What medical facilities are there in power supplies

Power supplies for medical devices in the home environment

The use of medical devices in one's own home is increasing. Today, patients can carry out many treatments outside of the hospital: Blood pressure monitors or ventilators for the treatment of sleep-related breathing disorders (SBAS) are often found in private households. Electronic devices with a communication connection offer new possibilities for outpatient therapy, which is usually more efficient and cheaper than a lengthy hospital stay. The electrical medical devices must, however, meet special requirements for their use in a domestic environment, which will be explained in more detail in the following article

Essential standards for the use of medical devices in the home environment

The requirements for the devices are defined, among other things, by the IEC60601-1-11 standard. The standard deals with the essential performance characteristics for medical care in the home environment and defines the corresponding safety precautions for medical electrical (ME) devices and systems. The standard defines the home environment as both the apartment in which a patient lives and other places where patients may be (e.g. nursing homes or vehicles), but not professional health care facilities or facilities for emergency medical services.

The current version of IEC 60601-1-11 was published in April 2016 as "German version EN 60601-1-11: 2015", a transition period for the previous standard ends on December 31, 2018. The essential performance features as well as the safety of medical devices should be preserved under almost all circumstances, which should be achieved by means of the safety precautions set out in the further course of the article. In addition to the safety requirements from IEC 60601-1-11, stricter requirements for electromagnetic compatibility in accordance with IEC60601-1-2 also apply in this area of ​​application.

Special electrical requirements for ME devices and their power supply units

The line voltage in AC power supply networks is usually assumed to be +/- 10% of the nominal voltage. This defines the area in which the devices must function. Since in many places - especially in old buildings - the design of the electrical cabling is poor, ME devices have to work in a broader range of 85% - 110% of the nominal voltage. For devices that are designed to keep a patient alive or to resuscitate him, even stricter requirements apply: They must reliably perform their tasks in the range of 80% - 110% of the nominal voltage.
When selecting the power supply unit, the manufacturer of the ME device must ensure that the power consumption matches the output data of the power supply unit in these applications. It should also be noted that ME devices that are not permanently connected to the power supply:

  • may only be operated with power packs of protection class II or with an internal power supply
  • may not use functional earth
  • only type BF (body floating, body reference with current flow) or CF (cardial floating, heart reference with current flow) applied parts may be used.

You should therefore pay particular attention to the presence or absence of these symbols for the power supply unit:

The background of the electrical requirements

The requirement for protection class II is based on the fact that many houses do not have a functioning earthing. With devices of protection class I, in the event of a fault, a current flows to earth via the protective conductor and triggers the residual current circuit breaker (RCD, formerly called FI) or a fuse. In a building installation with inadequate or completely missing earthing, this can lead to a fatal electric shock. Devices of protection class II, on the other hand, have double insulation and are safe in the event of this fault.
The functional earth is used for electromagnetic interference suppression in devices. If there is no grounding, this can lead to malfunctions due to impermissible interference levels. However, this is not the case for devices without functional earth.
We speak of applied parts when there is an electrically conductive connection between the patient and the device. In this case, the patient connection must be isolated from earth and the AC supply network. The current that flows to earth when the patient touches the patient connection must not exceed the limit values ​​of 100 µA for type BF devices and 10 µA for type CF devices for applied parts. Such an application part is easier to implement if the leakage current of the power supply unit already complies with the corresponding limit values ​​for BF or CF.

Special protection requirements against ingress of water and foreign bodies

With ME devices that are used in a domestic environment, it is assumed that there is an increased risk of water ingress. For this reason, IEC 60601-1-11 basically stipulates the IP protection class IP01. For devices that can be moved during operation as well as for hand-held applications, the increased protection class IP02 is required in accordance with IEC 60529. Furthermore, the devices must also be designed to be safe to touch for children (protection against the ingress of solid foreign bodies ≥ 5.6 mm) and thus not only meet IP21 or IP22.
Because of the closed plastic housing, external power supplies often meet protection class IP40 by default - however, it is a widespread misconception that because of the closed housing there is also automatic protection against ingress of water. The information and test results of the manufacturer as well as the permissible usage positions according to the operating instructions must be carefully observed here.

