “Product” and “Material” A4. Other Specifications of Ferrites

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Table of ContentB.CMC

B1. CMC PrincipleB2. CMC DesignB3. CMC Failure Example

C.Power Choke and TransformerC1. Power ChokeC2. Coupled Inductor (Flyback Transformer)C3. Failure Example

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A1. B-H Curve (Magnetizing Curve)4

Flux density B

Permanent magnetics

Soft magnetic material

Bsat

Why is B-H curve (magnetizing curve) so important? … yet so misleading！

A1. B-H Curve (Magnetizing Curve) 5

measurable unmeasurable derivative

B-H Curve is the derivative of V-I curve at specified conditions

Electrical quantities

Magnetic characteristics


Why is B-H curve (magnetizing curve) so important? … yet so misleading！Only two laws are applied to the whole electromagnetic conversion:

Faraday’s law of induction

X’

Rotation machine

Ampere’s law

Same equation


Faraday’s law of induction

changing to integral form

The time integral of the voltage across the component is the “flux linkage”

Where the Volt-second balance comes from.

Ampere’s law

with no air gap (toroid core)

或

So the battery or any power outlet are the magnetic source which generate flux all the time?


a. B-H curve

slope = “material”(derivative)

slope = single turn inductance“core (material + geometry)(derivative ， very inaccurateif insisted to measure in this way)

slope = inductance(Only real measurable parameter)

What Ampere’s law and Faraday law of magnetic

induction are based on

Trilogy of Magnetizing Curve: (1) Complete device (2) Ferrite Core (fixed geometry) (3) Ferrite material


The derivative of flux linkage to current (instantaneous slope) is the “inductance” (magneto-electrical)

The inductance L Links the behavior of the flowing through current and the voltage across a device (electro-electrical)

By Specification In Real Application1 Fixed geometry and closed loop Diversified cores with gaps2 Low frequency sine wave

excitation (1k, 10k/25kHz)Operational frequency > 50kHzMostly square wave or pulses

3 All specs are tested under low flux density case except Pv

Flux density pushed as high as possible(reducing core size)

4 Bsat (you never dare to apply) Bmax (A design choice restricted by the core size and material)

Why is B-H curve (magnetizing curve) so important? … yet so misleading！


B-H curve is a “derivative” property that 1. It is obtained from a fixed closed-loop geometry (toroid)

why? Most power applications use cores other than toroid and almost always with gaps

2. It is obtained from a fixed condition (low frequency sinusoidal excitation), why? Most SMPS drives the core in mid-to high frequency range (50k~2MHz) by PWM square-wave like excitation

By the above two reality, the ferrite’s material specifications (especially the B-H curve) are like TV commercials most of the time. what you see is not always what you get!

A1. B-H Curve (Magnetizing Curve) 11 Typical soft ferrite datasheet

A1. B-H Curve (Magnetizing Curve) 12 Look at the specification, which stage of the ferrite in

your mind?This or these?


Fe2O3

MnO2

ZnO……

Ferrite production is a time consuming process with high variations. It can be seen form the sheet that “tolerance” is usually high.


Bsat= 520mT obtained at H =1200A/m, just for brag!

Only when Hmax (<150A/m) ， there is or permeability ， over it the core goes to saturation and no usable inductance for SMPS

For ferrites, only this short portion is good for SMPS/filtering application

P4 B-H Curve (ACME)

A1. B-H Curve (Magnetizing Curve) 15 Only ferrite industry does the brag? It’s a common practice in magetics

Silicon Steel case:

=79.58A/m


Large scale in PDF is useless but everybody does it this way

B-H curve on printed page is useless if the resolution is low. B-H curve can be manipulated like the I-V curves of diodes and transistors.


Only Ferroxcube does it better, amplified the low H region. The rest are useless where it’s needed


B-H curve is an important material quality index for its maker. All the product roadmap and application classification are based on the B-H curves.

On the other hand, in real application, the core’s mechanical property (geometry and gap, etc.) plays the same important role as the material property. The are complimentary to each other is magnetic devise design with ferrites.

Beside the material specification and its limitation,a magnetic component engineer must also know the role that the core geometry plays to provide justified designs in various applications (adapter, converter, and WPC, etc.).

