Safety is absolutely paramount in the medical arena and, to achieve this, there are many standards that must be met before a product can be placed on the market. While approvals are necessary, in times of crisis they can slow down the delivery of new products to where they are needed.
The regulatory environment for medical power
There are a huge variety of medical devices available, with more being developed and introduced to the market at an ever-increasing rate, reflecting society’s interest in their own well-being. While an increasing number of devices are portable and battery-powered, a significant proportion of devices (especially those for use in professional scenarios such as hospitals and clinics) remain mains powered.
As various types of medical devices are attached to patients and some, such as electrocardiogram (ECG) machines incorporate electrically conductive pads that are directly affixed to the patient, there is the potential that a hazardous voltage could be applied to the patient during a fault condition.
Given this unique situation, the standards surrounding mains-powered medical equipment are unique and stringent, as one would hope. The main regulatory framework is IEC 60601 which comprises a number of standards that were originally developed in the 1970s and have been subsequently updated to meet changing needs and evolving technologies. Introduced in later editions, the concepts of ‘Means of Operator Protection’ (MOOP) and ‘Means of Patient Protection’ (MOPP) are used to define the design requirements to prevent any risk of unintended electrical current passing through the body of the patient or operator. Together, these Means of Protection (MOPs) rely upon physical separation and galvanic isolation for protection. The 3rd Edition of IEC 60601 requires two MOPs, meaning that two independent isolation barriers must be present, such that multiple and unrelated insulation system failures would need to occur before an operator or patient is put at risk.
The regulations for MOPPs are more stringent than those for MOOPs, requiring larger creepage and clearance distances as well as thicker insulation. Additionally the insulation breakdown voltage has to be higher and permissible leakage currents are significantly less.
However, there are a number of other factors to be taken into account including the mains supply voltage (which can vary from 90V to 240V for single-phase), the overvoltage category of the system, the material group type for creepage surfaces, pollution degree category and operating altitude. Each of these factors can influence the design requirements. For example, a power supply that is to be used at a high elevation should increase clearance distances – meaning that requirements for use in an alpine region are different for those in the Netherlands.
As technology has moved on, so have the standards relating to medical devices. IEC 60601 is now in its 4th Edition which brought some significant changes, particularly with regard to power solutions. As medical devices are increasingly being used away from hospitals – often in the patient’s home, they will be more exposed to EMC from the increasing number of connected devices such as smartphones, laptops, tablets, smart speakers etc. Even within professional healthcare environments, wireless technology is becoming more prevalent. None of these devices were invented when IEC 60601 was first published, so changes to recognise this technology shift were necessary.
Earlier versions of the standard looked at equipment categories, including definitions such as ‘life-supporting’. The 4th Edition changed the approach to consider ‘intended use environments’ including professional healthcare facilities, home healthcare and ‘special environments’ recognizing that where the equipment is to be used is often the most important criterion.
If only to further emphasise that the world of medical approvals is constantly changing, the new Medical Device Regulation (MDR) came into full force after a 3-year transition period ending on 26th May 2020, thereby replacing the Medical Devices Directive (93/42/EEC). Manufacturers of medical devices for sale within the EU now have to comply with even stricter guidelines if their products are to be able to be sold within the EU.
Modern medical power solutions
With the complexities associated with ensuring that a power solution is compliant with IEC 60601 and the other regulations that will apply to medical devices, as well as being efficient, small, reliable and reasonably priced, it comes as no surprise that sourcing an off-the-shelf power solution is the most reliable route to get a product to market quickly. Indeed, as many of these sub-systems already carry the necessary approvals, they can save significant time and remove risk from the approval of the end product.
Artesyn’s LCC600 series – fully enclosed 600 W conduction cooled AC-DC power supplies that employ a thermal baseplate to allow them to deliver full power at ambient temperatures as high as +85C. The fanless operation makes them ideal for medical applications where acoustic noise would be unwelcome. A total of four models in the series offer adjustable outputs of 12 V, 28 V, 36 V or 48 V, along with a 5 V / 1.5A standby output for auxiliary functions. LCC600 power supplies include a number of protection features and up to five units can be paralleled using active current share for higher power applications. They include I2C / PMBus communications for monitoring and control. Along with standard ITE approvals, the LCC600 units are approved to IEC 60601 for medical applications.
The uMP series of configurable power supplies is also from Artesyn. These units offer almost limitless output combinations at peak power levels as high as 1800 W and are able to deliver full power up to 50C, with derating to 70C. Their ability to be configured rapidly makes them ideal for use where a non-standard output configuration is needed, yet the manufacturing volumes are not sufficient for a custom solution – as is often the case in medical applications.
These rugged units are suited to medical and industrial applications and can survive shock and vibration in excess of 50G. uMP units offer 2x MOPP protection and are compliant with IEC 60601 making the process of achieving medical approvals on the end equipment far quicker and easier.
At the lower end of the power spectrum is Meanwell’s MPM series of encapsulated PCB-mount AC-DC power supplies. These 20 W rated modules are very compact (2.06”x1.07” footprint) yet they offer multiple protections including short circuit, overload, overvoltage and over temperature. The devices are approved to IEC 60601 and offer 2x MOPP. These devices are particularly useful in producing voltage rails that are suitable for use in patient contact (BF – body floating) applications where the front-end power supply does not carry the necessary medical approvals.
A further mid-range power solution is the 650 W PQU650 series from Murata Power Solutions. This U-channel based product can deliver up to 650 W with forced airflow at +50C or 450 W with convection cooling. It is also possible to deliver a short duration ‘power boost’ of 800 W which is particularly useful when starting up into transient loads.
The PQU650 is approved to IEC 60601 3rd Edition and designed to meet the EMC requirements of the 4th Edition.
About the author:
Oskar Czechowski is Product Development Manager Central Europe – Power Supplies, at TTI, Inc – www.ttieurope.com