Some considerations when selecting EMI power filters

What is an EMI power filter? What does it do? A power filter, also called an EMI power filter, is a common tool for suppressing electromagnetic noise. It is mainly composed of resistors, inductors, capacitors and other components. It can filter out electromagnetic interference outside a certain frequency band. noise, and obtain a relatively pure power signal within a specific frequency band. The power filter is passive and is connected between the load and the power supply. It filters out the power supply noise and provides a relatively pure power supply to the load. When selecting a filter, you should select from the following aspects.

1. Consider the rated voltage

The rated voltage of the power filter refers to the highest voltage when the filter is working. When selecting the filter, the rated voltage of the filter must be higher than the input voltage, generally 30%-50% higher. Taking the single-phase 220V voltage of 50/60Hz as an example, the rated voltage of the filter is generally 250V or even greater.

2. Consider the rated current

The rated current of the filter refers to the maximum continuous current that can pass under the condition of rated voltage. The current will flow through the inductor inside the filter. If the current exceeds the rated current, the filter will not be damaged immediately, but the inductor coil. Prolonged heating can cause damage to the insulation layer.

3. Consider insertion loss

For filters, insertion loss is a very important parameter. On the same load, the ratio of the power received by the load before the filter is connected to the power received by the load after the filter is connected is the insertion loss, and its unit is It is decibel dB. Its decibel/frequency characteristic curve is shown in the figure below.

When selecting a model, choose one with a larger dB. The larger the dB, the stronger the anti-interference ability.

4. Consider the certification situation

Today's electronic products require a lot of certifications, and different countries have different certification requirements, such as UL certification in the United States and CE certification in the European Union. Products sold in these areas need to comply with their certifications, so choose filters according to the certification status. Also very important. The above are some considerations for selecting EMI power filters. I hope they can help you.