EMI Filter and RFI Filters

What is EMI Filter and RFI Filter.

1. EMI / RFI Filters

EMI / RFI FILTERS

All electrical equipment produced today consist of EMI/RFI filtering
circuits. These EMI filtering circuits are engaged so the end product
complies with applicable EMC standards.





RFI/EMI Filters
Electromagnetic
Interference Filters
Types of EMI Filters
How to Select an
EMI Filter
When Extra Filtering
is Needed
EMI Filter Design
Solutions for Single-
Phase Applications
AC Power Noise
Issues
Questions and
Answers
Glossary

2. EMI / RFI Filters

ELECTROMAGNETIC INTE RFERENCE FILTERS
EMI (Electromagnetic Interference ) Filters is a passive electronic device used to
suppress conducted interference present on any power or signal line. That is also known as
also known as RFI (Radio Frequency Interference ) Filters. Electromagnetic Interference
(EMI) is unacceptable electromagnetic emissions, natural or man-made, which result in the
degradation or malfunction of electronic or electrical equipment.
Most electrical and electronic devices can generate and/or be affected by EMI. Sources are
everywhere and include ac motors, fluorescent bulbs/ballasts, light dimmers, microwave
ovens, microprocessors, computers, and switch-mode power supplies. Within switch-mode
power supplies, a high dc voltage is chopped or switched at a high frequency that can range
from 50 kHz to 1. However, as a side effect, this switching generates unwanted EMI. In fact,
most conducted EMI within switch-mode

In either power supplies or electronic equipment, it is the function of the EMI filter to keep
any internally generated noise contained within the device and to prevent any external ac
line noise from entering the device. EMI filters usually comprise a network of passive
electronic components including capacitors and inductors that form L-C circuits.

3. EMI / RFI Filters

Since unwanted EMI is at much higher frequencies than normal signals, the EMI filter works
by selectively blocking or shunting unwanted higher frequencies. Basically, the inductive
part of the EMI filter is designed to act as a low-frequency pass device for the ac line
frequencies and a high-frequency blocking device.

Other parts of the EMI filter use capacitors to bypass or shunt unwanted high-frequency
noise away from the sensitive circuits. The net result is that the EMI filter significantly
reduces or attenuates any unwanted noise signals from entering or leaving the protected
electronic device.

Help Meet EMC Directive
Solve High Frequency Interference Problems
Have Minimal Panel Space Requirements
RFI Filter Installed Base over 15,000
APPLICATIONS OF EMI FILTERS

4. EMI / RFI Filters
TYPES OF EMI FILTERS

5. EMI / RFI Filters

HOW TO SELECT AN EMI FILTER?

Although much has been written about the selection of EMI filters, the actual process is one
of trial and error. Fortunately, a wealth of experience is available to aid the designer in
selecting an effective filter. EMI filters work by creating a mismatch condition between
source and load impedance at high frequencies. This mismatch is created by series
inductance and shunt capacitive elements. Since the filter must usually work with unknown
terminating impedance, it is an error to use insertion loss data obtained with fixed 50-ohm
terminations as a true indication of filter performance in actual situations.
In most applications, power line impedance is almost always low, but equipment impedance
may be low or high, depending upon the device. Switching regulators or power supplies are
low-impedance loads, but linear power supplies may be high impedance. To achieve
maximum mismatch, the filter must present a high series impedance or inductance to the
power line and a low shunt impedance or large capacitance to a high impedance load. If the
equipment impedance is low, the filter must also present a high series inductance between
line and load. In general, the power source appears as a relatively low impedance. Some of
the requirements for these specifications are given in the Glossary of Terms.
1. For high equipment impedance, use: Capacitance to load.

2. For low equipment impedance, use: Inductance to load and line.

6. EMI / RFI Filters

Other filter considerations are:
Current and voltage rating.
Temperature, shock, vibration, and humidity.
Physical dimensions and mounting.
Terminal configuration.

TYPICAL RATINGS

Temperature rating: -20 degree to +45⁰ Celsius nominal operating to +85⁰ Celsius with
de-rating.
Humidity test: 21 days at 40⁰ Celsius and 95% relative humidity.
Test voltage:
Line to ground, 2250 VDC.
Line to line, 1450 VDC.
Current overload test: 140% rating for 15 min or 6X rated for 8 sec.
Voltage drop: Less than 1 % of rated voltage.