Special environmental conditions

Unless otherwise stated in the instructions for use of the ME device, the devices must be operational under the following conditions:

Special requirements for mechanical strength

Portable devices such as power supply units that are inoperable while moving must pass a shock test, impact test and drop test, a shock test with 15 g (IEC 60068-2-27) and a vibration test (IEC 60068-2-64).

Shock exam
Peak acceleration: 15 g
Duration: 11ms
Pulse shape: sine half-wave
Number of shocks: 3 per direction and axis (18)

Broadband random vibration test
Acceleration amplitude: 10Hz - 100Hz: 1.0 (m / s²) ² / Hz
100Hz - 200Hz -3dB / octave
200Hz - 2kHz 0.5 (m / s²) ² / Hz

Other requirements from IEC60601-1-11

In the case of medical devices for use in a domestic environment, there are also some requirements for the operating instructions. Among other things, the untrained and non-specialist patient as an operator must be explicitly addressed here. This must also be considered in the risk analysis.

Special requirements for EMC from IEC60601-1-2
Medical devices in a domestic environment must meet at least the same, but in some cases also higher, requirements than medical devices in a professional environment. This is due, among other things, to the greater exposure to unknown transmission power in the various frequency bands (radio, television, amateur radio, Bluetooth, WLAN, GSM, UMTS, LTE, etc.).
The interference immunity must be higher for the following electromagnetic phenomena.

• for radiated high frequency (IEC61000-4-3) 30MHz-2.7 GHz the interference level increases to 10V / m
• For conducted high frequency (IEC 61000-4-6) 150kHz - 80MHz, the 6V interference level applies not only to the ISM frequencies, but also to the amateur radio frequencies

The devices also have to cause fewer electromagnetic emissions when it comes to emitted interference: they must meet Class B of CISPR 11. This requires a limit value that is 10 dB lower than class A, which is required for use in hospitals and clinics.


FRIWO's “FOX” power supply family meets the requirements

With the device family FOX (FRIWO One-Click Xchange), the German power supply specialist FRIWO offers extremely efficient power supply units that are also suitable for use in domestic environments. The devices meet the strictest energy efficiency standards such as DOE Level VI. Although this is not yet required in the medical sector, it offers future security, which should also be taken into account when selecting the power supply from an environmental and resource perspective.
In addition to the very high efficiency of the devices, the minimum standby losses are decisive.

Double locking of the housing, minimum leakage currents of ≤ 10 µA and the construction of the insulation according to 2x MOPP ensure maximum security. This makes it possible to design a medical device with a patient connection, which is considered an applied part of class CF.

The devices have been developed and tested in accordance with the special requirements of IEC60601-1-11. Thanks to the interchangeable adapter system and wide-range input from 80 to 264 VAC, they can be used worldwide. In order to meet the requirements of IEC60601-1-11, the optional FOX interchangeable adapter system with IP42 protection can be used. In practical use, this means that the devices can be wiped down with a damp cloth and cleaned. In addition, the devices are also optionally available with a white housing, which further enhances the visual appearance of the FOX family, especially for use in medical technology. In addition, the devices already meet the EMC standard IEC60601-1-2: 2014 (4th Edition) for medical devices, both for use in professional and domestic environments.

The individual members of the FOX device family provide outputs of 7.5 W (FOX6M), 12 W (FOX12M), 18 W (FOX18M) and 30 W (FOX30M) and cover voltage variants from 5 to 48 VDC in the standard portfolio. The product family also includes solutions with a USB output in the 11 W (5 V / 2200 mA) power class, which are also available with medical approval in accordance with IEC 60601-1.

In addition to the devices with an interchangeable adapter system, FRIWO also offers variants with a fixed base for country-specific use and a 30 W version as a desktop variant. The standard goods from the catalog cover Europe, USA / Japan, UK and Australia. Other country-specific device versions can be implemented on request.
In addition to direct sales and purchase from FRIWO's distribution partners, the devices can also be purchased in small and very small quantities from the company's own online shop at www.friwo-shop.de.