POWER & ENERGY EFFICIENCY HANDBOOK
Coming: New safety ratings for power adapters Prepare yourself for the updated standards about to take hold in power equipment that includes external adapters.
A
power adapter is a barrier between lethal ac mains voltage and the dc power line for end equipment. Different environments, however, demand different adapter construction to meet safety levels.
Ron Stull • CUI Inc.
product’s application. To complicate matters, not all countries have adopted “international” safety standards; some have written their own, and others base their standards on the general framework of the international standard. One facet of safety, as it applies to a power adapter and the equipment it powers, is to ensure a user cannot make contact with lethal ac line voltages. Also, safety goes beyond the potential for electrical shock, to require that the adapter body uses low flammability materials that can enclose any fire that might arise. For the majority of commercial and domestic equipment, standards IEC 60950-1 and IEC 60065 apply, although these are both intended to be withdrawn in Dec. 2020. Thereafter, IEC 623681 applies. IEC 60950-1 covers the broad category of IT and office equipment, and IEC 60065 covers an equally broad range of audio and video equipment from video projectors and media players. At this time, IEC 62368-1 coexists with the other two, and prudent power adapter manufacturers are certifying their products against IEC 62368-1 and IEC 60950-1. When selecting an external power adapter, check the manufacturer’s datasheet to find out with which safety standard the adapter complies.
For example, domestic, IT, industrial, and medical end-uses all have their own safety requirements. The primary concerns are the amount of separation through air and across surfaces between hazardous voltages and outputs or casings. However, such criteria are application-dependent and also vary with the over-voltage category of the ac supply, degree of environmental pollution, the type of user who has access, and even operating altitude. Other parameters also can be critical such as the fusing arrangement and earth leakage current, particularly in medical environments. Safety rating requirements also depend on the point of geographical use with different countries adopting local variants of international standards or their own national versions. Of course, the selection of an ac-to-dc power adapter involves evaluating your product’s overall voltage and maximum-current requirements. Besides looking at the obvious parameters, you should also confirm the adapter conforms to the applicable safety Energy source Effect on the body standards. These can vary depending on the geographic Not painful, but may be detectable Class 1 regions of the world where the Painful, but not an injury product is distributed. Class 2 There are several internationally recognized Injury Class 3 safety standards that apply to power adapters. Some of these are specific to the
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DESIGN WORLD — EE NETWORK
10 • 2020
Effect on combustible materials Ignition not likely Ignition possible, but limited growth and spread of fire Ignition likely, rapid growth and spread of fire
Classification of energy sources.
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