Are EMI and EMC filters the same thing?

There are a variety of terms used by manufacturers to describe their filters; they include “noise filters”, “EMI filters” and “EMI/EMC” filters.  To best answer this question “are they the same thing?” we need to review the differences between EMI and EMC.

From a legislative viewpoint, EMI (ElectroMagnetic Interference) is the measurement and restriction, to defined limits, of unwanted conducted or radiated electrical noise from a product.  Under this term, a power supply and/or the equipment it is powering is considered the “source”.

EMC (ElectroMagnetic Compatibility) immunity on the other hand is the ability to withstand, again to defined limits, a variety of external electromagnetic signals.  Under this term, a power supply and/or the equipment it is powering is considered the “victim”.

Regulation of both the “source’s” emissions and the ability of the “victim” to function under those emissions (and other external influences), guarantees the end product a defined level of performance.

Regulation of conducted and radiated EMI in Europe is commonly defined by two standards. EN 55011 covers industrial, scientific and medical appliances and EN 55022 information technology and telecommunications equipment.  The less stringent Class A level is used for industrial and Class B for medical and household applications.

Fig 1Conducted EMI Plot (level B) for TDK-Lambda’s Medical ZMS100 power supply

Regulation of EMC immunity in Europe is defined by EN 61000, which is a very broad set of standards.  For the purpose of this article, only the two sections applicable to a typical EMI/EMC filter used with a power supply will be discussed.

EN 61000-4-4: Electrical fast transient/burst immunity test – here bursts of electrical noise are injected on the input lines to simulate inductive switching, relays, etc.

EN 61000-4-5: Surge immunity test – here single pulses are injected on the input lines to simulate lightning strikes and high energy switching.

It should be noted that both of the above sections include different test voltages (ranging from 500V to 4,000V peak) and different performance criteria. With criteria A the product will continue to operate as normal during the test, B states a recovery after the test, C requires user intervention to restart the product and D is a loss of function that is not recoverable.

Certainly any filter with suitable attenuation characteristics will reduce EMI and can to some extent improve EMC immunity due to their inductive and capacitive content.

Filters like TDK-Lambda’s RSAL and RSMN series contain amorphous cores that attenuate the bursts and pulses described in the EMC immunity EN 61000-4-4 & -5 sections and allow the product to be compliant. (Link to “Selecting a line filter to reduce input transients” article)

Are EMI and EMC filters the same thing? Yes, although actual product EMC immunity performance will depend on the filter characteristics, the test voltage level and the desired performance criteria.

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Specifying Low Leakage Current EMI/EMC Filters for Power supplies

Leakage current is the current flowing through the earth ground connection. This current may be generated not only by the AC-DC power supply or supplies, but also from any additional external line filtering used to further reduce electrical noise.

Most manufacturers of power supplies use “Y” capacitors connected from the line and neutral to ground as part of their integral EMI filter. These specially rated capacitors provide a low impedance path to the ground for high frequency noise to reduce EMI. The larger those “Y” capacitors are, the lower the measured noise.

Fig 1

There are, however, limits for maximum leakage current put in place by the safety standards for electrical and electronic equipment. That limit depends on the application and what ground connection is used. Medical, because sick patients are more vulnerable to electric shock, is the most stringent. Below are the limits for the most common applications.

IEC 60950-1 Information Technology Equipment
Handheld 0.25mA
Moveable (not handheld) or pluggable 3.5mA
Permanently connected 3.5mA (or higher for some applications)

IEC 60601-1 Medical (Body Float – B category)
0.5mA Europe
0.3mA in USA

Let us assume we are designing a portable piece of medical equipment to be used globally, thus our leakage current “budget” is 300μA. We are also going to assume that we may need an additional external filter because of some additional system noise.

For our power supply we have chosen TDK-Lambda’s EFE300M series and from the datasheet it says that the leakage current is 246μA at 240Vac (60Hz).

According to the manufacturer, the input current rating of the EFE300M is 6.1A. We have a choice of TDK-Lambda filters in the 10A range, allowing for some filter derating.

The two filters that we can use are the RSEN-2010L or the RSAN-2010L with a leakage current of just 10μA at 250VAC. We cannot use a filter with a higher leakage current as the power supply leakage + the filter leakage will be greater than 300μA.

As this is a hospital environment, we can probably go with the RSEN-2010L without spike pulse attenuation. A look at the attenuation characteristic plot shows we will have a good margin for the application and will not need a higher performance two stage filter.

Fig 2

A look at the datasheet for the RSEN-2010L shows that there are no Y capacitors between line/neutral and ground, hence the filter design has very low leakage.

Fig 3

One note of caution – a two power supply scenario is quite common. Often the leakage current budget will be affected by an ATX PC power supply driving a computer, or a power supply driving the flat panel display. A good piece of advice is to always check the system block diagram to see where the AC input is being routed to!

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Local duo raise £1,391 for Cancer Research UK by cycling from John O’Groats to Land’s End

TDK Corporation is pleased to announce that two TDK-Lambda UK employees have raised a total of £1,391 for Cancer Research UK by cycling from John O’Groats to Land’s End. The 916-mile journey took Richard Davey (Product Quality Development Engineer) and Paul Dyer (Trainee Electronics Technician) just nine days to complete.

