Medical

Medical Grade Power Supplies

Reliable medical grade power supplies for medical devices

FiDUS power understands the issues faced by our customers selecting power supplies for medical devices. In an era of dramatic transition in both legislation and market trends, it is vital to keep focus on core values of reliability, safety and EMC compliance. With the 3rd edition of IEC60601-1 placing more emphasis on risk management, collateral EMC standard IEC60601-1-2 4th edition placing harsher demands on ESD, Radiated and RF immunity, correct power supply selection is vital for ease to compliance.

Advancement in technology, an ageing population and government healthcare reforms are driving some of these legislative changes. There is a move towards home healthcare options being available instead of hospital or outpatient clinic visits, extensive use of wireless technologies and implanted medical devices. These trends have brought a need to modernise the legislation. We now have the possibility of a mobile phone switching off a home ventilator, when used in close proximity!

The balance from the power designer point of view is the demand for smaller, power dense, efficient, cost effective power supplies whilst maintaining reliability. FiDUS have an interesting range of products that meet these criteria.

Medical safety & EMC information

Safety standards

IEC60601-1 3rd Edition is the key standard applicable to meeting the safety requirements in electrical medical devices. The base standard is 60601-1, there are collateral standards numbered 60601-1-X that define requirements for certain elements of safety and performance. In these, elements may take precedent over the general standard with respect to specific aspects of a product design. Examples of this are -

  • IEC60601-1-2 Electromagnetic compatibility
  • IEC60601-1-8 Alarm systems in medical devices
  • IEC60601-1-11 Medical equipment in home healthcare

The third element are particular standards numbered 60601-2-X which provide requirements for specific product types such as high frequency surgical equipment or endoscopic equipment. National deviations of the 3rd edition in the US are ANSI/AAMI ES60601-1, Canada CAN/CSA C22.2 No.60601-1 and Europe EN60601-1.

MOPP & MOOP

IEC60601-1 3rd edition has an emphasis on implementing a risk management system compliant with ISO14971. It distinguishes between the operator and the patient with MOPP (Means Of Patient Protection) and MOOP (Means Of Operator Protection). This allows the designer relaxation in terms of creepage and clearance distances if through risk assessment, the equipment will not come into contact with the patient under normal operation or under a single fault condition. However, whether the product is MOOP or MOP the leakage current requirements must be met.

The standard requires that you have two Means of Protection, which can be implemented using three methods used in combination - Protective earth, Insulation & Protection impedance. These methods are employed in a system so that should one fail the product will retain protection from any potential shock hazard for either operator or patient. The table below shows the different building blocks and the MOP provided.

Method Means Of Protection provided
Protective Earth 1
Basic Insulation 1
Supplementary Insulation 1
Double Insulation 2
Reinforced Insulation 2

Designers must make the decision if the insulation class of the system is Class I or Class II with no protective earth. Also the classification of the Applied part. The Applied part is the part of the medical device that comes in contact with the patient to do its job. Three classifications -

  • Type B - No conductive contact with the patient. May be earthed
  • Type BF - Conductive contact with the patient. Floating.
  • Type CF- Conductive contact with the patient’s heart. Floating

The power supply will meet defined limits for its insulation characteristics. However, it is advisable to draw up a system isolation diagram including all relevant parts that can influence system compliance

Creepage & Clearance

Below are the air clearance and creepage distances that are designed into PSUs and need to designed into systems for MOOP & MOPP. When designing in an open frame power supply into a system it is key that you maintain the correct distances. Standoff height and distances from lids become important to consider. In tightly packed applications insulation such as Nomex is commonly used to reduce required distances.

Insulation

MOOP

MOPP

Air Clearance

Creepage Distance

Test voltage

Air Clearance

Creepage Distance

Test voltage

Basic (1 x MOP)

2.0 mm

3.2 mm

1500 VAC

2.5 mm

4 mm

1500 VAC

Double/Reinforced (2 x MOP)

4.0 mm

6.4 mm

3000 VAC

5.0 mm

8.0 mm

4000 VAC

Leakage current

Below are defined leakage currents from IEC60601-1 and definitions -

  • Earth leakage is the Current flowing in the earth conductor
  • Enclosure leakage is the Current flowing to earth via the patient from the enclosure.
  • Patient leakage is the Current flowing to earth via the patient from an applied part.
  • Patient auxiliary is the Current flowing between two applied parts

Leakage Current

Type B

Type BF

Type CF

NC

SFC

NC

SFC

NC

SFC

Earth Leakage*

500 uA

1 mA

500uA

1 mA

500 uA

1 mA

Enclosure Leakage*

100 uA

500 uA

100uA

500uA

100 uA

500 uA

Patient Leakage

100 uA

500uA

100uA

500 uA

10 uA

50 uA

NC = Normal Conditions SFC = Single Fault conditions. *Patient care equipment maximum earth and enclosure leakage current for the US is 300 μA. Figures quoted are for portable equipment.

EMC

The collateral standard for medical device EMC is IEC60601-1-2 currently 3rd Edition. From a component power point of view, we need to meet multiple basic performance standards IEC61000-4-X (ESD, conducted noise, surge, EFT etc.) and achieve compliance as part of the system. Our power supplies will be tested to these standards and meet certain performance criteria stand alone.

The new 4th Edition of this standard is intended to catch up with the impacts of modern wireless technologies and update immunity levels based on the reasonably foreseeable maximum. Also to take into account the environment of intended use (Hospital, clinic, home etc.).

Some of the key differences include: Standby mode needing to be considered and new test for patient cable common mode for emissions. Documentation updates for EMC test plan and reports are part of risk management process. Key for the power supply design and test are the updates in the 4th Edition for the immunity standards. See below for an immunity comparison of 3rd and 4th Edition -

IEC60601-1-2 Tests

Edition 3 Levels

Edition 4 Levels

CISPR 11 Conducted emissions

Class A/B

Class A/B

CISPR 11 Radiated emissions

Class A/B

Class A/B

IEC61000-4-2 ESD

6KV Contact, 8KV Air

8KV Contact / 15KV Air

IEC61000-4-3 Radiated immunity

3V/m / 80-2500MHz AM modulation

3V/m / 80-2700MHz AM modulation. 30V/m 80-6000MHz. Selected Telecom bands. Digital Mod.

IEC61000-4-4 EFT/Burst

2KV AC lines / 1KV I/O lines

2KV AC lines / 1KV I/O lines

IEC61000-4-5 Surges

2KV AC lines

2KV AC lines

IEC61000-4-6 Conducted RF

3V rms

3V rms & 10V rms ISM frequencies

IEC61000-4-8 Magnetic fields

3 A/m 50/60Hz

30 A/m 50/60Hz

US Volume navigation

IEC61000-4-11 Dips/ Interruptions

>5% Un; 0.5 & 300 Cycles/40%/70%

0% Un; 1 Cycle/300 Cycles / 70%

IEC61000-3-2 Harmonics

No change

No change

IEC61000-3-3 Flicker

No change

No change

The new mandate for compliance to 4th Edition goes into effect April ‘17 for new products in the US and for all products in the EU by August ‘17

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