A2. Specifications – Power/High Perm Materials19 Ferrite’s main material specifications

a. Permeability and (from B-H curve)

b. Saturation flux density Bsat andThe maximal workable flux density Bmax @ highest applicable Hcore

c. Core loss density Pv

d. Effective bandwidth

Other Specifications:

Remanence Brms 、 Coercivity Hc 、 Hysteresis Material Constant ηB 、 Disaccommodation Factor (DF) 、 and Quality Factor (Q)

In Power and Filtering applications ， the weight of each specification is different

20 Permeability and

Freq. Flux den. Temp. P45 P46 P47

Initial Permeability μi ≤ 10KHz 0.25mT 25°C 3100 ± 25% 3300 ± 25% 3000 ± 25%

25°C > 5000 > 4500 > 5000

100°C > 5000 > 4500 > 5000

Unit Measuring Conditions Wide Temperature Low Loss Materials

Amplitude Permeability μa 25KHz 200mT

Symbol

On the sheet, and are just fixed numbers which is the typical values of a set condition.

In fact, permeability is a nonlinear function with strong temperature and load correlation.

“Load”…… Does it mean voltage or current?

A2. Specifications – Power/High Perm Materials

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Permeability of Power Ferrite is a function with strong temperature correlation.

A2. Specifications – Power/High Perm MaterialsPermeability and

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So does the high-permeability materialAny thing fishy found?


A121/A151 were not fully/correctly sintered

A13 is no use in real temperature range

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Permeability vs. Frequency is as important as Permeability vs. Temperature


A121/A151 were not fully/correctly sinteredas there is no “resonating peak” which is supposed to exist

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If TSMP (the second maximal point) lies in 20~30℃, it will render the high-perm material out of spec in higer temperature range

N42, telecom CMC/filtering material


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Permeability is a function of load, depicted by COUPLING the Faraday’s induction law and the Ampere’s law ：

Under closed loop core, when then

This equation is not valid with “big”

gap. That is, Faraday and

Ampere’s law are decoupled when

fringing effect cannot be ignored

There is no simple formula for under big gap scenario


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Permeability is a function of load

If the current is sinusoidal ， then the voltage is the same form with phase lag.

Taking out the time varying term


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Permeability is a function of load

(in fact, only LI is certain, not L) means under the load (), the generated flux linkage for magneto-electrical conversion.

So it is important to understand that it’s the flux linkageΛ supporting the conversion, not the flux density . The design is to make sure the core size/material can sustain the Λ without beyond the limit to have the conversion failed.

Permeability and


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Things are even more clear by SMPS square-wave drive

means under the load (), the generated flux linkage for magneto-electrical conversion

Volt-second balance is the key of E-M conversion

The area (V x time) in positive and negative period is equal (V-T balance)


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ui actually is ua under extreme low load situation

A2. Specifications – Power/High Perm MaterialsPermeability and How about ?

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B-H curve is a “Hysteresis loop” (Pętla histerezy)

Flux Density B[T]

Magnetic Residue Br

Coercive Force Hc

Magnetic FieldH [A/m]

Saturation (Bsat)

Hmax


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Przenikalność początkowaInitial Permeability

0H0i H

Bµ1µ

0.1mT

A2. Specifications – Power/High Perm MaterialsPermeability and and many

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µi initial permeability

µm maximal permeability

µa amplitude permeability

µdif or µrev reverse permeability

)1.0,25(

)1.0,25(

)1.0,25(

)( mTBkHzf

mTBkHzf

mTBkHzf

ACDCrevdif

ACa

ACi

iiii


33 DC-DC Application udiff or urev

HHrev

ACHB

µµ

0

1


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Reversible permeability at different operating points


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Why in most case, no big deal if ui and ua are not differentiated? The effect of load is not noticed generally. And except extreme case, the effect of temperature is not so critical?

