Key parameters needed to consider while selecting the filter

The EMI/EMC filters come in various types, designs, shapes, and configurations. Here are the key specification parameters to consider while selecting an EMI/EMC filter.

Type: It represents the type of EMI/EMC filter. The filters are available in various types, including the DC Filter, Single Phase EMI/EMC Filter, Three Phase EMI/EMC filter, Dual phase EMI/EMC filter, signal/data line filters, and more.

Rated voltage (V): It represents the maximum line voltage level that can be handled by the filter. Select the filter that has the rated voltage more than or equal to the maximum input line voltage applied to the load. Note that EMI filters for AC power supply lines can also be utilized for DC power supply lines.

Rated current (A): It is the maximum steady-state current load current (nominal value) that can be handled by the filter without exceeding the safe temperature range.   The rated current of the filter must be greater than or equal to the maximum load current that the device will take when powered. Filters can handle in-rush current, but the filter will fail when handling current higher than its rated current for a longer time.

Leakage current: It refers to the current that flows from the 'line' and 'neutral' to the 'ground' connection in the AC power line connected EMI filter.   This current is caused by ‘line’ to ‘ground’ (Y) capacitors in the filter and expressed in the mA range.   In so many applications, standards limit the total leakage current of the device. Hence, it is necessary to consider leakage current to avoid compliance issues with safety standards, such as IEC60601 for medical equipment, EN 60950-1 for information technology equipment, and EN 55014 for appliances.

Resistance: It is the resistance value (DC resistance) between the input and output of the filter in both directions. This value includes the resistances of the filter's coils as well as any resistance introduced by connections between the coils and terminals. It is measured in ohms. The voltage drop due to the EMI filter is represented by the following expression.

Voltage drop = DC resistance x Load current

Insulation resistance: It is the resistance value that indicates the degree of insulation between the conductive components and the ground or other conductive elements in the filter. It is usually in the megohms range.   A high insulation resistance indicates good insulation that prevents leakage current between the conductive components and the ground or other conductive elements in the filter.

Dielectric Strength: It is the high DC voltage (VDC) applied between the lines and the mounting plate (ground) of the filter to check the insulation strength.

Package type: The EMI filters are available in various package types like Screw Mount, Chassis Mount, Panel Mount, and Flange Mount.

Operating temperature: It is the safe operating temperature range of the filter, measured in ºC.