The dual functions of X and Y EMI capacitors

摘要

Devices that plug into an ac mains outlet need protection from EMI. A pi filter, as shown in Fig. 1, is often used for this application. Safety standards exist to protect people and equipment should the components in this filter fail. Capacitor manu- facturers offer devices for this application known as "X/Y caps," "EMI filters," or "safety EMI capacitors." These are capacitors that pass safety approvals for use in ac-line EMI filters.