7. EMI / RFI Filters

WHEN EXTRA FILTERING IS NEEDED

Although all ac/dc power supplies have internal EMI filters that comply with the various EMC
standards, there are cases where the circuits or systems they provide power to generate
much more electrical noise than the filter can suppress by itself. In other cases, when
multiple power supplies are working off the same ac power source, the small amount of
noise that is not filtered or contained by each supply’s internal EMI filter can combine to
form an unacceptable level of noise. In addition, there are times when the ac power line
entering the power supply has so much noise on it that an additional EMI filter is required.
This incoming noise can be in the form of a spike or burst of energy. It can be generated
from natural Causes such as a lightning storm or be man -made by someone operating a
piece of industrial equipment containing large motors, actuators, solenoids, etc. In all of
these cases, it may be necessary to install an external or auxiliary EMI filter to bring the
electrical noise down to acceptable levels. These EMI considerations apply to the design and
installation of all electronic products or systems. Standard external EMI filters typically have
single-stage L-C circuits. For higher performance EMI filtering, two-stage L-C circuits may
be required. And, if electrical spikes from motors or lightning strikes are a potential problem,
EMI filters with high voltage pulse attenuation should be used.

TESTING FOR EMC COMPLIANCE

As mentioned previously, the usual frequency range specified in most EMC standards for
conducted EMI emissions is from 150 kHz to 30 MHz. To confirm that an electronic device
meets the limits of a specific standard, it must be tested with a spectrum analyzer and a
line impedance stabilization network (LISN). Ac power is routed through the LISN to the
device under test. The LISN standardizes the measurement impedance to 50 Ω and provides
an isolated RF output to a spectrum analyzer, which provides a plot of the conducted
emissions coming from the device.

8. EMI / RFI Filters

EMI FILTERS DESIGNS

EMI filtering circuits are employed so that the end product complies with the applicable EMC
standards.
Filter Design
The basic setup shown in Figure2 consists of Line Impedance Stabilization Network (LISN),
Equipment under Test (EUT) which is a 2-transistor SMPS circuit, mains power supply and
a noise separator circuit.


Line Impedance Stabilization Network (LISN)
The conducted EMI measurement procedure requir es a 50 W/ 50 MH Line Impedance
Stabilization Network (LISN) to be inserted between the equipment under test (EUT) and
the ac utility line to provide specified measuring impedance for noise voltage measurement.

9. EMI / RFI Filters

Noise Separators
The common mode and differential mode noises from the measured output are separated
using a noise separator. DM noise rejection is done using a passive circuit while an active
circuit is used for CM noise rejection.

Basic EMI filters
There are numerous EMI filters that could be considered for noise reduction, but the most
popularly used are the LC inductor filter and the π filter for CM and DM noises respectively.
The aim is to obtain the maximum impedance mismatch between the filter and the outside
system.

A better solution over the inductor filter is the choke filter. Chokes withstand high DC
currents without degradation of filtering performance. Chokes reduce noise considerably
over the entire desired frequency range.
Inductor filter
The inductor filter was placed between the LISN and EUT and the filter circuit was tuned to
obtain insertion loss greater than the loss obtained before embedding filter across the
desired frequency range.
The obtained CM noise voltage, VcmifdB was measured across the output of noise separator
in AWR-Microwave Office. It could be observed that noise output reduced considerably by
using the inductor filter.
Choke filter
It shows that by using choke filter there is a tremendous reduction in noise for frequencies
less than 300 KHz and over the entire range till 1.5MHz.

10. EMI / RFI Filters

Followings are the designs i.e. schematic and mechanical drawings of miscellaneous level
EMI Filters (e.g. by Radius Power Inc.) used for different purposes:
RP100 Series Compact Single Stage Power Line Filter
Description
RP100
COMPACT TO 10A
CHASSIS MOUNT FILTER
Used for General Purpose Applications

Schematic:

Mechanical Drawing:

11. EMI / RFI Filters

RPM6000 Series MIL/COTS DC EMI Power Line Filter

Description
RPM6000
MILITARY/ COTS TO 60A
NON-GRND & GRND RETURNS
MIL-STD-461/ DO-160
High Performance Applications at Military stations

Schematic:

Mechanical Drawing:

5/10A

12. EMI / RFI Filters


20/30A

50A
60A

13. EMI / RFI Filters

RP185 High Perf IEC Inlet MEDICAL GRADE FILTER

Description
RP185
MEDICAL GRADE FILTER
IEC INLET TO 15A
Medical Appliances
Schematic:

