A power line filter is a type of passive component that creates an electronic filter to deliver appropriate frequency characteristics to electrical circuits. Power line filters connect the electronic device with an external line to reduce conducted frequencies like radio frequencies (RFI) or electromagnetic interference (EMI) between the equipment and the connecting power line. This prevents any degradation in the circuit's performance.
Power line filters are useful in emission reduction in switched-mode power supplies or machinery producing steam, smoke or carbon dioxide. These filters are also necessary to decrease levels of electromagnetic interference which may cause undesired behaviour in radio transmission equipment and nuclear operations.
Power line filters can be used in single phase, three phase or DC (direct current) power applications, depending on the equipment in question. Electric and electronic devices like switched-mode power supplies, motor controllers, induction cooking and food service equipment make use of single phase filters. Three phase filters are common in frequency converters, motor drives, and machine tools. DC filters are typically found in cell phones, flat screen TVs and electric or hybrid vehicles.