Power Supplies for Medical Applications

Innovative Power Supplies for Medical Applications

Power Supplies for medical ApplicationsAs shifts in global demographics push the rise of healthcare standards, engineers face increasing pressure to achieve innovative designs that deliver both practically and aesthetically whilst boasting impressive efficiency and meeting all relevant medical standards. To facilitate the groundwork for the work of medical electronic designers, Ideal Power focuses on providing power supplies for medical applications that are optimised to deliver industry-leading performance and meet relevant safety standards for worldwide applications. It is through this commitment that we are able to offer a robust range of competitively priced power supply solutions designed for medical applications meeting quality standards ISO 13485 and ISO 14971.

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Today, external switchmode PSUs (Power Supply Units), internal AC/DC PSUs and DC/DC converters can be found in a wide array of medical instruments; including radiotherapy equipment, dialysis machines, X-ray, CT and MRI (Magnetic Resonance Imaging) scanning devices and diagnostic equipment. The safety of medical electronic equipment is paramount to not only the patient (who may be susceptible to even small leakage currents) but the operator too.

Applied Parts Classification and Types of Medical Power Supply Units

In order to achieve the safety of medical electronics, IEC/UL/EN 60601-1 prescribes three categories for electronic medical devices and medical power supplies, known as applied parts classification. An applied part is any piece of electronic medical equipment that comes into contact with the patient, under normal use. These applied part categories consist of ‘Type B’, body type, ‘Type BF’, body floating type and ‘Type CF’, cardiac floating type. The purpose of these categories is to determine the appropriate level of attributes such as isolation voltage, leakage current, creepage and clearance. The tables below give more detail on applied parts classifications and medical PSUs; the appropriate levels of associated attributes and examples of the type of medical electrical equipment each classification is likely to relate to.

Applied Part Classification Input to Output Isolation Voltage Input to Ground Isolation Output to ground Isolation End product examples
Type B PSU 4000V AC 1500V AC 500V AC These are grounded devices that work within 6 feet of the patient vicinity and do not require electrical contact; examples include lighting, hospital beds, automated medication dispensers and X-ray machines or scanners.
Type BF PSU 4000V AC 1500V AC 1500V AC These devices have conductive contact with the patient; examples include incubators, blood pressure monitors and electrosurgical devices.
Type CF PSU 4000V AC 1500V AC 1500V AC This is the most stringent classification and refers to devices that heart; examples include intracardiac ECG electrodes, defibrillators, or external pacemakers.

 

Leakage Current Type B Type BF Type CF
NC SFC NC SFC NC SFC
Earth Leakage Current 500µA 1µA 500µA 1µA 500µA 1µA
Enclosure Leakage Current 100µA 500µA 100µA 500µA 100µA 500µA
Patient Leakage Current 100µA 500µA 100µA 500µA 10µA 50µA

 

You will note from the above table that leakage current does not exceed 500µA in any instance, regardless of classification and UL approved devices will not exceed 300µA.

Means of Protection (MOP)

When choosing power supplies for medical applications, a vital consideration is Means of Protection, which protects patients and operators from electric shock. There are different classifications of MOP for both Means of Patient Protection (MOPP) and Means of Operator Protection (MOOP), isolation and creepage distances are essential to MOP.

Classification Required Isolation Required Creepage Required Insulation
MOOP 1500V AC 2.5mm
2 x MOOP 3000V AC 5mm Reinforced
MOPP 1500V AC 8mm
2 x MOPP 4000V AC 8mm Reinforced

IEC/UL/EN 60601-1 4th Edition

IEC (International Electrotechnical Commision) published the updated revision of the EMC (ElectroMagnetic Compatibility) requirements for ‘Medical electrical equipment – Part 1-2: General requirements for basic safety and essential performance -Collateral Standard: Electromagnetic disturbances – Requirements and tests’ (IEC 60601-1-2:2014 or more commonly, IEC 60601-1 4th Edition) in 2014. The effective date of this standard was 1st April 2017, however, IEC standards are voluntary whilst the US, UK and Europe (among others) have adopted the standard (UL 60601-1-2:2014 and EN 60601-1-2:2015 retrospectively) and these will become compulsory in their respective territories on 31st December 2018.

The revision makes changes to ElectroMagnetic Immunity (EMI) requirements, and required risk assessments, ensuring these consider the effects of electromagnetic disturbances caused by other electronic devices in the intended environment. This revision also includes a much-needed update on types of environments; professional healthcare, home healthcare and special environments. This accounts for the types of electrical devices, such as smart phones or high voltage equipment.

Alongside the new environment categories, comes ‘intended use’ and ‘normal use’ definitions; where intended use refers to the devices intended medical purpose and normal use refers to purposes such as maintenance, transport and standby.

The Technical changes to EMC testing

Given today’s technological advances and the everyday use of medical devices and PSUs in different types of environments, the technical requirements for medical device testing have been raised to ensure EMC safety in a devices intended or normal use.

The New risk assessments

  • manufactures required to submit the risk analysis and test plan before proceeding with testing
  • reasonable electromagnetic disturbances to be considered in risk assessments
  • operation modes to be established by the results of risk aassessments
  • Subsystem testing to be allowed if risk analysis recommends

The New EMI Testing

  • immunity test levels have been harmonized with IEC 60601-1-11
  • Generic EMC standards IEC 61000-6 port by port convention has been applied to 4th edition immunity testing
  • immunity to RF Wireless Communication proximity fields is now included, with a minimum seperation distance of 30cm
  • a procedure for testing equipment which has been damaged by an immunity test field has now been introduced

The New Immunity Test Levels

  • previously 2.5GHz (3rd edition) radiated immunity has been increased to 2.7GHz
  • voltage dips and interruptions at additional phase angles
  • magnetic immunity is 30A/m
  • conducted immunity  6V on ISM bands
  • ElectroStatic Discharge (ESD) has been moved from 6kV contact and 8kV air to 8kV contact and 15kV air, respectively

Our guarantee is you will always receive high-quality and highly efficient products meeting all applicable standards (EN60601-1, UL60601-1 and IEC60601-3rd edition core and 4th edition) whether choosing from our standard products or developing a customised unit in partnership with our dedicated support team. contact us today to find out more.