Mechanical Drawing:

14. EMI / RFI Filters

POWER LINE FILTER SOLUTIONS FOR SINGLE-PHASE APPLICATIONS

In an Enphase® Micro inverter System™, the micro inverters and the Emphases’ Envoy
Communications Gateway™ use power line communication (PLC) technology to connect and
communicate. The Enphase Micro inverter System transmits communication signals at 144
kHz across the same conductors that carry on-site AC system power. When multiple Envoys
are located on a single utility transformer, or when site loads generate electrical noise that
disrupt communications, power line filters may be required, either to separate individual
Envoy domains, or to filter out electrical noise. There are a number of good power line filter
solutions available to filter out unwanted electrical noise from Envoy and micro inverter
transmissions. When installing a power line filter with an Enphase Micro inverter System,
follow these requirements:
Separate the Envoy and the micro inverters from other site loads.
Place the power line filter in-line between the micro inverter subpanel and the
main AC load Center.
Size the filter for the Ampacity (current rating) of the system.
Protect the filter with an appropriate circuit breaker.
Radius Power (www.radiuspower.com) manufactures EMI (electromagnetic interference)
filters that provide power line filtering when applied in Enphase installations. Enphase
provides this information about Radius Power filters but recommends that you contact the
manufacturer or the Radius Power distributor to determine the exact PLC filter requirements
for your PV installation. Although the Radius Power RP125 series is ad equate for some
single-phase systems, a more reliable and robust solution for PLC filtering incorporates the
Radius Power dual-stage design RP230 or RP240 series. The dual-stage design provides
higher performance.

15. EMI / RFI Filters

AC POWER NOISE ISSUES

First install a separate 5ft. copper ground rod in to the earth just outside of the studios.
Connect a copper strap about 2 inches or a copper wire such as a number 6 to the ground
rod. Solder the connection to the copper rod do not use a mechanical clamp as this will
corrode over time. Bring the grounding strap into the building and place it into the studio.
Next, connect only the studios to this earth ground.
Now Separate or remove the existing transmitter ground from the studios. You want to be
separate from the RF ground system. Over the years my experience has shown me by
separating the studio ground from the transmitter ground I have greatly reduced the AM
and FM radio frequency noise in the studio wiring. The copper strap should connect directly
to the audio consoles chassis.
You may use short wire jumpers from the copper strap to your other equipment to ground
them. Try to keep these wire jumpers as short as possible as not to act as an antenna.
Make sure there are no audio wiring shields connected to the transm itter room. Connect
your studio audio wiring shields only at the studio end and not to the transmitter room. For
the AC power noise issue use an AC isolation transformer between the AC power feed and
the studios equipment.
Another alternative when dealing with RF and AC power noise issues is to install an EMI
filter between the AC power feed and the studio equipment. Your connection would work
like this. AC Power feed EMI Filter Equipment Check out the following links lots of variety
here.
http://www.radiuspower.com/single_phase_filters.html
http://www.directindustry.com/industrial-manufacturer/emi-filter-73520.html
You can install a filter for each AC power circuit as several of these units are rated for 25 to
40 amp ratings. Install one filter for each studio power feed. In a typical studio you would
have all the AC outlets for that room connected to just one circuit breaker.
Electricians typically will wire 6 to 8 outlets on to one circuit breaker. I would use one EMI
filter for each circuit breaker output. If there is room you can mount the filter inside the AC
power box. If that doesn’t work you can install a separate box for your filters and mount it
next to the AC power box.

16. EMI / RFI Filters

Your AC power connection flow would work like this:
Circuit Breaker  EMI Filter  AC Outlet
Another suggestion that was provided by a customer was to remove, clean and reconnect
the AC power box hot (black), neutral (white) and ground (copper) wire connections. He
discovered an intermittent ground loop problem. I know this engineer and his audio wiring
in the studios is very clean and quite beautiful he cleaned up the AC power breaker
connections and his ground loop noise cleared up as well. I must say that was a very
interesting solution to this particular problem.
WARRING! This procedure has potentially fatal voltages turn off the main breaker or power
feed before attempting or better yet have a trained electrician do this for you.

