TT Electronics/Welwyn's EMC series is aimed at line (mains) input inrush limiting in power supply applications where UL approval is necessary. The EMC series has UL recognition, which is a component status indicating that a sample has been tested and verified by Underwriters Laboratories as suitable for use in a safety critical application. The relevant standard is UL1412, which covers fusing resistors designed to prevent fire by safely breaking a circuit under fault conditions. EMC parts perform three circuit protection functions in a single component:
- The series provides protection against supply line voltage transients, often in conjunction with a shunt element such as a varistor or transient voltage suppressor (TVS). This enables the designer to achieve the required level of immunity to conducted lightning induced surges.
- EMCs restrict the peak inrush current at switch-on to levels suitable for the rectifier bridge and consistent with good EMC design.
- EMCs prevent fire by fusing safely under fault conditions such as rectifier or capacitor breakdown.