4145 Datasheet, PDF (1/8 Pages) API Technologies Corp – POWER DIVIDERS

Application Note 4145
Electromagnetic Compatibility for Power Converters
www.fairchildsemi.com
Electromagnetic Compatibility (EMC) has become a house-
hold name of the past decade. In the mid 1990's, Europe
required a reduction on the level of radiated and conducted
emission in products that were sold into the region. From
that point on many products today have in their design cycle
EMC testing.
In North America, radiated EMI is most often measured in
the frequency range from 30 MHz to 10 GHz (according to
the FCC), while conducted EMI is most often measured in
the frequency range of several kHz to 30 MHz (according to
the FCC).
A common question asked is, what is EMC? EMC is the
ability of a device, product, or system to operate properly in
its intended electromagnetic environment (presence of EMI),
without degradation and without being a source of interfer-
ence. There are bodies that produce EMC standards that
must be followed such as IEC and CISPR.
This application note speaks about EMC regulations dealing
with both radiated and conducted emissions. Conducted
emissions consist of both common mode and differential
mode noise. In order to deal with common and differential
mode noise, an AC power main filter is required and a
description and example of one is provided. These noises can
reside on the power lines entering the unit, but are also pro-
duced by internal switching devices.
EMC Regulations
In order to achieve a solid EMC design, one must understand
the EMC requirements. The requirements that will follow do
not deal with module power supplies; rather they deal with
system level standards in both Europe and in North America.
Figure 1. EN 55022 Conducted Emissions
The International Electrotechnical Commission (IEC) is
responsible for deriving the European requirements, in say-
ing that, the Comite International Special des Perturbations
Radioelectriques (CISPR) – International Special Committee
on Radio Interference is responsible for the EMC require-
ments with CISPR 22 defining the strictest limits on con-
ducted emissions. These limits (conducted emissions) are
described in the product standards EN 55022 (Figure 1) and
EN 55011 (Figure 2). The class A and class B requirements
on Figure 1 and Figure 2 refer to the industrial standard and
the domestic standard respectively. Depending on the
antenna used for detecting the noise, the European standards
give two limits. The higher limit for a quasi-peak antenna
and a lower limit for an average antenna, but both limits
must be met for the equipment to pass the requirement.
The FCC standards used in North America have similar
specifications to the European EN requirements (see note
below Figure 2). Two European standards that are used in
testing power supplies are EN 55011 and EN 55022. Figure
3 and Figure 4 show the radiated levels of EN 55011 and the
FCC part 15 subpart B (North America) respectively.
Figure 2. EN55011/FCC Part 15 Subpart B
Conducted Levels
Note: After May 23, 2004 the FCC Part 15 Subpart B and the
EN 55011 will have the same noise conduction level specifi-
cation.
REV. 1.0 4/6/04