Reviewing the Latest Safety Standards for Medical-Grade Power Supplies

By Ashok Bindra

Contributed By Hearst Electronic Products


Power supplies for medical equipment, just as for industrial, telecom, and military systems, continue to evolve in the areas of efficiency, density, and size. However, medical-grade power supplies must also meet safety requirements imposed by international standards like IEC60601-1, which itself continues to evolve, spawning regional versions such as UL60601-1 and EN60601-1. These regional versions demand additional safety requirements like creepage, clearance spacing, and leakage current that is beyond the general safety standard.

These safety requirements are stringent because power supplies that have been designed and certified safe in industrial or telecom applications may not be safe for use in medical equipment. What is more, according to TDK-Lambda’s article “What to look for in a medical power supply,”¹ medical equipment tends to be more sensitive to electromagnetic interference (EMI) than most industrial equipment, thereby making electromagnetic compatibility (EMC) a key concern in medical applications.

This article will examine the latest evolution in the safety standard IEC60601-1 for medical-grade power supplies, and will also identify some suppliers meeting these requirements. In addition, it will highlight key features of recently introduced medical-grade power supplies certified to the third edition safety standard, a differentiating factor in this competitive environment.

Evolving standards

Per TDK-Lambda’s paper, for most of the world, including North America and Europe, safety standards for medical power supplies are contained in the International Electrotechnical Commission’s IEC60601-1 standard, which is in its third edition and was the result of a comprehensive review of the 2nd edition, which originated in 1988. The original IEC 60601-1 standard was published in 1977. Since the worldwide shift to IEC 60601-1 3rd edition is ongoing, second- and third-edition standards must coexist in medical equipment intended to ship internationally, according to a white paper “IEC 60601-1 Medical Design Standards-3rd Edition”² by CUI. The coexistence creates an added level of complexity for product designers who must now meet both editions of the IEC safety standard.

The IEC 60601-1 3rd edition (Figure 1), first adopted in Europe by the European Union (EU) with member states passing legislation in 2006, is now enforced in Europe, Canada, and, starting this year, in the U.S. Consequently, as of June 2012, the 2nd edition has been withdrawn and all new and existing products must be certified to the third edition, known in Europe as EN60601-1:2006.

U.S. is enforcing IEC 60601-1 3rd edition

Figure 1: Starting in 2014, the U.S. is enforcing IEC 60601-1 3rd edition, also known as ANSI/AAMI ES60601-1:2005, for medical-grade power supplies.

The U.S. version, labeled ANSI/AAMI ES60601-1:2005, originally went into effect in July 2013, but the FDA announced an extension to give U.S. medical device designers a slight reprieve to December 31, 2013. Unlike the EU, the U.S. standard requires only new products launched after the transition date (and not existing products) to comply with the 3rd edition. Likewise, Canada effectively adopted its 3rd-edition version CAN/CSA60601:2008 in April 2013, and it is applicable only to new products launched after the effective date.

Meanwhile, Japan, Australia, New Zealand, and China continue to mandate the 2nd edition. As there is no clear timetable for the third edition in China, it will continue to mandate the 2nd edition of IEC 60601-1 for some time to come.

More protection

Unlike the 2nd edition, the IEC60601-1 3rd edition separates the requirements for protection of the patient and the operator. Consequently, the third edition standard must now be certified as to the means of operator protection (MOOP) as well as the means of patient protection (MOPP). These classifications provide greater protection for patients who may be more vulnerable to the medical equipment in use. By comparison, MOOP is more closely aligned to the traditional IEC 60950, the standard of protection for information technology equipment (ITE), and MOPP requires better isolation, insulation, and creepage specs (Table 1).

Third-edition requirements of isolation, creepage, and insulation

Table 1: Third-edition requirements of isolation, creepage, and insulation for protection of operator and patient.

The 2nd edition classifies medical equipment as type B (body), type BF (body floating) and type CF (cardiac floating). This classification determines what levels of isolation, insulation, creepage, clearance, and leakage would be allowed.

