New Medical Grade AC/DC Power Supply

When specifying an internal AC/DC power supply for a medical application, it is safe to choose a product that is certified to IEC/EN 60601-1. However, there are still some issues to consider, such as external fuses and EMI filtering requirements. This article will explore these requirements and introduce some available power supplies to assist with final product certification.

Power supplies for medical applications are in high demand, especially as the health crisis sweeps the world. With more and more ventilators, analyzers, and life-support devices needed, product designers must choose power supplies that meet the requirements of the latest medical standard IEC 60601-1:2005 and its annexes. And there are national standards: ANSI/AAMI ES 60601-1:2005 in the United States, EN 60601-1:2006 in Europe, and other national standards around the world, all with local regulatory content. IEC 60601-1 Amendment 2 (IEC 60601-1:2005 + A1:2012 + A2:2020) was officially released on August 20, 2020, and the revision updates outdated standard references, aligns more closely with IEC 62368-1 (Safety requirements for audio/video, information and communication technology equipment), corrects errors, and provides detailed instructions. The annexes EMI standard IEC 60601-1-2 is now in its 4th edition.

Use built-in medical grade power supply

Medical devices that consume more than 100W usually have a built-in AC power supply rather than an external adapter. Product designers have an obligation to take this into account, as there are unsafe voltages and energy in today's devices. Although a built-in power supply can obtain medical certification, the entire final product must still meet electrical safety and EMC requirements, including labeling, connectors, fuses, and internal AC power wiring. For example, if the device's AC power cable has a connector, it must use a double fuse for the live and neutral wires.

There are some things to be aware of when adding an EMI filter between an internal power supply and external connections. The fourth edition of the medical electromagnetic compatibility standard IEC 60601-1-2 is more complex than previous editions, and care must be taken not to allow mains leakage current to exceed the levels specified by the standard when using additional EMI filters. Even if the filter claims to be medical compliant to a certain degree, it may exceed the allowable range when added to the leakage current in the internal power supply. Ideally, the internal AC/DC power supply should be connected directly to the power socket of the medical device as directly as possible and be double-fused and without EMI filtering. If the power supply has the highest level of medical-grade certification and has good EMC performance, then there can be a high degree of confidence that the safety and EMC performance of the end product are fully met.

In some cases, non-medical power supplies can be used in medical applications, but the following precautions need to be taken. For example, a power supply certified to standard IEC 62368-1 with reinforced mains isolation would be considered to have double measures of protection (2MOOP) and therefore suitable for laboratory test environments without patient contact. However, the fourth edition electromagnetic interference requirements also apply to the operator environment and therefore many non-medical power supplies do not meet the requirements. If the same power supply is used, assuming that its 2MOOP is equal to 1MOPP, there is also a risk, and the application must be evaluated for overvoltage, pollution, altitude and the medical environment in which the product may be used. The risk assessment will indicate which environment is relevant, such as professional institutions, home healthcare or special environments, such as in ambulances where RF communication systems emit high levels of electromagnetic radiation.

Safety is the only choice

A safe solution is to use a power supply with 2MOPP certification and appropriate leakage current and EMC performance for the target application, such as RECOM’s RACM230-G, RACM550-G, and the recently released RACM-1200V (Figure 1).

Figure 1: The medically certified RACMxx series power supplies are rated at 230W, 550W, and 1200W from left to right.

These power supplies are intended for medical built-in applications and are rated at 230W, 550W and 1200W with forced air cooling. They can all provide 160W, 300W and 800W continuous power ratings with baseboard cooling and no airflow, without the need for fans which are often not allowed in medical environments. Each power supply type has a 2MOPP/250VAC rating, a maximum operating altitude of 5000m, and leakage current suitable for patient connections of Type B (body, grounded) (RACM230) and Type B/BF (body/body floating) (RACM550/1200) for direct contact with the patient. The RACM230 meets the IEC 60101-1-2 third edition electromagnetic interference requirements, while the RACM550/1200 has been certified to the fourth edition.

The RACM550-G and RACM1200-V products feature +5V 1A/1.2A isolated standby outputs, and all types are equipped with intelligent fan outputs to control system fan cooling if needed. The products feature industry-standard form factors: 4” x 2” for the RACM230-G, 5” x 3” for the RACM550-G, and 9” x 3.8” for the RACM1200-V, and offer leading power density. The newly launched RACM1200-V is available with a single output of 24V, 36V or 48V, with an efficiency of over 95% and meets EuP Lot 6 standby loss requirements.

The safety configuration of each RECOM power supply is shown in Figure 2.

Figure 2: RACM230/550/1200 series safety barrier

The RACM1200-V also features a PMBusTM interface that can be controlled and monitored inside medical products. If this interface is connected externally to the product, it will be classified as a SIP/SOP (signal input/output part) and must be isolated with a double patient protection (2MOPP) level. Alternatively, for lower power, a medically certified 2MOPP DC/DC converter can be inserted between the power supply and the patient connection (Figure 3), which can ensure lower leakage current. Suitable DC/DC converters include RECOM's REMxx series, which are rated from 1W to 30W.

Figure 3: SIP/SOP connections may require additional levels of isolation

The latest version of the safety standard IEC 60601 has made it less feasible to use commercial or AV/IT grade AC/DC power supplies for medical equipment with "additional" modifications and/or usage restrictions. Considering product development, test house costs and time to market, medically certified power supplies, such as RECOM's RACM series, are the best and most economical solution to make the certification process smoother and the end product more widely available.

RECOM products are supported by a global distributor network, which offers technical support and services to help customers integrate AC/DC power supplies into medical products with the fastest possible design cycles.