Medical power supplies: trends, challenges and design approaches
by Peter Blyth, Industry Director, XP Power, Vendor website, Jun 01 2009
Focus:
As in other areas of power supply development, there is ongoing market pressure to reduce the size of medical power supplies for given output power ratings. The demand for smaller size in turn requires both an increase in switching frequency and an increase in power supply efficiency, which are generally conflicting goals. This article discusses the design techniques that power supply manufacturers such as XP Power are using to manage design tradeoffs and achieve smaller size and higher efficiency in medical power supplies, while also meeting requirements for reliability and cost. Techniques discussed include use of stacked, two-stage input EMI filters, SiC diodes in the PFC stages, resonant topologies, ceramic heatsinks, synchronous rectifiers (MOSFETs), and more-integrated control circuits. The article includes a discussion of how power supply package size influences maximum allowed power dissipation in medical supplies, and graphs the maximum allowed power dissipation (under forced air or convection cooling) for a range of common power supply footprints. It then explains how to graphically extrapolate from the maximum allowed power loss to the efficiency required for a desired output power level.
What you’ll learn:
- How to understand design options for increasing both the efficiency and power density of medical power supplies
- How to determine the maximum allowed power dissipation of a medical power supply as a function of package size and cooling method
- How to determine the minimum power supply efficiency required to achieve a desired output power for a given power loss
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