Weak current College】 【filters technical parameters and the correct use of】.

<br> <br> (1) insertion loss is important technical noise filter parameters in the design and choice should be the main consideration. In the filter safe, conventional electrical performance, environmental, and mechanical, and other conditions are met, you should .try to select the insertion loss values. <br> <br> When did not add filter, signal source output voltage V1, when filter access, filter the output of the measured signal source voltage of V2. If the output impedance of signal generator and .receiver input impedance equal, is 50 Ω, filter insertion loss are: <br> IL = 20log (V1/V2) (1) <br> <br> <br> Because power noise filter can attenuate common-mode noise and differential mode ., so it is a common mode insertion loss and differential mode insertion loss. <br> <br> But in the actual selection of filter, you should be aware of the product manual for the given insertion loss curve, are in accordance with the standard .provided for in its input and output impedance 50 Ω is measured under the conditions. Because the actual filters at both ends of the impedance is not necessarily in the full frequency range is 50 Ω, therefore it on EMI signal attenuation, and is not equal to .the product manual for insertion loss values. Especially when you use the install did not at that time, also be far less than the standard for the given insertion loss. <br> <br> (2) power supply noise filter is a kind of .reciprocity of passive network. In practical application to make it effective in suppressing noise matching should be reasonable. As shown in Figure 4 to select the filter you can network structure and parameters for better EMI Suppression effect. <br> <br> When the filter .output impedance and load impedances are not equal in this port will produce reflection, the greater the difference between the two impedances, port of reflection. When the filter is on both sides and external impedance-impedance are not equal, the EMI signals will be in .its input and output are generated reflection. When power line filter for electromagnetic noise attenuation, and filter inherent insertion loss and reflection loss related to this point more effectively inhibit the EMI noise. In the actual design and select use EMI filter, to filter the correct .impedance, to cause as much reflection to filter in a wide frequency range resulting in higher impedance mismatch, resulting in better performance for electromagnetic interference suppression. <br> <br> (3) in the practical application of the power line filter, request its .shell and system to have a good electrical connection and should make the grounding line as far as possible short, because overly long grounding line increases resistance and inductance, and severe reductions of filter common mode rejection, at the same time also have common ground impedance coupled .problems. As shown in Figure 5, grounding line is too long, then filter the input and output coupling impedance between public Zg is too large to load voltage: <br> V0 = VZ + Vg = VZ + (Ii-IO) Zg (2) < .br> Type: Ii to filter AC input circuit noise current; <br> IO to filter output circuit noise current. <br> <br> By type (2), electromagnetic interference signal attenuation through the filter, the output side noise current significantly .less than the input noise current, that is, public pressure drop due to the grounding impedance (Ii-IO) Zg will greatly, Zg, will produce a very high voltage electromagnetic interference, through public ground loop coupling to filter the output, which can .substantially reduce noise filter for EMI noise suppression capabilities. <br> <br> Reduce public impedance coupled the best way is to use equipment of the electromagnetic shielding, the noise filter for input and output isolation, at the same time filter Earth wire to make .short, so that both the filter input and output of electromagnetic coupling between reduced to a minimum, without undermining the shield structure for the device for electromagnetic interference suppression of noise. <br> <br> (4) above, the use of power supply .noise filter should note the following points: <br> <br> ① filter should be as close as possible to the entrance of the installed equipment AC, should not filter based on the AC inlet on the device as short; <br> ② filter .capacitor leads should be as short as possible, so as not to lead inductive reactance and capacitance at low frequencies on the resonance; <br> ③ filter Earth wire with large current flow, will produce electromagnetic radiation, response filter for good shielding and grounding; .<br> ④ filter's input and output lines cannot be tied together, wiring to increase the distance between them, to reduce the coupling between them, you can add separators or shielding layer. <br> <br> <br> <br>.