Accordingly, as per CUI, the IEC60601-1 third edition requires improved isolation between the AC input to the power supply, the internal high-voltage stages, and the DC output to make the product safer, and, thereby, prevent any electric shock to the user or the patient. For high isolation, a double layer of insulation or reinforced insulation, including minimum distances between conductors and components, is recommended for medical power supplies. One result is that it must be subjected to a much higher voltage testing, making the design process more challenging. For instance, medical supplies that operate from a 240 VAC mains must withstand a dielectric test of 4 kV as compared to 3 kVAC for industrial equipment.

Furthermore, the third edition requires the establishment of a “Risk Management Process” and record file retention in compliance with the ISO standard ISO14971. As a result, certification to the IEC60601-1 3rd edition requires an audit of the manufacturer’s compliance with ISO14971, which includes a risk management file where identifiable fault conditions are identified and assessed.

Certified examples

As a result, many vendors are working to meet both versions of IEC60601-1 in the same design, which requires additional time and effort. To help ease the compliance process for medical device designers, CUI offers a comprehensive line of medical-grade AC/DC power supplies ranging from 20~400 W that have been certified to IEC 60601-1 3rd-edition two MOPP standard. At the low end is 20 W VMS-20 series featuring no-load power of <0.3 W and efficiency up to 85 percent, while at the high-end the power factor corrected VMC-365 series delivers 365 W continuous power with a power density of 19 W/in.³ in an open-frame 3 x 5 in. industry-standard footprint (Figure 2). This series excels at delivering high power in an extremely compact package, making it ideal for applications where space is limited and energy efficiency is a high priority. CUI’s medical-grade power supplies also are designed to handle universal input.

CUI’s open-frame external AC/DC supply VMS-365

Figure 2: CUI’s open-frame external AC/DC supply VMS-365 is certified to IEC 60601-1 3rd-edition two MOPP standard.

Another contender in this space is TDK-Lambda Americas, offering its digitally-controlled 300 to 400 W single-output CFE400M series, boasting 4 kVAC reinforced input-to-output isolation with dual fusing and an output-to-ground isolation of 1500 VAC to meet IEC/EN/UL/CSA 60601-1 editions 2 and 3 safety approval. Other features include 94 percent efficiency (typical), remote On/Off and remote sense with a small size of 7.0 x 3.94 x 1.6 in. (Figure 3).

TDK-Lambda Americas’ medical-grade CFE400M

Figure 3: TDK-Lambda Americas’ medical-grade CFE400M meets safety approval for both the second and third editions of IEC60601-1.

Similarly, XP Power recently unveiled a 150 W, low profile, medical-grade AC/DC supply designated the ECP225 series that meets the latest, stringent third edition medical safety standards ANSI/AAMI IS 60601-1 and IEC/EN60601-1. It can deliver a maximum of 225 W when a forced air flow of only 10 CFM is applied. With a very-low profile of 25.4 mm (1.0 in.) and a footprint measuring 63.5 x 127 mm (2.5 x 5.0 in.), these ultra-compact power supplies occupy significantly less volume than similarly-rated power units on the market, according to the manufacturer. The units also comply with the internationally-recognized EMC standards EN55011 and EN55022 Class B specifications for conducted noise and Class A limits for radiated emissions.

In conclusion, while applicable safety standards are getting more stringent and complex to ensure patient and operator safety under various operating conditions, key manufacturers of medical-grade power supplies are keeping up with these changes, offering products that comply with the latest safety standard editions.

For more information on the products discussed in this article, use the links provided to access product pages on the Digi-Key website.

References:
  1. What to look for in a medical power supply” by Mel Berman, David Norton, Andrew Skinner and Robert Taylor, TDK-Lambda, Medical Design, March 2009, p.33-35.
  2. White paper “IEC 60601-1 Medical Design Standards-3rd Edition”, CUI Inc.
Electronic Products Logo

Disclaimer: The opinions, beliefs, and viewpoints expressed by the various authors and/or forum participants on this website do not necessarily reflect the opinions, beliefs, and viewpoints of Digi-Key Corporation or official policies of Digi-Key Corporation.