General Technical Information
1
Inductive components for electronic equipment
Especially in this age of fully-electronic and highly-integrated equipment, inductive components are
indispensable. They are used to store energy intermittently in switch-mode power supplies and
DC/DC converters, as parts of high-frequency circuits, as filter elements and last but not least as
interference suppression components to ensure EMC.
Of course, the demands placed on inductors depend on how and where they are to be used. In HF
circuits, coils with high quality factors and resonance frequencies are needed. In EMC applications,
high inductances are required in order to achieve good interference suppression characteristics, low
Q
factors being more desirable here due to the need to avoid resonances.
EPCOS provides suitable inductive components for all applications. This data book contains a wide
selection of standard components, from SMT types (starting with SIMID 0402) right up to the 4-line
high-current inductors for power electronics applications.
Attention is drawn to the excellent HF characteristics and the extremely high reliability of the com-
ponents, achieved thanks to large-scale production automation and many years of experience in
the manufacture of this kind of components.
An overview of typical applications for inductors and chokes
Application
HF circuits,
resonant circuits
EMC
Filter circuits
Switch-mode
power supplies,
DC/DC converters
Inductance
low
high
high
∗
Current rating Resonance
frequency
low
very high
∗
high
∗
high
high
medium
Q
factor
very high
low
low
high
DC resistance
low
very low
very low
low
∗
depends on the specific application
1.1
HF circuits
SMT styles (SIMID product range) and leaded RF chokes are especially suitable for RF and other
high-frequency circuits. Typical applications are resonant circuits and frequency-selective filters of
the type being increasingly used in telecommunications engineering and automotive electronics. In
some cases, special demands on the inductive components arise, for example, when used in trans-
mitter output circuits of mobile telephones (high
Q
factors and resonance frequencies) and in air-
bag control circuits (high pulse currents).
1.2
Filter circuits
When inductive components are used for filters in power supplies for electronics, high inductances, the
lowest possible DC resistance and a low
Q
factor are required. The impedance should have a wide-
band frequency characteristic. In addition to the current rating, the maximum permissible pulse current
(switching transient currents) and adequately high core material saturation are of importance.
Chokes belonging to all type series presented here can be used for this range of applications, from
the SIMID types right up to chokes with powder cores and one or two lines.
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General Technical Information
1.3
Switch-mode power supplies, DC/DC converters
Inductive components are used for magnetic energy storage in all kinds of switch-mode power sup-
plies and DC/DC converters. For example, the SIMID 1812 product range is used in low-power step-
up converters in automobile electronics and in battery-powered equipment. They can be subjected
for short periods to currents which are the quadruple of their current rating without any saturation
effects occurring.
1.4
EMC applications
For broadband interference suppression, current-compensated chokes with ring cores or D cores
and powder core chokes are especially suitable.
Apart from use as filters in mains and other power supply lines, such chokes are important for data
lines as used in telecommunications engineering, e. g. in NTBAs (Network Termination Basic Ac-
cess Units, ISDN), in line cards in telephone exchanges (ISDN and analog) and in the fast-expand-
ing CAN bus application field (CAN = Controller Area Network) in automotive electronics.
Almost all the component families are approved in accordance with the main international stan-
dards. All chokes for low-frequency mains networks are dimensioned and tested in compliance with
the applicable EN and IEC standards.
Inductive components with particularly good RF characteristics are achieved by the use of ungapped
cores. The manufacturing methods developed by EPCOS lead to good reproducibility of the attenua-
tion characteristics and enable the production of high-quality components at a favorable price.
The company’s many years of experience guarantee that customers quickly and economically ob-
tain just the right solutions to their EMC problems. Our own EMC laboratory in Regensburg or one
of our European EMC partner laboratories is at your disposal at all times to help with professional
advice and in carrying out measurements (also refer to the
chapter on “Services”).
1.4.1
Propagation of interference
Interference voltages and currents can be grouped into common-mode interference, differential-
mode interference and unsymmetrical interference:
1a
1b
1c
U
s
U
as
U
us1
U
us2
U
=
V
= voltage
SSB1465-P
asymmetrical
asymmetrische
propagation
Ausbreitung
symmetrical
symmetrische
propagation
Ausbreitung
unsymmetrical
unsymmetrische
propagation
Ausbreitung
SSB1465-P
Fig. 1
Propagation modes
s
Common-mode interference (asymmetrical interference):
– occurs between all lines in a cable and reference potential (fig.
1a),
– occurs mainly at high frequencies (from approximately 1 MHz upwards).
s
Differential-mode interference (symmetrical interference):
– occurs between two lines (L-L, L-N) (fig.
1b),
– occurs mainly at low frequencies (up to several hundred kHz).
