High Frequency Magnetics; Black Magic, Art or Science?

Magnetics Core Loss

Dr. Ray Ridley

APEC Industry Session on Magnetics

Wednesday March 23 2016

www.ridleyengineering.com1

Introduction

Core loss calculations and measurements

New core material needs

Need for extensive data

Approximations to data

Different excitation waveforms

Temperature variations

Standardized data base proposals

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Immediate Goals for Core Materials

10K 100K 1 M 10 M 100 M

CORE

LOSS LIMITEDSATURATION LIMITED

FERRITE

MPP

0.3 T

0.6 T

Would be nice to at least extend saturation range further

Frequency (Hz)

SATURATION

LOSS

Improvements

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B-H Loop and Core Losses

Core loss calculations and measurements

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H

B

𝛥𝐵

Core Loss MPP 200u

300 kHz 0.1 T 5 W/cm3

5000 mW/cm3

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Core Loss PC95

300 kHz 0.1 T 0.350 W/cm3 > 10 times better than MPP

350 mW/cm3

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Core Loss Steinmetz Equation

Steinmetz equation can

be used to approximate

the actual loss measurements

Three coefficients define the

loss for a given material

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x

c

yP fk B

Steinmetz Equation Limitations

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x

c

yP fk B

Equation assumes curves are

1) Equally spaced with frequency

2) Equal slopes at different frequencies

Modifying the Steinmetz Equation

Discrete step changes in coefficients from Mag Inc.

a c d<100 kHz 0.074 1.43 2.85

100-500 kHz 0.036 1.64 2.62

>500 kHz 0.014 1.84 2.28

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x

c

yP fk B

Steinmetz Equation Changing Coefficients

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x

c

yP fk B

k x y<100 kHz 0.074 1.43 2.85

100-500 kHz 0.036 1.64 2.62

>500 kHz 0.014 1.84 2.28

Ridley-Nace Variable Steinmetz Equation

1.729 ( 0.00076 2.8332)( 3.626ln 28.32) f

cP f f B

Continuously-variable coefficients with Ridley-Nace formula

Five coefficients needed to describe materials

Example for Magnetics R material:

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( )( ln ) c d

c

efP f f Ba b

Continuously Variable k Term

12

0.01

0.1

1

10

100

1000

10000

0.005 0.1

Magnetics R Material Measured Core Loss

0.01 0.2

3/mW cm

Loss

Flux Density T

Frequency

200 400 600 800 10000

0

20

16

12

8

4

3.626ln 28.32k f

Measurements

( )( ln ) c d

c

efP f f Ba b

3.626 28.32a b

Continuously Variable y Term

13

0.01

0.1

1

10

100

1000

10000

0.005 0.1

Magnetics R Material Measured Core Loss

0.01 0.2

3/mW cm

Loss

Flux Density T

Frequency

200 400 600 800 10000

0

3

2

1

0.00076 2.8332y f

( )( ln ) c d

c

efP f f Ba b

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0.00076 2.8332d e

Oliver Variable Steinmetz Equation

(Powdered Iron Core Material)

14

2 2

3 2.3 1.65

core da b c

fP f B

B B B

Continuously-variable coefficients with Oliver formula

Four coefficients needed to describe materials, plus 2.3 and

1.65 exponents subject to change with different materials

www.micrometals.com/appnotes/appnotedownloads/coreloss update.pdf

© 2016 Ridley Engineering Inc

Core Loss Temperature Variation

15

Six coefficients needed to describe temperature variation

Every material has a different curve

Does the curve also change with frequency and flux level?

-60 0 60 120

Temperature

1

2

3

4

5

Loss Multiplier

5 4 3 2

5 4 3

1

2

0( )g T T T T T Ta a a a a a

Manufacturer’s Data

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Different Core Excitations

16

Need to modify equations to suit each of these waveforms

B

t

B

t

B

t

B

t

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General Triangular Flux Waveform

1 2

1 22 2

( ) fcD

c fcD

P D PD DP

B

t1 sDT 2 sD TsT

2 B

( )( ln ) c d

c

eff f Ba bP

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Duty Cycle Core Loss Multiplier

1 2

1 22 2

( ) fcD

c fcD

P D PD DP

0

1

2

3

4

5

6

0 0.1 0.2 0.3 0.4 0.5 0.6

B = 0.15 T

: 'DCM D D

: ' 1CCM D D

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Putting it All Together

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What We Need from the Manufacturers

1) Raw core loss sinewave test data over wide range of

frequency, B, temperature

2) Who is going to fund the modeling into a standard

format database?

20

Magnetics Forecast

High-ripple current inductor designs will dominate the practical high-performance market

Practical “high performance” means converters up to 5 MHz

Core material improvements will be just incremental (unless some breakthrough material emerges)

Insufficient funding is going into fundamental magnetic material research to give a

good chance of any breakthroughs.

Data Standardization is badly needed from the core manufacturers to ease confusion

Core loss raw data is needed, not just curves.

Creative core geometries need to be applied to POL inductors and other high-ripple parts

Magnetic core will not go away (however much it is wished for)

Isolation transformers will creep back into PoL applications to boost efficiency – More magnetics!

Multi-converter processing will continue to proliferate.

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Some References

Cliff Jamerson: Targeting Switcher Magnetics Core Loss Calculations,

Power Electronics Technology, Jan 2001.

Ed Herbert: http://www.psma.com/technical-forums/magnetics/core-loss-studies

Christopher Oliver: www.micrometals.com/appnotes/appnotedownloads/coreloss update.pdf

Power Supply Design Center Articles http://www.ridleyengineering.com/design-center.html

[89] Core Loss Modeling

[90] Core Loss Modeling with Non-Sinusoidal Waveforms - Part II

[91] Core Loss Modelling - Sinewave Versus Triangle Wave - Part III

Ray Ridley and Art Nace

[A03] Modeling Ferrite Core Losses

Christopher Oliver

[A06] Core Loss Modeling & Measurement

Power Supply Design Software http://www.ridleyengineering.com/software.html

22© 2016 Ridley Engineering Inc