Evolving Standards Reshape Medical Power Supplies

Apr 1, 2007 12:00 PM
By Peter Resca, Director of Engineering, and Dave Murray, Senior Product Engineer, Astrodyne, Mansfi

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The design of medical-grade power supplies or the integration of such supplies into medical equipment has long posed unique challenges to engineers and system designers. The performance of power supplies in such applications can be potentially life saving. With the burgeoning market for medical apparatuses, designers have become more familiar with the particular compliance standards required. However, advances in technology have led to changes in standards that will continue to significantly affect the power-supply designer and system integrator.

New standards are being proposed that would change the medical-device approval process, literally turning the current method upside down. These new standards would change the method of approving medical equipment from simple parameter testing to an involved collaboration of risk declaration and the methods applied to identify and minimize those risks.

Current Standards

Today, global compliance for medical power supplies is based on IEC 60601 “Medical Electrical Equipment, Part 1: General Requirements for Safety.” Most of the medical power-supply compliance standards are based on this, including UL 60601-1, EN 60601-1, JIS T 0601-1 and CSA C22.2 No. 606.1 (Table 1).

The IEC standard has helped define and ensure that the components and systems designed for medical equipment are safe. The IEC 60601 document sets the parameters for the design of medical power supplies such as the unit shown in Fig. 1.

This document and another document, the IEC 60950 for information technology equipment (ITE), use a common approach to power-supply evaluation. The medical supply standard includes the definition of requirements for creepage, clearance and isolation. The requirements in medical design are more stringent and must be accommodated in the design.

New terms and definitions were introduced to those familiar with ITE design and integration. There are three classifications defined for the type of applied part including B, BF and CF. Type B allowed the use of an earth-ground connection, while type BF is floating. Type CF is floating and the most stringent, designated for cardiac contact.

IEC 60601 also included other related standards of importance to any medical supply design effort. The standards are classified as collateral and particular, and attempt to address unique aspects of given applications. Collateral standards are designated 60601-1-X, also referred to as horizontal standards because they provide additional considerations outside of the base standard. Particular standards are identified by 60601-2-X, also sometimes referred to as vertical standards because they add detailed requirements for specific medical devices, such as X-ray machines and hospital beds.

Perhaps the most important collateral standard for power-supply design is IEC 60601-1-2 for electromagnetic compatibility. This standard impacts all steps of the development process, from power-supply design to integration and product testing.

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