Reviewing power supply safety reports

The manufacturer’s datasheet provides a variety of information about the features and ratings of a power supply, but more information is needed for a correct and reliable installation. This type of information can be found in the product’s safety reports. If these often over-looked points are not noted, then delays may occur when safety certification is sought for the complete system.

For the purposes of this article, we will just consider a power supply that is certified to the IEC 60950-1 standard.

Typically there are three pieces of documentation, the CB test certificate, an EN 60950-1 test report (often included in the IEC 60950-1 CB report) and a UL 60950-1 report. Often manufacturers will restrict the circulation of full reports, because of confidential information, and may require the signing of a non-disclosure agreement. Fortunately the safety bodies realise this and permit reproduction of a selected number of pages from the report.

The information in the two page CB test certificate is fairly limited. Its primary function is to inform other NCBs (National Certification Bodies) that a sample of the product complies with the requirements of the standard. The name of the applicant, address and manufacturing location is stated, along with the models covered and their ratings. The standard used for evaluation with the appropriate revisions is very important information. This shows that the power supply status is current and is suitable for designing in to a new system or product. It should be noted that as many power supplies now use the CE mark (Low Voltage Directive) to show compliance to EN 60950-1, the CB test certificate may state “Additionally evaluated to EN 60950-1”.

The IEC 60950-1 CB or UL 60950-1 report, even if it is an abridged version of the complete report which often contains 200 or 300 pages, is more useful. Under the section “Engineering Conditions of Acceptability” are the important notes for product installation. Here one will find such information as:

Which model output voltages are SELV (Separated or safety extra-low voltage). Outputs that are not SELV should be insulated to ensure the operator or maintenance person does not come in contact with them, hence avoiding an electric shock.

If any of the outputs have hazardous energy levels. A power supply that has a VA rating of more than 240VA can cause sparking and/or burns if a metallic object shorts the output. Busbars for example, should be protected.

Can the power supply terminals be field wired? For an embedded power supply, the answer is usually “no” and any cabling attached to the product has to be done at the factory by trained personnel. A DIN rail power supply though is designed for field wiring as the task is simpler, often not requiring crimped tags, having a lower risk of stray wire strands and a stronger clamp for the wiring connection.

The maximum investigated branch circuit rating is stated as during power supply abnormal testing, the input will be protected by a circuit breaker. During testing that breaker is not allowed to trip.
The Pollution Degree rating is stated. A PD rating of 2, for example, is common for office, lab and test equipment where only occasional condensation may occur. On the other hand, a PD rating of 4 indicates the power supply is suitable for outdoor applications, and can be subject to rain or even snow. Using a product with the right rating is critical for both reliability and safety.

The requirement for earth bonding is listed. If “required” is stated, then the power supply earth connection to the end-product earth has to be correctly bonded.

As the maximum temperatures of magnetic components are a safety concern, guidance to the inspector on which Class (temperature rating) insulation system is being used is given. Class A for example is 105oC, and measured temperatures when installed in the end-product cannot exceed that.

Generally an industrial power supply is not designed to be a stand-alone part, like say a power supply used on a bench or a phone charger. Clarification is provided as to the type of enclosure the power supply should be housed in.

Other comments may be made by the inspector – what orientation of the product was used for testing, or if the output voltage adjustment range of the power supply was considered.

Gladly, it is becoming more popular among most of the larger power supply manufacturers to post this type of documentation on their websites; even some of the on-line distributors are now doing this too. The challenge is to keep the information current, particularly with the number of amendments and revisions that are required!


How to use the CUT75 as a dual output power supply

The CUT75 auxiliary outputs are electrically isolated from the main 5V. TDK-Lambda explains how to configure the power supply to provide 5V / 24V or 5V / 30V in this new video.


To read more about the CUT75 series, please visit:

If you have a question you’d like to ask TDK-Lambda, please feel free to use the online FAQ form and we’ll get back to you with an answer to your question as soon as possible.


IEC/UL/EN 60950-1 Amendment 2

In August 2013, CENELEC published Amendment 2 to EN 60950-1:2006 covering the general safety requirements of ITE (Information Technology Equipment). July 2nd, 2016 is the expiry date for Amendment 1 of EN 60950-1, and manufacturers are working through their 60950-1 reports to update their files.

For Europe, this amends EN 60950-1:2006 and its Amendments 1 and 12. Safety files will now state EN 60950-1:2006/A2:2013 or EN 60950-1:2006 + A11:2009 + A1:2010 + A12:2011 + A2:2013. It has been widely stated that this will be the last change to the 60950-1 standard.

Oct 14, 2014 was the publication date by UL and CSA for the update to UL/CSA 60950-1 and safety files will now refer to UL 60950-1, 2nd Edition, 2014-10-14 and CAN/CSA C22.2 No. 60950-1-07, 2nd Edition, 2014-10. In UL/CSA’s case, upgrading to Amendment 2 is not mandatory on existing product files.

