Selecting a line filter to reduce input transients

In addition to EMI (Electro Magnetic Interference) reduction, some EMC line filters are able to provide protection against input transients. These external influences can come from a number of sources and their energy level (measured in Joules) varies accordingly.

High frequency noise is usually generated by power supplies and motor drives. The voltage level is small and the energy level minimal – only several mJ. This can be easily handled by a standard EMI/EMC filter.

Impulsive noise is generated from relay switching or induction motors. Voltages can be in the thousands of Volts with an energy level of hundreds of mJs, significant enough to cause problems with a power supply. Although the IEC 61000-4-4 standard covers product immunity to electrical fast transient voltages on the input lines, the test limits for this are only +/-2kV. For more noisy environments, a filter containing additional protection is recommended.

Surge noise is caused by lightning, and can have significant energy content. The voltage is very high, in the 10s of kVs. This level of energy is best clamped using special lightning arresters.

Fig 1

TDK-Lambda uses amorphous cores to reduce impulsive noise spikes, rather than metal oxide varistors (MOVs) or voltage dependent resistors (VDRs). MOVs clamp spikes, but degrade over time following multiple line surges. Amorphous cores are made from very thin (μm) ferromagnetic amorphous metal strips wound to form a doughnut shaped core, and do not degrade.

Although the ferrite cores used in most EMI/EMC filters do reduce the amplitude of voltage spikes, they can saturate and cause a significant decrease in attenuation.

Shown below is a comparison between a ferrite core and an amorphous core, and the test method used. It can be seen that the amorphous core out performs the ferrite core.

Fig 2

Fig 3

TDK-Lambda’s R series filters that have amorphous cores for high voltage pulsed noise prevention can be found in this selector guide.

Models include:
RSAL 250VAC 0.5 to 6A General purpose
RSAN 250VAC 3 to 60A General purpose
RSMN 250VAC 3 to 60A Two stage filter for better performance
RTAN 500VAC 3 phase 6 to 60A General purpose
RTMN 500VAC 3 phase 6 to 60A Two stage filter for better performance

Power supply failure analysis reports often include independent laboratory test reports that state “component over voltage stress”. The reaction of the recipient is often one of disbelief, claiming that at the time of failure there was no abnormal AC line activity.

Without appropriate protection, input surges can damage a power supply over a long time period, with the effect not seen immediately. High voltage surges will stress and damage both semiconductors and passive components alike, leading to premature failure in the field.

Using a slightly more expensive EMI/EMC filter with pulse attenuation can improve system up-time and reduce expensive service calls.


Wide range input DC-DC converters deliver 30W in a 1 x 1 inch footprint

CCG30_24_48 PR Jun15

TDK Corporation announces the introduction of the CCG30 series of 30W DC-DC converters. Packaged in the industry standard 1 x 1 inch footprint, the CCG series can operate over a wide 4:1 input range. Enclosed in a metal case with six-sided shielding, these high performance converters are suitable for use in data and tele-communications, industrial control, test and measurement, broadcast and portable battery powered equipment.

Accepting either a 9 to 36Vdc or 18 to 76Vdc input, the CCG series can provide output voltages of 3.3, 5, 12 or 15Vdc and currents of up to 7A. Operation from 12V and 24V, or 24V and 48V nominal inputs assists with material control and inventory availability.

Measuring just 25.4 x 25.4 x 9.9mm, the high efficiency units, up to 91%, will operate in ambient temperatures of -40°C to +85°C. Standard features include +/-10% output voltage adjustment, remote on-off, over-current, and over-voltage protection. All CCG30 models carry a five-year warranty.

The CCG series is fully isolated with an input to output isolation of 1,500Vdc and 1,000Vdc input or output to case. Safety certification includes IEC/EN 60950-1, UL/CSA 60950-1 with CE marking for the Low Voltage and RoHS2 Directives.

For more information about the full range of TDK-Lambda CCG series of DC-DC converters, please call TDK-Lambda directly on +44 (0)1271 856600 or visit the TDK-Lambda website at:


Local Manufacturer helps AS-Level students qualify for CREST Gold Award

LA3875 - Image
TDK Corporation is pleased to announce that TDK-Lambda UK is continuing to support Blundell’s School AS-Level students qualify for their Engineering Education Scheme certificates and British Science Association CREST Gold awards. This award is widely recognised and respected by UCAS for university admissions in STEM subjects.

This year’s project involved establishing a method for controlling the ambient temperature for the surface mount component placement production lines and goods-in area. Previous projects included a method to calculate the facility’s carbon-footprint and developing a wind tunnel.