Case 1: if it’s an inductor, it’s because of air gap, by T25x15x10, le=60.18mm= 60180um


Gap flattens the curve

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Case 1: the bigger the ui ， the stronger the gap effect ， ue (equivalent permeability with gap) gets flattened faster

𝜇𝑒≈𝜇𝑖𝑙𝑒

𝑙𝑒+𝜇𝑖 𝑙𝑔


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P48 T25x15x10


B-H Curve without (red) and with (green) gap

P48 T25x15x10

Hair

Hcore

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Open loop: rod/tube

RFID ferrite bare can use Area/Lengthratio to get similar table

A2. Specifications – Power/High Perm MaterialsPermeability and have no difference under extreme

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Case 2: For transformer (except flyback), it is due to that the magnitude of the magnetizing current is much smaller than the load current


Sketch of transformerIdeal transformer model

Sketch of flux linkage and the equivalent circuit model

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Winding intrinsic inductance and leakage

From B-H curve

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Using the B-H curve of ACME P45 T25x15x10_100℃

In sinusoidal drive



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Time

49.950ms 49.955ms 49.960ms 49.965ms 49.970ms 49.975ms 49.980ms 49.985ms 49.990ms 49.995ms 50.000msi(R1)+i(R3)

-100mA

0A

100mA

SEL>>

i(R1) i(R3)-10A

0A

10A10A

100mA

Magnetizing current contributes very tiny portion of the overall current thus the nonlinearity is tolerable

Input/output current

Magnetizing current



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Square wave drive



Using the B-H curve of ACME P45 T25x15x10_100℃

Time

19.970ms 19.975ms 19.980ms 19.985ms 19.990ms 19.995ms 20.000msi(R1)+i(R2)

0A

20mA

-30mASEL>>

i(R1) i(R2)

-10A

0A

10A

44

15A

30mA

In SMPS, the Lm and are important design topics

Input/output current

Magnetizing current



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Ferroxcube 3C95 “material” specification (on the paper)Pv @100kHz/200mT/25 = ℃ 350mW/cm^3Pv @100kHz/200mT/100 =℃ 290mW/cm^3

Ferroxcube 3C95 “product” specification (things you get and cannot complain!!)PQ26/25

Pv @100kHz/200mT/25 = 4.0W/6.530cm^3=℃ 613mW/cm^3Pv @100kHz/200mT/100 =3.8mW/6.530cm^3=℃ 582mW/cm^3

PQ35/41Pv @100kHz/200mT/25 = 11.5W/18.5cm^3=℃ 622mW/cm^3Pv @100kHz/200mT/100 =10.8W/18.5cm^3=℃ 584mW/cm^3

Pv Issue - which most of the tricks play here


46 Pv Issue - which most of the tricks play hereA2. Specifications – Power/High Perm Materials

Anyone can show his ferrite is better than others, depending who knocks your door

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Material Specification from TDK

Pv Issue - which most of the tricks play hereA2. Specifications – Power/High Perm Materials

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PQ32/25 Ve=12.44cm^3

30℃ Pv= ~ 580mW/cm^3

100 ℃ Pv= ~400mW/cm^3

80 ℃ Pv= ~335mW/cm^3

Pv on Pg. 46 and 47 do not exist in real world


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By comparing Pg. 46 to 48 ， for Pv Issue1. Pg. 46, 47 are for “material” ， T25x15x10 closed loop

core used.

2. Pg. 47 is for “product”, the real core used in power transformer design (PQ). It can be seen that the Pv vs. temp trend is shifted in all vendors (slightly better in TDK). All materials shows Pv_min at 100℃ but all real product shows in between 80~90 ℃. This is the tradeoff between quality and cost (also the practical manufacturing limitation) .

3. All paired cores will have higher Pv due to air gap, no matter how smooth the contact surface is.

4. Your odd of really catching the Pv difference is slim in most cases ！


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TDG TPW33 Pv = 469mW/cc @ 100 / 200mT/100kHz℃ DMEGC DMR95E Pv = 480mW/cc @ 100 / 200mT/100kHz℃

Competitors Benchmark Reference

　 PQ cores losses (kW/m^3)

25℃ 100℃ Note

DMR95E PQ26/20 447.81 551.53 5pcs from customer

TPW33 PQ26/20 548.06 574.24 5pcs from customer

3C95 PQ26/20 & 20/20 480.23 446.00 10pcs from FXC product batch

3C95 Material Pv spec 350 290 HB2009

3C95 smaller core Pv spec 590 560 HB2009

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Pv will be an issue only in transformer applications (including flyback)


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affects the inductance and power losses, along with the operational stability

Pv will be an issue only in transformer applications (including flyback)


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Critical in common mode choke design selection

Another important ferrite specification that sets the application limitation on high per material


Which means that, for higher perm material to have wider frequency response is against the law of physics.

