Power Supply Redesign Raises EMC Issues

Focus:

Even simple changes to a power supply design can cause it to fail FCC and CE tests for electromagnetic compliance (EMC). The culprit can be changes that create antennas that radiate electromagnetic interference (EMI) and increase EMI above the acceptable levels. Difficulties may be compounded if the redesign is migrating a power supply that meets Class A EMI requirements into an application that demands the more-stringent Class B requirements. This article discusses common EMI design and troubleshooting problems, and presents tips and guidelines for alleviating them. Topics include the advantages of multipoint grounding in suppressing emissions at high frequencies; use of ground planes and ground conductors to eliminate noise loops; and filter design and selection for reduction of conducted emissions.

What you’ll learn:

• How to maintain or improve electromagnetic compliance (EMC) when redesigning a power supply
• How to enhance a power supply design that meets Class A EMI levels so that it meets Class B EMI levels
• How to avoid common design errors that cause a power supply to fail EMI tests

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Author & Publication:

Leo Brunk, EMC & Safety Engineer, Sypris Test & Measurement, Billerica, Mass. , Power Electronics Technology, Sep 01 2005

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