News @ Astrodyne

Application Segment Overview – Medical

Introduction

The role of power in medical electronics continues to grow in importance as advances in technology push the industry forward.  An aging population along with research and development investments to address this growing market are accelerating the growth in technology.  Power sources in the medical field have similar characteristics as traditional commercial and industrial power supplies but have some unique attributes that typically centre on isolation and safety considerations.  Within the medical power arena, the volumes are typically lower than their commercial counterparts and often require custom solutions to meet the particular needs. 

The imaging market, including X-ray, magnetic resonance (MRI) and computed tomography (CT) is benefiting from increased computing power which allows for greater resolution and storage capabilities.  These applications often require higher power to accommodate the motors and electronics.  The imaging market often necessitates low emissions profiles to prevent interference in the imaging output.  Medium and low power applications are being driven by advances in battery technology which facilitate the equipment to be brought to the patient.  The ability to provide bedside care significantly increases utilization for a hospital or allows for outpatient treatment.  Finally, new fields including patient record keeping and medicinal dispensing are utilizing embedded computing to bring intelligent networks to the healthcare system.  This results in the specifier of the equipment in a healthcare network often being the CTO as opposed to medical professionals.  A segment of the medical electronics market utilizes power supplies generating 1kV and higher outputs.  Applications requiring high voltage including medical lasers are not considered in this review.

Geography plays an important role in the rapid growth of the market.  Developed countries are leading the research front and pushing the technology envelope in the areas of power density, control and features.  China offers the greatest opportunity.  The Chinese market is expanding rapidly and accelerating the implementation by introducing joint ventures between major medical OEM’s and local companies.  In addition, the Chinese standards authorities have introduced regulations closer aligned to Western standards creating the opportunity to develop a product that is appropriate for both markets.   Less developed nations are aggressively pursuing trailing edge technologies including refurbishing older equipment.  This trailing market offers additional prospects for industry participants.

Key Market Drivers  

The move to portable applications includes patient monitors, therapeutic (homecare and hospital care) and medical carts which require efficient solutions and increased electronics.  Considerations include charging technology for batteries (Nickel Metal Hydride, NiCad, Lithium Ion and newer lithium ion polymers).  The charging technology for the newer chemistries is far more sophisticated than mature choices such as Lead Acid.  Options may include adjustable charge rates, battery recognition and communication features for remote monitoring.  The application may derive power from an offline source when AC voltage is provided or may run off strictly battery which may require additional DC/DC converters.  This power train may also feature communication interfaces.  The communication may be one way (Vout, temperature) or bi directional which may have fan speed controlled by temperature or data logs of events.  The result in the power stage is the increased need for higher efficiency and lower power consumption in standby mode.  The efficiency may be achieved through a distributed architecture with non-isolated point of loads or direct conversion for specified outputs.  No load power consumption in medical electronics continues to benefit from advances in IC technology.  Commercial IC’s can be utilized to introduce advances included pulse skipping and phase shedding to reduce the battery drain.  The impact of higher efficiency and lower no load power consumption is longer run times for battery supported equipment.  Longer run times are important for a variety of reasons including practical use, longer range and charging station optimization.

In addition to increases in efficiency, reduction in size is a critical market driver.  In portable applications, size and weight are important to allow healthcare professionals to move equipment easily.  In fixed applications, the physical size of the equipment is equally important.  Space on shelves, walls, or racks is limited and always at a premium.  Higher efficiency reduces the need for heat sinks, enabling density improvements.  Improved design approaches including resonant topologies also assist by reducing the size of the input filter to meet EMI concerns.  Smaller filter components including common mode chokes can have a significant benefit on the physical size.

Reliability is a general concern for all power supplies.  Lifetime, Mean Time Between Failure (MTBF),  Mean Time to Failure (MTTF) are all measures used to demonstrate the robustness of the design and process.  In medical electronics, this is critically important as disruption in operation or performance can have severe consequences.  For this reason, great care is taken at the design and integration level to qualify the component selection, design and failure modes.  Component stress ratings are paramount to this effort.  Fortunately, the ambient environment for these applications is typically benign. Thermal considerations more commonly result from plastic enclosures, fan cooled inlet/outlets and device locations which are often stacked or placed in a secondary cabinet or cart.