The five person team from Blundell’s school in Tiverton worked under the guidance of Tim Puttick, Production Manager for TDK-Lambda UK. Tim provided support and assistance to the pupils as needed. “The project team took the challenge and over a six month period produced a solution that allowed the ambient temperature of the two areas to be controlled either automatically or manually. A combination of low cost industrial materials and coding with a Raspberry Pi were utilised.”

These projects allows students to develop skills that are not usually used in a class room environment, and included project planning, writing program code, building prototypes, analysing return on investment for decision making and working as a focus team.

CREST is a UK award scheme that recognises success, enabling students to build their skills and demonstrate personal achievement in project work. It offers educators an easy-to-run framework for curriculum enhancement and is student-led, which means that young people take ownership of their projects and choose to undertake them in areas they enjoy or see as relevant. The CREST Gold award requires about 70 hours of project work and is the highest of four levels.


How does an input EMI filter work?

Most electronics contains an EMI filter, either as a separate device, or embedded in circuit boards. Its function is to reduce high frequency electronic noise that may cause interference with other devices. Regulatory standards exist in most countries that limit the amount of noise that can emitted.

EMI, or Electro-Magnetic Interference, is defined as unwanted electrical signals and can be in the form of conducted or radiated emissions. Conducted EMI is where the noise travels along the electrical conductors and radiated EMI is where the noise travels through the air as magnetic fields or radio waves.

EMI is generated from the switching of electrical current and comes from a variety of sources including electronic power supplies. Power supplies convert an input voltage into regulated and isolated (in most cases) DC voltages to run a host of electronic components. That conversion is performed at high frequencies ranging from several kHz to more than a MHz. LED lighting, computers, motor drivers, DC relays and battery chargers all rely on power supplies to operate.

An EMI filter for a power supply normally consists of passive components, including capacitors and inductors, connected together to form LC circuits. The inductor(s) allow DC or low frequency currents to pass through, while blocking the harmful unwanted high frequency currents. The capacitors provide a low impedance path to divert the high frequency noise away from the input of the filter, either back into the power supply, or into the ground connection.

Figure 1 shows a simple single stage power supply filter

Fig 1

In addition to assisting to meet EMI regulations, the filter also has to meet safety standards. The inductor temperature rise is measured and for mains operation, the minimum electrical spacing between line, neutral and ground are controlled. This reduces the risk of fire and electrical shock. The capacitors are also individually safety certified, depending on their position in the circuit. Special “X” capacitors have to be used across the input terminals and “Y” capacitors from the AC circuit to ground.


Grounding Open Frame Power Supplies

Users of open frame power supplies are often surprised when they test a unit on the bench and measure output noise higher than the published specification. This prompts a call to Technical Support, who will then advise that the product has to be correctly grounded, or earthed.

TDK-Lambda’s open frame ZPSA60 power supply

Enclosed power supplies, like TDK-Lambda’s HWS series, have a metal chassis, and can be easily tested without any such concerns. Why is this?

If a power supply is a Class I type (needing a ground connection) input and output noise suppression usually involves ceramic capacitors between line/neutral to ground and DC output to ground. A typical connection is shown below.

On the AC input, high frequency noise flows through the low impedance path of the capacitors to the earth ground. This avoids the electrical noise being transmitted back down the AC input and causing problems with other equipment in the form of EMI (Electro-Magnetic Interference). On the DC output, the capacitors have the same function, this time avoiding high frequency noise appearing on the output of the power supply and causing problems with the load. Note in some cases there may be only one output to ground capacitor.

Looking at the (unpopulated) printed circuit board of the ZPSA60 power supply, the red arrow indicates the location of the two input side capacitors, CY2 and CY3. A copper trace connects them to the bottom left mounting hole. The blue arrow indicates the location of the output capacitor CY1, this time connected to the bottom right mounting hole.

(We can ignore the top two mounting holes as they have no connection made to them.)

When the power supply is tested on the bench, there is no earth ground connection to the power supply (just line and neutral and the output). An earth connection can be made to the bottom left mounting hole, there still is no connection between the two holes, effectively disconnecting the output noise filter capacitor(s).

Once the unit is mounted on the metal chassis of the system (with metal standoffs and screws), all the capacitors are in circuit. At this point, the power supply will operate within its specification.

Some open frame power supplies like TDK-Lambda’s ZMS100 series are capable of operating with or without an earth ground connection, and can be used within a plastic enclosure. An internal wire (indicated by the pointer) links connects the two mounting-hole points together to ensure compliance to the output noise specification.