17. EMI / RFI Filters

LET'S MOVE ON TO THE QUESTIONS AND ANSWER S

If the system isn't working, then we all share the blame.
A: That's right! EMI has been cited as one of the fundamental threats to the Amateur Radio
service. Complex electronic circuitry is found in all sorts of devices used in the home. This
results in a vast interference potential that didn't exist in earlier, simpler decades. One of
our ARRL Laboratory Engineers recently noticed an advertisement for a computer-controlled
ac-power outlet strip. He wryly observed that this wonderful new product would now allow
him to interfere with his neighbor's extension cord! It's always important to remember our
place as Amateur Radio operators in the overall scheme of things. Consider the fact that
national governments extend to amateurs the privilege to operate in valuable portions of
the radio spectrum. Amateurs have gained these privileges because the world benefits from
our existence. In addition to the emergency communications services we provide, the world
gains a reservoir of self-trained radio operators, skilled in operating practices and
electronics technology. Solving your neighbor's EMI problem as well as your own is an
excellent application of your technical skills.
Well, my family is finally satisfied with the TV, but we still can't use the
telephones. What can I do?
A: There is hope. Several companies manufacture telephone EMI/RFI filters and most work
quite well. Some of these manufacturers are QST advertisers. Remember the three rules of
EMI control and follow them religiously as you install the filters. A few companies also make
interference-resistant telephones. Many of these companies are listed in the appendix.
Carefully inspect the telephone system. Corroded wiring (common in damp basements) or
a defective lightning protector (common in areas where the protector has done its job!) can
rectify the RF signal. Unlike your TV problem, the resulting audio interference cannot be
filtered out. Rectification can also occur in telephones and other devices connected to the
system. Before you begin connecting filters, disconnect all telephones and accessories
except one. Remember to use the systematic divide-and-conquer approach, beginning with
one device and working forward.
Take a careful look at the wiring while you're investigating the problem. Sometimes the
twisted pair has been spliced with nonstandard wiring, such as zip cord. This type of jury-
rigging is more prone to interference pickup. If you discover a problem with the lightning
protector or outside wiring, leave those items for the telephone company to fix or replace.
The responsibility for inside wiring may vary from one area to another. Check with your
phone company for guidance. For more information on telephone interference, read the
October 1992 QST "Lab Notes" column on Telephone Interference. An electronic copy of
this information is available on the ARRL Web page.

18. EMI / RFI Filters

I've tested my station from top to bottom and everything looks fine. When I
checked around the house, I still found interference to my VCR, video -game
machine, stereo TV and video intrusion monitor. All of these devices are connected
to each other by an 8-way splitter! Where do I go from here?
A: I can hardly imagine a worse case! (I say "hardly" because we get some real strange
telephone calls and letter here in the ARRL Lab!) Now is the time to state the second rule
of EMI control: Simplify the problem! Connect the incoming CATV cable (or antenna feed
line) to only one TV (assuming you have more than one). For the time being, completely
disconnect the VCR and other video goodies. The result will uncover an important clue. One
troubleshooting technique is to try an EMI cure and see what happens. This brings us to the
third rule of EMI control (and all other troubleshooting, for that matter): Always try the easy
things first! This rule applies to the susceptible equipment and the suspected EMI source.
Begin by installing the appropriate filter on your TV. For an antenna-connected TV this is a
high-pass filter. (For a CATV-connected TV, a common-mode choke should be tried first.)
I installed the chokes and the TV looks much better! What about the other devices?
A: If you've cured the EMI at the TV, start hooking up the other devices one by one,
eliminating any additional EMI as it appears. If you're lucky, you'll eliminate all of the
problems. If not, at least you can point to one particular piece of equipment and say, "That's
the culprit!" As you put the system back together, do not create a tangle of wires and cables.
All cables should be connected properly, routed neatly and no longer than necessary. An 8-
foot piece of cable picks up a lot more RF energy than a 1-foot piece!
Your suggestion made a big difference! Even so, I still see a trace of interference.
What gives?
A: EMI control is a complex business. The tiny bit of interference could mean a lot of things.
You may need a bit more attenuation of the common -mode or differential-mode signal. In
some cases, an additional high-pass filter or common-mode choke may help. If you add
more filters, experiment with their placement if possible. Sometimes a second filter works
best when it's positioned a few feet away from the first one. You may also be dealing with
interference that results from more than one cause.
Thanks for the warning. By the way, I've found that EMI also makes my stereo act
up. Do you have a magic cure for that too?
A: We're almost out of room, so I'll give you a short answer. Many problems with stereos
can be traced to common-mode propagation on long speaker leads and interconnecting
cables. You can often effect a cure by keeping wire lengths to a minim um. If you can't
shorten the wires, use common-mode chokes. Low-value bypass capacitors can be used on
input leads (try 100-500 pF), but do not use capacitors on speaker leads unless you check
with the stereo manufacturer first. Adding capacitors to speaker wiring can cause some
amplifiers to launch into an ultrasonic, full-power oscillation--often resulting in permanent
damage. If you think you had a problem before you destroyed the family stereo, wait until
you see what happens after you do.