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where:fg – gyromagnetic critical frequencyγ ~0.22 ΜΗz m/A is the gyromagnetic ratio for an electron

i.e. the ratio of magnetic moment and torqueBs – saturation flux densityμi,0– initial permeability * J. L. Snoek, Physica 14, 207, 1948

sig Bf 34)1( 0, Snoek Limit


For higher perm material to have wider frequency response is against the law of physics.

55 Characteristics of Mn-Zn and Ni-Zn Ferrite in the sense of ui vs. frequency All governed by Snoek limit.


Limit is here roughly by the advances of ferrite research

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In the real application (such as CMC), not always the higher initial the better

Note ： the mass-production A151’s bandwidth and will be so good or not is really another question

　 Z (Ω)Hz A07H A151100k 1.648E+03 3.343E+03150k 2.568E+03 4.109E+03200k 3.517E+03 4.609E+03500k 9.086E+03 5.938E+031000k 1.486E+04 5.938E+03


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A3. Differences between “Product” and “Material”A101EP7L in CMC with 80 turns of winding The common mode resistance’s real measurement

Note that Peak close to 300kHz

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A3. Differences between “Product” and “Material”A101EP7L in CMC with 80 turns of winding The differential mode resistance’s real measurement

Note that Peak close to 900kHz

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A3. Differences between “Product” and “Material”A101EP7L in CMC with 80 turns of winding The common mode resistance calculated from and table

Big difference from the real measurement,WHY?

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High turns’ number makes the parasitic capacitance dominant

𝑍 𝑐𝑜𝑟𝑒=(𝑁2𝜔𝜇0

𝐴𝑒

𝑙𝑒)¿

𝑍 𝑐𝑎𝑝=1/ 𝑗𝜔𝐶𝑝

|𝑍𝐶𝑀𝐶|=|( 1𝑍𝑐𝑜𝑟𝑒

+ 1𝑍 𝑐𝑎𝑝 )

−1|

When no parasitic capacitance, the CMC impedance is

With parasitic not ignorable,

A3. Differences between “Product” and “Material”

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A3. Differences between “Product” and “Material” By just 4pF parasitic capacitance added in the calculation, the CMC impedance changed totally (from light blue to purple line as show below)

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The core is qualified under few turns of wire to minimize effect of external R and C. If mass-production windings was not adopted in the very beginning, it is not the fault of core makers.

A X’fmer using P4PQ26/25， the customer specified that under 100kHz,1V condition, LS=110uH+/-25% by the real bobbin and windings. It’s a 4 layer copper film wiring structure.

Problem ： From the Ls vs. frequency measurement, L increases dramatically after 10kHz and peaks around 60kHz. The customer wished to control the inductance of 100kHz, but it’s found difficult to control, it is very sensitivity external disturbance, by holding the cores tighter or looser can have the inductance vary from 100 to 200uH.

A3. Differences between “Product” and “Material”Real Case: Core is core, transformer is transformer. Core is part of the transformer, not “the transformer”

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Because of the bobbin, after this point, the Z becomes capacitive, this point is the resonant frequency. The right Z-frequency figure can show this more intuitively.


64

From the AL vs. freuqnecy figure (by 10 turns), it can be seen that the core is absolutely OK.

Core is innocent in this complaint！！


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9.11 Updated test with different bobbins

# 10TS AL 禾旺線圈松貿線圈 1# 松貿線圈 2# 1 5212 139.8 193.9 171.4 2 4955 120.1 156.9 138.8 3 5638 131.1 208.8 206.9

1、 Test： 100kHz，1V 2、禾旺線圈和松貿線圈測試的產品存在較大差異。 3、 No regularity can be found for all different makers’ bobbins!

Ferrite maker cannot be responsible for the finishedd products

This is a typical example when the magnetic component engineer did not pay attention to the differences between “Product” and “Material”!!


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Other main specifications are listed below ( except item 6 is the “finished product” spec related to power and filtering application, the rest are mainly for signaling and filtering applications)

1. Remanence Brms and Coercivity Hc,

2. Loss Factor ,

3. (Hysteresis Material Constant ηB,

4. Disaccommodation Factor (DF) and Temperature Factor of Permeability (αF)

5. Total Harmonic Distortion (%THD)

6. Quality Factor (Q) [mathematically, Q is , but there is difference in real applications]

.

