How is isolation specified?
• Isolation rating • Working voltage (or rated mains voltage) • Transient immunity (common-mode rejection) The degree to which an isolator successfully insulates one side of an isolation barrier from high voltages on the other side is commonly described by the isolator’s isolation rating and by its maximum working voltage (or rated mains voltage). In addition, the degree to which an isolator continues to correctly transfer a signal across an isolation barrier in the presence of a common-mode transient is described by its transient immunity (or common-mode rejection). Each of these three parameters is described below. What is isolation rating? An isolator’s isolation rating (also called the test voltage) is a measure of the protection provided against short-duration, common-mode voltage differences. Usually specified in terms of a 60 Hz RMS value, it is a rating of how much voltage can be safely applied between the input and output terminals of the device for a duration of one minute. A
