Embedded power supplies for the home healthcare market
Rarely a day goes by without a news article commenting on the rise in healthcare costs, the strain on government run services and general affordability. Reports on the medical market forecast CAGRs (Compounded Average Growth Rates) for electronics, double or triple those of traditional computer or datacom markets.
The world’s population is aging, even in China, where statistics indicate that by 2050 more than a quarter will be over 65-years-old. Care quality has improved significantly, driven by capital expenditure, but the number of chronic lifestyle-related diseases continues to expand. The solution for many countries is home healthcare. Patients are being treated cost effectively in the comfort and familiarity of their homes avoiding long, expensive, stressful hospital stays.
Home healthcare solution assists many countries
In addition kidney dialysis treatment, for example, is more effective when performed over a longer period of time rather than in multiple, short visits to the local hospital. Results show that hemodialysis, cleaning and filtering blood, when performed every day for 2-3 hours comes closer to replacing the steady work that healthy kidneys normally do.
The use of infusion pumps, oxygen concentrators and the treatment of other breathing disorders at the home are now quite common. A large number of people use PAP (positive airway pressure) machines at night to avoid sleep apnea. The widespread use of home wireless networks assists with the remote monitoring of the patients.
Home healthcare, however, brings new challenges for both medical equipment and power supply manufacturers. Hospital power quality is traditionally excellent, along with clean, sterile, controlled environments. Equipment is installed by licensed electricians and maintained by trained professionals. In the home environment that may not always be the case where equipment has to contend with pets, clutter and dust.
Medical equipment requires safety certification
More significantly, it is estimated that in North America and Europe less than 50% of the homes do not have a reliable earth ground connection. In the event of an electrical fault, normally current would flow through a low impedance ground wire and trip an earth leakage breaker. Inadequate house wiring could lead to an electrical shock, with serious implications to an already weakened patient.
In response, the safety certification committees require that medical equipment for home use now has to meet the IEC 60601-1-11 (2010) standard. This came effective in 2013 for the U.S. and 2012 for Europe. It mandated that a ground connection is not required for safe operation, effectively meaning that power supplies have to be designated Class II. It is already common for many consumer products, where the use of a two prong ac plug is prevalent. Instead of relying on a ground connection, the user is protected from electrical shock using double or reinforced insulation.
Industrial power supplies (Class I) rely on that ground connection to meet conducted and radiated noise emission standards. Noise current is diverted from interfering with the AC source into the ground connection. A Class II power supply requires additional internal filtering and soft-switching techniques to meet the level B standards.
Medical power supplies also have to meet the IEC 60601-1 3rd edition safety standard. Most manufacturers ensure their products can withstand 4,000Vac input to output isolation. Where patient connection is possible, two levels of protection is provided, often referred to as 2 x MOPPs (Means of Patient Protection).
External supplies subject to energy use directives
External power supplies are subject to multiple North American and European directives for energy usage. Medical versions of those tend to lag consumer restraints by a few years. Embedded power supplies are not covered by that legislation, but often the designers of medical equipment will want to demonstrate a green initiative. This has led to the introduction of many “open frame” power supplies with high average efficiency levels and off-load power draws of less than 0.5W.
In a home environment, medical equipment needs to be able to operate in dusty or dirty conditions. The use of vents in the enclosure can cause problems and is usually avoided. Likewise, fans are not accepted as they produce irritating acoustical noise that can disturb a patient during a procedure. From an embedded power supply perspective, this can lead to increased capacitor temperature rises resulting in premature field failures.
Long-term (one to three years) reliability is very important for home healthcare. Equipment failures in a hospital can be addressed relatively quickly, through either on-site repair or a replacement. At home, in a remote area, it can lead to complications, particularly if a procedure has to be stopped until a replacement can be delivered the next day.
With TDK-Lambda’s new ZMS100 open frame medical power supply, particular care was taken in regard to product field life. A capacitor’s life degrades by 50% for every 10oC rise in ambient temperature, sometimes resulting in a field lifetime as short as 4 months. Where possible, for example in the capacitor used for power supply start-up, the electrolytic was replaced by a ceramic or polyester capacitor. Such failure modes would not become apparent until the equipment was moved or after a power outage. Targets were set in TDK-Lambda’s ZMS100 design stage to achieve capacitor lifetimes of up to 10 years.
Medical-based certification recognizes traceability
Power supply manufacturers are now upgrading their ISO processes and procedures to include ISO 13485. This medical-based certification is recognition for the highest level of traceability and quality control through the product development schedule and the product’s lifetime in the field. The aspects are far ranging throughout the organization and include the design, manufacturing, procurement, sales, distribution, product support and service of power supplies for medical applications.
For designers of home healthcare medical equipment, the power supply selection should be a careful one. New, efficient products have been launched in the last year that can ensure long time reliability, while still meeting all of the new regulatory requirements. More importantly, these power supplies come at a surprisingly affordable price.