Richard Davey - left - and Paul Dyer reach Land's End

Richard Davey – left – and Paul Dyer reach Land’s End

“We would like to thank all those who have donated towards such a great cause, helping us to raise well-over our original target of £1,000, which really means a lot to us,” said Richard Davey. “It was a tough 9-day ride; we had our ups and downs but we had a lot of fun at the same time.”

The donation page is still live and any donations will be gratefully received:

Cancer Research UK is the world’s leading charity dedicated to beating cancer through research.


Safety Standards for EMI/EMC filters

Safety standards for EMI/EMC are different than those used with power supplies. The International Electrotechnical Commission (IEC) has published IEC 60939-1, but as of March 2015, the standard IEC 60939-1 has not been formally adopted globally.

Europe has adopted the standard with EN 60939 – relating to “passive filter units for electromagnetic interference suppression for use within, or associated with, electronic or electrical equipment and machines”.

In the USA, UL 1283 is the standard – “requirements cover electromagnetic interference (EMI) filters installed on, or connected to, 1000 V or lower potential circuits, 50 – 60 Hz, or up to 1500V dc, and installed in accordance with the National Electrical Code”.

Even Canada with CSA C22.2 No.8 has a different standard – applying to “applies to filters intended for suppressing electromagnetic interference in, or with, apparatus and machines that are to be connected to an ac supply with nominal system voltages of up to 750V and a nominal frequency of up to 60 Hz or connected to a dc supply up to 1060 V dc, intended to be used in nonhazardous locations in accordance with the Canadian Electrical Code, (CEC) Part I”.

Canada and the USA are cooperating on safety certifications and the cULus recognised logo can be seen on filters along with the European certified test houses (TUV, VDE, NEMKO, SEMKO, DEMKO, ENEC and others).

Fig 1

What will not be present is the CE mark as filters are excluded from the current EU directives, as they are classified as components.

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Ilfracombe electronics firm supports Big Bang South West

TDK Corporation is pleased to announce that TDK-Lambda UK has sponsored the STEM Club Best Club Project South West Region heats again this year. The Best Project award, which was presented during The Big Bang Fair South West held in June at the University of Exeter, went to Treviglas College based in Newquay for its project entitled: “How does the size of the hole used to create a vortex affect its power?”

“TDK-Lambda has been actively involved with local schools and academies on a number of STEM related projects over the years,” says Phil Scotcher, General Manager, TDK-Lambda UK. “Sponsoring the STEM Club Best Club Project award reiterates our commitment to supporting education in the South West.”

Each STEM project undertaken at TDK-Lambda’s Ilfracombe facility is developed and closely monitored by local management to ensure all Health & Safety requirements are met, and that the content fulfils the course needs. Recent projects included component reviews using TDK-Lambda’s state-of-the-art test & measurement equipment, and controlling the ambient environment for the surface mount component placement production lines and goods-in area.

STEM Club projects from across the South West region are judged against the National Science and Engineering Competition criteria. The best entries are invited to the national finals held every year in March at the Big Bang Fair UK at the NEC, Birmingham.

The Big Bang Fair South West is managed by Education Business Partnership South West and is the region’s biggest celebration of youth science, technology, engineering and maths (STEM).


Mobile air compressor


Diesel powered portable air compressors are used extensively by construction companies to provide large amounts of pressurised air to power pneumatic tools. The available DC voltage to operate control circuits is often unregulated, requiring any DC-DC converter to operate over a wide range dc input. TDK-Lambda’s DPX30-12WS12 DIN rail mount DC-DC converters are able to operate reliably from a 9.5 to 36Vdc input. This, and a modification to provide a regulated 6V output, was the reason one manufacturer is using the DPX series in their latest mobile air compressors.


UHF/VHF Radio for Defence Industry

PFE series AC-DC power module

TDK-Lambda’s baseplate cooled PFE500SA AC-DC power modules are used in a number of deployable equipment applications around the world. The need for rugged and dependable operation is paramount. A manufacturer of UHF/VHF radios designed in the 28V version of the PFE500SA for their integral power source, because of proven field reliability and local technical support.


Imaging Mass Spectrometry


Imaging mass spectrometry (IMS) is providing a useful tool for the analysis and study of tissue samples. New machines are now capable of reviewing hundreds to thousands of molecules in one tissue section simultaneously. The TDK-Lambda medically certified SWS1000L-48 power supply is now being used by a leading manufacturer of IMS machines, chosen for its proven performance across the medical industry and for local sales and technical support.


Static Phase Converters

PFE series AC-DC power module

When only a single phase AC voltage is available and a load is a three phase motor, a static phase converter is used to provide power to initially start the motor. Once running, the static converter is disconnected and the motor continues to operate off the single phase. Two of TDK-Lambda’s baseplate cooled power modules, the 28V output PFE500SA-28 and the 360V output PF1000A-360, are being used in static phase converters for railway stations. Technical support and cost effectiveness were the primary reasons for the selection.


Pulse Electron Deposition


The Pulsed Electron Deposition (PED) technique enables thin films of materials to be deposited on substrates for semiconductor manufacturing. This method is now being used as an alternative to Pulsed Laser Deposition, with the benefit of lower system costs. The 20kV output ALE-202A power supply, with a 2200 J/s peak charging rate, was chosen for this application because of its excellent pulse to pulse repeatability and TDK-Lambda’s, and three 7,500W TX plug in power supplies.

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