Seminario - Würth Elektronik

© 2011 – Wurth Midcom 1

WURTH ELECTRONICS MIDCOM

2011

SMPS EMI SEMINAR 2011

Introduction to Concepts and

Techniques 1


Our Products

http://www.we-online.com/

http://www.we-online.com/web/en/passive_bauelemente_-_standard/toolbox_pbs/Toolbox.php

Wurth Electronics Midcom Inc. Headquarters Phone: (605) 886-4385 Fax: (605) 886-4486

E-Mail: [email protected] 121 Airport Drive

Watertown, SD 57201 United States


TRILOGY of Magnetics

1. Electromagnetics Fundamentals

2. Passive Components and their characterisitics

3. Principles of Filter

4. Over 300 Detailed Applications

An Excellent Resource for EMC


Basics

EMI = Electromagnetic Interference

EMC = Electromagnetic Compatibiltiy

NOT THIS: E= 𝑚𝑐2 OR THIS: HipHop Band

How much a device„s own noise affects other components

How well a device can handle noise from other components


EMI / EMC (CISPR vs. FCC)

* International Special Community on Radio Interference, Pub.22

** Federal Communications Comission, Part 15

CISPR* (22)

FCC** (15)

Non-regulatory agency, but CISPR has been adopted as part of the EMC tests and limits

Regulatory agency that sets the USA EMC tests and limits

0.15MHz to 30MHz

30MHz to 1000MHz - radiated

- conducted

0.15MHz to 30MHz

30MHz to 1000MHz - radiated

- conducted

>1000MHz - accordance to FCC


f [MHz] CISPR 22 - conducted

f [MHz] FCC 15 - conducted

f [MHz] CISPR 22 - radiated

f [MHz] FCC 15 - radiated

>1000 0.15 - 0.5

0.1 1 10 100 1000 f [MHz]

0.45 – 1.6

30 - 88 0.5 - 30

1.6 - 30

0.15 - 0.5

0.455 – 1.6

0.5 - 5

1.6 - 30

5 - 30

30 - 88

88 - 216 216 - 960

88 - 216 216 - 1000

30 - 88

30 - 88

88 - 216 216 - 960

88 - 216 216 - 1000

Class A

Class B

>1000

>1000

>1000

960-1000

0.5 1.6 5 30 88 216

• Class A

commercial, industrial, business environment equipment

• Class B

residential environment equipment

differential mode noise common mode noise

CISPR vs. FCC


Basics

30 MHz is roughly equivalent to a wavelenght of ~32 feet (10 meters)

900 MHz is roughly equivalent to a wavelenght of 1 foot (~.33 meters)

In practical terms, the wavelength of a signal and the length of its an antenna need

to be equal to radiate the signal at full power

Short little cables are unlikely

to radiate noise below 30MHz

Why 30Mhz the cutoff between the conducted and radiated emissions?

Most common house cables, wires or power lines are less than 10 meters long!


Differential–Mode signal

Types of Noise Signals

switching

supply

switching

supply

connection chassis &

Earth GND

connection chassis &

Earth GND

Common–Mode signal

• Noise flows along both lines

in the same direction

• returns by some parasitics path

through system GND

• Noise flows into one line and

exits through another

•Independent from GND


f [MHz] CISPR 22 - conducted

f [MHz] FCC 15 - conducted

f [MHz] CISPR 22 - radiated

f [MHz] FCC 15 - radiated

>1000 0.15 - 0.5

0.1 1 10 100 1000 f [MHz]

0.45 – 1.6

30 - 88 0.5 - 30

1.6 - 30

0.15 - 0.5

0.455 – 1.6

0.5 - 5

1.6 - 30

5 - 30

30 - 88

88 - 216 216 - 960

88 - 216 216 - 1000

30 - 88

30 - 88

88 - 216 216 - 960

88 - 216 216 - 1000

Class A

Class B

>1000

>1000

>1000

960-1000

0.5 1.6 5 30 88 216

• Class A

commercial, industrial, business environment equipment

• Class B

residential environment equipment

differential mode noise common mode noise

CISPR vs. FCC


Shields radiated noise

Common types of noise countermeasures


Filtering for conducted and radiated noise

Common types of noise countermeasures

Low Pass Filter

High Pass Filter

Band Reject Filter

Band Pass Filter


Field model

N

O

R

T

H

S

O

U

T

H

Magnetic field H

Current I

The Magnetic Field (H)

13


averageR

IHHH

221 1B 2B?

