Powering Medical Homecare Equipment

Apr 22, 2022
Healthcare icons on blue hexagons
Homecare medical devices have to potentially withstand more challenging and uncontrolled conditions than those used in the clinical environment. This article looks at the standard that applies to electrical equipment safety, its particular requirements, and the way they can be met with by off-the-shelf products.

Table of contents

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 power supplies and devices, 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 adequate 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 portable medical devices 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 device 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 health monitoring and alerts. 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.
Medical equipment connection diagram
Fig. 1: Isolation characteristics of a medical Class II power supply
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 (2MOPP). In Class II equipment, this would be achieved by increased creepage and 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 2MOPP. 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, radiated RF immunity 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 always, 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

Technical drawing with dimensions and 3D view of RECOM RACM40-K series
Fig. 2: The RECOM RACM40-K 40W AC/DC, suitable for homecare medical devices
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. RECOMs portfolio covers parts rated from 6W up to 65W, all with 2MOPP (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 2MOPP certification to 5000m altitude, the RACM40-K is also certified as per information technology, 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 medical power supply units from 15W up to 1200W are also available with medical certifications.
Product of RECOM's REM10 series next to a 1€ coin
Fig. 3: RECOM REM10 series – 10W, 2MOPP certified DIP 24 DC/DC converter
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 1W to 60W output range. These DC/DCs have 2 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.

2MOPP 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 power-efficient as possible, and compact solutions can be found in RECOM’s wide range of non-isolated parts in all form factors and power levels.

Applications
  Series
1 AC/DC, Single Output RACM40-K Series
Focus
  • 1.6“x3“, open card units; optional 2“x3“
  • 1.8“x3.2“, encapsulated modules
  • 40W power from -40°C up to +65°C ambient
  • Operating temp. up to +85°C with derating
2 DC/DC, 10 W, THT REM10 Series
Focus
  • Reinforced insulation for 250VAC working voltage
  • Clearance and creepage distance: 8mm
  • 5kVAC I/P to O/P 2MOPP isolation
  • 2µA patient leakage current