Why power supply evaluation reports are useful

TDK-Lambda has for many years posted graphical and detailed test reports on the website. So why are they useful when the product specification gives all of the parameter limits?

  • Test methods – A specification or datasheet does not tell the reader how the product was actually tested. Where are the voltage and current meters situated? How is the output ripple and noise measured? Is the earth leakage current recorded with a regular ammeter?
  • Design margin – Often limits are described as “typical”. True test data can eliminate uncertainty (or the need to retest by the customer) and show what kind of margin the product has.
  • What really happens to the power supply during the test? – Load and line regulation changes are given for a variety of inputs and load conditions. This can be used to avoid any surprises when exporting a product to a country that operates on a different input voltage.
  • Over load – When overcurrent is specified it is quite often just stated as “>120%”. A plot will show if the power supply output current folds back, folds forward or remains constant through to a full short circuit. This helps determining cable sizes and pcb trace widths. As the current is often sensed on the primary side of the converter, seeing how the product behaves at different input voltages is also important.
  • Start-up and shutdown characteristics – This will indicate if the power supply has monotonic rise and fall times and how long the product takes to start up. Products that have glitches during start-up can cause issues with certain load types.
  • Actual hold-up times – Important if the power supply does not have active power factor correction, as hold-up times at 115Vac inputs are half those at 230Vac. It is informative to see what the hold-up performance is at different loads as some circuit topologies can have very small hold up times at light loads. Customers who need extended hold up can also review the data for a higher wattage model to see if that will meet their needs.
  • Dynamic load response – This is a good indication of how stable the power supply is. If the output voltage oscillates after a load change, then the control circuit or output filter may be marginally designed.
  • Leakage current – This data shows how the current leakage current not only changes with AC input, but also with power supply output load.
  • EMI performance – Knowing what design margin the power supply has can determine if an external filter is required. A product with a low EMI signature can result in cost savings by eliminating a system filter.

Purchasing a power supply without such detailed data can result in having to requalify another power supply if last minute issues do show up, leading to launch schedule delays and loss of revenue. For customers that do perform extensive power supply testing, it allows those tests to be simplified, again saving money.

Immunity and reliability data is also available for many models on the TDK-Lambda website:


Do power supply manufacturers need to be early adopters replacing IEC 60950-1 and IEC 60065 with the new IEC 62368-1:2014 standard?

The IEC published the 2nd edition of IEC 62368-1 in 2014 and it has now been accepted as a mandatory requirement for CE marking for the Low Voltage Directive. Since Europe’s publication on September 2014, North American based agencies UL and CSA have followed suit and published UL/CSA 62368-1 on December 1st.

This Hazard-Based Safety Engineering (HBSE) standard is intended to replace new submittals for IEC 60950-1 and IEC 60065 as of June 2019. It covers hazard and hazard prevention for both ITE (Information Technology Equipment) and A/V (audio, visual) and other similar apparatus.

IEC 62368-1 is technology independent, whereas IEC 60950-1 and IEC 60065 standards are classed as “prescriptive” and closely control product design. Some of those design rules have been retained, but performance options may give some design flexibility.

The safety compliance industry has made two things clear; it is not a simple merger of 60950-1 and 60065 and although the term “hazard” is used, a formal risk analysis like that defined in the medical standard 60601-1 is not required.

Should the power supply industry start the transition now? The IEC has recognised that a sudden influx of companies requesting testing to the new standard would impose a large burden on test houses and manufacturers alike. Certainly at this early stage it would be wise to attend seminars and training. A date of withdrawal (DOW) for the 60950-1 and 60065 standards has not been announced yet, but a five-year transition to 2019 is expected.

The recommendation is that if a product or series is going to be withdrawn from the markets by 2018, then keep the old standards in place. If it is anticipated that production will continue beyond that, then look into obtaining certification to IEC 62368, but keep the 60950-1 and 60065 files current.


Supporting local school’s STEM project

TDK Corporation is pleased to announce that TDK-Lambda UK is again supporting 6th form Diploma students at The Ilfracombe Academy with a new STEM (science, technology, engineering and mathematics) project.

Developing skills and practicing scientific practical techniques is core to the Applied Science curriculum. The unit involves students in a range of practical sessions, which involves the analysis and separation of substances and the use of various high-tech test and measurement instruments and sensors.