A4. Other Specifications of Ferrites

67 Ferromagnetic Material

Magnetic Field H

Flux density BPermanent magnetics

Soft magnetic material

Bsat

Brms1

Brms2

Brms3


68 1. Remanence Brms and Coercivity Hc

Brms is the core’s residue flux when H=0

Hc is the opposite H needed for removing Brms Brms and Hc are the important indicator to distinguish soft from hard magnets.

The area of the B-H curve encompassed by Brms and Hc is the energy loss density.

Unit of H Unit of B why?


69 The vector dot integral on and will obtained the loss density of the core . (unit )

(unit ) To reduce the loss, Brms and Hc mus be as low as possible

☆ Usually NiZn material has higer Brms or lower Bsat/Brms ratio, thus sometime the misjudgment happens

Low Loss Material EMI-Suppression Material Low Loss Material

Freq. Flux den. Temp. P41 K15 K081

Initial Permeability μi ≤ 10KHz 0.25mT 25°C 2400 ± 25% 1500 ± 25% 800 ± 25%

25°C 495 330 41025°C 170 200 27225°C 11 10 27

Symbol Unit Measuring Conditions

H=1200A/m

mT 10KHz

Saturation Flux Density Bms mT 10KHz

H=1200A/m

Coercivity Hc A/m 10KHz H=1200A/m

Remanence Brms


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LS(uH)DCR

AppliedVoltage

LS(uH) LS(uH)DCR

AppliedVoltage

LS(uH)

BeforeDCR （mV）

AfterDCR Before DCR （mV） After DCR

1 128 36.6 0.326 8.91E-03 129 3.80 127 41.6 4.25 1.02E-01 104 43.622 132 38.2 0.339 8.87E-03 134 3.79 131 42.1 4.45 1.06E-01 112 45.153 130 47 0.298 6.34E-03 132 2.70 129 38.3 3.85 1.01E-01 111 42.884 132 36.8 0.32 8.70E-03 133 3.71 129 40.5 4.22 1.04E-01 104 44.455 128 37.2 0.331 8.90E-03 129 3.80 129 41.8 4.3 1.03E-01 102 43.886 131 35.4 0.326 9.21E-03 133 3.93 133 40.8 4.19 1.03E-01 105 43.867 129 35.2 0.313 8.89E-03 130 3.79 128 40.5 4.15 1.03E-01 101 43.738 129 48.8 0.318 6.52E-03 130 2.78 129 39.5 4.13 1.05E-01 102 44.639 129 39.8 0.31 7.79E-03 130 3.32 129 39.5 4.1 1.04E-01 99 44.2510 129 33.4 0.298 8.92E-03 130 3.81 127 38.4 3.99 1.04E-01 102 44.38

ACME Inductance Check before/after DCR test 2014.9.24

Sample #

K081T14*8*9CTest Condition: 100kHz/0.1mAWinding: 0.5mm*14TsACME: WK3620 Precision Bridge

MDM016552000

DCR(mΩ) DCR Idc (A) H (A/m) DCR(mΩ) DCR Idc H (A/m)

Measured by local instrument

DCR GainKaiTa 502B

If the unbalanced type of multi-tester is used to measure the DCR, it will encounter the inductance drop after DCR measurement. It is affected by the Brms (especially in NiZn) and this is the key source of complaint and controversy.


71 The way multi-tester measure DCR is pouring as much current as possible till the minimal resolution voltage can be obtained. This will cause the ferrite to stay closely to Brms point after the measurement. When measuring the inductance again, of course the inductance will be lower (as L is the derivedslope of B-H curve).

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 2000

50

100

150

200

250

300

350

400

450

500K081 Saturation Flux Density V.S. Magnetic Field

H (A/m)

B (m

T)A4. Other Specifications of Ferrites

72 2. Loss Factor Ferrite’s permeability model is a complex number with the loss in the imaginary part, so the inductance is a complex number and function of frequency. 3

)

Where is very important in EMC/EMI applications such as CMC. Loss factor is defined as the tangent of the real and imaginary part of “Loss Factor”


73 2. Loss Factor

From the measurement condition, it is know that is not a “power” specification. It is in signal level. Only MnZn or NiZn for EMI/EMC filtering will have this specification listed.

