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The role of power filter

Date:March 19-23, 2017 Hits:877

1 What is radio frequency interference (RFI)?
RFI is generated when the radio communication, the use of a frequency range of unwanted electromagnetic energy. Conduction phenomena 10kHz to 30MHz frequency range between; radiation phenomena frequency range between 30MHz to 1GHz.

2 Why pay attention to the RFI?
The reason must be considered RFI, based on two reasons: (1) their product must be in its working environment running, but the work environment is often accompanied by severe RFI. (2) that their products can not be radiated RFI, to ensure non-interference are essential for the health and safety of radio frequency (RF) communications. Law has made a reliable RF communications requirements to ensure that electronic equipment RFI control.

3 What is the mode of transmission of RFI?
RFI is by radiation (electromagnetic waves in free space) to spread, and by the signal line and the AC power system conduction.
Radiation - the RFI radiated from electronic devices a primary medium is the AC power cord. Since the length of the AC power cord of the digital switching power supply device and the wavelength corresponding to the frequency 1/4, which constitutes a good efficient antenna.
Conduction-RFI on the AC power system based on two conduction mode. Total membrane (asymmetrical) RFI is online - ground (LG) and the neutral - ground (NG) two kinds of paths appear, and differential mode (symmetrical) RFI voltage form places online - neutral (LN) on .

4 What is the power line interference filter?
With the rapid development of today's world, more and more high-power power generation, and at the same time more and more low-power electrical energy is used for data transmission and processing, so that the impact produced a more even destroy electronic equipment noise. Power line interference filter is a primary filter means, for controlling the access from the electronic device (the potential for equipment malfunction) and out (for other RF communication systems or potential interference) of the RFI. By controlling RFI import plug, power line filter also significantly inhibited the RFI radiation.
Power line filter is a low pass filter with a double structure arranged, multi-channel network passive components. A network for common mode attenuation and another for differential mode attenuation. Network in the filter of the "stop band" (usually above 10kHz) to provide attenuation of RF energy, while passing a current (50-60Hz) substantially without attenuation.

5 power line noise filter is how to work?
As a passive, bilateral networks, power line interference filter with a composite conversion characteristics, this feature greatly depending on the source and load impedance. Conversion characteristic value shows attenuation performance of the filter. However, in the power line environment, the source and load impedance is uncertain. Therefore, the industry has been a standard practice for consistency validation filter: with 50 ohm source and load terminal resistive attenuation measurements. The measured value is defined as the filter insertion loss (IL)
I.. L. = 10 log * (P (l) (Ref) / P (l))
Where P (l) (Ref) is transformed from the source to the load power (without filter);
P (l) is inserted between the source and the load after a power conversion filter.
Insertion loss can also be used as voltage or current ratio expressed in the form:
IL = 20 log * (V (l) (Ref) / V (l)) IL = 20 log * (I (l) (Ref) / I (l))
Where V (l) (Ref) and I (l) (Ref) is a non-measured values ​​of filter,
V (l) and I (l) is a band filter the measured values.
Worthy of attention does not mean that the insertion loss of the power line environment, RFI attenuation provided by the filter performance. The power line environment, the source and load impedances relative measure must be estimated, and select the appropriate filter structure, the maximum possible appears at each terminal impedance mismatch. This depends on the terminal impedance filter performance, is "not matching network" concept is based.

6 How conduction test?
Conducted RF test requires a quiet environment - a shielded enclosure - a line impedance stabilization network, and an RF voltage equipment (such as FM receiver or spectrum analyzer). The RF test environment should be at least below the required specification limits of 20dB, so as to obtain accurate test results. To line impedance stabilization network (LISN) for the power cord to a desired input source impedance, as the impedance directly affect the level of radiation measured, the test procedure is therefore a very important part. In addition, the measurement receiver is properly test broadband is a key parameter.

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