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© 2011 – Wurth Midcom 1
WURTH ELECTRONICS MIDCOM
2011
SMPS EMI SEMINAR 2011
Introduction to Concepts and
Techniques 1
© 2011 – Wurth Midcom 2
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: midcom@we-online.com 121 Airport Drive
Watertown, SD 57201 United States
© 2011 – Wurth Midcom 4
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
© 2011 – Wurth Midcom 5
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
© 2011 – Wurth Midcom 6
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
© 2011 – Wurth Midcom 7
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
© 2011 – Wurth Midcom 8
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!
© 2011 – Wurth Midcom 9
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
© 2011 – Wurth Midcom 10
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
© 2011 – Wurth Midcom 11
Shields radiated noise
Common types of noise countermeasures
© 2011 – Wurth Midcom 12
Filtering for conducted and radiated noise
Common types of noise countermeasures
Low Pass Filter
High Pass Filter
Band Reject Filter
Band Pass Filter
© 2011 – Wurth Midcom 13
Field model
N
O
R
T
H
S
O
U
T
H
Magnetic field H
Current I
The Magnetic Field (H)
13
© 2011 – Wurth Midcom 14
averageR
IHHH
221 1B 2B?
Current I
averageR
1H2H
averageR
The Magnetic Flux (B)
14
© 2011 – Wurth Midcom 15
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.
© 2011 – Wurth Midcom 16
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
© 2011 – Wurth Midcom 17
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
© 2011 – Wurth Midcom 18
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
The air gap and its purpose
© 2011 – Wurth Midcom 26
Saturation Current (power inductor)
© 2011 – Wurth Midcom 27
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
© 2011 – Wurth Midcom 28
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
|||
© 2011 – Wurth Midcom 29
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
© 2011 – Wurth Midcom 30
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
© 2011 – Wurth Midcom 31
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)
© 2011 – Wurth Midcom 32
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
© 2011 – Wurth Midcom 33
Source Load Signal path
Common mode
VCC
GND
D-
D+
e.g.: USB
Filtering
Common Mode Filter – Signal theories
33
© 2011 – Wurth Midcom 34
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
© 2011 – Wurth Midcom 35
Common mode choke - construction
bifilar sectional
35
© 2011 – Wurth Midcom 36
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
Common mode choke - construction
36
© 2011 – Wurth Midcom 37
1
10
100
1000
10000
1 10 100 1000
WE-SL2 744227
bifilar winding WE-SL2 744227S
sectional winding
f/MHz
Common mode choke - construction
37
© 2011 – Wurth Midcom 38
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
Common mode choke - construction
38
© 2011 – Wurth Midcom 39
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
Transformers for EMC – Example 2
• With adjusted Snubber
• With common mode choke
• Without adjusted Y-Cap
EMC- Test Failed
Peak
Avg.
QPeak
Avg.
Transformers for EMC – Example 3
EMC- Passed
• With adjusted Snubber
• With common mode choke
• Without adjusted Y-Cap
Peak
Avg.
QPeak
Avg.
Transformers for EMC – Example 4
EMC- Passed
Peak
Avg.
QPeak
Avg.
• Without adjusted Snubber
• With common mode choke
• Without adjusted Y-Cap
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