Medical Power Supplies

Medical power supplies are the AC/DC or DC/DC power supplies that keep medical equipment operational. They can be found in medical electrical equipment for both home and hospital use from handheld tools like thermometers to large equipment like MRI scanners.

As medical supplies have been advancing over the years, power supplies have become an increasingly more essential component to keep things running smoothly. As equipment has advanced, power supplies that keep them running have had to advance as well. Specifications have become more stringent to ensure the safety of both the operator of the equipment and the patient receiving care. Essential specifications include proper safety approvals, high MTBF and reliability, isolation, and high efficiency.

No matter the application, safety is a huge concern with any medical power supply. To be classified as a medical device power supply, compliance with IEC 60601 is required. Other factors like efficiency, MTBF, leakage, isolation, and reliability are crucial specifications to medical power supply. Due to these more stringent specifications, medical power supplies typically have a longer design cycle, but have a longer life expectancy.

Safety
The most important medical safety standard is IEC 60601-1. This standard outlines the basic safety requirements for electrical equipment used in a medical practice.

Efficiency
Efficiency in a power supply measures how much power is lost in the power conversion process. The less efficient a power supply is, the shorter its lifespan will be, so efficiency is crucial in medical applications.

Reliability/MTBF
Reliability is crucial for any medical power supply. Reliability ensures that a supply will continue to continue working for a long period of time and will not fail at a crucial moment. The higher the MTBF for a medical power supply, the better. Reliability is typically higher in supplies that have simple designs, but if this is not an option, reliability can also be improved through protection circuits, using high quality components, and conservative design practices. Bellcore/Telcordia TR-322 is an MTBF standard that can be applied to medical power supplies.

Isolation
Isolation is the separation of incoming high voltage (mains) to the low voltage output. Isolation helps prevent voltages from passing between components and can help prevent electrical shock and breaks ground loops. According to IEC 60601-1, medical equipment needs to isolate its circuits form the supply mains on all poles simultaneously and have very low leakage current.

Leakage
Leakage current is the current that still flows input to output during supply operation. It is important for leakage current in medical power supply to be low because any additional current that reaches the patient or the caregiver that is not intended to could cause serious harm. Leakage requirements in a medical power supply are determined by IEC 60601-1.

*These values are only applicable to equipment having multiple applied parts.

Note: Above chart is based on information from IEC 60601-1 Ver. 3 and may not necessarily be the most current information.

To help reduce leakage current, medical power supplies should be properly grounded, double insulated or reinforced for to meet the requirements of the standard.

Shock
Shock is a huge risk when it comes to medical supplies because shock an electric shock from a power supply could severely harm a patient or caregiver. Means of Operator Protection (MOOP) and Means of Patient Protection (MOPP) laid out in IEC 60601-1 outline how supplies can be designed and tested to reduce the risk of electric shock to both the operator and the patient. Both MOOP and MOPP have to meet specific dielectric strength, creepage/clearance, and protective earth connection requirements to be certified as IEC 60601-1 and appropriate for medical devices.

Properly isolating components like the AC input, DC output, and the supply itself can help reduce the risk of shock and damage to the supply. Isolation is especially important around conductors.

Creepage/Clearance
Creepage and clearance in a supply offer space between conductive parts in a supply. Creepage measures this distance along the surface insulation, while clearance measures it through the air. It is important for medical equipment to have proper creepage to protect against deterioration caused by tracking, and proper clearance in order to prevent dielectric breakdown within the supply. Proper creepage and clearance also helps ensure compliance with MOOP and MOPP.

Minimum Creepage Distances and Air Clearances Between Parts of Opposite Polarity of the Mains Port

Minimum Air Clearances Providing MOOP from the Mains Part

* Air clearances for working voltages above 20kVr.m.s. or 28 KVDC can be prescribed by particular standards if necessary.

Minimum Creepage Distances and Air Clearances Providing MOPP

The standards for medical power supply units are primarily defined by the International Electrotechnical Commission (IEC). The primary medical safety standard that applies to medical equipment safety is IEC 60601-1, but CISPR 11: 2015 also covers some specifications for medical power supplies.