With the upcoming June 2019 transition to IEC 62368-1:2014 for both IEC 60950-1 and IEC 60065, what was changed? Fortunately for the power supply manufacturers, the changes to IEC 60950-1 are mainly “clarifications”. Both TÜV Rheinland® and UL reported that in general there would be no impact requiring product changes and/or that it was reflecting their current practice.

For IEC 60950-1 the main changes for power supplies are:

  • Clause requires that any graphics used are to comply with ISO standards and should be explained in the manual. These include some (not widely used) earth grounding symbols.
  • Clause 2.9.2 introduced humidity testing to equipment designated for tropical regions. Chinese CCC and CQC safety standards have been concerned about this for some time.
  • Likewise 2.10.3 refers to a common requirement in China for a higher maximum altitude, typically 5,000m, or the addition of a symbol indicating operation at a maximum of 2,000m. This is not an issue for UL, EN or CB.
  • Clause 4.3.8 requires non lead acid batteries to comply with IEC 62133, with the exception of button style batteries. This will only affect a very limited number of power supplies.
  • The use of VDRs (voltage dependant resistors), which was a major change for Edition 1, have had a flammability requirement added.

Indeed this amendment is widely seen by the safety bodies as a way to ensure a smoother transition into IEC 62368-1:2014.


What are the key features of the CUT75 power supplies?

TDK-Lambda highlights the key features of the CUT75 triple output power supplies in this new video. This includes the product’s 3×5 inch footprint, a low 27mm height and isolation from the main to auxiliary outputs.


To read more about the CUT75 series, please visit:

If you have a question you’d like to ask TDK-Lambda, please feel free to use the online FAQ form and we’ll get back to you with an answer to your question as soon as possible.


What is the usable power in a DC-DC converter?

The term “high usable power” is widely used by the manufacturers of DC-DC converters to describe their product’s performance.  Many Engineers though tend to focus on the datasheet’s rated current and assume that by selecting a more expensive, higher power converter, it will give them more derating and improved reliability.

To determine which converter is best suited for your application there are a number of steps that have to be taken in addition to determining the input and output voltage.

Looking at the industry standard quarter brick, it is obvious from the construction, even with an integral baseplate and some heat conduction to the card it is mounted on, the converter will need some airflow, a heatsink, or both.  Cold plate is not usually available in most applications.

Fig 1

Fortunately most manufacturers do a very good job of providing a host of curves and their specified test methods. Below are the curves for TDK-Lambda’s iQG 500W DC-DC converter against various airflow rates and the test method.

Fig 2

Fig 3

The test method simulates vertically mounted cards in telecom and datacom cabinets.

How does this relate to our original subject regarding usable power? Below is a simplified pair of curves for 2m/s airflow. The blue line is for an 800W 12V 67A DC-DC converter, and the green line for our 500W 12V 42A converter. Even though the 800W model is 1.6 times more powerful at low ambient temperatures, in the yellow area at higher ambients the ratio drops to 1.35 times at 70oC and 1.24 times at 85oC. Typically customers operate DC-DC converters in the 65 to 80oC range.


Although the 800W converter has more available power, the 500W unit has more usable power (as a % of its rated power), demonstrated by a much less steep derating curve. It can be seen that at higher ambient temperatures, it would be more cost effective to use the 500W converter.


Nuclear magnetic resonance spectroscopy

Vega AC-DC Power Supply

Until recently Nuclear magnetic resonance spectrometers were very expensive, due in part to the need to cool the magnets used in the process. Modern, lower cost, devices are now available that use permanent magnets requiring less cooling.

Designers of one bench-top NMR analyser selected TDK-Lambda’s Vega series of modular power supplies, as their system required eight outputs, including 7 and 3.45 voltages! Vega power supplies can be quickly assembled with pre-built, wide range output modules and are available with a number of standard options.


HVDC Input Power Module Series Extended With Additional Output Voltages

TDK Corporation announces an extension to the PH-A280 series of high voltage input DC-DC converters. Capable of operating from 200 to 425Vdc, the new 3.3V, 15V and 28V output power modules are suitable for use in data centres, tele-communications and renewable energy applications utilising a 380V nominal high voltage DC bus.

LA005383 - PH-A

The six new models are rated at 3.3V 15A or 20A, 15V 5A or 10A and 28V 2.7A or 5.4A. This extends the existing 50 to 150W PH-A280 product range of 5V, 12V, 24V and 48V outputs. The outputs of the new models can be adjusted by -20% to +10% (-10% to +20% for the 3.3V output) to accommodate non-standard voltages.

Following the industry standard quarter-brick package (37.2 x 12.7 x 58.3mm), the high efficiency units, up to 90%, can provide full load with -40°C to +100°C baseplate temperatures. The converters can also be conduction cooled making it suitable for use in sealed outdoor enclosures or liquid cooled applications.

Standard features include remote on-off, over-current, and over-voltage protection. All PH-A280 models carry a five-year warranty. The series is fully isolated with an input to output isolation of 3,000Vac and are safety certified to 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 PH-A280 series of DC-DC converters, please call TDK-Lambda directly on +44 (0)1271 856600 or visit the
TDK-Lambda website at:


Convection cooling power supplies

Convection cooled power supplies are ideal for applications where acoustical noise cannot be tolerated or when there is a possibility that dirt, dust and other materials can be drawn in by a cooling fan. With power supply efficiencies now commonly in excess of 90%, more fan-less products are entering the market, particularly in the 100-300W power range.