Freq. Flux den. Temp. A10 A102 A121 A151

Initial Permeability μi ≤ 10KHz 0.25mT 25°C 10000 ± 30% 10000 ± 30% 12000 ± 30% 15000 ± 30%

10KHz < 10 < 10 < 10 < 10

100KHz < 60 < 60 < 60 < 110

25°C 410 380 380 400

100°C 210 180 180 170

High Permeability Materials

25°C

Saturation Flux Density Bms mT 10KHz H=1200A/m

tanδ/μi

Symbol Unit Measuring Conditions

10-6Relative Loss Factor < 0.25mT


74 2. Loss Factor

represents the sum of all intrinsic core losses (hysteresis, eddy current, and residual losses); itself is also a function of frequency and load.

If ui=10,000, it means the decay of signal will be 1/ with a phase angle of 45∘at 100kHz, this is an important topic if filtering and feedback control.


75 3. Hysteresis Material Constant ηB This parameter extracts the hysteresis part only from the loss factor

(unit as shown below

( in 1.5~3mT usually)

This is an intrinsic material property, forknowing the core’s quality, normally

Power material usually does not list this parameter, some vendor even skip it in high perm material, as this is a more material basedspecification. In real application, it is the overallloss/performance that matters


76 4. Disaccommodation Factor (DF) and Temperature Factor of Permeability (αF)

Disaccommodation is understood as a time variation of the initial permeability occurring after each demagnetization under constant operating conditions. It has been proven by experiments that initial permeability decreases in a linear way by plotting time on a logarithmic scale.

(unit: dimensonless

In real practice, only under the special and important circumstance (e.g. space) and need uninterrupted service, will this parameter be paid attention to. (Can you see what’s missing in the test condition?)

　Symbol Unit Measuring Conditions High Permeability Materials

Freq. Flux den. Temp. A10 A102 A121 A151Initial Permeability μi 　 ≤ 10KHz 0.25mT 25°C 10000 ±

30%10000 ±

30%12000 ±

30%15000 ±

30%

Disaccommodation Factor DF 10-6 10KHz <

0.25mT 25°C < 2 < 2 < 2 < 2


77 4. Disaccommodation Factor (DF) and Temperature Factor of Permeability (αF)

DF checks the variation over time, αF checks the case of temperature variation

(unit:

is independent from gap, so the inductor’s variation over temperature can be written as

Note, as the TSMP concept introduced earlier, if the gap is small, the selection of temperature points is critical. If gap is big enough, this parameter has no particular use in general. So this is a parameter for the “stability” over temperature only applied in special occasions.

Power material does not list it generally.


78

Even with big enough gap, general ferrite’s ui vs.Temp characteristics will have the design failed under extreme condition. Only special NiZn can have nearly temperature independent permeability

Everything in life is a result of trade-off and compromise, so does ferrite’s specification.

The trade-off of F50 and F51 is their low Tc, for NiZn,Tc usually > 200℃

A4. Other Specifications of Ferrites 4. Disaccommodation Factor (DF) and Temperature Factor of Permeability (αF)

79 5. Total Harmonic Distortion (%THD) When excited by a single sinusoidal magnetic field (H: by current ), due to the non-linearity of B-H, the core will induced a voltage that is not a perfect mimic of the exciting source (, voltage is the measurable form). The summation of the Fourier components of the voltage versus its fundamental one is the THD.

is not a constant but a function of H

%THD

dB form is more generally used in communication field.


80 5. Total Harmonic Distortion (%THD)

-60dB means V3(3rd harmonic) is 1/1000 of V1(=1)

-67dB means V3 is of V1(=1)

7dB means more than doubled difference

V3/V1dB -67 -66 -65 -64 -63 -62 -61 -60

Absolute 4.467E-04 5.012E-04 5.623E-04 6.310E-04 7.079E-04 7.943E-04 8.913E-04 1.000E-03

66 vs. 67 112.20%

65 vs. 67 125.89%

64 vs. 67 141.25%

63 vs. 67 158.49%

62 vs. 67 177.83%

61 vs. 67 199.53%

60 vs. 67 223.87%

THD


81 5. Total Harmonic Distortion (%THD)

Communication type of applications generally impose strict THD requirements. But beside the material and make of the component, interference should be avoid to ensure the validity of measurement.