19. EMI / RFI Filters

GLOSSARY ITEMS

EMI Filter: EMI is Electromagnetic Interference and EMI Filter is an electronic device which
is used in order to suppress conducted interference generated by a device or by other
equipment in order make a device more resistant to electromagnetic interference signals
present in the environment.
RFI Filter: RFI is radio-frequency interference, these are same as EMI Filters those reduce
the electrical noise generated from industrial, telecommunication, commercial, military and
medical Devices.
L-C Circuits: An oscillating circuit consisting of an inductor and a capacitor. It is a tuned
circuit that can store electrical energy vibrating at its resonant frequency.
EMC: It is the ability of electrical equipment to operate without being effected by or causing
Electromagnetic Interference (EMI).
Microprocessors: A programmable device that accepts digital data as input, processes it
according to instructions stored in its memory, and provides results as output.
Impedance: The measure of the opposition that a circuit presents to a current when a
voltage is applied.
Capacitance: A parallel plate arrangement and is defined in terms of charge storage. The
capacitance is independent of the potential difference between the conductors and the total
charge on them.
Inductance: The behavior of a coil of wire in resisting any change of electric current
through the coil.
Actuators: A type of motor that is responsible for moving or controlling a mechanism or
system.
Solenoids: A coil of wire can be used to generate a nearly uniform magnetic field similar
to that of a bar magnet.
Choke: A choke is an inductor used to block higher-frequency alternating current in an
electrical circuit, while passing lower-frequency or direct current.
LISN: Line Impedance Stabilization Network, a device used in conducted and radiated
radio-frequency emission and susceptibility test.

20. EMI / RFI Filters

SMPS Circuit: Switch Mode Power Supply, a device that transfers power from a source,
like mains power, to a load.
Enphase: Enphase introduces new energy management system and is the leader in solar
micro inverter systems.
EUT: Equipment under test, the electronics industry to refer to any electronic assembly
under test.
Schematic: Map to Designing, Building, and Troubleshooting Circuits.
Mechanical Drawing: The act and discipline of composing plans that visually communicate
how something functions or is to be constructed.
PLC: Power line communication, a communication technology that enables sending data
over existing power cables.
Radius Power Inc.: A Global Designer and Manufacturer of standard and custom EMI
filters.
AC Power Box: A Rare Modification Item used for upping the odds for John III. It is a small
device which is to be plugged in any of the AC sockets.
Circuit Breaker: An electronic device that cut the power until somebody can fix the
problem.
CATV Cable: Community antenna television, bringing television programs to those millions
of people throughout the world.
VCR: Video Cassette Recording, is an electromagnetic device that was used in early
domestic analog recording format designed by Philips.
Oscillation: The repetitive variation, typically in time, of some measure about a central
value (often a point of equilibrium) or between two or more different states.

21. EMI / RFI Filters

REFERENCES:
http://www.murata.com/~/media/webrenewal/support/library/catalog/products/em
c/acline/c09e.ashx
http://www.digikey.com/Web%20Export/Supplier%20Content/Lambda_285/PDF/T
DKLambda_all_about_emi_epmag.pdf?redirected=1
http://www.saepower.com/pdf/emi -filter_catalog.pdf
http://www.radiuspower.com/images/stories/virtuemart/product/techinfo.pdf
http://www.arrl.org/files/file/Technology/RFI%20Main%20Page/InterferencePrimer. pdf
http://enphase.com/global/files/Power_Line_Filter_Single-Phase_TechBrief.pdf
http://arrakis- systems.com/pdfs/Grounding%20and%20AC%20wiring%20Techniques.pdf
http://enphase.com/global/files/Power_Line_Filter_Single-Phase_TechBrief.pdf
http://literature.rockwellautomation.com/idc/groups/literature/documents/in/drives -
in001_-en-p.pdf
http://arrakis- systems.com/pdfs/Grounding%20and%20AC%20wiring%20Techniques.pdf
http://www.interferencetechnology.com/wp -content/uploads/2012/04/TDG11.pdf