ABSTRACT
Electromagnetic interference (EMI) filters, also known as RFI filters or radio-frequency interference filters, are electrical devices or circuits that reduce the high-frequency electromagnetic noise prevalent on power and communication lines. Motors, electronic controllers, power supplies, inverters, clock circuits, microprocessors, appliances, electronic gadgets, and other electrical and electronic equipment produce high-frequency noise. This noise generally has a frequency range of 9 kHz to 10 GHz and can damage or impede signal transmissions and/or the intended functioning of electrical or electronic devices. Lower-frequency Electromagnetic (EM) noise components can also have an effect on power quality. The industrial EMI filters give a low-impedance channel to the high-frequency noise and attenuate it by cancelling or grounding its line and neutral components. Insertion loss is a measure of an EMI/RFI filter’s efficacy (in dB over the frequency range). An EMI filter is often most beneficial for electromagnetic noise carried over cables in the 9 KHz to 30 MHz frequency range. Beyond 30 MHz, frequencies are frequently radiated (travel through the air), necessitating shielding and input/output isolation. The filter installation is more important than the insertion loss performance for radiated frequencies. Some of the EMI/EMC filter components are installed on the power supply’s input, some on the power supply’s output, and some between the power supply’s input and output. The EMI/EMC components can be used to reduce radiated and conducted noise on the power supply’s input or output, to reduce the effects of voltage transients applied to the power supply’s input or output, to reduce the input surge current when voltage is first applied to the power supply’s input, and to protect the input power source and conductors if the power supply fails. This chapter will discuss EMI filters, including their design and types, as well as their components and types.