“We have been working closely with the course tutor and STEM lead, Vikki Cooper to develop a session that fulfils the needs of Unit 4 in their Diploma that focusses on scientific practical techniques but also ensures that all Health & Safety requirements are met,” says Anne Sutton, Training and Development Officer at TDK-Lambda UK.

Working with the component engineering team, groups of students had the opportunity to review some electronic components, before analysing them in more detail using TDK-Lambda’s state-of-the-art test & measurement equipment. The merits of all the different practical techniques used throughout the day were compared and contrasted by all of the students during the closing session.

“Many TDK-Lambda employees began their careers in engineering with apprenticeships, internal training and graduate paths,” Anne adds. “This type of STEM activity can provide invaluable help and advice to students looking to take their first steps on the career path and, interestingly, all of the engineers involved in this project attended The Ilfracombe Academy for their own formative education.”

TDK-Lambda UK has manufactured electronic power supplies in Ilfracombe since 1966 and offers a large number of career development opportunities. For more information on the current opportunities available, please email your interests with Anne Sutton directly at:


Electronic Design Automation Software Equipment

HFE Front End Power supply

The design of integrated circuits requires complex software to analyse the substrate layouts of radio frequency and mixed signal devices. This in turn drives the need for a high performance, yet compact computer drawing large amounts of DC power. At the request of one such manufacturer, TDK-Lambda’s Power + Solutions team created a space saving custom 175mm high enclosure assembly containing one 2,500W HFE, and three 7,500W TX plug in power supplies.


Understanding output regulation with multiple output power supplies

Specifying which low wattage, multiple output power supply to use can be complex if the user does not fully understand how output loading affects the product’s regulation characteristics.

An application powering a single board with fixed loads is fairly simple. The power supply is turned on, and the output voltages are monitored to ensure that they are delivering the correct voltage for the circuit card operation.

If the power supply is being used in a system with multiple cards, particularly when the end product is configurable for different user options, trying to predict output voltage changes requires more care and testing.

The block diagram of a traditional, low cost triple output is shown in figure 1.

Figure 1

The power supply control circuitry senses the output voltage of the +5V output, and if the voltage changes, it will compensate accordingly. The two other outputs, +V and –V, are not part of the control loop and are classed as semi regulated.

There are three types of conditions which will cause the voltages to vary.

Line regulation

This is the change in output voltage due to variations in the AC input, usually specified from minimum to maximum AC (90-264Vac). When the AC input is reduced, the power supply’s control loop will compensate accordingly by increasing the pulse width of the switching section. The actual line regulation on all three outputs will be quite small, just a few mV.

Load regulation

This is the change in output voltage due to variations in output load. A change in the +5V load will again be a few mV as the control loop will compensate. On the +V & -V, because they are semi regulated, the voltage regulation will be much higher, in the order of +/-360mV for the +/-12V outputs. Most manufacturers will also stipulate a minimum load condition for the regulation, sometimes as high as 25%. A point to note is that if the minimum load is not applied, the power supply will not be damaged, but the change in output voltage becomes much greater.

Cross regulation

When the 5V load is changed, the control circuitry adjusts the pulse width of the switching section as before, but this significantly alters the +V and –V output voltages. Even with a minimum load of 25%, voltage changes of 700mV can be expected.

If the +5V has a trim potentiometer to adjust the output voltage, then the +V & -V outputs will rise or fall by a similar percentage.

For systems that cannot tolerate such large variations, or if minimum loading requirements are not desired, there is a solution available. TDK-Lambda’s CUT75 triple output power supply utilises a two converter topology, one to power the 5V output and one to power the +12V & -12V outputs. The block diagram is shown in figure 2.

Figure 2

The result is a dramatic improvement over a one converter solution. Measured line and load regulation on the +/-12V outputs is only 300mV for a 0-100% load change.

  • The two converter approach also has other benefits:
  • No minimum loading requirements
  • No cross regulation from +5V to the +/-V outputs
  • The 5V can be adjusted up to 5.25V to compensate for cable drops, without affecting the +V & -V output voltage levels
  • The +V and –V outputs are electrically isolated (tested to 500Vac) from the 5V, allowing them to be connected in series as one output. For example, the dual +/-12V can be configured to provide an isolated 24V output.
  • The two transformer design also allows lower profile magnetics to be used, giving the CUT75 a height of only 38mm.

Traditionally post regulators are used in low power multiple output designs to improve regulation performance. In the CUT75 these have been eliminated with a novel passive circuit. This gives the CUT75 an efficiency rating of 85%, enabling the series to operate without the need for forced air cooling.

More details on the CUT75 can be found on this link