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As part of our education series, TRACO Power’s Florian Haas delves into the safety concerns that must be considered when a patient is connected to an electrically powered medical device, and how to best protect that patient by avoiding electrical failure.

People and power don’t mix well, and this is particularly true when people are medical patients. Aside from the more usual environment of a medical facility, patients are also increasingly using medical devices at home. Medical equipment is therefore heavily regulated by standards-based requirements and subsequent product testing to ensure the safety of patients and healthcare professionals alike.

Medical equipment with Power Supply & DC/DC Converter
The most pressing safety concern related to medical devices comes into play when the patient is physically connected to an electrically powered device, such as the conductive pads of an electrocardiograph. These are defined as applied parts (AP). The route to ensuring patient safety lies in the implementation of IEC 60601, “Medical electrical equipment,” the standard central to the safety of electronic and electrical medical equipment power supplies.

Understanding Key Definitions

To safeguard patients connected to an AP medical device, IEC 60601 dictates that all medical devices must contain at least one means of protection (MOP), which could include insulation, earthing systems, air gaps, minimum creepage distances, or other protective electrical impedances.

Since the release of the third edition, the standard makes a clear distinction between equipment that is designed to be used by operators and equipment that may come into contact with patients. Different levels of protection are required, defined as Means of Operator Protection (MOOP) and Means of Patient Protection (MOPP), respectively. MOPP regulations are the stricter of the two because of the additional risk that a patient might be unconscious when an electrical fault occurs. In addition, more than one MOP may sometimes be required in case one fails.

Traco Power
There are three classifications for AP devices: cardiac floating (CF) for conductive devices that could come into direct contact with the patient’s heart; body floating (BF) for conductive devices that may have prolonged contact with the patient’s body; and lastly body (B) for devices that are not normally conductive and can immediately be released from the body. Types CF and BF require a minimum of 2 x MOPPs.

Protecting Devices Against EMI

IEC 60601 has evolved over the past 40 years to keep up with advancements in technology. With wireless communication technology becoming more abundant in hospitals and homes, there is a need for these sensitive circuits to be impervious to electromagnetic interference (EMI). The fourth edition of the standard has, therefore, now increased the acceptance levels for electromagnetic compatibility (EMC).

TRACO Power TPP450 Series

Risk Reduction and QMS

Two significant new introductions to the standard have been the requirements for the manufacturers of medical devices to undertake risk assessments, which must be undertaken in compliance with ISO 14971, “Medical devices – Application of risk management to medical devices,” to define best practice throughout the entire life cycle of an AP medical device.

Component manufacturers must also implement an ISO 13485 compliant quality management system (QMS) to demonstrate their ability to consistently meet both customer and regulatory requirements.

Practical Tips for Meeting the Standards

For AP medical devices to meet IEC 60601, the first step would usually be to select a medically approved AC/DC supply. Many designers will specify a power supply with 2 x MOPPs to simplify the qualification process and risk assessment, even if the highest level of protection is not actually required for the device’s application.

The most pressing safety concern related to medical devices comes into play when the patient is physically connected to an electrically powered device, such as the conductive pads of an electrocardiograph. These are defined as applied parts (AP). The route to ensuring patient safety lies in the implementation of IEC 60601, “Medical electrical equipment,” the standard central to the safety of electronic and electrical medical equipment power supplies.

Traco Segment Medical

However, it can become challenging to source a medical-grade stand-alone AC/DC power supply with a BF-compliant 2 x MOPP rating, particularly when the DC voltages needed for the AP instrument are different to the main system DC voltage. In this case, a 2 x MOPP IEC 60601 DC/DC converter combined with an ITE 62368 rated AC/DC power supply can easily be used to obtain compliance instead of trying to source a custom AC/DC power supply for the task.

Specialized DC/DC converters are available that meet the standard 2 x MOPP requirements. With up to 5000 V AC of isolation, double insulation and 8 mm of creepage distance through its galvanically isolating transformer, a DC/DC converter can provide protection in the event of a mains failure (see Figure 1). By providing this, the DC/DC converter avoids mains voltage levels appearing at any patient AP points.