At first glance it seems that they are easier to install. No need to direct forced air at the power supply or calculate how much air is needed – the product will operate correctly without any concern. There are, however, some considerations that the user should be aware of.

The definition of convection cooling is the transfer of heat by the movement of fluids or gas. Hot air rises, being is less dense than cold air, causing the circulation of air through or around a heat dissipating product.

In the case of an open frame power supply, it is often mounted horizontally on standoffs to provide clearance for solder joints and under board components. Figure 1 shows the direction of the air currents, with the cooler air being drawn in at the bottom.

Fig 1Figure 1

The speed of this air is quite low, in the order of 0.3m/s, but it is enough to reduce the power supply’s component temperatures and avoid “hot spots”. The safety bodies (BSI, TUV, UL, etc) perform thermal testing in this orientation and state on the conditions of acceptability that thermal measurements should be repeated in the end equipment.

To avoid restricting the natural convection air currents, sufficient clearance should be provided around the power supply. A 50mm space is considered adequate.

In some applications a vertical orientation is required (figure 2) and care should be taken to examine if heatsinks and other bulky parts will restrict the air currents. To increase field life it is good practice to ensure that electrolytic capacitors are situated at the bottom where they will operate cooler.

Fig 2Figure 2

Often manufacturers will state a recommended mounting orientation and suggest a derating factor if that is not possible. Mounting a convection cooled power supply upside down (with the circuit board at the top – Figure 3) can dramatically reduce field life. This is usually forbidden.

Fig 3Figure 3

If you have concerns, consult the manufacturer’s installation manual, or contact their technical support. With high density power supplies, there is usually a list of maximum component temperatures for the critical parts. To avoid potential delays during safety certification, it is best to check those before submitting your product.


GenesysTM 3U 15kW programmable power supply series adds high current 30, 40 and 50V models

TDK Corporation announces the introduction of three new models to TDK-Lambda’s Genesys™ series of programmable DC power supplies . The series is now available with outputs of 30V at 500A, 40V at 375A and 50V at 300A and output powers of 15kW. These higher current units address the requirements for applications in the OEM, Industrial, Aero-space and ATE markets including: Semiconductor and Automotive Test, Component Test/Burn-in and Magnet supplies.

LA2880 - Gen 3U High Current

Carrying a 5-year warranty, the TDK-Lambda Genesys™ high current models have the same features and compact dimensions (3U high and 19” (483mm) wide) as the existing 60V to 600V 15kW models. The units can operate in either constant current or constant voltage mode and accept three-phase 400VAC or 480VAC inputs, with passive Power Factor Correc-tion.

Higher power systems can be configured using the Master/Slave “Advanced” Parallel operat-ing mode. This mode configures the Master unit to be the single point for programming, measurement and status of the total current of the paralleled system. Thus, four units can operate as a single 60kW power supply, increasing the flexibility for system designers.

Common to the entire Genesys™ family is the embedded 16-bit RS-232/RS-485 Multi-Drop digital interface. Using this digital interface, up to 31 power supplies may be controlled in a daisy-chain over the RS-485 communication line.

Other optional digital and analog interfaces include the LXI Class C compliant LAN and the IEEE (IEEE488.2 and SCPI-compliant) Multi-Drop digital interfaces, which include a selection of instrument drivers such as NI LabVIEW and NI LabWindows™. Isolated Analog program-ming/monitor interface options included use either 0-5V/0-10V or 4-20mA control.

Common to all Genesys™ models the safety features included are Safe/Auto Re-Start, Last Setting Memory and built-in protective functions. With Safe Start configured, the power supply returns to its last operation settings after a power interruption but with the Output disabled, while with Auto Re-Start, the power supply returns to the last used operation settings after a power interruption. Last Setting Memory retains settings such as the Output volt-age/current, Output ON/OFF, OVP/UVL level, Foldback and Start-Up mode at each AC Input turn-off sequence. Built-in protective functions include over voltage protection (OVP), under voltage limit (UVL), fold-back protection (FOLD) and over-temperature (OTP) protection.

CE marked in accordance with the Low Voltage Directive, the GenesysTM 3U 15kW power supply series conforms to conducted and radiated EMI in accordance with EN55011A and FCC Part 15J-A. Safety agency certifications include UL60950-1 and EN60950-1.


Swimming Pool Shutters

DRF DIN Rail Power Supplies

In addition to saving energy and water usage, automated swimming pool covers and shutters provide a level of security against drowning for both children and pets. Utilising isolated, low voltages to drive the motors to open and close the shutters also eliminates the risk of electrocution.

TDK-Lambda’s relationship with a supplier of pool accessories allowed a demonstration of the features, reliability and energy saving features of the DRF DIN rail mounted power supplies. Convection cooling, a high 94% efficiency and low off-load power draw enables the products to be used outside of traditional industrial applications.