4.Power Line Filter Selection and Notice

1. How to Select a Power Line Interference Filter?

Some users may think that the value of insertion loss is higher, the EMI filter is better and more stages of the filtering networks, the EMI filter is better. But in fact, this is not always true to select EMI filter. Otherwise, more stages of the filtering networks, the EMI filter becomes very heavy and expensive. The only way to select and qualify a power line interference filter is to test the unit in your equipment. As mentioned above, the performance is highly dependent on equipment load impedance. Filter performance cannot be derived from single impedance (5 0 ohm) insertion loss data. Performance is a complex function of filter element impedances and equipment impedances which vary in magnitude and phase over the frequency spectrum of interest. Filter selection testing should be performed in your equipment to your required level of performance for both conducted emission control (FCC, VDE) and susceptibility control.

2. Do All Filter Networks with the Same Circuit and Element Values Perform Identically?

All filter networks with the same circuit and element values do not perform identically. Element values are specified and measured at a single frequency (usually 1kHz). Filter performance is required over the entire frequency spectrum, not just at the frequency of component measurement. The type of component construction and method of incorporation into a filter are extremely important to filter performance.

3. Is Installation Important to Filter Performance?

Mounting and wiring of the filter are critical influences on its performance. A power line filter is best installed at the power input point of your equipment. The filter is a barrier to high frequency signals. Its purpose must not be defeated by stray capacitance coupling the power input leads to the power output leads, or to any other conductors in the protected equipment.
When doing assembling, pay attention to below items. 1) Well connected with filter’s housing and euipment’s grounding side. Do not assemble it on insulated or spray-painted panel. It must be put on metal ones. Besides, it should be avoided to use too long grounding line, which will decrease common mode performance a lot. 2) While packing equipment’s cable, do not pack “In” and “Out” cable together, which will cause much coupling between filter’s “In” and “Out” terminal and destroy the restraining performance of EMI Filter. 3) Do not assemble EMI filter into the internal side of equipment’s shielding, which will destroy the restraining performance of EMI Filter. 4) Using the current shielding of equipment, try to well isolate the “In” and “Out” terminal to control the coupling into lowest level. Normally the case of the filter is bolted to the framework or chassis of the electronic equipment it protects. The line side leads should be kept short and well separated from the load side leads. The ideal isolation system is a bulkhead-mounted filter incorporating a line cord connector.

See attached recommended installation of EMI filter:

4. Recommended Impedance mismatch

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