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General Technical Information
s
Unsymmetrical interference:
– This term is used to describe interference on a single line, relative to the reference potential
(fig.
1c)
1.4.2
Characteristics of interferences
In order to be able to choose the correct EMC measures, we need to know the characteristics of the
interferences, how they are propagated and the mechanisms by which they are coupled into the cir-
cuit. In principle, the interferences can also be classified according to their range (fig.
2).
At low fre-
quencies, it can be assumed that the interference only spreads along conductive structures, at high
frequencies only by means of electromagnetic radiation. In the MHz frequency range, the term cou-
pling is generally used to describe the mechanism.
Analogously, conducted interference on lines at frequencies of up to several hundred kHz are main-
ly symmetrical (differential
mode),
at higher frequencies, they are asymmetrical (common
mode).
This is because the coupling factor and the effects of parasitic capacitance and inductance between
the conductors increase with frequency.
X capacitors and single chokes are suitable as suppression measures for the differential mode com-
ponents. Where asymmetrical, i.e. common-mode interference has to be eliminated, current-com-
pensated chokes and Y capacitors are mainly used, the prerequisite for this being, however, a well-
designed, EMC-compliant grounding and wiring system.
The categorization of types of interference and suppression measures and their relation to the fre-
quency ranges is reflected in the frequency limits for interference voltage and interference field
strength measurements.
SSB1558-D
Differential mode
Common mode
Field
Interference
characteristic
Line
Coupling
Field
Interference
propagation
X cap
Pc ch.
Y cap
Cc ch.
Ground
Shielding
Remedies
Interference voltage
10
_
2
Field strength
10
1
10
2
Max. ratings
10
_
1
10
0
MHz 10
3
f
Fig. 2
Frequency range overview
Pc ch. = Iron powder core chokes, but also all single chokes/ X cap = X capacitors
Cc ch. = Current-compensated chokes / Y cap = Y capacitors
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General Technical Information
2
2.1
Electromagnetic compatibility (EMC)
Introduction
For as long as electronic transmission equipment such as radio, television, and telephone has been
in existence, it has had a history of susceptibility to interference from other electronic devices. Legal
regulations on interference suppression (electromagnetic and radio frequency interference, EMI
and RFI) have been in existence since 1928. These regulations protect transmission paths and re-
ception equipment by limiting the emitted interference.
In view of the increasing number of electrical and electronic appliances in use, not only the princi-
ples of interference suppression must be observed, but also, in the sense of electromagnetic com-
patibility (EMC), it must be ensured that all equipment is able to operate simultaneously without
problems. EMC is defined as the ability of electrical equipment to function satisfactorily in its elec-
tromagnetic environment without affecting other equipment in this environment to an impermissible
extent.
The European Communities’ EMC Directive (89/336/EEC) came into force on the 1. 1. 1996. It has
been transformed into corresponding legislation in the individual EU (European Union) member
states. With this, it has become mandatory to design electronic equipment to comply with the pro-
tection objectives of this Directive; i.e. to meet the requirements for electromagnetic emission and
electromagnetic immunity as laid down in the corresponding EN standards (European Standards).
The concept of EMC includes both electromagnetic emission (EME) and electromagnetic immunity/
susceptibility (EMS), see
fig. 3.
EMC = Electromagnetic
compatibility
Susceptibility
EMC
Emission
EME
CE
RE
Interference
source
Fig. 3
EMC terms
Conducted
EMS
CS
RS
EME = Electromagnetic
emission
EMS = Electromagnetic
immunity/susceptibility
CE
CS
= Conducted emission
= Susceptibility to
conducted emission
= Radiated emission
= Susceptibility to
radiated emission
Radiated
Propagation
RE
Disturbed
equipment
RS
An interference source may generate conducted or radiated electromagnetic energy, i.e. conducted
emission (CE) or radiated emission (RE). This also applies to the propagation paths and to the elec-
tromagnetic susceptibility of disturbed equipment.
In order to work out economical solutions, it is necessary consider both phenomena, i.e. propaga-
tion and susceptibility, to an equal extent, and not just one aspect, e.g. conducted emission.
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General Technical Information
EMC components are used to reduce conducted electromagnetic interference to the limits in an
EMC plan or to reduce this interference below the limit values specified in the EMC regulations.
These components may be installed either in the source of potential interference or in the disturbed
equipment (fig.
4).
RE
RE
Power supply
CE
Disturbed
equip-
ment
Source
CE
CE
CE
RE
RE
CE
Control line
CE
Filter
Interference currents
Interference voltages
RE
SA
CE
Signal line
Electric field
Magnetic field
Electromagnetic field
Fig. 4
Susceptibility model and filtering
EPCOS offers EMI suppression components with a well-balanced range of rated voltages and cur-
rents for power supply lines as well as for signal and control lines.
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