dc biased chokes for high frequency power applications...dc chokes use only narrow range of flux...

DC Biased Chokes for High Frequency Power ApplicationsM.Sc. Martin Grübl

Overview of PIRATE-technology

2© SUMIDA. All rights reserved.

P ermanentmagneticI nlay forR everse-BiasA ctivityT echnologyE xtension

• Basic core out of soft magnetic ferrite with very high saturation flux density SUMIDA Fi339

• Together with hard magnetic inlay with outstanding inner resistance for low eddy current lossesSUMIDA Fi701

• Both materials are SUMIDA developments and unique on the world market.

• Mechanical limits of the magnet:height: min 1 mm; surface area max. 50 cm²

Applications for PIRATE-chokes

3© SUMIDA. All rights reserved.

DC Chokes use only narrow range of flux density capability

Used flux density

Flux density capability of a common ferrite core


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PIRATE eliminates DC Offsets• Cores can get smaller• Saturation performance rises

Unused capability of the core

Flux density capability of the core

© SUMIDA. All rights reserved.


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Rule of Thumb: PIRATE Technology is possible if winding losses are three times higher than core losses𝑷𝑷𝑾𝑾𝑷𝑷𝑪𝑪

> 𝟑𝟑

0,0

1,0

2,0

3,0

4,0

0 100 200 300 400

L /µ

H

I /A

without Magnet

with Magnet Fe701


Sample project using PIRATE-choke

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Component: PV converter DC boost choke 550µH, 30ASumida Project No: EI 140 514 11


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Sample project with PIRATE-chokes

EI 140 514 11 42Original design

EI 140 514 11 32PIRATE

Advantages of PIRATE design

Weight 2,63 kg 1,93 kg -26%

Volume 700 cm³ 525 cm³ -25%

Turns 45 28 -37%

Rdc 18 mΩ 12 mΩ -33%

Pv (@23A, 100°C) 12,4 W 8,2 W -33%

Rs (@20 kHz) 440 mΩ 370 mΩ -16%

fres 1,5 MHz 1,7 MHz +13%


Lifetime Test Result - Industrial Application

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Magnet temperature 90°CDC-Offset: 260 mTΔB = 200 mTf = 18 kHzL= 500 µH

Degradation of the energy maximum (0,5*L*I²) of a PIRATE Choke


Co-sintered air gap

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Distributed air gaps in ferrites decrease fringing of magnetic flux.

Original technology for distributed air gaps: Sandwich gluing of ferrites and plastics.

Disadvantage: thermal insulation due poor thermal conductivity of plastic material

New patented Sumida technology: Co-sintered air gap

Advantages:• Homogeneous structure of the ferrite column• Better heat flow conditions • Cost neutral against original technologies• Minimum air gap: 1 mm


Co-sintered air gap

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Comparison of thermal behaviour:Original glued air gap vs. co-sintered air gap

Fi010 FR4

Characteristics Fi010 FR4

µi (air gap material) 1,1 1,0

Thermal conductivity [W/m/K] 5 0,25

Hot Spot [°C] 114 122

Thermal expansion [ppm/K] 8 70

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Thank you for your attention!

Further Questions ?

Backup Folien

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Datasheet of SUMIDA Fe701 Hard Magnetic Compound

Item ValueBasis NdFeB

µi 1,1

Hcb -300 kA/m

Hcj -970 kA/m

Br 420 mT

Spec. resistance 38 Ωm

Density 4,4 g/cm³

Spec. Losses (@ 100°C, 72kHz. 70mT)

<200 mW/cm³

Tmax 150 °C


Other outstanding ferrite technologies of Sumida

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Plastoferrite (plastic bonded ferrite particles)• Overmoulded busbars for DM – filtering• Free-shaped geometries and narrow tolerances• µ = 0 – 22 possible• Cost ~1,5x costs of common production (pressed ferrite)

Injection Moulded Ferrites• Free-shaped geometries• µ = up to 4000• Similar properties to common ferrite cores• Cost ~ 1,5x costs of common production (pressed ferrite)

Thin-slide ferrites• 0,6 mm possible• Ideal for shielding


dc biased chokes for high frequency power applications...dc chokes use only narrow range of flux...

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