Current I

averageR

1H2H

averageR

The Magnetic Flux (B)

14


The Magnetic Field

15

The H field corresponds to what is called the magnetic field strength. It is measured in amps / meter (A/m).

In free space or in air the B field represents magnetic flux density which is

given in units of Tesla by B = μₒ H where μₒ is the absolute

magnetic permeability of free space

More magnetic flux can be produced by the same H value in certain (magnetic) materials, notably iron, and this is accounted by introducing another factor, the

relative permeability μr, giving B = μₒμr H for magnetic

materials.


What is Permeability? µ

H

Br

0

1

Typical permeability µr :

50 ~ 150

40 ~ 1500

300 ~ 20000

Relative Permeability

Describes the capacity of concentration of the

magnetic flux in the material

Is a factor of energy needed to magnetize

• Iron power / Superflux :

• Nickel Zinc :

• Manganese Zinc :

16


R

IH

2

R

INH

2

l

INH

Straight wire

Toroidal

l

R

R

Rod choke

The magnetic field strength

depends on:

• dimensions

• Number of turns

• current

but

NOT ON THE MATERIAL

THROUGH WHICH IT

FLOWS

The Magnetic Field (H)

17


Air (Ceramic)

Rod core ferrite Ring core ferrite

N

O

R

T

H

S

O

U

T

H

The Magnetic Field (B)

N

O

R

T

H

S

O

U

T

H

N

O

R

T

H

S

O

U

T

H

HB r 0HB r 0

Induction in air:

Linear function because µr = 1

(a constant)

Induction in Ferrite:

Non-linear function, because the relative

permeability depends on:

HB 0

Frequency

Temperature Material

Current

Pressure

18

Reluctance ( A measure of stored magnetic energy)

Characteristics Magnetic Parameters H and B (Linear & Hysterises Models)

Area of Operation for a Flyback Transformer

Area of Operation for a Filter Inductor

The Ideal Transformer

The air gap and its purpose


Saturation Current (power inductor)


Permeability and Core Material Properties

Permeability depends on temperature

µr = ? 1 +15 %

-20 %

-50 50 150 250

1000

T / °C

500 540

670

770

-40°C 23°C 85°C

µr

27

Curie

Temperature


Permeability – complex Permeability

Impedance of winding with

core material

Impedance of winding

without corematerial Core material

R

L0L

|||

|||

j

j

jXRjLjZ

j

|||

0

|||

jXRjLjZ

j

|||

0

|||

jXRjLjZ

j

|||

0

|||


1

10

100

1000

10000

1 10 100 1000 10000

Reihe1

µ`

µ``

µr=350

f/MHz

||

0LR |

0LjX L

Frequency dependent

core losses (hysteresis & eddy current losses)

Inductance reactance (energy storage)

jXRjLjZ

j

|||

0

|||

Permeability – complex permeability

29


0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0,01 0,1 1 10 100 1000

Core Material Properties and Applications ( Inductors for Storage)

f/MHz

XL(NiZn) XL(MnZn) XL(Fe)

Imp

ed

ance

„0“-200kHz „0“-10MHz „0“-40MHz

30


0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0,01 0,1 1 10 100 1000

f/MHz

R (NiZn) R (MnZn) R (Fe)

Imp

ed

ance

200kHz-

4MHz

3-60MHz 20-

2000MHz

31

Core Material Properties and Applications ( Inductors for Filtering)


Reduction of noise

• From device to environment

• From environment to device

Conclusion:

• “Almost” no influencing of the signal

• High attenuation of noise

Differential mode

Common mode

Common Mode Filter

32


Source Load Signal path

Common mode

VCC

GND

D-

D+

e.g.: USB

Filtering

Common Mode Filter – Signal theories

33


When will be the signal attenuated?

