MEDICAL ELECTRONICS

New AC/DC Power Supplies For Medical Applications

Abstract:

When specifying a built-in AC/DC power supply for a medical application, a product pre-certified to IEC/EN 60601-1 is a safe option. There are however still issues to consider, such as requirements for external fusing and possibly EMI filtering. This article discusses the requirements and introduces some available power supplies that make end product certification easier.

Power supplies for medical applications are in great demand, especially with health crises sweeping the world. With more equipment needed for ventilators, analysers and life support in general, product designers must choose appropriate power supplies that meet the latest medical standards based on IEC 60601-1:2005 and its collateral documents. There are national variants: ANSI/AAMI ES 60601-1:2005 in the US, EN 60601-1:2006 in Europe and yet more round the world, all with local deviations. On the 20th August 2020, IEC 606011 amendment 2 was issued (IEC 60601-1:2005 +A1:2012 + A2:2020). This amendment updates out-of-date references to other standards, aligns the standard more closely with IEC 62368-1 (safety of audio/video, information and communication technology equipment), corrects errors and makes clarifications. Collateral electromagnetic disturbance standard IEC 606011-2 is at edition 4.

Using built-in medical power supplies

Medical equipment taking more than around 100W will normally have a built-in AC mains power supply rather than use an external adapter. This places obligations on the endproduct designer as there are now unsafe voltages and energy sources within his equipment. Although a built-in power supply can be medically certified, the whole end-product must also comply with electrical safety and EMC requirements so there are standards to apply to the endproduct in areas such as labelling, connectors, fusing and internal AC mains wiring. For example, if the AC supply cabling to the equipment features connectors, double fusing, in live and neutral, must be used.

There are also considerations to be aware of with any EMI filter added Michael Schrutka, MSc. between a built-in power supply AC/DC Product Manager, and external connections. The RECOM medical EM disturbance standard, IEC 60601-1-2 4th edition, is more onerous than the previous edition, but care must be taken not to increase mains leakage current beyond the proscribed level for the application by applying additional EMI filtering. Even if an added filter claims medical leakage compliance to a certain level, this adds to any existing leakage current in the built-in power supply and may exceed the allowed limits. Ideally, a built-in AC/DC power supply should connect as directly as possible to the medical equipment power inlet with double fusing at that point and with no further EMI filtering. If the power supply holds the highest levels of medical certification and has good EMC compliance margin, there is then a high level of confidence that overall product safety and EMC performance is compliant. It has been possible to use non-medically certified power supplies in medical applications with some extra precautions; a power supply certified to standard IEC 62368-1 for example, with reinforced mains isolation, can be considered to have two measures of operator protection (2MOOP) suitable for lab testing environments with no patient contact. However, the new 4th edition EM disturbance requirements also apply

to operator environments so a non-medical power supply many not be compliant. Using the same power supply, assuming its 2MOOP is equivalent to 1MOPP is also a risk; the exact application must be evaluated for over-voltage category, pollution degree, altitude and the potential medical environment that the product may be used in. A risk assessment will indicate which environment is relevant, for example, ‘professional facility, ‘home healthcare’, or ‘special’, which might be in emergency vehicles where the levels of electromagnetic emissions could be intentionally high from RF communication systems.

The safe option is the only option

The safe solution for medical applications is to specify a power supply with 2MOPP certification and appropriate leakage current and EMC performance for the intended application. Examples are the RACM230-G, RACM550-G and recently released RACM-1200V product ranges from RECOM (Figure 1).

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

These power supplies are for medical built-in applications with power ratings of 230W, 550W and 1200W with forced air or peak power without airflow. They all feature the ability to operate with baseplate cooling at continuous ratings of 160W, 300W and 800W, avoiding the need for fans which are often disallowed in medical environments. Each power supply type has 2MOPP/250VAC rating up to 5000m altitude and leakage currents suitable for patient connection in the B (Body, earthed) category (RACM230) and B/BF (Body/Body Floating) category (RACM550/1200). The RACM230 is compliant to IEC 60101-1-2 3rd edition EM disturbance requirements and the RACM550/1200 are 4th edition certified.

The RACM550-G and RACM1200-V products include an isolated +5V 1A/1.2A standby output and all types feature a ‘smart fan’ output which can control system fan cooling, if required. The products are in 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, giving them class leading power density. The latest release, the RACM1200-V has single 24V, 36V or 48V outputs, operates with an efficiency of over 95% and meets EuP Lot 6 requirements for standby losses.

The safety arrangement of each of the RECOM power supplies is shown in Figure 2.

Figure 2: Safety barriers RACM230/550/1200 series

The RACM1200-V parts also have a PMBusTM interface which may be used internally within the medical product for control and monitoring. If this interface connects outside of the product, it is classified as a SIP/SOP (Signal Input/Output Part) and must have 2MOPP isolation to the patient connection. Alternatively, at low power, a separate medically-certified DC/DC converter with 2 x MOPPs can be interposed between the power supply and patient connection (Figure 3). This can also guarantee yet lower leakage current. Suitable DC/DC converters include the REMxx series from RECOM with ratings from 1W to 30W.

Figure 3: Extra levels of isolation may be required with SIP/ SOP connections

Latest editions of the IEC 60601-1 safety standard have made it less viable to use commercial or AV/IT grade AC/ DC power supplies in medical equipment with ‘added-on’ modifications and/or declared restrictions on use. For an easy passage through the certification process and for the widest applicability of an end product, a fully medically-certified power supply such as one from the RECOM RACM series is the best and ultimately the cheaper solution when product development and test house costs, along with time to market are factored-in.

RECOM products are supported by a global network of distributors offering technical application support for customers wishing to incorporate AC/DC power supplies into their medical products with the minimum of difficulty.