IEC 60601-1/UL 60601-1
This standard was originally published in 1977 and has since consisted of 4 updates, the most recent published in January 2020. This standard covers a variety of specifications that medical electronics need to meet and be tested against before they are used in hospital or home healthcare. Some of those standards include the following.

Environmental Tests
Medical equipment needs to be tested to meet proper temperature, humidity, and atmospheric pressure conditions as indicated by IEC 60601-1.

Protection against Electrical Hazards
IEC 60601-1 outlines protections and limitations that medical equipment will need to have for electrical hazards like shock, water/particulate matter, and leakage current. It also outlines the standards required for methods of protecting against electrical hazards like protective earthing, MOOP, MOPP, leakage, insulation, creepage and air clearances, and layout.

Protection Against Mechanical Hazards
Medical equipment needs to have proper protection against certain mechanical hazards such as moving parts, expelled parts, instability, acoustic energy and vibration, and pneumatic and hydraulic pressure. IEC 60601-1 addresses the hazards that are associated with these moving parts and how the risk created from moving parts coming in contact with one another can be reduced.

Protection Against Unwanted/Excessive Radiation
Medical equipment is prone to exposure to unwanted or excessive radiation, given the environment it is used in. IEC 60601-1 outlines radiation limitations for x-radiation, alpha, beta, gamma and neutron particle radiation, microwave radiation, infrared radiation, and UV radiation.

Classifications

Class
Class classification identifies protection against electric shock.
Class I: Powered by an external power source, reliable protective earth
Class II: Powered by an external power source, no reliable protective earth, reinforced insulation
Class IP: Internal power supply

Type
Type classification identifies the type of patient applied part or patient lead. It covers devices with circuitry or parts that will come into direct contact with patients.
Type B: Patient applied part earthed
Type BF: Patient applied part floating (surface conductor)
Type CF: Patient applied part floating or use in direct contact with the heart

CISPR 11: 2015
This standard applies to medical electrical equipment (as well as industrial and scientific equipment) that will be operating in the frequency range of 0-400GHz. It covers the limits and methods of measurement for radio frequency disturbance characteristics, as well as requirements to control RF disturbances.

Commercial supplies and a medically approved power supply differ primarily in their safety, reliability, and longevity. A standard commercial supply may not be compliant to IEC 60601-1, which is crucial for a medical power supply. A commercial power supply may also be lacking in the proper environmental protections, reliability ratings, and MTBF that are key specifications for a medical power supply.

A commercial power supply will also not have Means of Patient Protection or Means of Operator Protection. These two specifications are vital for medical supplies because they protect both the operator and the patient from shock that could cause serious harm. A standard, commercial supply may have protections against shock, but they will not be to the extent that MOOP and MOPP are approved for. This aligns itself with the safety criteria which is the major difference between commercial power supplies and medical power supplies.

Medical power supply units are used in electrical medical equipment in hospitals and home care. They can be either internal or external supplies and either AC/DC or DC/DC. Depending on the application, different medical power supplies will be needed and different specifications will need to be met.

Hospital

Hospitals need to be equipped with a wide range of electrical medical devices in order to care for a wide range of patients. Medical equipment for a hospital can include devices such as heart rate monitors, blood pressure monitors, ventilators, incubators, x-ray machines and CT scan machines, just to name a few. Medical power supplies play a vital role in helping this equipment functioning and working properly.

In-Home

Medical equipment for home care will typically be smaller in size and more suited to individual care than hospital grade equipment. Home medical equipment can include devices such as portable ventilators, sleep apnea machines, hearing aids, and different types of monitors and meters. Power supplies are used to keep these medical electronic devices running and can be found internally in devices or externally as chargers.

As a medical power supplier, Wall Industries is here to ensure the highest quality supply for your medical application. We have standard open frame, wall mount, and desktop medical grade power supplies if AC/DC is needed, as well as surface mount and through hole options for DC/DC. We also offer extensive custom capabilities and have many years of experience designing highly efficient power sources that meet IEC 60601. Whether a medical supply is needed for hospital or home use, Wall can find something that will fit your specifications. Explore our solutions or get in touch with us today.