EMI filters are electronic devices that are designed to eliminate the effects of electromagnetic interference or “noise” in electrical and electronic systems. An EMI filter cannot eliminate the noise; however, it can suppress it, mitigating its impact. When installed, they operate as a passive system component, and because of the many types and variations in EMI, there is virtually no limit to the type of EMI filter that can be engineered. Some of the more common types include C, Single L, Single p, Single T, Double L, Double p, and Double T.
Like any filter, an EMI filter eliminates noise through resistance; by delivering higher resistance to high-frequency signals, it filters out the high-frequency noise. Typically, EMI filters do this through a combination of inductors and capacitors. Inductors are basically very small electromagnets, and hold electric current in a magnetic field. As the current passes through, voltage is reduced. The capacitors are designed to let alternating current (AC) pass, while hindering direct current (DC), which is where the lion’s share of EMI enters an electrical system. The capacitors used in an EMI filter are also known as “shunting capacitors”, as they shunt specific high-frequency signals away from the circuit.
When selecting an EMI filter, there are some device parameters that are essential to the selection process and include rated voltage, current, frequency, and insertion loss. These are the basic considerations; others that may affect the ultimate choice include voltage drop, DC resistance, leakage current, insulation resistance, dielectric withstanding voltage, and power dissipation.
If your system has MIL-STD-461 compliance requirements, many of the DC-DC converters on the market will not be compliant. The EMI filters listed below have been designed to meet this requirement. In addition, custom voltages/current ratings/size can be designed to meet your specific application.
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