Regulatory vs. Market Needs
Generally, manufacturers are only required to have their medical device endproducts meet many of the standards, especially those relating to IEC 60601-1 family of technical standards for medical equipment. However, designers will find that starting out with power supplies designed from the ground up to meet those standards will greatly simplify achieving final compliance while accelerating time-to-market for their end product, particularly since power and safety issues are the basis for many key facets of the standards.
For example, internal type power supplies are meant to be handled only during the manufacturing process, as parts are installed in end equipment. There - fore, the assumption might be that the power supply should be designed for, and tested based on, that use. However, as internal power supplies are increasingly being designed into portable devices, such as home healthcare equipment, power supplies meeting the more stringent test parameters will provide the end system designer a more robust power supply, potentially allowing easier system compliance to more demanding certifications. (See Figure 2)
IEC 60601-1 General Standard
This key standard is a widely accepted benchmark for medical electrical equipment. Compliance has become a requirement for electrical medical equipment marketed in many regions globally. However, the standard functions on several levels and is not always well understood. While compliance may be a de facto requirement, it is not the same as device approval, only a recognized step in the approval process. The current 3rd Edition of the standard places emphasis on usability engineering, risk assessment, and use in home healthcare applications.
In addition to regional variations, the 60601-1 standard also encompasses Collateral Standards (numbered 60601-1-x) that define requirements for certain aspects of safety and performance. Requirements for the general standard may be overridden or bypassed by specific language in the collateral standards that are applicable to specific aspects of product design, such as:
- IEC 60601-1-2 – Electromagnetic Compatibility
- IEC 60601-1-3 – Radiation Protection for diagnostic use of X-rays
- IEC 60601-1-4 – Programmable electrical medical systems
- IEC 60601-1-8 – Alarm systems
- IEC 60601-1-11 – Home healthcare environments.
A further set of Particular Standards (numbered 60601-2-x) provides supplementary definitions and requirements for specific product types such as defibrillators, MR scanners, electroencephalograms, and insulin pumps.
Means of Protection
Medical equipment is required to incorporate Means of Patient Protection (MOPP) or Means of Operator Protection (MOOP), with patient protection being the more stringent standard. Primary distinctions between MOPP and MOOP relate to allowable creepage distance, isolations, and insulation. Each Means of Protection has a basic level and a 2x level with 2 MOPP referring to the highest level of protection with 4000 Vac isolation, 8mm creepage distance, and double insulation.
On the surface, MOOP and MOPP may appear to address distinct markets; however, the increasing use of home healthcare devices is blurring the lines between these applications. For that reason, it can be advantageous to design to the more stringent 2 MOPP levels, as long as it is not cost prohibitive. Increasing volumes resulting from home healthcare demands can, in many cases, mitigate the cost of increased levels of protection.
As mentioned above, final product certification is not dependent upon whether the power supply manufacturer specifies MOOP or MOPP isolation compliance. However, if compliance is not specified, it will be the end product designer’s responsibility to ensure that the final product meets the overall requirements.
EMC Compliance Requirements
It is important for designers to review and specify their product’s performance acceptance criteria. It is not enough to just state the IEC standard. There are four levels for acceptance criteria, and designers need to be clear on the level that is acceptable for each application.
- Normal performance within the specification limits.
- Degradation or loss of function, which is not recoverable due to damage of equipment or software or loss of data. In all cases, equipment shall not become dangerous or unsafe as a result of the application of the tests. The performance acceptance criteria can be different for the various levels or the test.