A single-phase EMI/EMC filter is an electronic device used to suppress unwanted electrical disturbances, i.e., the conducted electromagnetic interference (EMI) or radio frequency interference (RFI) present on the single-phase AC power supply line. It is a type of power line EMI filter. 

Figure: Single Phase EMI FilterConducted EMI means the emission of noise currents at radio frequencies (called conducted emission) from an electrical and electronic device during operation. These noise currents travel via power lines or other connected lines and can affect the performance of other devices connected to the same line. For example, a drilling machine operating in a neighboring room can disrupt the functioning of a computer connected to the same line. Additionally, high-frequency noise currents flowing through power lines can cause the power line to act as an unintentional antenna, radiating electromagnetic interference (EMI) signals that may disrupt nearby electronic devices or AM radio signals.  

Common causes of conducted EMI include SMPS, electric motors, DC/DC converters, non-linear load switching operations, RF transmitters, microcontrollers, and other electronic devices.

The purpose of the single-phase EMI/EMC filter is to attenuate the high-frequency noise currents (conducted EMI or RFI) present on the single-phase power lines. By suppressing the noise current, the filter prevents conducted EMI from entering or escaping from a filtered electrical and electronic device, keeping the device working smoothly without disrupting other connected equipment. The EMI/EMC filter is installed or connected at the power entry point (POE) of a device/system. The filter can be used as a separate device or can be integrated with electrical and electronic devices. 

Construction and working principle of single-phase EMI/EMC filter:

The single-phase power line EMI/EMC filter is typically constructed by using passive components such as capacitors, inductors, and resistors arranged in a specific configuration to create a low-pass filter effect. The filters are designed to attenuate both common mode and differential mode noises. 

The filter operates as a low-pass filter that allows power frequency (50/60Hz) current to pass freely while attenuating the high-frequency noise current on the single-phase power supply lines. The filter operates by diverting the unwanted noise current away from the device to be protected to the ground. Certain filters route the high-frequency noise back to the EMI noise source or absorb it. 

Figure: An example circuit of a single-phase EMI/EMC passive filter (filters may use various circuit designs)

In this way, the filter prevents noise current (i.e., conducted EMI) entry into or escape from the filtered device or equipment. Furthermore, by suppressing noise current emission from a device, the filter prevents the noise current flow along the power lines, thereby preventing the power lines from acting as an unintentional antenna, hence reducing the radiated EMI. Thereby, the filter ensures the filtered device or equipment can operate properly in its intended electromagnetic environment without disturbing any other devices connected in the same lines. It ensures electromagnetic compatibility (EMC) of the device that operates on the single-phase AC power supply. 

The filter helps to enhance the EMC performance of a device or product in terms of both the conducted EMI and radiated EMI. By incorporating a single-phase EMI/EMC filter into electrical systems, manufacturers can ensure compliance with electromagnetic compatibility standards and regulations, minimize the risk of electromagnetic interference, and enhance the reliability and performance of their products.

Applications:

The Single-phase EMI/EMC filters are ideal for use in various applications, including power supplies, consumer electronics, industrial equipment, medical devices, machine tools, office equipment, telecommunication equipment, and military equipment. 

How to select a single-phase power line EMI/EMC filter?

While selecting a filter for an application, the following factors need to be considered. 

Rated Voltage (V): Select a filter that has a voltage rating more than or equal to the maximum line voltage of the application. 

Current Rating (A): Select an EMI filter that has a current rating of more than or equal to the maximum current of the equipment or load to prevent overload or failure.

Leakage current: It is important to consider the leakage current rating of the filter to avoid compliance issues with safety standards. 

Insulation resistance (MΩ): Choosing a single-phase power line EMI filter with high insulation resistance is crucial as it minimizes leakage current, thereby ensuring the safety and reliability of electrical systems. 

Insertion loss: Selecting a filter with higher insertion loss provides effective attenuation of EMI signals.  The insertion loss is usually measured in dB.  

Filter Type: Choose between common filter types such as single-stage, two-stage, or multi-stage filters based on the level of attenuation required and the specific characteristics of the noise in the application.

Package type: The single-phase EMI/EMC filters are available in various package types, including Screw Mount, Chassis Mount, and through-hole.