Difference between medical AC/DC Power Adapter and general-use models

What is the difference between medical AC/DC Power Adapter and general-purpose AC/DC Power Adapter? We explain, from the perspective of a power supply manufacturer, the differences in applicable safety standards, classification of applied parts, insulation distances, and allowable leakage current values.

"There is such a thing as a medical AC/DC Power Adapter, but what is the difference from a standard AC/DC Power Adapter?" We receive this question very frequently. It is asked not only by companies developing medical devices, but also by companies working on equipment unrelated to medical applications.

In conclusion, the two are not in a relationship of a "premium version and standard version" of the same Products. They are subject to different safety standards, and as a result, the design itself differs. Below, we explain in detail.

Applicable safety standards differ

AC/DC Power Adapter safety standards are determined by the intended use of the equipment in which it is used.

In addition, safety standards appropriate to their use apply to household equipment and measurement/control equipment. Furthermore, the required standards and certifications vary depending on the country or region where the Products is sold.

For details about IEC 60601-1, please see What is the medical standard IEC 60601-1?.

Why are requirements for medical power supplies so strict?

The most critical accident to prevent in electrical Products is electric shock. The severity of injury caused by electric shock depends on the path and magnitude of the current flowing through the body. Even a small amount of current flowing directly through the heart can become life-threatening.

Patients connected to medical electrical equipment are in a different situation from typical users of general devices.

• They may be unable to perceive danger due to poor health or the effects of anesthesia
• Even if they experience electric shock, they may be unable to immediately move away
• Electrical circuits may come into contact with the human body through skin contact or insertion into the body
• Multiple devices may be connected to a single patient at the same time

Strict requirements are imposed on power supplies for medical equipment because of these conditions. What the standards demand is not merely achieving high numerical values, but designing with the assumption that patients may be unable to protect themselves.

Classification of Applied Parts

In IEC 60601-1, applied parts are classified into the following three categories depending on how the equipment comes into contact with the patient. This classification serves as the starting point for determining the level of protection required for the power supply.

In addition, when equipment is placed near the patient (patient vicinity), regulatory requirements also apply. Even equipment that is not directly connected to the patient must be verified.

Means of Protection (MOPP/MOOP) and the Difference from Insulation

MOP refers to protective measures intended to prevent people from coming into contact with hazardous voltages (exceeding 42.4 V peak AC, approximately 30 V RMS, or 60 V DC). In the 3rd edition of IEC 60601-1, these were classified into "Means of Patient Protection (MOPP)" and "Means of Operator Protection (MOOP)." Since operators are assumed to be healthy individuals who are trained in handling the equipment, the requirements for patient protection are defined more strictly.

The manufacturer of the equipment determines which classification to apply. This decision is based on whether there is a possibility that a patient may come into contact with the equipment. In vitro diagnostic devices and other equipment that patients never touch are often classified as MOOP only.

The differences in protective measures appear in dielectric strength and required distances. For medical electrical equipment, 2 x MOOP or 2 x MOPP achieved by double or reinforced insulation is required.

*The above values are representative examples. The actual required distances are not fixed and vary depending on conditions such as operating voltage, insulation material group (CTI), pollution degree, and overvoltage category.

For more details about the concept of MOP, please refer to The distinction between operator and patient in medical standards and the concept of MOP.

Creepage and Clearance Distances Change the Power Supply Design Itself

Clearance distance is the shortest distance through air between two conductive parts, while creepage distance is the shortest distance along the surface of an insulating material between two conductive parts.

Even with the same "double/reinforced insulation," there are differences between operator protection (2xMOOP) and patient protection (2xMOPP), such as 3,000VAC versus 4,000VAC in test voltage and 5.0mm versus 8.0mm in creepage distance. This difference cannot be addressed simply by making the insulating material thicker.

As the required distances increase, it becomes necessary to redesign the wiring that runs near the insulation boundary, the transformer bobbin structure, and the component layout. This is to ensure the required distances are maintained while keeping the Products within a practical size. Medical power supplies tend to be larger than general-purpose ones because these distances must be secured.

Another approach is to add a DC/DC Converters for Industrial & Embedded to an existing power supply to provide an additional insulation layer. While this is a common method of adding protective measures, it may be disadvantageous in terms of efficiency and cost.

Differences in Allowable Leakage Current Values

Leakage current is a current that flows through or over the surface of insulating materials and is not related to the intended function of the device. In medical electrical equipment, it must be designed so that the leakage current remains within allowable limits not only under normal conditions but also under a condition where one component has failed (single fault condition).

The allowable values vary depending on the classification of the applied part.

*Each column shows the allowable values under "normal condition / single fault condition." A single fault condition refers to a state in which one component or wiring point has failed, such as a broken earth conductor.
*Representative values according to IEC 60601-1 (3rd edition). The allowable values for earth leakage current were revised from the 2nd edition and may also vary depending on the device classification and installation conditions.

For Type CF, which makes electrical contact with the heart, the allowable value for patient leakage current is one-tenth that of Type B and Type BF. This difference affects not only the insulation structure of the power supply but also the overall design of the equipment.

Leakage current is also explained in What is Leakage Current?.

Other Design Differences

In addition to insulation and leakage current, power supplies for medical equipment require design considerations that differ from those for general use. For example, a configuration that includes fuses on both the L and N sides (double fuse) is used.

Regarding EMC (electromagnetic compatibility), compliance with IEC 60601-1-2 for medical electrical equipment is also required. In medical settings, there is a possibility of electromagnetic interference from wireless devices and other medical equipment, and any resulting disturbance of measurement values is directly related to patient safety. In the 4th edition, the requirements concerning electromagnetic interference were made stricter than in the 3rd edition.

Just because it says "medical use" does not mean any product can be used

As we have seen, the level of protection required for a medical power supply varies depending on the equipment. The required specifications differ according to the classification of applied parts, the overall insulation configuration of the equipment, the environment in which it is used, and EMC requirements.

It is not as simple as choosing a power supply that supports the most stringent 2 x MOPP for peace of mind. Increasing the level of protection makes the power supply larger in order to secure insulation distances and also increases costs. Conversely, if the required protection is insufficient, it will not comply with standards.

About our proposal:We do not recommend a uniform configuration for every inquiry regarding medical power supplies. After understanding the equipment configuration and the environment in which it will be used, we propose Products that meet the required level of protection. We believe that identifying the necessary level is also the role of a power supply manufacturer.

If you have trouble selecting a medical power supply, please feel free to contact us. It is fine even if the specifications have not yet been finalized. Our sales and technical representatives will review the details and propose feasible solutions, including standard products, semi-custom options, and full custom designs.

Consult us about medical power supplies