Key Metrics

Medical power supplies are evaluated on many of the same criteria as industrial or commercial power products.  Efficiency is a key measure to insure battery life (as mentioned earlier) along with overall power dissipation resulting in heat.  Line and load regulation or cross regulation in multiple outputs is important to application performance.  For offline products, input voltage across a 100-240Vac nominal line along with power factor correction above 75Vac is required for global markets.  However, there are other factors which take on increased importance for these markets.

Electromagnetic compatibility (EMC) is a key parameter reviewed by medical electronics designers.  It is categorized within the medical standards as the unintended impact of interference can have a critical effect.  The general requirements are listed under the collateral standard of IEC60601-1-2, General requirements for basic safety and essential performance - Collateral standard: Electromagnetic compatibility. This factor has increasing relevance as more equipment is moved into the room and more wireless devices are implemented for monitoring or record keeping.  Within EMC, the most critical aspects are conducted and radiated emissions along with susceptibility which can cause a disruption of operation (shutdown, dropout, etc).

Leakage current is also addressed in the applicable safety standards and is another key factor when evaluating medical power supplies.  Filter components along with transformer leakage are the principal elements contributing to leakage current.  Capacitors attached from the mains to ground help minimize the emissions profile but allow a leakage current path.  In the system, the leakage capacitance contributed by individual parts can drive system levels beyond acceptable limits.  This can occur with multiple power supplies or any component utilizing filters to improve the EMC profile.

Trends

Within medical electronic equipment and specifically the medical power arena there is a major change underway in the applicable standards.  The evolution from products approved to IEC 60601-1 2nd edition and its derivatives (EN 60601-1, UL 60601-1, etc) to IEC 60601-1 3rd edition is having a significant impact in the market.  There are several aspects to the standard which have a major impact on the design and qualification process.  These include the concepts of essential performance and risk management.  Many customers in the market are looking for product approved to the 3rd Edition today as the planned requirement date for many countries is June 1, 2012.

The new standard attempts to break away from defined tables and limits and assign the risk analysis on the manufacturer.   Within this scope is the term “essential performance” which requires the manufacturer to determine performance levels that remove any unacceptable risk.  To support the process, companies are expected to have a Risk Management File (RMF), which details the likely potential issues (for example a single fault condition) and how the product will insure an acceptable level of risk.

Beyond the concepts of essential performance and risk management there are other distinctions brought in by the 3rd edition.  For example, levels of patient connect including CF, BF and B have been replaced by “MOOP” means of operator protection and “MOPP” means of patient protection as they pertain to evaluating risk.  In a similar manner, “touch current” has replaced enclosure leakage current. With the introduction and implementation of the new standard, manufacturers will have to adjust their design, analysis and submittal processes, to meet the requirements of the market.

Other trends in the market include the movement towards off the shelf solutions and conduction cooled solutions at higher power.  Off the shelf options may include configurable supplies, external adapters or reference designs. Utilizing a standard approach affords greater flexibility in the supply chain.  It also reduces development time devoted to the power source.  Manufacturers often implement a power architecture and then replicate the platform for related equipment.  Conduction cooled power sources eliminate issues related to fan life and audible noise in the healthcare environment.

Challenges

• Long product life cycle:  Medical equipment may take years to gain approval and then have useful lifetime extending for 10 years beyond that.  Technology implementation leveraged from commercial products may have shorter lifetimes and therefore care must be taken in the selection of components.
• Standards Education:  It is important for vendors and users to understand the rapidly shifting standards landscape and the impact it may have on their particular segment.
• Pushing technology in low volume/customized environment:  The medical market is not typically large enough to demand unique solutions it often requires.
• Efficiency Improvements:  Enhancements to improve efficiency in the power chain is critical to many areas including product life (reduced heat), battery powered applications (longer run times) and product acceptance.
• Reliability:  Applications are often life critical and therefore proper operation is extremely important.  Improvement in the design, qualification and test process in addition to component improvements will be needed.

 

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