• the Differential mode-Impedance will also attenuate the signal

1

10

100

1000

10000

1 10 100 1000

• The CommonMode-Impedance attenuates just the noise

f/MHz

Common Mode Filter Attenuation feautures

34


Common mode choke - construction

bifilar sectional

35


Bifilar Sectional

• Less differential impedance

• High capacitive coupling

• Less leakage inductance

• Low capacitive coupling

• High leakage inductance

• High differential impedance

• Data lines

USB, Fire-wire, CAN, etc.

• Power supply

• Measuring lines

• Sensor lines

• Power supply input /output filter

CMC for mains power

• High voltage application

• Measuring lines

• Switching power supply decoupling


36


1

10

100

1000

10000

1 10 100 1000

WE-SL2 744227

bifilar winding WE-SL2 744227S

sectional winding

f/MHz


37


e.g. 74271712

WE-split ferrite – Is it a CMC?

comparable with bifilar winding CMC

• both will absorb Common Mode interferences

• Yes, CMC with one winding


38


Increase the number of turns means:

0

200

400

600

800

1000

1200

1400

1600

1800

2000

1 10 100 1000f/MHz

Common mode choke: ferrite core

39

Why Filter? – example: Fly back-Converter

Which filter we need?

L1

N

PE

Parasitic capacities

e.g.: collector to cooling element

40

Lorandt Fölkel © Würth Elektronik eiSos 2011

Transformers

Transformers and EMI

• Center leg gap only

– Windings shield

• No gaps in outer legs

– Nothing to shield

No Gaps here

Gap here

No external gaps

Inductors and EMI

Drum core style

Very large gap

Much radiation

Not a good solution!

Transformers for EMI – Gap issues

• Gap must be perpendicular to flux lines

• Uneven gaps are inefficient. => Why?

– Core saturates at minimum gap

– Requires a larger gap

• Also larger gap – More potential EMI

Transformers and EMI – Internal shields

• Shield both conducted and radiated noise

• Copper foil or wound magnet wire?

• Copper foil shields – Expensive, => Why?

– Must build shield

– Must be covered with tape

– Winding machine stopped to apply

• All shields take away from winding area

Internal

shield

Transformers and EMI

Y-Cap termination

• Y-Cap across transformer reduces noise

• Tune the capacitor for optimum loss vs. noise

reduction

• Capacitor usually in the 470pF to 4.7nF range

• Place as close to transformer as possible

Noise couples through the transformer via

CParasitic

• Noise seeks path to primary circuit

• Without path, noise may become conducted

emissions

Transformers for EMI – Power Supply

Current Compensated

Choke WE-FC Transformer

Output filter

WE-TI

Switch IC

Y-Cap Snubber

Transformers for EMC – Schematic

Current Compensated

Choke WE-FC

Transformer Output filter

WE-TI

Snubber

Switch IC

Y-Cap

Transformers for EMC – Example 1

EMC- Test Failed

Peak

Avg.

QPeak

Avg.

• With adjusted Snubber

• Without common mode choke

• Without adjusted Y-Cap



• With common mode choke


EMC- Test Failed

Peak

Avg.

QPeak

Avg.


EMC- Passed




Peak

Avg.

QPeak

Avg.


EMC- Passed

Peak

Avg.

QPeak

Avg.

• Without adjusted Snubber



Transformer for EMC – Conclusion for this power supply

• Necessary to pass EMI:

– Current compensated Choke

(CMC)

– Y-Caps

• Not necessary to pass EMI

– Optimized Snubber

Simple EMI detector

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