Powering Medical Homecare Equipment

Statistics say that we are all living longer (on average), with the best figure achieved by Japanese women at over 87 years, based on 2019 data [1]. Ironically, though, we are also living unhealthier lifestyles, with rates of obesity and chronic illness such as diabetes and heart disease being on the rise. The result is that there is an increasing number of older and unfit people requiring ongoing medical treatment, which puts a strain on healthcare systems.

To alleviate the burden on institutional medical services and improve quality of life, the trend to provide more treatment in home settings has emerged. This has become increasingly effective, with technology facilitating the use of more sophisticated and portable equipment, supported by ‘telehealth’, the remote, electronic provision of health-related services and monitoring. It is now big business and is predicted to be worth over $500B globally by 2028 [2].

Home healthcare equipment is in a precarious environment

We often think of industrial or professional medical environments as being ‘harsh’, with exacting cleanliness and safety standards applied to equipment; however, the operating conditions are at least well defined. In a home setting, there is a host of other variables that can affect the performance of medical equipment, and device designers are required to anticipate these in their risk assessments. Apart from the obvious domestic temperature and humidity variations, equipment can be incorrectly used by insufficiently trained users and carers in an environment that includes children and pets. There may be spilled liquids, household dust, food debris, pet hair, and medical waste also present. The electrical supply may not have an effective ground connection, and excessive voltage dips, spikes, and surges may be present. Moreover, radiated and conducted electromagnetic interference from other household equipment could also affect operation. Operating complex medical equipment may be confusing and difficult for someone who is old or ill.

To address these concerns, medical electrical (ME) equipment in the home setting must meet specific safety, performance, and EMC standards. The top-level document for medical equipment safety and essential performance is IEC 60601-1, and this is supported by the collateral standard IEC 60601-1-11 “Requirements for medical electrical equipment and medical electrical systems used in the home healthcare environment.” Currently, the standard is dated to 2015 with amendment A1:2021.

Particular requirements of IEC 60601-1-11, additional to those in the professional healthcare environment, include the ability of mains-powered equipment to operate with 15% drops in supply voltage from nominal or 20%, if the equipment is intended for life support or resuscitation. In such cases, there must also be a mechanism for maintaining the essential performance of the equipment for a “sufficient” amount of time after the total loss of mains power as well as alarms to indicate the hazardous situation. In practice, this means that this class of equipment must have battery backup with “state-of-health” monitoring and alarms. If the equipment operates on a DC supply, there are also extra requirements to withstand voltage variations and 30 second dips.

Homecare portable medical devices must now be Class II

A more far-reaching requirement is that AC-powered homecare ME equipment must now be Class II, with no need for a functional earthing. This means that it must be double insulated (Figure 1). The standard still allows Class I ME equipment with a metallic case and protective earthing but only as part of a hard-wired “fixed” installation. Even then, there are stringent requirements for verifying the integrity of the ground connection before use by a qualified installer with additional safety labelling.

As in hospital environments, if simultaneous connection of the equipment to the patient and a mains supply is possible, typically through a battery charger, two measures of patient protection against electric shock are required (2 x MOPP). In Class II equipment, this would be achieved by enhanced creepage/clearance distances and/or sufficient solid or multi-layer insulation systems. The scale of the isolation/insulation depends on the mains supply voltage, expected pollution degree, and even altitude. Any connection to the patient, such as a wired sensor, must meet or exceed the body floating (BF) designation that defines the maximum allowable AC mains patient leakage current.

If the medical device can make electrical contact with the patient and is also designed to connect to other unspecified equipment, typically through an optional USB or LAN connection for monitoring or logging data, the interface must also be isolated to meet 2 x MOPP. This is so that a fault in the unspecified equipment cannot cause a dangerous current to flow to the patient through the device under consideration. Similarly, as is the case for hospital equipment, BF (and CF) applied parts must have isolation from any ground connection that might be present, for example, via a screen in a cable to other unspecified equipment. This is to prevent dangerous current flowing from other faulty, unspecified electrical equipment, through the patient, to the device under consideration and to the ground.

Class B EMC conducted and radiated emission levels are now mandatory

To address the potential conducted and radiated EMI emissions problem in a home setting, IEC 60601-1-11 requires all equipment to comply with CISPR 11 (latest edition 2015/AMD2:2019) Class B levels. In hospital environments, Class A is the minimum, which is less rigorous than Class B. Among other changes, immunity to radiated RF must also be enhanced from 3V/m to 10V/m in home settings, as it is more likely for other household equipment to interfere. Additionally, as a new requirement, device basic safety and essential performance must be maintained during the specified levels of interference.

There are many other requirements of IEC 60601-1-11, including environmental, mechanical strength and accessibility, water and particulate ingress, maintenance, labelling, documentation, and more. As ever, a device manufacturer must examine the standards in detail, assess the possible hazards, and address them during the product design stage.

AC/DCs are a critical safety element

A main element of electrical safety is, of course, any integrated AC/DC power supply. As homecare devices are often small and portable, modular board-mount AC/DCs are popular. The range from RECOM covers many requirements with parts rated at 18W, 30W, and 40W, all with 2 x MOPP (240VAC minimum) certification, Class II earth-free operation, and minimum BF-level patient leakage current rating.

The input range of all parts goes down to at least 90VAC to include the homecare specification of 115VAC nominal less 20%. An example product is the RACM40-K (Figure 2), an encapsulated AC/DC just 1.8” x 3.2” x 1.2”. The part operates up to 85 °C with derating and has a range of single outputs from 5V to 48VDC. Along with medical 2 x MOPP certification to 5000m altitude, the RACM40-K is also certified as per IT, multimedia, household, and industrial safety standards and can be used in overvoltage category III environments.

For fixed homecare installations, chassis-mount open frame or enclosed power supply products from 60W up to 1200W are also available with medical certifications.

Isolated external interfaces to homecare medical devices often require isolated power rails, and these can be provided by DC/DC converters, with parts available from RECOM in the range 1W to 30W. These DC/DCs have 2 x MOPP isolation and a wide variety of input/output voltage options. An example is the REM10 series (Figure 3), packing 10W into a compact DIP24 format with a wide 4:1 input range and just 2µA patient leakage current. An optional shutdown control limits standby consumption to 12.5mW for energy-sensitive battery powered applications.

2 x MOPP isolated DC/DC converters may also be used in combination with higher power AC/DC products to provide isolation between input channels on multi-parameter patient-connected equipment, in order to achieve higher overall isolation ratings or a lower patient leakage current.

Power conversion efficiency is also an issue

In homecare medical devices, there will most likely also be requirements for on-board non-isolated switching converter power modules to generate various internal power rails. Although the medical standards do not relate to these parts directly, the application will be typically battery-powered for either normal use or as back-up. So, battery lifetime is important. Any DC/DC conversion should, therefore, be as efficient as possible, and perfect solutions can be found in RECOM’s wide range of non-isolated parts in all form factors and power levels.

References

[1] https://www.nippon.com/en/japan-data/h00788/
[2] https://www.researchandmarkets.com/reports/5450245