An important part of the protection lies in a low coupling capacitance between the primary and secondary transformer windings to ensure that there is negligible transfer of current across the isolation barrier. Traco Power, for example, offers both AC/DC and DC/DC solutions for medical applications, all of which fulfill the 2 x MOPP requirement. Compliant with the EMC requirements of IEC 60601-1 (4th edition), they are suitable for all patient-connected, AP medical devices (BF compliant). The AC/DC products range from small 5W PCB-mounting modules, to a range of mid-power open frame designs, and enclosed power supplies offering power levels of up to 850 W. The company’s medically approved DC/DC converters offer 5000 VAC rms of input-output isolation, rated for a 250 VAC rms working voltage. This, along with leakage currents below 2 μA, make them ideal choices for use in conjunction with non-approved AC/DC PSUs in safety-critical medical applications.

Conclusion

The healthcare market is growing rapidly and the applicable standards that govern medical products will no doubt continue to evolve to keep safety standards high. Understanding the differences between Means of Operator Protection (MOOP) and Means of Patient Protection (MOPP) is key to properly safeguarding patients. Protecting against EMI but also applying ISO 14971 can ensure that devices are safe when the patient is physically connected to an electrically powered device. Partnering with reliable and experienced power supply manufacturers such as TRACO can greatly simplify the process.This article was written by Florian Haas, Director of Marketing for TRACO Power Group, San Jose, CA.

As an authorized distributor of TRACO Power, Sager Power Systems is well positioned to support your medical design requirements. TRACO Power offers a wide selection of medical products, including their TPP Series of AC/DC power supplies and the THM series of DC/DC converters, all of which have medical approval, meet 2xMOPP and are BF Complaint. A Sager Power Systems Sales Engineer is ready to help you design-in one of these solutions:

Series Features & Benefits
THM3
  • Ultra wide 4:1 input voltage 3 W DC/DC converter in a compact DIP-24 plastic case
  • I/O isolation 5000 VACrms rated for 250 VACrms working voltage
  • Certification according to IEC/EN/ES 60601-1 3rd edition for 2xMOPP
  • Risk management process according to ISO 14971 including risk management file
  • Acceptance criteria for electronic assemblies according to IPC-A-610 Level 3
  • Low leakage current < 2µA
  • Extended operating temperature range -40°C to 90°C.
  • EMC compliance to IEC 60601-1-2 4th edition and EN55032 class A
  • Operating up to 5000m altitude
  • 5 year product warranty
THM 3 Traco Power
 TPP450
  • High power density 3″ x 5″ open frame medical power supply
  • 450 Watt with forced air cooling, up to 320 Watt convection cooled without derating up to 50°C
  • Medical certification to IEC/EN/ES 60601-1 3rd edition for 2 x MOPP
  • EMC compliance to IEC/EN 60601-1-2 4th edition
  • Risk management process according to ISO 14971 incl. risk management file
  • Acceptance criteria for electronic assemblies acc. to IPC-A-610 class 3
  • Isolation (4000 VAC) and leakage current (<100 µA) rated for BF applications
  • Standard features: 5 V standby output 12 V fan output, Remote On/Off, Power, Good Signal, variable fan speed
  • Operating up to 5000 m altitude
  • 5-year product warranty
 TRACO Power TPP450 Series
TIM3.5
  • Compact DIP-16-package
  • Wide 2:1 input voltage
  • I/O isolation 5000 VACrms rated for 250 VACrms working voltage
  • Certification according to IEC/EN/ES 60601-1 3rd edition for 2xMOPP and operation to 5000 m altitude
  • Low leakage current < 2 µA for BF-applications
  • High efficiency up to 83%
  • Extended operating temperature range –40°C to 90°C.
  • MC compliance to IEC 60601-1-2 4th edition and EN55032 class A
  • 5-year product warranty
 TIM 3.5 Traco Power

Visit the TPP Series of AC/DC Power Supplies page for more information on this product offering.

Visit the THM Series of DC/DC Power Supplies page for more information on this product offering.

Visit the TRACO Power page on power.sager.com for more information on their offering or contact a Sager Power Systems representative, the authorized Distributor for TRACO Power, at (866) 588-1750, power.sager.com or through the below form: