According to the characteristics of the interference source, frequency range, voltage and impedance and other parameters and load characteristics of the requirements, the appropriate selection of filters, generally consider:
For one, it is required that the electromagnetic interference filter can meet the attenuation characteristics and insertion loss requirements of the load requirement within the corresponding operating frequency band, and if a filter attenuation amount can not meet the requirements, it can be used multistage, can obtain higher attenuation than the single stage, different filter cascade, can obtain good attenuation characteristics and insertion loss in the broadband band.
Second, in order to meet the load circuit operating frequency and the need to suppress the frequency of the requirements, if the frequency to be suppressed and the frequency of useful signals is very close, it is necessary to have a very steep frequency characteristics of the filter, in order to meet the suppression of the interference frequency filter out, only allow the use of useful frequency signal requirements. Third, in the required frequency, the impedance of the EMI filter RFI filter must match the interference source impedance and load impedance connected to it, and if the load is high impedance, the output impedance of the power filter should be low resistance, and if the power supply or interference source impedance is low impedance, the output impedance of the filter should be high resistance
If the power impedance or interference source impedance is unknown or changes in a large range, it is difficult to obtain stable filtering characteristics, in order to obtain the filter has a good relatively stable filtering characteristics, can be in the filter input and output, at the same time and then a fixed resistor.
Four, the filter must have a certain pressure resistance, according to the power supply and interference source of the rated voltage to select the power filter, so that it has a high enough rated voltage, to ensure that all expected working conditions can be reliable operation, can withstand the impact of input instantaneous high pressure. Five, the power filter allows the pass to be consistent with the rated current running continuously in the circuit.
The high fixed current will increase the volume and weight of the EMI filter, and the low fixed current will reduce the reliability of the EMI filter. Six, the power filter should have enough mechanical strength, simple structure, light weight, small size, easy to install, safe and reliable.
Post time: Mar-30-2021
