power supply selection considerations For IVD applications where a risk assessment demonstrates that there is no significant chance of a patient coming into contact with the product, MOOP requirements may be satisfied using a power supply that simply conforms to IEC/EN 60950. However, it is the responsibility of the medical product manufacturer to demonstrate that the appropriate standard of safety has been achieved.


Power supplies that meet 2 x MOPP standards provide the highest level of protection. But, as noted earlier, when a power supply manufacturer describes a unit as ‘approved for medical applications’ it does not mean that the unit provides two MOPPs. If an AC-DC power supply only provides one MOPP, an additional MOP (MOOP or MOPP) may be introduced into the final product by designing the power system architecture to include an isolated DC-DC converter. This adds cost and complexity but may be the preferred solution, particularly where multiple DC rails are needed in the medical product.


Historically, medical power supplies were produced in relatively small quantities and were sufficiently different from industrial units that the price premium over the latter was significant. However, in recent years, the growth in volumes of medical equipment and advances in both components and power supply design techniques have reduced the


price differential. Many units are now listed as approved for both ITE and medical applications.


It can be advantageous to specify a 2 x MOPP power supply for most applications. Even if there is a small price premium over IEC/EN 60950 units, this approach simplifies qualification of the end product. It may also reduce inventory costs by enabling a common power supply to be used in more than one medical product.


Recently introduced AC-DC power supplies are more likely to meet the 2 x MOPP requirement than older designs. Examples of power supplies from six leading manufacturers, together with their EN/UL 60601-1 approval status, are shown in Figure 4 (left).


In general, if a manufacturer has gone to the effort of designing a power supply for 2 x MOPP isolation, it will make a feature of this on the data sheet. Wherever a more general term is used, such as ‘approved to IEC/EN 60601-1’, it is the responsibility of the medical device manufacturer to ascertain the degree protection to which the power supply is certified.


Distributors that represent a number of reputable power supply manufacturers are well placed to advise on the various options available.


Power-One MBC series converter ideal for medical applications


Power-One has launched the MBC series with medical equipment design in mind. It is a high quality AC-to-DC converter with high convection rating to minimize fan use. The power supply operates at a high efficiency to minimize temperature rise with a small form factor. The MBC series meets the latest Safety and Emission standards for medical equipment; it is approved to EN60601 3rd edition (2 x MOPP) with power from 40 to 450W.


Features » 2 x MOPP (Means of Patient Protection) » High convection rating » High efficiency » EMI level B » Small footprint » Inhibit signal for power control » Fan and Standby voltage on 150 W rated unit and higher


beneFits


» High convection rating is critical to eliminate the use of a fan which induces noise and reduces system reliability.


» Small footprint allows designers to increase system functionality so that they can provide a superior product to their customers, with


reduced emissions. 7 focus magazine - issue 17 For more information visit avnet-abacus.eu/powerone


» Meeting the latest Safety approvals reduces design and certification time, which allows customers to get to market faster.


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