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How to select an EMI power line filter

2021/09/30 > Back

First, see which of the situations you might confront:

1. An EMI filter has/had installed in your product: Please provide the type of model/specification of your EMI filter, and we will design an EMI filter with the same or better performance for you.

2. You know the noise band and intensity (dB) that need to be filtered out: Please tell us how much the attenuation requirement for the band (more accurate if the test graph is provided), and we will design a suitable filter for you.

3. You have designed/tested your products and found that it can not comply with the EMC standards:

3-1. Make sure there’s enough space in your products for installing an EMI / power line filter.

3-2. Confirm number of phases: Single phase or 3 phase.

3-3. Confirm rated voltage: 110/250/380/480/690VAC or DC voltage. The first consideration is to determine the voltage of the system. When determining AC voltage you will want to consider both line-to-line and line-to-ground voltage.

3-4. Confirm rated current: It may range from less than 1 Amp to well over 1000 Amps. The rated current of EMI power line filter should be selected according to the maximum operation current and ambient temperature possibly in the actual work. Rated current is critical, it determines the copper winding wire of inductive inside and the diameter of the lead wire. If the wire is too thin, it means that a large current will run in the thin wire like a small horse drawing a big cart, can cause severe heat to burn out.

3-5. Confirm your EMC standards: Each product needs to pass different safety standards, according to the standard to select the corresponding test band.

3-6. Confirm insertion loss: You can refer to the insertion loss data we provide, but do not take it as the only basis.
Because the insertion loss curve of the power line filter is generally tested under the standard impedance of 50Ω-50Ω, in fact, when it is installed into the application of the product, it is certainly not the impedance of 50Ω-50Ω, in which case the attenuation performance of the filter will often be greatly reduced; Therefore, when you choose insertion loss data, you not only have to meet the balance but also have 20 dB more.

For example, if you find that a product exceeds 13 dB at 100KHz and then finds that the insertion loss curve of a filter on the market is 20 dB at 100KHz and you think that filter can solve your problem, you're probably wrong. The filter you select should have an insertion loss of no less than 33 dB (13 dB + 20 dB).

In addition, the insertion loss is divided into common mode and differential mode, which is easy to measure with a spectrum analyzer. Common mode (CM): The signal is present on both sides of the line (fire line and neutral line) to the ground. Differential mode (DM): The signal is present on one side of the line (wire-to-wire).

Generally, when your interference is beyond 30MHz, common mode insertion loss is the key to meet the requirements; when your interference below 10MHz, differential mode insertion loss is the key to meet the needs.

Since you’re smart you should understand that in fact, the best way to evaluate a power line filter is to install it on your product for testing. Because the performance of the filter depends mainly on the load impedance of the product, it cannot be deduced from the insertion loss data of the 50-ohm impedance alone.

3-7. Confirm type of mechanism: PC board type, With IEC inlet or switch, chassis mounting etc.

3-8. Confirm type of connection: FASTON tab, wires, screw nuts, TB (terminal blocks) etc.

Data source:kknews