Functional safety for integrated circuits used in variable speed drives

Abstract:
Functional safety is the branch of safety related to correct functioning of electrical and electronic systems. Variable speed drives now play an important part in implementing functional safety. Previously functional safety for motor control applications was realized using safety relays and contactors external to the drive. But with safety integrated in the drive safety functions such as STO and SLS can be implemented within the drive offering productivity enhancements on the factory floor. Integrated safety requires the use of integrated circuits but interpreting the functional safety requirements for integrated circuits used in variable speed drives is challenging. Ideally all such ICs would be assessed to IEC 61508 but this would be expensive and is not demanded by the standards. This paper will attempt to summarize what guidance is available for integrated circuits being used in the design of variable speed drives. A goal of this paper is to provide an overview of the topics without the use of jargon.