82 5. Total Harmonic Distortion (THD)Example by PSPICE Simulation, by 10 turns (Example in Power) * TX22_14_13_3E27 CORE model (Ae=50.7mm^2, le=54.2mm).MODEL TX22_14_13_3E27 CORE+ MS=377.56E3 A=12.672 C=.20161 K=5.5151 AREA=.507+ PATH=5.4200

Excitation(100kHz)

Magnetic FieldStrength

FluxDensity(1st)

V1 THD (B) THD (B) THD (V) THD (V)

mA H (A/M) mT Volt % (Vn/V1) dB (Vn/V1) % (Vn/V1) dB (Vn/V1)

1 0.185 1.19 0.378 0.81% -41.81 2.52% -31.9610 1.845 15.01 4.764 6.00% -24.43 18.79% -14.5250 9.225 132.49 41.590 12.62% -17.98 38.79% -8.23

100 18.450 269.07 84.761 15.23% -16.35 47.15% -6.53200 36.900 398.77 125.052 19.48% -14.21 64.61% -3.79


83 5. Total Harmonic Distortion (THD)Example by PSPICE Simulation, by 10 turns * TX22_14_13_3E27 CORE model (Ae=50.7mm^2, le=54.2mm)

B-H curve can be simulated with ferrite core model incorporated

ACME ferrite models for PSPICE can be provided


84 6. Quality Factor (Q)

Quality factor Q and loss factor are relevant, but Q usually is the indicator of a “finished” magnetic component, cautions needs to be taken for the measurement and interpretation of Q 。

Q parameter is an effective indicator for CMC or “signal” level application. If it is applied to power choke, it will be quite misleading and controversial if the basics are not carefully taken care of.


85 6. Quality Factor (Q) The concept of “Q” (quality factor) originated from the half-power point of LC resonant circuit. It means its frequency “bandwidth”, and this is the “quality” of an LC filtering circuit.

When applying Q in L only without LC resonance (no matter serial or parallel), there are things to watch out.


86

LC fixed

smaller

larger

Illustration of serial resonant circuit

6. Quality Factor (Q)

𝜔2−𝜔1

𝜔𝑠=∆𝜔𝜔𝑠

= 1𝑄

𝑓 2− 𝑓 1

𝑓 𝑠= ∆ 𝑓𝑓 𝑠

= 1𝑄



When adopting Q as the quality indicator of an inductor, just like the difference of ui and ua, if the test condition is irrelevant to the real application scenario, it is misleading and means nothing.

the flux density of the inductor in use

The inductance of the choke is

is the single turn inductance or permeance.



To have reflect the core or choke’s real quality in operation, the flux level of measuring Q, must be as close to the real scenario as possible.

Example: A core of Ae=146.67mm^2, le=61.36mm with 22 turns for power choke purpose. It will operate under Bmax >> 200mT, Using 200mT for testing the Q of this choke (no DC pure sinusoidal), the voltage required is

(assuming 100kHz switching frequency) BIG power amplifier needed ！



But the specification sheet said the Q was measured under 1Vrms/100kHz. In this source, the flux density for this test is

The Q obtained with this condition has nothing to do with the Q under 200mT. Using extreme low load Q to predict the Q of extreme high load is simply meaningless.

One may argue, generally (except flyback), the Δi 和 ΔV of DC-DC choke is small, theoretically using small Vrms value to measure the Q should be feasible. But …….

To validate this claim, Idc needs to be superimposed so , only in this way, the measured Q is justified.



Idc cannot be ignored in measuring Q ， why? and


91

7. Skin effect applies to ferrites, too

Skin depth

ρ(Ω/m) 5　　　　μo 1.26E-06　　　　μr 3000　　　　freq (Hz) 1.00E+031.00E+04 1.00E+05 1.00E+06 2.00E+06δ(cm) 64.97 20.55 6.50 2.05 1.45

ρ(Ω/m) 5　　　　μo 1.26E-06　　　　μr 10000　　　　freq (Hz) 1.00E+031.00E+04 1.00E+05 1.00E+06 2.00E+06δ(cm) 35.59 11.25 3.56 1.13 0.80

Only MnZn with low surface resistivity has the concern but normally the depth is not an issue for designing a part.


Open DIscussions92

Thank You~Acknowledgement: In this presentation, many materials are from existing handouts of my previous works (Ferroxcube and ACME), also from the presentations available on the internet. I did not list any does not means I want to take the credit fully. Just that all materials are from the internet and this is a “non-profit” no IP involved promotion of basic ferrite knowledge.

201606_ferrites,_cmc,_and_power_transformer_(1)e

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