By Patrick le Fèvre, Powerbox Marketing Director
The global population is both living longer and experiencing an increasing rate of chronic disease. Combine that with economic factors driving the increase of healthcare in the home and there is a growing demand for medical electrical equipment designed for use in the home environment requiring power supply manufacturers to not only consider standards and regulations but patient comfort and environment as well. From topology to mechanical design, power designers have to address a broad range of areas, which we will review in this article.
Topology and Optimization – Taking into consideration standards and regulations, patient comfort and safety, power supply designers are facing a number of challenges, which can all be solved by using proper technologies. But they also require a significant level of innovation to package more power in a confined spaced with limited, or no ventilation. Add to that MTBF, low EMI, compliance with IEC60601-1-2 and ITE requirements the designers’ challenges are becoming very exciting!
Choosing the right technology at the very early stage of the project is a key to success! In the case of external power supplies for medical equipment the topology is an important factor when considering space, cost and performance. Conventional topologies usually use around 200 components. Considering an innovative approach, similar to One Step Conversion combined with passive Power Factor Corrector (PFC) can result in reducing count parts by about 40% to around 120 components (figure 01) which directly benefit the MTBF and also makes the power supply more compact.
In theory, reducing the number of components to such low number seems to be easy, but in practice it is much more complicated. With a goal to exceed 90% efficiency, a power factor correction >0.90 to meet IEC60601-1-11 regulations, the ability to operate in free air convection or a sealed box and to reduce the zero-load power consumption to a level close to 0.3W, power designers have to be very innovative and creative, which is fun!
Developing One Step Conversion with a limited number of components requires a very high knowledge of transformer and coupling to achieve high performance, low leakage current and EMC compliance with IEC60601-1-2. One example of a product based on this approach is the Powerbox OFM225 shown in figure 02.
Mechanical with patient in mind – As we said earlier in this article, designing external power supplies for medical applications and especially for home healthcare requires power designers to work in very close cooperation with end-users; to not only secure the highest level of electrical safety but also usability in the patient environment.
Conventional housing for external power supplies for medical equipment over 150W are very similar to PC adapters, rectangular parallelepiped with sharp edges, which in case of homecare might create mobility problems, for example wheelchair blocking. Another parameter often not taken into consideration when designing such type of power supply is when housekeeping cleans the patient’s room. The parallelepiped shape is not easy cleanable when the operators clean the floor, requiring extra attention and time.
Teamwork with a group of users resulted a concept based on a half lenticular shape, avoiding wheelchair blocking, easy to clean with conventional Sweepers with the added bonus of a nice look and feel. Very important for the patient when such a product is visible or placed on a desk.
Once the shape was approved by the user group, the next challenge for power designers was to integrate a 225W power supply in the center part of the half lenticular and to guarantee that the product would operate at full power in patient’s room conditions. With a limited number of components and compact design, the One Step Conversion makes this possible. Combining all in one, the Powerbox EXM225 is the first product on the market designed to meet patient comfort expectations (Figure 03).
Another important safety aspect is to guarantee that input and output cables are secured by proper locks to avoid power supply disruption in case cables are pulled out accidentally. AC input connector is protected and locked to sustain a traction of 100 Nm pull strength while the output connector is secured by a mechanical lock, requiring an action from the operator to unlock (Figure 04).
Designing a power supply for medical application, operated in home healthcare environment, requires power designers to fully understand how the final product will be operated. Taking into consideration end users and in this specific case the patient environment is business critical, requiring innovation and different thinking, which for power designers is a great opportunity to explore new territories.
PRBX (Powerbox) Ltd.
Phone: +44 1264 337800
Fax: + 44 1264 334 337